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Theses and Dissertations
2010
Ionic liquids : solvation characteristics and cellulose
dissolution
Leah Terencia Basa
The University of Toledo
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A thesis
entitled
Ionic Liquids: Solvation Characteristics and Cellulose Dissolution
by
Ma. Leah Terencia N. Basa
Submitted to the Graduate Faculty as partial fulfillment of requirements for
The Master of Science in Chemistry
______________________________
Dr. Jared L. Anderson, Committee Chair
________________________________
Dr. Patricia R. Komuniecki, Dean
College of Graduate Studies
The University of Toledo
August 2010
Copyright 2010, Ma. Leah Terencia N. Basa
This document of copyrighted material. Under copyright law, no parts of this document
may be reproduced with the expressed permission of the author.
ii
An Abstract of
Ionic Liquids: Solvation Characteristics and Cellulose Dissolution
by
Ma. Leah Terencia N. Basa
Submitted to the Graduate Faculty in partial fulfillment of the Requirements for
The Master of Science in Chemistry
The University of Toledo
August 2010
Due to their characteristic advantages, ionic liquids (ILs) are gaining considerable
attention as replacement solvent systems in organic chemistry as well as
separation/extraction media in analytical chemistry.
ILs possess a variety of unique
properties including negligible vapor pressure, high thermal stability, wide viscosity
range, and can undergo a multitude of different solvation interactions. In addition, the
structural tuneability of these compounds allows for them to be tailor-made for specific
applications. However, it is currently not well-understood how the structural make-up
and composition of ILs affect their overall solvation properties. In this research, the
development of a structural model based on the solvation parameter model for pyridinium
and imidazolium-based ILs was demonstrated. In particular, the IL solvation properties
were analyzed and compared utilizing various substituents on the imidazolium and
pyridinium ring while studying ILs employing different anions with fixed cation
structures. Furthermore, the gas chromatography stationary phases containing binary
iii
mixtures of ILs were examined and the effect of the IL structure and composition on the
solvation properties were reported. The quantitative evaluation of ILs were used as a
basis in the study of cellulose dissolution.
iv
ACKNOWLEDGEMENTS
Science amazes me ever since when I am little. I was fond of reading science
books, watching television shows and seeing anything that involves science. I used to
remember when I am about 9 years old, I am watching a variety show in television when
the host asked the contestant, “what do you want when you grow up?” The kid replied,“ I
want to be scientist”. At that moment I was so curious what it meant so I looked it up in
the dictionary and encyclopedia to know what it is. After carefully reading, I thought that
is a very interesting profession and I told myself that someday I would become a scientist.
After years of hardwork and patience, finally, I became one. And as I now
conquer my journey as a scientist, I am so grateful that I met and surrounded by people
with both talent and love for science that shaped and molded me for what I am now. It is
to these people that I now am honored to acknowledge.
My deep gratitude is extended to my advisor, Dr. Jared L. Anderson that showed
and taught me chemistry beyond enchantment. I am grateful for the experience, the
passion and discipline I have developed. The experience I have, help me to be more
prepared to become a better person and researcher.
To my committee members, Dr. Kirchhoff, Dr, Bigioni, Dr, Schall whose
suggestions and comments helped me to write and come up with a better manuscript that
I could be really proud of.
To Prof. Kippenhan, my teaching mentor who I will always be indebted to
because of her trust and encouragement of my teaching that built my confidence as a
public speaker and educator.
v
To my labmates and friends whose encouraging words and advice, help me go on
in my research.
To The University of Toledo, who gave me a chance to be part of their
community. This is one part of my life that I will always treasure.
To my family who, even thousand of miles away, are my source of inspiration.
My heartfelt gratitude especially to my parents who taught how to become patient,
hardworking and to never lose hope in life. They are forever the reason that kept me
going with my life. They constantly reminded me that things may not come as you want
to but God will give the best for you.
To God almighty, who is my confidant and my savior. He made all things
possible for me and always encircled me with great people who molded me into the best
that I could be.
To you all, this thesis is humbly dedicated.
vi
Table of Contents
Abstract
iii
Acknowledgements
v
Table of Contents
vii
List of Tables
xvi
List of Figures
xx
Chapter 1. Ionic liquids and Application in Analytical Chemistry
1
1.1 History of ionic liquids
1
1.2 Structural features
2
1.2.1 Anion
4
1.2.2 Cation
5
1.3 Application of ionic liquids in analytical chemistry
6
1.4 Bibliography
9
Part One. Structural composition of imidazolium and pyridinium based
11
ionic liquids that influenced cellulose dissolution
12
Chapter 2. Examination of cellulose dissolution in ionic liquids
2.1 Introduction
12
2.1.1 Cellulose
12
2.1.2 Cellulose dissolution
13
2.1.2.1 Using conventional solvents
13
2.1.2.2 Using ionic liquids
15
vii
2.2 Experimental
16
2.2.1 Materials
16
2.2.1.1 Chemicals used in the synthesis of ionic liquids
16
2.2.1.2 Chemicals used in cellulose dissolution analysis
16
2.2.2 Methodology
17
2.2.2.1 Syntheses of ionic liquids
17
2.2.2.1.1 Imidazolium-based ionic liquids
17
2.2.2.1.1.1 Acid-base reaction of imidazolium-based ionic liquids
17
2.2.2.1.1.1.1 Synthesis of EMIM-acetate
17
2.2.4.1.1.1.1.1 Synthesis of EMIM-OH
18
2.2.2.1.1.1.2 Synthesis of EMIM-propionate
19
2.2.4.1.1.1.3 Synthesis of EMIM-formate
20
2.2.2.1.1.1.4 Synthesis of EMIM-trifluoroacetate
20
2.2.2.1.1.1.5 Synthesis of EMIM-succinate
21
2.2.2.1.1.1.6 Synthesis of EMIM-aspartate
21
2.2.2.1.1.2 Alkylation reaction of imidazolium-based ionic liquids
23
2.2.2.1.1.2.1 Synthesis of EMIM-Br
23
2.2.2.1.1.2.2 Synthesis of DMIM-phosphite
23
2.2.2.1.1.2.3 Synthesis of EMIM-phosphite
24
2.2.2.1.1.2.4 Synthesis of HMIM-bromide
24
2.2.2.1.1.3 Metathesis reaction of imidazolium-based ionic liquids
25
2.2.2.1.1.3.1 Synthesis of HMIM-acetate
25
viii
2.2.1.2 Pyridinium-based ionic liquids
28
2.2.2.1.2.1 Alkylation reaction of pyridinium-based ionic liquid
28
2.2.2.1.2.1.1 Synthesis of EMPyr-Br
28
2.2.2.1.2.1.2 Synthesis of PMPyr-Cl
30
2.2.2.1.2.1.3 Synthesis of B(2)MPyr-Cl
30
2.2.2.1.2.1.4 Synthesis of B(3)MPyr-Cl
31
2.2.2.1.2.1.5 Synthesis of B(4)MPyr-Cl
31
2.2.2.1.2.1.6 Synthesis of A(2)MPyr-Cl
32
2.2.2.1.2.1.7 Synthesis of A(3)MPyr-Cl
32
2.2.2.1.2.1.8 Synthesis of A(4)MPyr-Cl
33
2.2.2.1.2.1.9 Synthesis of HEPyr-Cl
33
2.2.2.1.2.2 Metathesis reaction of pyridinium based ionic liquids
34
2.2.2.1.2.2.1 Synthesis of EMPyr-Ac
35
2.2.2.1.2.2.2 Synthesis of BMPyr-Ac
35
2.2.2.1.2.2.3 Synthesis of A(2)MPyr-Ac
35
2.2.2.1.2.2.4 Synthesis of A(3)MPyr-Ac
37
2.2.2.1.2.2.5 Synthesis of A(4)MPyr-Ac
37
2.2.2.1.2.2.6 Synthesis of HEMPyr-Ac
37
2.2.2.1.3 Bulk synthesis of pyridinium-based ionic liquids
38
2.2.2.1.4 Alternative method in the synthesis of imidazolium and
pyridinium-acetates ionic liquids
39
2.2.2.1.4.1 Imidazolium-based ionic liquids
40
2.2.2.1.4.1.1 Synthesis of EMIM-OH
40
ix
2.2.2.1.4.1.2 Synthesis of EMIM-Acetate
41
2.2.2.1.4.2 Pyridinium-based ionic liquids
41
2.2.2.1.4.2.1 Synthesis of AMPyr-OH
41
2.2.2.1.4.2.2 Synthesis of AMPyr-Ac
41
2.2.2.2 Examination of solubility
42
2.3 Results and Discussion
44
2.3.1 Effect of type of cations
44
2.3.2 Effect of type of anions
46
2.3.3 Effect of isomer
49
2.3.4 Analysis of the recovered ionic liquids after pre-treatment
50
2.4 Conclusions
57
2.5 Bibliography
58
Part Two. Evaluation of solvation properties of imidazolium and pyridinium
61
Based ionic liquids
Chapter 3. Characterization of Properties of Ionic Liquids Using Abraham
Solvation Parameter Model by Gas Chromatography
3.1 Introduction
62
62
3.1.1 Solvation properties of ionic liquids using gas-liquid chromatography 62
3.1.1.1 Kovats retention index system
62
3.1.1.2 Rohrschneider’s and McReynolds phase constant
64
3.1.1.3 Abraham’s solvation parameter model
65
3.2 Experimental
67
x
3.2.1 Materials
67
3.2.1.1 Probe molecules used in Inverse Gas Chromatography analysis
3.2.2 Methods
67
68
3.2.2.1 Instrumentation
68
3.2.2.2 Static coating technique
68
3.2.2.3 Inverse Gas Chromatography analysis
70
3.3 Results and Discussions
73
3.3.1 Characterization of pure and mixed ionic liquid stationary phase
using Abraham solvation parameter model
73
3.3.1.1 Imidazolium-based ionic liquids
74
3.3.1.2 EMIM-based ionic liquids
78
3.3.1.3 Pyridinium-based ionic liquids
83
3.3.1.3.1 Effect of cations
83
3.3.1.3.2 Effect of anions
83
3.3.2 Effect of ionic liquid stationary phase composition on the
retention factor of analytes
87
3.3.2.1 Imidazolium-based ionic liquids
87
3.3.2.1.1 Alkyl-functionalized ILs
87
3.3.2.1.2 Alkene-functionalized ILs
88
3.3.2.1.3 Ether-functionalized ILs
88
3.3.3.1.2 EMIM-based ionic liquids
92
3.3.1.2.1 Monocarboxylic acid-based ILs
92
3.3.1.2.2 Dicarboxylic acid-based ILs
92
xi
3.3.1.2.3 Haloacetic acid-based ILs
92
3.3.1.2.4 EMIM-thiocyanate
93
3.3.1.2.5 EMIM-ethylsulfate
93
3.3.1.3 Pyridinium-based ionic liquids
99
3.3.1.1 Effect cation type
99
3.3.1.2 Effect of anion type
100
3.3.3 Effect of stationary phases composition on the chromatographic
selectivity of ionic liquids
103
3.3.3.1 Imidazolium-based ionic liquids
103
3.3.3.1.1 Alkyl-functionalized ILs
103
3.3.3.1.2 Alkene-functionalized ILs
104
3.3.3.1.3 Ether-functionalized ILs
104
3.3.3.2 EMIM-based ionic liquids
108
3.3.3.2.1 Monocarboxylic acid-based ILs
108
3.3.3.2.2 Dicarboxylic acid-based ILs
108
3.3.3.2.3 Haloacetic acid-based ILs
109
3.3.3.4 EMIM-thiocyanate
109
3.3.3.5 EMIM-ethylsulfate
110
3.3.3.3 Pyridinium-based ionic liquids
116
3.3.3.3.1 Effect of cations
116
3.3.3.3.2 Effect of anions
116
3.4 Conclusion
120
3.5 Bibliography
121
xii
Part three. Binary mixture of ionic liquids as gas chromatography
123
Stationary phases
Chapter 4. Evaluation of solvation properties of pure and binary mixture
Gas chromatographic stationary phases ionic liquids
124
4.1 Introduction
124
4.2 Experimental
124
4.2.1 Materials
124
4.2.1.1 Probe molecules used in inverse gas chromatography analysis
4.2.2 Methods
124
125
4.2.2.1 Instrumentation
125
4.2.2.2 Static coating technique
125
4.2.2.3 Inverse gas chromatographic analysis
125
4.3 Results and discussion
125
4.3.1 Comparison of solvation properties between pure and
binary mixture ionic liquids
125
4.3.2 Comparison of retention factor of analytes between pure and
binary mixture ionic liquids
130
4.3.3 Comparison of chromatographic selectivity between pure and
binary mixture ionic liquids
131
4.4 Conclusion
134
4.5 Bibliography
134
xiii
Part four. Correlation of solvation properties to cellulose dissolution
136
Chapter 5. Influence of evaluated solvation properties and structural
composition of ionic liquid to the dissolution of cellulose
137
5.1 Introduction
137
5.2 Results and Discussion
138
5.2.1 Imidazolium-based ionic liquids
138
5.2.2 EMIM-based ionic liquids
139
5.2.3 Pyridinium-based ionic liquids
140
5.3 Bibliography
144
Part five. Thermophysical properties of imidazolium and pyridinium-based
145
Ionic liquids
Chapter 6. Onset column bleed temperature of synthesized ionic liquids
146
6.1 Introduction
146
6.2 Experimental
147
6.2.1 Methodology
147
6.3 Results and discussion
149
6.3.1 Onset column bleeding temperature of imidazolium based, pyridinium
based and binary mixture ionic liquid stationary phases
149
6.3.1.1 Effect of cation type
149
6.3.1.2 Effect of anion type
150
6.3.1.3 Effect of isomer
152
6.3.1.4 Comparison between pyridinium chloride and pyridinium acetate 152
xiv
6.3.1.5 Comparison between pure ILs and binary mixture
stationary phases
152
6.3.1.6. Thermally unstable ionic liquids
153
6.4 Conclusion
153
6.5 Bibliography
154
Appendix A. 1H-NMR of the synthesized imidazolium based and pyridinium
based ILs Accompanying Chapter 2. section 2.2.2.1
156
Appendix B.1H-NMR of the Alternative Route on the Synthesis of EMIM-acetate
accompanying Chapter 2 Section 2.2.2.1.4
172
Appendix C. 1H-NMR and 13C-NMR Analysis of the recovered EMIM-acetate after
Pre-treatment analysis accompanying chapter 2 Section 2.3.4
xv
174
List of Tables
2.1 Solubility of Cellulose in Ionic Liquids
45
3.1 List of probe molecules and their corresponding solute descriptors used
in the solvation parameter model
72
3.2 System constants of the imidazolium chloride based IL stationary phase
at three temperatures
76
3.3 Imidazolium-based ILs analyzed using solvation parameter model and their
corresponding structures
77
3.4 System constants of the EMIM-based IL stationary phases
at three temperatures
81
3.5 EMIM-based ionic liquids analyzed using solvation parameter model and
their corresponding structures
82
3.6 System constants of the pyridinium-based IL stationary phase
at three temperatures
85
3.7 Pyridinium-based ionic liquids analyzed using solvation parameter model
and their corresponding structures
86
3.8 Retention factors obtained at 70ºC for selected probes in EMIM-Cl,
HMIM-Cl, OMIM-Cl and OBIM-Cl IL stationary phases
89
3.9 Retention factors obtained at 70ºC for selected probes in AMIM-Cl
and AVIM- Cl IL stationary phases
90
3.10 Retention factors obtained at 70ºC for selected probes in
MEMIM-Cl and MMMIM-Cl IL stationary phases
3.11 Retention factors obtained at 40ºC for selected probes in
xvi
91
EMIM-formate, EMIM-acetate and EMIM-propionate IL stationary phases 94
3.12 Retention factors obtained at 70ºC for selected probes in
EMIM-aspartate and EMIM-succinate IL stationary phases
95
3.13 Retention factors obtained at 70ºC for selected probes in
EMIM-tricholoroacetate and EMIM-trifluoroacetate IL stationary phases
96
3.14 Retention factors obtained at 70ºC for selected probes in
EMIM-thiocyanate IL stationary phase
97
3.15 Retention factors obtained at 70ºC for selected probes in
EMIM-ethylsulfate IL stationary phase
98
3.16 Retention factors obtained at 70ºC for selected probes in BMPyr-Cl,
AMPyr-Cl, HEMPyr-Cl IL stationary phases
101
3.17 Retention factors obtained at 70ºC for selected probes in BMPyr-Cl
and BMPyr-Ac IL stationary phases
102
3.18 Effect of EMIM-Cl, HMIM-Cl, OMIM-Cl and OBIM-Cl stationary phases
on the selectivity of selected analyte pairs at 70ºC
105
3.19 Effect of AMIM-Cl and AVIM-Cl stationary phases on the selectivity of
selected analyte pairs at 70ºC
106
3.20 Effect of MEMIM-Cl and MMMIM-Cl stationary phases on the selectivity
of selected analyte pairs at 70ºC
107
3.21 Effect of EMIM-formate, EMIM-acetate and EMIM-propionate
stationary phases on the selectivity of selected analyte pairs at 40ºC
111
3.22 Effect of EMIM-aspartate and EMIM-succinate stationary phases
on the selectivity of selected analyte pairs at 70ºC
xvii
112
3.23 Effect of EMIM-trichloroacetate and EMIM-trifluoroacetate stationary phase
on the selectivity of selected analyte pairs at 70ºC
113
3.24 Effect of EMIM thiocyanate stationary phase on the selectivity
of selected analyte pairs at 70ºC
114
3.25 Effect of EMIM-ethylsulfate stationary phase on the selectivity
of selected analyte pairs at 70ºC
115
3.26 Effect of BMPyr-Cl, AMPyr-Cl and HEMPyr-Cl stationary phases
on the selectivity of selected analyte pairs at 70ºC
118
3.27 Effect of BMPyr-Cl and BMPyr-Ac stationary phase
on the selectivity of selected analyte pairs at 70ºC ionic liquids
119
4.1 System constants of pure EMIM-acetate and 1,3-dimethyl imidazolium phosphite
(DMIM-phosphite) and binary stationary phase mixtures at three temperatures 127
4.2 EMIM-acetate and DMIM-phosphite used as binary mixture analyzed using
solvation parameter model and their corresponding structures
128
4.4 Retention factors obtained at 70ºC for selected probes on four different ILs
stationary phases varying the weight percentages of EMIM-acetate and
DMIM-phosphite IL stationary phases
132
4.5 Effect of neat EMIM-acetate, DMIM-phosphite and their binary mixture
stationary phases on the selectivity of selected analyte pairs at 70ºC
133
5.1 Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of imidazolium-based ILs
141
5.2 Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of EMIM-based ILs
xviii
142
5.3 Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of pyridinium-based ILs
143
6.1 Onset column bleeding temperature of neat and binary ionic liquid
stationary phases
151
xix
List of Figures
1.1 Structure of Ethylammonium nitrate
3
1.2 Structures of commonly used cations and anions
8
2.1 Structure and the intra- and intermolecular interaction
hydrogen bonds in cellulose
14
2.2 Acid-base reaction of imidazolium-based ionic liquids
22
2.3 Alkylation reaction of imidazolium-based ionic liquids
26
2.4 Metathesis reaction of imidazolium based ionic liquids
27
2.5 Alkylation reaction of pyridinium-based ionic liquids
29
2.6 Metathesis reaction of pyridinium-based ionic liquids
36
2.7 Alternative method in the synthesis of imidazolium and
pyridinium acetate ionic liquids
43
2.8 Pyridinium based ionic liquids examined for dissolution of cellulose
47
2.9 Imidazolium based ionic examined for dissolution of dissolution of cellulose 48
2.10 Comparison of 13H-NMR between pure EMIM-acetate from recovered
EMIM-acetate after used in pre-treatment analysis
52
2.11 Comparison of 13C-NMR between pure EMIM-acetate from recovered
EMIM-acetate after used in pre-treatment analysis
53
2.12 1H-NMR and 13C-NMR of 1-Ethyl imidazole
54
2.13 1H-NMR and 13C-NMR of Acetic acid
55
2.14 MS of EMIM-cation
56
4.1 Correlation between stationary phase weight percentage of EMIM-acetate and
DMIM-phosphite and the resulting hydrogen bond basicity
xx
129
6.1 Onset column bleeding analysis of stationary phases using
gas chromatography
148
xxi
CHAPTER 1
IONIC LIQUIDS AND APPLICATION IN ANALYTICAL CHEMISTRY
1.1 History of ionic liquids
The earliest discovery of ionic liquids (ILs) was in the mid 19th century when “red
oil”, generated by Friedel-Crafts reaction, was used as a solvent for separation analysis
(1). Early in the 20th century (1914), Paul Walden reported the first widely-known ionic
liquid, ethyl ammonium nitrate (Figure 1.1). In his paper he discussed the application of
organic salts on the electronic conductivity. The organic salts which possess a low
melting point limit the degree of thermolysis of both the solvent and the dissolved salt in
the molten salt. The low melting point property allows the reproducibility of the
observation of melts of anhydrous salts to be examined at low temperature whereas
before it was limited at high temperature (2). At that time, Walden’s great discovery did
not draw attention to researchers. In 1934, two decades after a long silence, the first IL
was registered for patent. This IL was composed of a pyridinium cation paired with a
halide anion and was used in application in cellulose dissolution (1, 2).
Interest in the study of ionic liquids became more intense in 1963, after the
research project of Major (Dr.) Lowell A. King of the US Air Force Academy. Their
research involved the replacement of the LiCl-KCl molten salt electrolyte used in thermal
batteries. Initially, the binary mixture of 1-butylpyridinium chloride and aluminum
1
chloride, but it suffered serious problems such as reduction in the electrochemically and
air-sensitivity. Thirty years later, in 1990, a visiting professor from the US Air Force
Academy, Dr. Mike Zaworotko, discovered the solution which gave a new dimension for
the application of ionic liquids in electrochemistry (1, 2). Since then, ionic liquids have
drawn the interest of many scientists and even industries for their exceptional properties
and possible use. And the second generation of ILs emerges with various combinations of
cation and anion pairs which were synthesized, tested and used in several chemical
processes.
1.2 Structural features
In chemical process industries, large quantities of organic solvents are consumed
in chemical reactions, synthesis and formulation. The problem of waste disposal from
these methods is of great concern because it contributes to the expanding environmental
crisis. Scientists and researchers are constantly searching for alternative solvents that do
not have deleterious effects on the environment and human health. The discovery of ionic
liquids made a breakthrough in chemical industry. Nowadays, it is used as a substitute
solvent to common organic compounds for liquid-liquid extraction and separation
analysis because they represent a viable class of environmentally friendly replacements
for the currently used organic solvents (4, 5).
Ionic liquids (ILs) are salts in their liquid or molten state at room temperature and
possess melting points below 100 ºC (1, 3, 4). They are also referred to as room
temperature molten salts, low temperature molten salts, ambient temperature molten salts,
2
H
H
H
H
C
C
N
H
H
H
O
H
O
N
Figure 1.1: Structure of Ethylammonium Nitrate
3
O
liquid organic salt and designer solvents (1, 6). They are composed of an organic cation
and an inorganic or organic anion in which the ions can be tailored for specific
applications. The overwhelming attention to these compounds is due to the uniqueness of
their properties such as variable viscosity, low or negligible vapor pressure, and high
thermal stability. The tunability of cations and anions results in the variable viscosity of
the solvent. Moreover, due to the tailoring of the cation and anion they are capable of
achieving high thermal stability, (>400 ºC) (1, 7, 8). They have very low or negligible
vapor pressure (1, 3-4). With this, they are often categorized as green solvents (5).
1.2.1 Anion
The anion component of the ionic liquid largely defines its chemistry and functionality
(7). The broad range of anions can be divided into four groups: a) system based on
aluminum chloride (AlCl3) (6) and organic salts such as 1-butyl-3-methyl imidazolium
chloride (BMIM-Cl); b) anions based on hexafluorophosphate [PF6]-, tetrafluoroborate
[BF4]-, c) anions such as trifluoromethane sulfonate or triflate [CF3SO3]-, Bis(trifluoromethanesulfonyl) amide [(CF3SO2)2N]- or bistriflamide [NTf2]-, tris
{(trifluoromethyl) sulfonyl} methanide [(CF3SO2)3]- and d) anions based on alkylsulfates
and sulfonates (4).
The first group of anions was formed via Friedel-Crafts reaction (1, 4, 6). The
disadvantages of these ILs were their extremely hygroscopic characteristics. The second
group resolved the stability issue of group one. However, they were not an ideal choice of
anion because [PF6]-, in the presence of moisture releases HF (3-5). Hydrophobic anions
define the third set of anions which were developed by Grätzel and co-workers. They
4
appear to be more stable towards reaction and possess low viscosity and large
electrochemical windows. (2, 4). The fourth group of ILs involves the substitution of
[NTf2]- to the bis (methanesulfonyl) amide ([Ms2N]-) which eliminates the fluorine
present in the IL and improves the electrothermal stability of the corresponding salt (4).
These ILs still bear some weaknesses, including, costly synthesis and disposal problem.
Still, the quest for better ILs are the subject of extensive research. Figure 1.2 shows the
commonly used anions and cations.
1.2.2 Cation
The cation component of the IL largely determines the stability and properties of
the IL (9). The unsymmetrical structure of the cation with respect to the anion, is largely
responsible for the low melting point of ILs. Figure 1.2 presents the commonly used
cations
which
are;
alkylimidazolium
[R1R2IM]
+
,
alkylpyridinium
[RPy]
+
,
tetraalkylammonium [NR4] + and tetraalkylphosphonuim [PR4] + ions (1, 4).
Cations may be functionalized to achieve a better combination with the anion for
a specific chemical reaction or separation. Tailoring of the anion and cation portion of the
IL produces a potential of 1018 compounds (10). The extensive variety of possible
combinations can modify the IL for specific properties and various applications, thus, the
subclass of ILs referred to as task-specific ionic liquid (TSIL) emerges.
5
1.3 Application of ionic liquids in analytical chemistry
In analytical chemistry, there is a constant challenge of searching for efficient and
effective quantification and identification of compounds. With the discovery of ionic
liquids emerges a new dimension in the analytical field.
In 1998, Rogers and co-workers studied partitioning of simple, substituted
benzene derivatives, carboxylic compounds and
water
and
the
room
temperature
14
ionic
C-labeled aromatic amines, between
liquid,
butylmethylimidazolium
hexafluorophosphate through liquid / liquid extraction. They observed that the
distribution coefficient (D) of the mentioned analytes are roughly an order of magnitude
lower than 1-octanol / water partition coefficient. The analysis is based on the solutes’
charged state or relative hydrophobicity (11).
Zhang et. al. (12), explored on 1-alkyl-3-methylimidazolium salts and Nbutylpyridinium salts as new mobile phase additives for separation of catecholamines,
epinephrine, norepinephrine and dopamine by reversed-phase high-performance liquid
chromatography analysis. They studied the effect of different pH values of the mobile
phase, concentration of ionic liquids, and different alkyl substituents on the cations or
different counterion of ionic liquids as it influence the separation of compounds. The
separation mechanism involves molecular interactions between ionic liquids and
catecholamines.
A study using capillary electrophoretic method for resolving phenolic compounds
found in grape seed extracts was investigated by Stalcup and co-workers (13) in 2001.
They explored on 1-alkyl-3-methylimidazolium-based ionic liquids which are used as the
running electrolytes and studied the separation and identification of polyphenolic
6
compounds isolated from the grape seed extract. The separation mechanism seems to
involve weak association between the imidazolium cations migrating away from the
detector with the analyte, polyphenols.
ILs are considered as complex solvents (15) and are capable of participating in
numerous solvation interactions due to the structure tunability of these compounds. ILs
when used as stationary phase in gas chromatography analysis exhibits a dual-nature
behavior that are advantageous in separating the complex mixture of polar and non-polar
compounds. Several studies on using ILs as stationary phase were explored. It is thus
interesting to analyze the solvation properties of these compounds.
In this thesis, the solvation properties of different imidazolium and pyridinium
based ionic liquids and binary mixture stationary phases of some ILs were quantitatively
investigated using inverse gas chromatography. These are all presented in Chapters 3 and
4. The cellulose dissolution in different ILs will be examined and is discussed in Chapter
2. Then, the correlation of evaluated solvation properties and structural composition of
ILs to cellulose dissolution experiment is explained in Chapter 5. Finally, the thermal
stability or the onset column bleeding temperature of ILs will be presented on Chapter 6.
7
A. Some typical cations
R2
R1
PR4
R2
N
N
NR4
N
R1
Phosphonium
Pyridinium
Imidazolium
Ammonium
B. Some typical anions
F
F
F
F
B
F
F
P
F
F
tetrafluoroborate
NO3
F
X
F
nitrate
hexafluorophosphate
CF3SO3
AlCl4
aluminum
halide
tetrachloride
CH3SO3
(CF3SO2)2N
Trifluoromethane sulfonate
Methane sulfonate
Bis-(trifluoromethanesulfonyl) imide
(triflate)
(mesylate)
(NTf2)
Figure 1.2: Structures of commonly used cations and anions
8
1.4 BIBLIOGRAPHY
1. Wasserscheid, P. and Welton, T., Ionic Liquids in Synthesis, 2008, Wiley-VCH
2.
Plechkova, N. and Seddon, K, “Application of ionic liquids in chemical industry’,
Chemical Society reviews, 2007, 123-150
3.
Pinkert, A., K. N. Marsh, et al. “Ionic Liquids and Their Interaction with Cellulose”,
Chemical Reviews, 2009, 109(12): 6712-6728
4.
Chiappe, C. and D. Pieraccini, “Ionic liquids: solvent properties and organic
reactivity “, Journal of Physical Organic Chemistry, 2005, 18(4): 275-297
5.
Huddleston, J. G.; Rogers, R. D. “Room temperature ionic liquids as novel media
for 'clean' liquid-liquid extraction”, Chemical Communications, 1998, (16), 1765
1766
6.
Earle, M. J.; Seddon, K.R., “Clean synthesis in ionic liquids”, Proceedings –
Electrochemical Society, 2002, 2002-19(Molten Salts XIII), 177-189
7.
Zhao, Q. and Anderson, J L.,”Highly selective GC stationary phases consisting of
binary mixtures of polymeric ionic liquids”. J. Sep Sci, 2009, 33, 1-9
8.
Baltazar, Q.Q.; et. al. “Binary ionic liquid mixtures as gas chromatography
stationary phases for improving the separation selectivity of alcohols and aromatic
compounds”, Journal of Chromatography A, 2008, 1182(1), 119-127
9.
Uerdingen, E. Processing of cellulose with ionic liquids, BASF
10. Carmichael, A. J. and Seddon, K.R, Polarity study of some 1-alkyl-3methylimidazolium ambient-temperature ionic liquids with the solvatochromic dye,
Nile Red. Journal of Physical Organic Chemistry, 2000, 13(10), 591-595
9
11. Huddleston, J. G.; Rogers, R. D. “Room temperature ionic liquids as
novel media for 'clean' liquid-liquid extraction”, Chemical Communications
1998, (16), 1765-1766
12. Zhang, W. et. al., “Effect of ionic liquids as mobile phase additives on retention of
catecholamines in reversed-phase high-performance liquid chromatography”
Analytical Letters, 2003, 36(4), 827-838
13.
Yanes, E. G.;et. al., “Capillary electrophoretic application of 1-Alkyl-3methylimidazolium-based ionic liquids”, Analytical Chemistry, 2001, 73(16),
3838-3844
14.
Baker, G. A. et. al., “An analytical view of ionic liquids “, Analyst, 2005, 130,
800-808
10
PART ONE
Structural composition of imidazolium and
pyridinium based ionic liquids that influence
cellulose dissolution
11
CHAPTER 2
EXAMINATION OF CELLULOSE DISSOLUTION IN IONIC LIQUIDS
2.1 INTRODUCTION
2.1.1 Cellulose
The growing need of alternative energy resources that are more sustainable to the
environment, renewable, and are produced at low cost production is of great importance.
Cellulose which is the most abundant natural polymer in the environment (1, 2) is the
most inexhaustible raw materials and found to be an effective substitute as fuel source. It
constitutes the major fraction of lignocellulose material (~ 30-50%) found in the cell wall
of the plants (2). It is a highly crystalline polymer of D-glucose units linked together by β
1-4 glycosidic bonds (Figure 2.1). The size of the molecule depends on the degree of
polymerization or the number of repeating sugars that can vary from 20 to about 10,000.
The linear structure is cause by the rotation of the glucose by 180º with respect to its
neighbor (1). Cellulose contains three hydroxyl groups that can form intra-and
intermolecular hydrogen bonds. These bonds influence the reactivity and solubility of
cellulose (4). Usually, it is insoluble in most solvents due to the highly the strong
hydrogen bonding and van der Waals forces that holds the polymer chains together (13).
The extensive hydrogen-bonding networks of the molecule pose challenges to researchers
of finding suitable solvent to disrupt these bonds for its dissolution.
12
The first attempt to dissolve cellulose was in the 1920s but was unsuccessful due to the
solvent toxicity or its insufficient solvation power (1). Graenacher in 1934 used Nethylpyridinium chloride but the concept of dissolution process was not well-understood.
In 2002, from the research of Swatloski and co-workers, the cellulose research intensified.
They reported on using several ILs for the regeneration of cellulose and for the chemical
modification of polysaccharides. In the dissolution of process, they used imidazolium
based cation with different linear alkyl chain substituents and paired with Cl-, Br-, SCN-,
BF4- and PF6- anions. They have used different dissolution techniques to analyze which
among the processes could effectively dissolved cellulose. One of their observations was
the dissolution of cellulose can be influenced by the increasing linear alkyl chain in
cationic portion of the IL. As well as the effect of presence of water in the ionic liquids
that decreases the solubility of cellulose due to its competing hydrogen-bonding to the
cellulose microfibrils (5). For this reason, it is recommended to dry the IL thoroughly
before performing solubility test.
2.1.2 Cellulose dissolution
2.1.2.1 Using conventional solvents
Over the past decades, several organic and inorganic solvents were used in
dissolution process. Solvents like lithium chloride (LiCl)/N, N-dimethylacetamide
(DMAc), LiCl/N-methyl-2-pyrrolidine (NMP), LiCl/1, 3-dimethyl-2-imidazolidinone
(DMI), dimethyl sulfoxides (DMSO)/tetrabuthlammonium fluoride trihydrate (TBAF),
DMSO/paraformaldehyde, N-methyl-morpholine-N-oxide (NMMO), aqueous solution of
NaOH (3). Recently, they have used molten salt hydrates such as LiX ● nH2O (X= I-, NO3-,
13
HO
6
4
O
5
O
3
O
2
3
1
O
H
HO
6
4
O
5
3
HO
2
O
6
OH
O
O
H
6
H
O
O
1
2
5
4
1
OH
HO
3
OH
O
O
HO
O
O
1
2
5
4
OH
H
O
OH
HO
H
O
O
O
O
HO
OH
Figure 2.1: Structure and the intra- and intermolecular interaction hydrogen bonds
in cellulose
14
CH3CO2-, ClO4-) that shows efficient in dissolution process as well (1). However, these
solvents suffer from many drawbacks. Such as dissolving capability, toxicity, high cost,
solvent recovery and instability during the process itself.
2.1.2.1 Using ionic liquids
Recent interest on using ionic liquids in various chemical processes stems
primarily on its unique property particularly the immeasurable vapor pressure which
minimizes impact on the air quality (3, 8). The high polarity property of ionic liquid
enhances its ability to dissolve biopolymeric compounds, such as cellulose.
The strength of cellulose dissolution in ionic liquid depends on the combination of
pairing of ions. The anion plays a major role in the dissolution process. It largely disrupts
the extensive intra- and intermolecular hydrogen bonds of cellulose three dimensional
networks (6, 7). While, the cation played essential role as well, it interacts with the
cellulose hydroxyl oxygen atom via non-bonding or π to π interaction due to electron rich
aromatic system of the imidazolium or pyridinium ring cation (2).
In this study, different imidazolium and pyridinium based ILs which were
functionalized with various cations and anions combination and analyzed for dissolution
of cellulose. The influence of the IL structural composition on the solubility of cellulose
experiment is reported.
15
2.2 EXPERIMENTAL
2.2.1 MATERIALS
2.2.1.1 Chemicals used in the synthesis of ionic liquids
Various imidazolium and pyridinium based ionic liquids were synthesized and
used to examine cellulose dissolution. The chemicals used were: 1-methyl imidazole, 1ethyl imidazole, bromoethane, silver nitrate, allyl chloride, lead acetate, isopropyl alcohol,
chloropropane, succinic acid, aspartic acid, glycine, 2-methyl pyridine, 3-methyl pyridine,
4-methyl pyridine, dimethyl phosphite and activated alumina which were purchased from
Sigma-Aldrich (St. Louis, MO, USA). Amberlite resins IRA-400 (OH), propionic acid,
acetic acid were purchased from Supelco (Bellefonte, PA, USA). Nitric acid, butyl
chloride, methylene chloride, tetrahydrofuran, potassium hydroxide, methanol, diethyl
ether, chloroform and sodium carbonate from Fisher Scientific (Fairlawn, NJ, USA).
Hydranal was purchased from Fluka (Bellefonte, PA, USA).
2.2.1.2 Chemicals used in cellulose dissolution analysis
Microcrystalline cellulose, Avicel PH 101 was purchased from Fluka (Steinheim,
Germany). Hot plate, screw thread vial with rubber line capped and 12 inch thermometer
which were purchased from Fisher Scientific (Fairlawn, NJ, USA).
16
2.2.2 METHODOLOGY
2.2.2.1 Syntheses of ionic liquids
2.2.2.1.1 Imidazolium-based ionic liquids
There are three general methods used in the synthesis of imidazolium-based ILs.
The first method is through acid-base or neutralization reactions where the process
involves the reaction of EMIM-OH aqueous solution which was prepared from the 1ethyl-3-methyl imidazolium bromide using an anion-exchange resin. An EMIM-OH
solution was reacted to both monocarboxylic and dicarboxylic acids to produce the
EMIM salts and water. Figure 2.2 shows the ILs that were synthesized using acid-base or
neutralization reaction. The second method is by an alkylation reaction where equimolar
1-alkylimidazole (usually methyl or ethyl) reacts with alkyl halide to generate a disubstituted imidazolium cation and halide anion. Figure 2.3 shows the ILs that were
synthesized using alkylation reaction. The third method is a metathesis reaction where
two moles of imidazolium halide react with lead acetate to generate two moles of
imidazolium acetate and water. The reaction is shown in Figure 2.4 and the spectra of all
the synthesized ILs are shown in Appendix A.
2.2.2.1.1.1 Acid-base reaction of imidazolium-based ionic liquids
2.2.2.1.1.1.1 Synthesis of 1-ethyl-3-methyl imidazolium acetate
(EMIM-acetate)
The synthesis involves an acid-base or neutralization reaction. An equimolar
amount of acetic acid (20 mmol) was slowly added to EMIM-OH. The solution was
allowed to neutralize for 24 hours at room temperature with constant stirring. After
17
removal of water by rota-evaporation, the product was placed in vacuum at 70 ºC for 1
day. The product was a pale yellow viscous liquid. The synthesized compound was
characterized by 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO): δ=1.396 (3H, t, 7.2
Hz), δ=1.552 (3H, s), δ=3.862 (3H, s), δ=4.205 (2H, q, 7.2 Hz), δ=7.759 (1H, s), δ=7.852
(1H, s), δ=9.924 (1H, s).
2.2.2.1.1.1.1.1 Synthesis of 1-ethyl-3-methyl imidazolium hydroxide
(EMIM-OH)
As been mentioned in previous paragraph, EMIM-OH is used as the base in the
neutralization reaction. The synthesis of EMIM-OH involved a two step process. First
was the regeneration of ion-exchange resin in the hydroxide ion form followed by the
exchange of the EMIM-Br to EMIM-OH. Detailed synthesis of EMIM-Br is in section
2.2.2.1.1.2.1.
In the regeneration of the ion-exchange resin, approximately 100 grams of
Amberlite IRA-400 (OH) resin, an anion exchange resin, was packed in a
chromatographic column. The resin was washed with 5 M NaOH several times. To
ensure that the resin was ready for exchange, AgNO3 / HNO3 test was performed. This is
done by obtaining a few drops of solution from the washed column, and then adding a
drop of AgNO3. If there was still bromide present in the resin, the solution will give a
white precipitate. However, the solution could produce a black precipitate, Ag2O which is
interference formed as a result of the reaction of silver cation and the excess hydroxide
anion yielding AgOH. Equations 2.1 and 2.2 are the chemical reactions involved in the
mentioned processes.
18
Ag+ + OH-
AgOH
2 AgOH
H2O + Ag2O (Black Precipitate)
(2.1)
(2.2)
The precipitate was dissolved by adding HNO3. If the solution turned clear then it
indicates that the precipitate reacted with HNO3, and the resin has been changed to the
hydroxide ion form. Equation 2.3 is the chemical reaction involved.
Ag2O + 2HNO3
2AgNO3 + H2O
(2.3)
If the precipitate in the solution did not dissolve, the resin was continuously
washed with NaOH.
The second step is the generation of EMIM-OH. To completely remove the
presence of halide in the resin, it was further washed with Milli-Q water several times.
Then, resin was packed again into the column. Water was continually added to aid in the
exchange process and to elute EMIM-Br from the column. The exchange process was
completed by again performing the AgNO3 / HNO3 test. The concentration of the EMIMOH that was collected was determined by acid-base titration, using 0.1 M HCl as titrant
and methyl orange as indicator.
Characterization of the EMIM-OH using NMR and MS could not be performed
since EMIM-OH is unstable when it is not in aqueous solution (14).
2.2.2.1.1.1.2 Synthesis of 1-ethyl-3-methyl imidazolium propionate
(EMIM-propionate)
Equimolar (54 mmol) amount of propanoic acid was slowly added to EMIM-OH.
The solution was stirred at room temperature for 24 hours. The water was removed using
19
rota-evaporation. To ensure complete removal of the solvent, the sample was oven dried
at 70 ºC for one day. The yellow viscous liquid product was characterized using 1H-NMR
(INOVA). 1H-NMR (600 MHz, DMSO) δ=0.866 (3H, t, 7.8 Hz), δ=1.395 (3H,t, 7.8 Hz),
δ=1.81 (2H, q, 7.2 Hz), δ=3.870 (3H, s), δ=4.214 (2H, q, 7.2 Hz), δ=7.780 (1H, s),
δ=7.874 (1H, s) δ=10.062 (1H, s).
2.2.2.1.1.1.3 Synthesis of 1-ethyl-3-methyl imidazolium formate
(EMIM-formate)
Sixty-four millimoles of formic acid were slowly added to EMIM-OH. The
solution was stirred at room temperature for 24 hours. The solvent was removed using
rota-evaporator and to ensure removal of the solvent, the sample was oven dried at 70 ºC
for one day. White solid IL was produced which was characterized using 1H-NMR
(Varian). 1H-NMR (400 MHz, DMSO): δ =1.405 (3H, q, 2Hz), δ=3.856 (3H, t, 2Hz),
δ=4.180 (2H, q, 2Hz), δ=7.745 (1H, d, 1.6Hz), δ=7.836 (1H, d, 1.6Hz), δ=9.573 (1H, s).
2.2.2.1.1.1.4 Synthesis of 1-ethyl-3-methyl imidazolium trifluoroacetate
(EMIM-trifluoroacetate)
An equimolar (22 mmol) amount of trifluoroacetic acid was slowly added to
EMIM-OH. The solution was stirred at room temperature for 24 hours. The water was
removed using rota-evaporation. To ensure removal of the solvent, the sample was dried
in vacuum oven at 70 ºC for one day. The pale yellow viscous liquid product was
characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO) δ=1.404 (3H, t, 7.8
20
Hz), δ=3.841 (3H, s), δ=4.186 (2H, q, 7.2 Hz), δ=7.705 (1H, s), δ=7.780 (1H, s), δ=9.157
(1H, s).
2.2.2.1.1.1.5 Synthesis of 1-ethyl-3-methyl imidazolium succinate
(EMIM-succinate)
Thirty millimoles of succinic acid were slowly added to fifty-nine millimoles of
EMIM-OH. The solution was stirred at room temperature for 24 hours. The water was
removed via rota-evaporation and the sample was dried in vacuum oven at 70 ºC for one
day to ensure complete removal of solvent. The yellow viscous liquid product was
characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO) δ=1.381 (3H, t, 7.2
Hz), δ=1.991 (2H, s), δ=3.874 (3H, s), δ=4.220 (2H, q, 7.2Hz), δ=7.800 (1H, s), δ=7.892
(1H, s) δ=10.248 (1H, s) and further analyzed using ESI-MS. ESI-MS= {OOCCH2CH2COO-} = 116 u.
2.2.2.1.1.1.6 Synthesis of 1-ethyl-3-methyl imidazolium aspartate
(EMIM-aspartate)
Twenty-eight millimoles of aspartic acid were slowly added to fifty-seven
millimoles of EMIM-OH. The solution was stirred at room temperature for 24 hours. The
water was removed via rota-evaporation and the sample was dried under vacuum oven at
70 ºC for one day to ensure complete removal of solvent. The yellow viscous liquid
product was characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO)
δ=1.398 (3H, t, 7.2 Hz), δ=1.681-1.722 (1H, m), δ=2.248 (2H, d, 14.4 Hz), δ=3.035 (2H,
d, 10.2 Hz), δ=3.864 (3H, s), δ=4.210 (2H, q, 7.2 Hz), δ=7.736 (1H, s), δ=7.821 (1H, s),
21
N
N
-
EMIM - hydroxide
N
N
-
acetic acid
+
N
-
OH
N
-
OH
CH3CH2COO-
propionic acid
EMIM – propionate
HCOO-
formic acid
EMIM – formate
EMIM - hydroxide
N
N
CF3COOH
+
N
N
HCOOH
EMIM - hydroxide
N
N
CH3CCH2COOH
+
CH3COO-
EMIM – acetate
N
OH
EMIM - hydroxide
N
N
N
CH3COOH
+
OH
trifluoroacetic acid
CF3COO-
EMIM – tifluoroacetate
O
O
O
2
N
N
-
N
N
+
O
O-
OH
O-
OH
OH
EMIM - hydroxide
succinic acid
EMIM – succinate
O
+
2
N
N
-
O
O
O
OH
OH
O-
N
-
O
OH
EMIM - hydroxide
N
NH2
aspartic acid
EMIM – aspartate
Figure 2.2: Acid-base reaction of imidazolium-based ionic liquids
22
NH2
δ=9.748 (1H, s) and was further analyzed using ESI-MS. ESI-MS= {-OOCCH2
NH2CHCOO-} = 131 u.
2.2.2.1.1.2 Alkylation reaction of imidazolium-based ionic liquids
2.2.2.1.1.2.1 Synthesis of 1-ethyl-3-methyl imidazolium bromide
(EMIM-bromide)
The synthesis involves an alkylation reaction where 1-alkylimidazole reacted with
alkyl halide which is usually added in an excess amount (10-15 %). The resulting IL is a
di-substituted imidazolium cation and halide anion. In the experiment, 1-bromoethane
(10-15 %) was added to 1-methyl imidazole drop by drop. The solution was refluxed at
50 ºC for two days. After the removal of the unreacted bromoethane, the sample was
placed under vacuum at 70 ºC overnight and gave a yellow viscous liquid. The resultant
IL was characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO): δ=1.404
(3H, t, 7.2 Hz), δ=3.854 (3H, s), δ=4.201 (2H, q, 7.2 Hz), δ=7,732 (1H, s), δ=7.824 (1H,
s), δ=9.241 (1H, s).
2.2.2.1.1.2.2 Synthesis of 1, 3-dimethyl imidazolium phosphite
(DMIM-phosphite)
The reaction includes the addition of an equimolar amount of dimethyl phosphite
(104 mmol) to 1-methyl imidazole prepared both in THF solution. The reaction is
exothermic so the addition of phosphite was done dropwise under N2 gas. The sample
was refluxed for 3 days at 90 ºC. After removal of THF via rota-evaporation, the sample
was washed repeatedly with diethyl ether. The solvent was removed under reduced
23
pressure and the product was dissolved in methylene chloride and passed through a
column packed with neutral activated alumina. The product was vacuum dried at 70 ºC
for one day. A clear to pale yellow liquid was characterized using 1H-NMR (Gemini). 1HNMR (200 MHz, DMSO) δ=3.261 (3H, d, 11.6 Hz), δ=3.851 (6H, s), δ=5.607 (1H, s),
δ=7.728 (1H, s), δ=7.735 (1H, s), δ=9.333 (1H, s).
2.2.2.1.1.2.3 Synthesis of 1-ethyl-3-methyl imidazolium phosphite
(EMIM-phosphite)
An equimolar amount of dimethyl phosphate (97 mmol) was added to 1-ethyl
imidazole both prepared in THF solution, dropwise under N2 gas. The sample was
refluxed for 3 days at 90 ºC. After removal of THF via rota-evaporation, the sample was
washed repeatedly with diethyl ether. Solvent was removed under reduced pressure and
the product which was dissolved in methylene chloride was passed through a column
packed with neutral activated alumina. The product was vacuum dried at 70 ºC for one
day. A pale yellow liquid was characterized using 1H-NMR (Gemini). 1H-NMR (200
MHz, DMSO) δ= (3H, t, 1.2 Hz), δ=3.241 (3H, d, 8.6, Hz), δ=3.857 (3H, s), δ=4.207 (2H,
q, 1.8Hz), δ=5.093 (1H, s), δ=7.765 (1H, d, 1.4 Hz), δ=7.858 (1H, d, 1.6 Hz), δ=9.489
(1H, s).
2.2.2.1.1.2.4 Synthesis of 1-hexyl-3-methyl imidazolium bromide
(HMIM-bromide)
An alkylation reaction where an equimolar amount of hexyl bromide (121 mmol)
was added to 1-methyl imidazole. To enhance the reaction, isopropyl alcohol was added
24
that acted as co-solvent. The reaction was stirred for at least twelve hours and the solvent
was removed under reduced pressure. The sample was dried under vacuum at 70 ºC for
one day. A brown viscous liquid was characterized using 1H-NMR (Varian). 1H-NMR
(400 MHz, DMSO) δ=3.261 (3H, t, 3.2 Hz), δ=1.741-1.765 (2H, m), δ=1.976 (6H, s),
δ=4.603 (3H, s), δ=6.800 (2H, t), δ=8.506 (1H, d, 1.2 Hz), δ=8.585 (1H, d, 1.6 Hz ),
δ=10.047 (1H, s).
2.2.2.1.1.3 Metathesis reaction of imidazolium based IL
2.2.2.1.1.3.1 Synthesis of 1-hexyl-3-methyl imidazolium acetate
(HMIM-acetate)
Thirty-three millimoles of lead acetate trihydrate were added slowly to the 66
moles of 1-hexyl-3-methyl imidazolium bromide. Both solutions were prepared in water.
The resulting yellow viscous IL was characterized using 1H-NMR (INOVA). The
presence of bromide ion was detected using AgNO3/HNO3 test. Bromide ion was
removed if the solution turned clear upon by doing the AgNO3 /HNO3 test. 1H-NMR (600
MHz, DMSO) δ=0.838 (3H, t, 10.2 Hz), δ=1.242 (6H, s), δ=1.660 (3H, s), δ=1.773 (2H,
d, 10.2 Hz), δ=3.866 (3H, s), δ=4.175 (3H, t, 11.4 Hz), δ=7.765 (1H, d, 2.4 Hz), δ=7.842
(1H, d, 2.4 Hz), δ=9.556 (1H, s).
25
O
N
N
Reflux
at 90ºC
+
P
H3CO
O
N
N
P
OCH3
-
H
1- methyl imidazole
O
OCH3
H
dimethyl phosphite
1, 3-dimethyl
imidazolium phosphite
O
N
N
+
O
Reflux
at 90ºC
N
N
P
P
H3CO
-
O
OCH3
H
H
1- ethyl imidazole
OCH3
dimethyl phosphite
1-ethyl-3-methyl
imidazolium phosphite
N
N
1-methyl imidazole
Reflux
at 90ºC
+
N
Br
N
Br-
1-bromohexane
1-hexyl-3-methyl imidazolium bromide
Figure 2.3: Alkylation reaction of imidazolium-based ionic liquids
26
N
+
N
Pb (CH3COO)2
3H2O
Br-
2
lead acetate trihydrate
1-hexyl-3-methyl imidazolium bromide
2
N
N
CH3COO-
1-hexyl-3-methyl imidazolium acetate
Figure 2.4: Metathesis reaction of imidazolium based ionic liquids
27
2.2.2.1.2 Pyridinium-based ionic liquids
Two general methods were used in the synthesis of pyridinium-based ionic liquids.
The first method involved an alkylation reaction where equimolar amount of 3-methyl
pyridine was reacted with alkyl halide producing a pyridinium alkyl halide. Figure 2.5
shows the ILs that were synthesized using this process. The second method is a
metathesis reaction where two moles of pyridinium alkyl halide were reacted with lead
acetate to generate two moles of pyridinium acetate and water. ILs synthesized using this
method is shown in Figure 2.6. And the entire spectra of the synthesized pyridiniumbased ILs were shown in Appendix A.
2.2.2.1.2.1 Alkylation reaction of pyridinium based ionic liquid
2.2.2.1.2.1.1 Synthesis of 1-ethyl-3-methyl pyridinium bromide
(EMPyr-bromide)
An excess amount of bromoethane (15 %, 1.14 mol) was added dropwise to 3-methyl
pyridine (0.99 mol). To enhance the reaction, isopropyl alcohol was added as co-solvent.
The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by rotaevaporation and to ensure all solvent was removed it was dried in vacuum oven at 70 ºC
overnight. The brown viscous liquid product was characterized using 1H-NMR (INOVA).
The presence of bromide ion was detected using AgNO3 test. Bromide is present if the
solution produced a precipitate upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3)
δ=1.708 (3H, t, 7.2 Hz), δ=2.637 (3H, s), δ=5.010 (2H, q, 7.8 Hz), δ=7.998 (1H, t, 7.8
Hz), δ=8.232 (1H, d, 7.8 Hz), δ=9.413 (1H, d, 3 Hz) δ=9.592 (1H, s).
28
Br-
N
+
N
Br
3-methyl pyridine
ethyl bromide
+
1-ethyl-3-methyl pyridinium bromide
N
Cl
Cl-
N
3-methyl pyridine
propyl chloride
1-propyl-3-methyl pyridinium chloride
N
+
N
Cl-
Cl
butyl chloride
3-methyl pyridine
1-butyl-3-methyl pyridinium chloride
N
Cl-
Cl
+
N
3-methyl pyridine
allyl chloride
1-allyl-3-methyl pyridinium chloride
N
Cl-
OH
+
N
3-methyl pyridine
Cl
HO
1-hydroxyethyl chloride
1-hydroxyethyl-3-methyl pyridinium chloride
Figure 2.5: Alkylation reaction of pyridinium-based ionic liquids
29
2.2.2.1.2.1.2 Synthesis of 1-propyl-3-methyl pyridinium chloride (PMPyr-Cl)
An excess amount of chloropropane (15 %, 5 mmol) was added dropwise to 3methyl pyridine (67 mmol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all of it was removed, the IL was dried in vacuum oven at
70 ºC overnight. The viscous brown liquid product was characterized using 1H-NMR
(INOVA). The presence of chloride ion was detected using the AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3)
δ=1.708 (3H, t, 7.2 Hz), δ=2.637 (3H, s), δ=5.010 (2H, q, 7.8 Hz), δ=7.998 (1H, t, 7.8
Hz), δ=8.232 (1H, d, 7.8 Hz), δ=9.413 (1H, d, 3 Hz) δ=9.592 (1H, s)
2.2.2.1.2.1.3 Synthesis of 1-butyl-2-methyl pyridinium chloride (B[2]MPyr-Cl)
An excess amount of chlorobutane (15 %, 62 mol) was added dropwise to 2methyl pyridine (53 mmol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed the IL was dried in the vacuum
oven at 70 ºC overnight. The light brown solid product was characterized using 1H-NMR
(INOVA). The presence of chloride ion was detected using AgNO3. Chloride is present if
the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3) δ=0.938
(3H, t, 7.2 Hz), δ=1.390 (3H, t, 7.8Hz), δ=1.500-1.550 (2H, m), δ=1.849-1.920(2H, m),
δ=2.959 (3H, s), δ=4.999 (2H, t, 7.8 Hz), δ=7.866 (1H, d, 7.8 Hz), δ=7.992 (1H, t, 7.2
Hz), δ=8.326 (1H, t, 1.2 Hz), δ=9.963 (1H, d, 6 Hz).
30
2.2.2.1.2.1.4 Synthesis of 1-butyl-3-methyl pyridinium chloride
(B[3]MPyr-Cl)
An excess amount of chlorobutane (15 %, 1.86 mol) was added dropwise to 3methyl pyridine (1.62 mol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed, the IL was dried in the vacuum
oven at 70 ºC overnight. The viscous brown liquid product was characterized using 1HNMR (Gemini). The presence of chloride ion was detected using AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3 and then precipitate dissolved
when HNO3 was added. 1H-NMR (600 MHz, CDCl3) δ=0.924 (3H, t, 6.0 Hz), δ=1.3371.398 (2H, m), δ=1.950-2.000 (2H, m), δ=2.627 (3H, s), δ=4.897 (2H, t, 7.2 Hz), δ=7.877
(1H, d, 6.0 Hz), δ=9.471 (1H, d, 5.4 Hz).
2.2.2.1.2.1.5 Synthesis of 1-butyl-4-methyl pyridinium chloride
(B[4]MPyr-Cl)
An excess amount of chlorobutane (15 %, 1.86 mol) was added dropwise to 3methyl pyridine (1.62 mol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed from the IL, it was dried under
vacuum at 70 ºC overnight. The pink solid product was characterized using 1H-NMR
(INOVA). The presence of chloride ion was detected using AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3)
31
δ=0.924 (3H, t, 6.0 Hz), δ=1.337-1.398 (2H, m), δ=1.950-2.000 (2H, m), δ=2.627 (3H, s),
δ=4.897 (2H, t, 7.2 Hz), δ=7.877 (1H, d, 6.0 Hz), δ=9.471 (1H, d, 5.4 Hz).
2.2.2.1.2.1.6 Synthesis of 1-ally-2-methyl pyridinium chloride (A[2]MPyr-Cl)
An excess amount of allyl chloride (15 %, 67 mmol) was added dropwise to 2methyl pyridine (59 mmol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed, the IL was dried under vacuum
oven at 70 ºC overnight. The viscous brown liquid product was characterized using 1HNMR (INOVA). The presence of chloride ion was detected using AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3)
δ=2.967 (3H, s), δ=5.155 (1H, d, 13.8Hz), δ=5.425 (1H, d. 10.2 Hz), δ=5.710 (2H, d, 6.6
Hz), δ=6.048-6.104 (1H, m), δ=7.939 (1H, d, 7.8 Hz), δ=8.003 (1H, t, 8.2 Hz), δ=8.407
(1H, t, 6.6 Hz), δ=9.697 (1H, s).
2.2.2.1.2.1.7 Synthesis of 1-ally-3-methyl pyridinium chloride (A[3]MPyr-Cl)
An excess amount of allyl chloride (15 %, 67 mmol) was added dropwise to 2methyl pyridine (59 mmol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed. The IL was dried under vacuum
at 70 ºC overnight. The viscous brown liquid product was characterized using 1H-NMR
(INOVA). The presence of chloride ion was detected using AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, DMSO)
32
δ=3.357 (3H, s), δ=5.238 (2H, d, 4 Hz), δ=5.395 (1H, d. 11.6 Hz), δ=5.439 (1H, d, 6.8
Hz), δ=6.131-6.148 (1H, m), δ=8.083 (1H, t, 4.4 Hz), δ=8.447 (1H, d, 5.2 Hz), δ=8.915
(1H, d, 5.2 Hz), δ=9.005 (1H, s).
2.2.2.1.2.1.8 Synthesis of 1-ally-4-methyl pyridinium chloride (A[4]MPyr-Cl)
An excess amount of allyl chloride (15 %, 67 mmol) was added dropwise to 3methyl pyridine (59 mmol). To enhance the reaction, isopropyl alcohol was added as cosolvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed, the IL was dried in the vacuum
oven at 70 ºC overnight. The viscous liquid brown product was characterized using 1HNMR (INOVA). The presence of chloride ion was detected using AgNO3 test. Chloride is
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, CDCl3)
δ=2.591 (3H, s), δ=5.260 (2H, d, 6.0Hz), δ=5.392 (2H, d, 7.8 Hz), δ=6.110-6.180 (1H,
m), δ=8.030 (1H, d, 6.0Hz), δ=8.970 (1H, d, 12.0 Hz).
2.2.2.1.2.1.9 Synthesis of 1-hydroxyethyl-3-methyl pyridinium chloride
(HEMPyr-Cl)
An excess amount of hydroxyethyl chloride (15 %, 65 mmol) was added dropwise
to 3-methyl pyridine (59 mmol). To enhance the reaction, isopropyl alcohol was added as
co-solvent. The mixture was refluxed at 50 ºC for three (3) days. Solvent was removed by
rota-evaporation and to ensure all solvent was removed, the IL was dried in vacuum oven
at 70 ºC overnight. The viscous liquid brown product was characterized using 1H-NMR
(INOVA). The presence of chloride ion was detected using AgNO3 test. Chloride is
33
present if the solution precipitated upon addition of AgNO3. 1H-NMR (600 MHz, D2O)
δ=2.492 (3H, s), δ=3.997 (2H, t, 4.8Hz), δ=4.609 (2H, t, 4.8 Hz), δ=7.891 (1H, t, 14.4Hz),
δ=8.339 (1H, d, 8.4Hz), δ=8.592 (1H, d, 6 Hz), δ=8.644 (1H, s).
2.2.2.1.2.2 Metathesis reaction of pyridinium-based ionic liquids
This reaction involves the exchange of an anion and is chemically referred to as
metathesis or double displacement reaction. Stoichiometically, two moles of pyridinium
halide are reacted with one mole of lead acetate trihydrate. Water was used as the solvent
since these ILs were water-stable compounds. The solution was stirred for a minimum of
1 hour. After constant stirring, the solution stood for another hour and was allowed to
separate completely into a two phase mixture. The upper layer contained the desired IL
and lower layer precipitate, PbCl2. Gravity filtration was performed to completely isolate
the pyridinium acetate IL from PbCl2 precipitate. Water was removed from the resulting
IL using rota-evaporation and was dried using a vacuum oven overnight at 70 ºC to
ensure removal of solvent. The exchange is complete after performing the AgNO3 / HNO3
test. A clear solution indicates that exchange was complete. If the solution appeared
cloudy, CH2Cl2 or CHCl3 was added to the IL to continue precipitating the remaining
halide. The mixture was again stirred for at least an hour, and then allowed to stand for at
least another one hour. Separation was again performed by gravity filtration. The solvent
was removed under reduced pressure and then oven dried overnight at 70 ºC to obtain the
pure IL. The test with AgNO3 / HNO3 was performed again to confirm if the metathesis
reaction was completed. The process from adding CH2Cl2 or CHCl3 to AgNO3 / HNO3
34
test was repeated until all halide was removed from the pyridinium acetate IL as indicated
by a clear solution.
2.2.2.1.2.2.1 Synthesis of 1-ethyl-3-methyl pyridinium acetate (EMPyr-Ac)
Lead acetate trihydrate (0.55 moles) was added slowly to 1.10 moles of 1-ethyl-3methyl pyridinium bromide. Solutions were both prepared in water. The resulting brown
viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, DMSO)
δ=1.536 (3H, t, 7.2Hz), δ=1.638 (3H, s), δ=4.496 (2H, q, 7.2Hz), δ=8.059 (1H, t, 7.2Hz),
δ=8.441 (1H, d, 7.8Hz), δ=8.978 (1H, d, 6.0 Hz), δ=9.071 (1H, s).
2.2.2.1.2.2.2 Synthesis of 1-butyl-3-methyl pyridinium acetate (BMPyr-Ac)
Lead acetate trihydrate (0.72 moles) was added slowly to 1.43 moles of 1-butyl-3methyl pyridinium chloride. Solutions were both prepared in water. The resulting brown
viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, CDCl3)
δ=0.700 (3H, s), δ=1.12-1.18 (2H, m), δ=1.580 (3H, s), δ=1.756-1.790 (2H, m),
δ=4.210(3H, s), δ=4.621 (2H, t, 8.0 Hz), δ=7.863 (1H, t, 8.0 Hz), δ=8.903 (1H, d, 8.0 Hz),
δ=8.991 (1H, d, 8 Hz), δ=9.074 (1H, s).
2.2.2.1.2.2.3 Synthesis of 1-allyl-2-methyl pyridinium acetate (A[2]MPyr-Ac)
Three mole of lead acetate trihydrate was added slowly to five moles of 1-allyl-2methyl pyridinium chloride. Solutions were both prepared in water. The resulting brown
viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR (600 MHz, D2O)
δ=1.867 (3H, s), δ=2.491 (3H, s), δ=5.123 (2H, d. 4.8 Hz), δ=5.483 (2H, d, 10.2 Hz),
35
+
Br-
N
Pb (CH3COO) 2·3H2O
1-ethyl-3-methyl pyridinium bromide
lead acetate trihydrate 1-ethyl-3-methyl pyridinium acetate
+
Pb(CH3COO)2·3H2O
1-propyl-3-methyl pyridinium chloride
lead acetate trihydrate
N
Cl-
N
+
Cl-
1-butyl-3-methyl pyridinium chloride
lead acetate trihydrate
Pb(CH3COO)2·3H2O
1-allyl-3-methyl pyridinium chloride
lead acetate trihydrate
Cl-
N
N
CH3COO-
1-butyl-3-methyl pyridinium acetate
N
CH3COO-
1-allyl-3-methyl pyridinium acetate
N
Pb (CH3COO) 2·3H2O
lead acetate trihydrate
1-hydroxyethyl-3-methyl pyridinium chloride
CH3COO-
1-propyl-3-methyl pyridinium acetate
Cl-
+
HO
N
Pb(CH3COO)2·3H2O
+
N
CH3COO-
N
CH3COO-
HO
1-hydroxyethyl-3-methyl pyridinium acetate
Figure 2.6: Metathesis reaction of pyridinium-based ionic liquids
36
δ=6.069-6.089 (1H, m), δ=7.897 (1H, d, 4.8 Hz), δ=8.331 (1H, d, 7.2 Hz), δ=8.600 (1H,
d, 3.0 Hz), δ=8.640 (1H, s).
2.2.2.1.2.2.4 Synthesis of 1-allyl-3-methyl pyridinium acetate (A[3]MPyr-Ac)
Three millimoles of lead acetate trihydrate were added slowly to five millimoles
of 1-allyl-3-methyl pyridinium chloride. Solutions were both prepared in water. The
resulting brown viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR (600
MHz, D2O) δ=1.904 (3H, s), δ=2.519 (3H, s), δ=5.151 (2H, d, 6.0 Hz), δ=5.430 (2H, d,
6.0 Hz), δ=6.084-6.101 (1H, m), δ=7.932 (1H, t, 13.8 Hz), δ=8.359 (1H, d, 7.8 Hz),
δ=8.621 (1H, d, 6.0 Hz), δ=8.662 (1H, s).
2.2.2.1.2.2.5 Synthesis of 1-allyl-4-methyl pyridinium acetate (A[4]MPyr-Ac)
Three millimoles of lead acetate trihydrate were added slowly to five millimoles
of 1-allyl-4-methyl pyridinium chloride. Solutions were both prepared in water. The
resulting brown viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR (600
MHz, CDCl3) δ=1.215 (3H, s), δ=2.680 (3H, s), δ=5.518 (2H, d, 9.6 Hz), δ=5.679 (2H, d,
6.6 Hz), δ=6.116-6.144 (1H, m), δ=7.840 (1H, d, 6.6 Hz), δ=9.337 (1H, d, 6.6 Hz).
2.2.2.1.2.2.6 Synthesis of 1-hydroxyethyl-3-methyl pyridinium acetate
(HEMPyr-Ac)
Three millimoles of lead acetate trihydrate were added slowly to eleven
millimoles of 1-ethylhydroxy-3-methyl chloride. Solutions were both prepared in water.
The resulting brown viscous IL was characterized using 1H-NMR (INOVA). 1H-NMR
37
(600 MHz, DMSO) δ=1.621 (3H, s), δ=3.822 (2H, d, 4.8 Hz), δ=4.571 (2H, t, 5.4 Hz),
δ=8.032 (1H, d, 6.6 Hz), δ=8.426 (1H, d, 7.8 Hz), δ=8.466 (1H, d, 6.0 Hz), δ=8.909 (1H,
s).
2.2.2.1.3 Bulk synthesis of pyridinium-based ionic liquids
Some pyridinium-based ILs namely; 1-allyl-3-methyl pyridinium chloride, 1butyl-3-methyl pyridinium chloride (7) were synthesized at bulk scale as these ILs exhibit
good solubility of cellulose based from the results of dissolution experiment (Table 2.1)
and from the literature (7). Furthermore, these ILs are cheaper and easier to synthesize.
Pyridinium ILs, 1-ethyl-3-methyl pyridinium bromide was also included to the list of ILs
for bulk synthesis. Imidazolium and pyridinium cation paired with halide anions,
particularly chloride, was reported to be more effective in dissolving cellulose (5, 7).
However, due to their high melting point and high viscosity, it limits their application in
cellulose solubility. Dissolving cellulose in ILs is usually performed at higher
temperature (>70 ºC) which could result in thermal degradation and could release
hazardous products like organohalogenides (13). Aside from this, imidazolium-based
chloride ionic liquids can corrode metals which pose hazardous effect in the environment
(12, 13). With these mentioned disadvantages it is more preferred to produce the
pyridinium and imidazolium acetate ILs because they resolve the harmful effect of the
imidazolium chloride to human health and environment. Hence, the acetate analogue of
the pyridinium based ILs, 1-allyl-3-methyl pyridinium chloride, 1-butyl-3-methyl
pyridinium chloride and 1-ethyl-3-methyl pyridinium bromide were also synthesized in
large amount.
38
In synthesis, difficulty was encountered with generating pyridinium acetate based
ILs. The ion-exchange reaction was troublesome. First, the exchange was very tedious
because of the very slow mass transfer of the chloride to acetate. Secondly, a lot of
solvent is needed to completely precipitate out the chloride anion because it is hard to
completely remove from the IL since it is very strong coordinating anion. Thus, it turned
out that the synthesis of pyridinium acetate IL was unsuccessful.
2.2.2.1.4 Alternative method in the synthesis of imidazolium and
pyridinium-acetates ionic liquid
Due to the unsuccessful attempt in using the ion-exchange route to transform the
chloride-based IL to an acetate-based ILs at the bulk scale, different paths were sought.
The aim was to find a process that could bypass the production of the halide anions
because of its disadvantages that were been mentioned in the previous section.
The synthesis involves the reaction of equimolar amount of KOH added to
EMIM-Br for imidazolium IL and AMPyr-Cl for the pyridinium-based IL. Reactions
were prepared with different co-solvents, including THF, methylene chloride and
chloroform, to compare which co-solvent was effective in precipitating KBr. Chloroform
was not used as co-solvent because it turned out to produce an exothermic reaction and
generate a black solution unlike with methylene chloride and THF. After stirring the
solution for 24 hours, it was filtered several times. The separated filtrate containing the
product was rota-evaporated to remove the co-solvent, washed with diethyl ether, and
then dried in vacuum oven overnight at 70 ºC. The concentration of the imidazolium and
39
pyridinium hydroxide was obtained by titrating with a standardized solution of 0.1 M
HCl using methyl orange as an indicator.
Neutralization reactions were performed for the imidazolium and pyridinium
hydroxides which were reacted with acetic acid. The same process was followed as in
section 2.2.2.1.1. The solvent was removed under pressure and dried in vacuum oven
overnight for 70 ºC. The samples were characterized by 1H-NMR. The obtained spectra
revealed that the imidazolium acetates were not synthesized successfully (See Appendix
B). The possible reason is that both co-solvents used have very low solubility with KBr
which is the minor product in the reaction. Figure 2.7 showed the reaction involved in the
synthesis of imidazolium acetate ILs.
2.2.2.1.4.1 Imidazolium-based ionic liquids
2.2.2.1.4.1.1 Synthesis of 1-ethyl-3-methyl imidazolium hydroxide
(EMIM-OH)
Equimolar amount of KOH (58 mmol) was dissolved in methylene chloride or
THF and was mixed with EMIM-Br. The solution was mixed vigorously at room
temperature and filtered to remove the KBr precipitate. EMIM-OH was washed with
diethyl ether, air dried, and dried under vacuum at 70 ºC overnight. Pure EMIM-OH was
re-dissolved in water. The concentration of the obtained EMIM-OH was determined.
40
2.2.2.1.4.1.2 Synthesis of 1-Ethyl-3-Methyl Imidazolium Acetate
(EMIM-Acetate)
Equimolar amount of acetic acid was slowly added to the EMIM-OH aqueous
solution. It was then neutralized for 24 hours at room temperature. The solution was rotaevaporated and then vacuum dried for one day to remove excess water. The brown and
viscous EMIM acetate compound was characterized using 1H-NMR, as shown in
appendix B.
2.2.2.1.4.2 Pyridinium-based ionic liquids
2.2.2.1.4.2.1 Synthesis of 1-Allyl-3-Methyl Pyridinium Hydroxide
(AMPyr-OH)
An equimolar amount of KOH was dissolved in methylene chloride or THF and
was mixed with AMPyrCl. The solution was mixed vigorously at room temperature and
then filtered to remove the KCl. AMPyr-OH was washed with diethyl ether, air dried and
then vacuum dried. The sample was re-dissolved in water and the concentration of the the
AMPyr-OH was obtained.
2.2.2.1.4.2.2 Synthesis of 1-Allyl-3-Methyl Pyridinium Acetate (AMPyr-Ac)
Equimolar amount of acetic acid was added to AMPyr-OH dropwise and water
was added to enhance the reaction. The mixture was neutralized for 24 hours at room
temperature and then rota-evaporated and vacuum dried for one day to remove excess
water. The synthesized compound was a very dark brown and viscous IL. The IL was not
41
subjected to 1H-NMR because no deuterated solvent was capable of dissolving the IL
completely. Figure 2.7 showed the route used in the synthesis of pyridinium acetate.
2.2.2.2 Examination of solubility
Approximately 25 mg of IL was measured into a vial and to this was added
approximately 10-20 mg of commercially available Avicel cellulose. The mixture was
immersed in an oil bath set at 100ºC. Avicel was added each time and allowed to dissolve.
The addition of Avicel is repeatedly added until the saturation point is reached. At this
point, the mixture turns dark in color or even black sometimes. Then, the amount of
cellulose dissolved in IL was calculated using weight to weight percentage (equation 2.4),
where:
% solubility =
total weight of cellulose dissolved (mg)
----------------------------------------------
x 100
weight of IL (mg) plus the total weight of cellulose dissolved
42
(2.4)
A. Imidazolium acetate ILs
N
+
N
+
Br
-
KOH
N
N
+
N
OH-
potassium hydroxide
1-ethyl-3-methyl imidazolium bromide
N
+
1-ethyl-3-methyl imidazolium hydroxide
+
OH-
CH3COOH
N
+
N
CH3COO-
acetic acid
1-ethyl-3-methyl imidazolium hydroxide
1-ethyl-3-methyl imidazolium acetate
B. Pyridinium acetate IL
N
N
Cl-
+
OH-
KOH
potassium hydroxide
1-allyl-3-methyl pyridinium chloride
N
1-allyl-3-methyl pyridinium hydroxide
OH-
N
CH3COO-
+ CH3COOH
acetic acid
1-allyl-3-methyl pyridinium hydroxide
1-allyl-3-methyl pyridinium acetate
Figure 2.7: Alternative method in the synthesis of imidazolium and pyridinium
acetate ionic liquids
43
2.3 RESULTS AND DISCUSSION
2.3.1 EFFECT OF TYPE OF CATIONS
The role of the cation in the solubility of cellulose involves the interaction with
the hydroxyl group of the cellulose via non-bonding or π electrons (2). In Table 2.1, it
can be seen that in ILs 16-19, only IL 16, EMIM-Cl solubilized Avicel cellulose. ILs 1719 showed no cellulose dissolution. This agrees with the study by Swatloski and coworkers (5). They reported that increasing linear alkyl group substituents in the
imidazolium ring cation within the given ionic liquid decreases solubility of cellulose
which may be due to reduced effective chloride concentration. The effect of alkyl chain
length was better demonstrated in ILs 5 and 9. The shorter alkyl chain of IL 5, P(3)MPyrCl, produced better solubility of cellulose than in IL 9 or B(3)MPyr-Cl. The solubility of
the former IL is higher by 1-2 % than the latter IL. The structures of the ILs are shown in
Figures 2.8 and 2.9.
On the other hand, functionalization of the cation can also affect the solubility of
Avicel in the ILs. For example, between ILs 5 and 11, the solubility of cellulose
decreased in IL 11 by 2–3 % as compared to IL 5. This was caused by the hydroxyl
substituents attached at alkyl chain on the nitrogen atom of the pyridinium cation. The
said functional group enhanced the hydrogen bond acidity of the IL. This is caused by its
ability to donate protons from the hydroxyl group but at the same time decreases its
hydrogen bond basicity characteristic. The calculated value is shown in Chapter 3, table
3.6. The functionalization of the cation has more pronounced effect on the solubility
study in ILs 2 and 9. IL 2 showed higher cellulose solubility as compared with IL 9. As
44
Table 2.1: Solubility of Cellulose in Ionic Liquids
Number
IONIC LIQUIDS
Abbreviation
Solubility of Avicel
1
1-Allyl-2-Methyl Pyridinium Chloride
A(2)MPyr-Cl
19–21 %
2
1-Allyl-3-Methyl Pyridinium Chloride
A(3)MPyr-Cl
23–26 %
3
1-Allyl-4-Methyl Pyridinium Chloride
A(4)MPyr-Cl
17–22 %
4
1-Propyl-2-Methyl Pyridinium Chloride
P(2)MPyr-Cl
did not dissolved
5
1-Propyl-3-Methyl Pyridinium Chloride
P(3)MPyr-Cl
18–21 %
6
1-Propyl-4-Methyl Pyridinium Chloride
P(4)MPyr-Cl
did not dissolved
7
1-Butyl-3-Methyl Pyridinium Acetate
B(3)MPyr-Ac
12-15 %
8
1-Butyl-2-Methyl Pyridinium Chloride
B(2)MPyr-Cl
6-9 %
9
1-Butyl-3-Methyl Pyridinium Chloride
B(3)MPyr-Cl
16–19 %
10
1-Butyl-4-Methyl Pyridinium Chloride
B(4)MPyr-Cl
did not dissolved
11
1-Hydroxyethyl-3-Methyl Pyridinium Chloride
HEMPyr-Cl
15–18 %
12
1-Hydroxyethyl-3-Methyl Pyridinium Acetate
HEMPyr-Ac
1-3 %
13
1-Allyl-2-Methyl Pyridinium Acetate
A(2)MPyr-Cl
11–14 %
14
1-Allyl-3-Methyl Pyridinium Acetate
A(3)MPyr-Cl
12-17 %
15
1-Allyl-4-Methyl Pyridinium Acetate
A(4)MPyr-Cl
13-15 %
16
1-Ethyl-3-Methyl Imidazolium Chloride
EMIM-Cl
13-16 %
17
1-Hexyl-3-Methyl Imidazolium Chloride
HMIM-Cl
did not dissolved
18
1-Octyl-3-Methyl Imidazolium Chloride
OMIM-Cl
did not dissolved
19
1-Octyl-3-Butyl Imidazolium Chloride
OBIM-Cl
did not dissolved
20
1-Ethyl-3-Methyl Imidazolium Formate
EMIM-formate
20-25 %
21
1-Ethyl-3-Methyl Imidazolium Acetate
EMIM-acetate
20-25 %
22
1-Ethyl-3-Methyl Imidazolium Propionate
EMIM-propionate
22-26 %
45
mentioned by Kilpeläinen and co-workers (12), the aromatic π-system of the cationic
moiety of the IL has strong ability for π - π interactions that can create stronger solvation
interactions for polymers capable of the same interaction. The dissolution of cellulose can
be further enhanced with the attachment of substituents in the aromatic ring that can
exhibit n - π or π - π interaction as was observed by Zavrel and co-workers (6).
Furthermore, the strong non-bonding or π electron interaction of IL 2 to IL 9 is supported
by the assessment of the ILs’ solvation properties using the Abraham solvation parameter
model. In Chapter 3, Table 3.6, the e – value of IL 2, is 0.85 ± 0.23, observed at 100 ºC,
which is larger than the e – value of IL 9 that is 0.61 ± 0.16, observed at 100 ºC.
2.3.2 EFFECT OF TYPE OF ANIONS
The anion portion of the IL plays the crucial role in solubility of cellulose. The
anion attacks the hydrogen of the hydroxyl group of cellulose and disrupts its rigidity (2).
The higher the calculated basicity of the IL results in high solubility of cellulose. The
quantitative evaluation of solvation properties of imidazolium and pyridinium-based ILs
were presented in chapter 3. This observation was evident with ILs 2, 20-22. All of these
ILs showed high basicity characteristics (Table 3.4 and 3.6) and the high solubility of
Avicel in the ILs.
ILs paired with chloride anion such as ILs 1-3; 9; 11 exhibited higher cellulose
solubility than ILs 13-15; 7; 12 with acetate anion analogues. This could be explained by
the smaller atomic radii of chloride ion which more easily associates with the cellulose
hydroxyl proton (2, 3) than those with an acetate anion. This observation was more
46
N
N
Cl-
1-ally-2-methyl imidazolium
chloride (IL 1)
N
N
1-ally-3-methyl imidazolium
chloride (IL 2)
N
Cl-
1-propyl-2-methyl imidazolium
chloride (IL 4)
Cl-
N Cl-
Cl-
N
N
Cl-
1-propyl-3-methyl
imidazolium chloride (IL 5)
1-ally-4-methyl imidazolium
chloride (IL 3)
N
Cl-
1-propyl-4-methyl
imidazolium chloride (IL 6)
Cl-
N
CH3COO-
1-butyl-3-methyl
imidazolium chloride (IL 7)
N
Cl-
Cl-
OH
1-butyl-2-methyl
imidazolium chloride (IL 8)
N
OH
CH3COO-
1-hydroxyethyl-3-methyl
imidazolium acetate (IL 12)
1-butyl-3-methyl
imidazolium chloride (IL 9)
N
1-butyl-4-methyl
imidazolium chloride (IL 10)
N
CH3COO-
1-ally-2-methyl imidazolium
acetate (IL 13)
1-hydroxyethyl-3-methyl
imidazolium chloride (IL 11)
CH3COO-
N
CH3COO-
1-ally-3-methyl imidazolium 1-ally-4-methyl imidazolium
acetate (IL 14)
acetate (IL 15)
Figure 2.8: Pyridinium based ionic liquids examined for dissolution of cellulose
47
N
N
N
N
-
Cl-
Cl
1-ethyl-3-methyl imidazolium chloride
(IL 16)
1-hexyl-3-methyl imidazolium chloride
(IL 17)
N
N
N
Cl-
Cl-
1-octyl-3-methyl imidazolium chloride
(IL 18)
N
N
1-octyl-3-butyl imidazolium chloride
(IL 19)
N
N
HCOO-
1-ethyl-3-methyl imidazolium
formate (IL 20)
N
CH3COO-
N
N
CH3CH2COO-
1-ethyl-3-methyl imidazolium
acetate (IL 21)
1-ethyl-3-methyl imidazolium
propionate (IL 22)
Figure 2.9: Imidazolium based ionic liquids examined for dissolution of cellulose
48
obvious between ILs 11 and 12. IL 11 or HEMPyr-Cl has 15-18 % Avicel solubility and
dramatically decreased to 1-3 % in HEMPyr-Ac IL.
2.3.3 EFFECT OF ISOMER
In Table 2.1, ILs 1-3; 4-6; 8-10 and 13-15 are examples of isomeric ILs. For these
ILs, the cellulose solubility is affected by the two factors; the position of methyl group
and the substituents present in the nitrogen atom of the pyridinium ring.
When the methyl substituent is in the meta-position with respect to the nitrogen
atom of the pyridinium ring (Figure 2.8), the IL showed the highest dissolution of
cellulose with ILs 2, 5, 9 and 14. Avicel has solubility ranging from a minimum of 1217 % as observed in IL 14 and as high as 23-26 % solubility as seen with IL 2. When a
methyl group is at the ortho-position such as ILs 1, 4, 8 and 13 low dissolution of
cellulose was observed with ILs 1, 8 and 13 while no observable dissolution was seen
with IL 4.
The effect of substituents on the solubility is seen in ILs 5 and 6, 9 and 10. ILs
with methyl group at meta-position like ILs 5 and 9 showed solubility of cellulose
compared to no solubility of ILs 6 and 10 having the methyl at para-position. On the
other hand, ILs 2 and 3; and ILs 14 and 15, showed good solubility. The significant
increase in solubility of ILs 3 and 15 is due to the alkene group attached to the nitrogen
atom of the pyridinium ring compared to alkane group in ILs 6 and 10. As has been
reported, the enhancement of cellulose dissolution with ILs can be attributed to its ability
to undergo π -π interaction with cellulose by the π aromatic system (12) and the π-
49
electron presence on its side-chain (6). Thus, explains the higher solubility of Avicel in
ILs 3 and 15 compared to ILs 6 and 10.
2.3.4 ANALYSIS OF THE RECOVERED IONIC LIQUIDS AFTER
PRE-TREATMENT
ILs were found to be an effective solvent for dissolution and pre-treatment of
cellulose (2). Pre-treatment is the process of separating the cellulose from the
hemicellulose and lignin in the lignocellulose for effective hydrolysis. The cellulose
which is the major constituent of lignocellulose, will serve as the source to generate the
biofuel. Upon pre-treatment, the cellulose will become amorphous which increases its
surface area of cellulose to improve the hydrolysis of the enzyme and converts the
complex structure of cellulose to simple sugar units. Through the fermentation process,
the sugar can easily converted to bioethanol (2, 8, 13). ILs used in pre-treatment offer
several advantages such as, large amount of cellulose can be dissolved even at mild
conditions (2), almost 100% of IL can be recovered after cellulose regeneration and the
recovered IL can be re-used for several pre-treatment process (7) and since IL has no
measurable vapor pressure (2, 14, 15) it has less impact to air quality (2, 13-15).
Among the ILs studied, EMIM-acetate was initially used for the said process.
This was due to its strong hydrogen bond basicity which as mentioned in section 2.3.2
playing a crucial role in the dissolution process of cellulose. Moreover, EMIM-acetate is
less toxic, non-corrosive (2) and more biodegradable (2, 3, 10) compared to other
cellulose dissolving ILs particularly with those having chloride anion. ILs with chloride
anions may have potential limitations in future industrial applications because of the
50
possible metal corrosion with the IL. Additionally, during the dissolution process at high
temperature, the release of hazardous products such as organohalogenides is expected (3).
Thus, from the aforementioned detrimental effects of the chloride anion interest of most
scientists shifted to alternative ILs for dissolution, process specifically EMIM-acetate IL.
EMIM-acetate selected for pre-treatment analysis was recovered and purified and
then characterized using 1H,
13
C-NMR and MS analyses ascertain to possible impurities
that could be introduced into the IL, as well as the ILs degradation products. The 1H and
13
C spectra seen in Figures 2.10 and 2.11 showed that all the signals that correspond to
the protons and carbons of the IL were present. Those additional signals which are
encircled in Figures 2.10 and 2.11. These are identified as signals of the starting material,
1-ethyl imidazole and acetic acid. Their spectra are shown in Figures 2.12 and 2.13. The
MS analysis for pure and purified IL seen in Figure 2.14, confirms the presence of EMIM
cation. Appendix C shows the other spectra of the recovered ILs after pre-treatment.
51
a
H
N
N
f
g
e
CH2CH3
3.85
H3C
1.53
d
e
CH3COO
f
H
H
b
c
1.40
g
f
9.5
9.0
8.5
8.0
1.39
4.20
4.19
c
7.5
7.0
6.5
6.0
5.5
5.0
ppm
4.18
4.21
7.81
7.72
9.58
b
2.50
d
a
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
12
11
10
9
8
1.31
1.41
1.32
2.50
4.20
4.19
3.97
2.39
6.86
7.80
7.80
7.62 7.72
1.00
7.18
9.44
1.40
3.85
1.66
Pure EMIM-acetate prepared in DMSO
2.41 3.46
7
6
5
ppm
4
4.98
3
2
1
0
-1
Recovered EMIM-acetate after used in several pre-treatment analysis prepared in DMSO
Figure 2.10: Comparison of 13H-NMR between EMIM-acetate from recovered
EMIM-acetate after used in pre-treatment analysis
52
b
f
e
H3 C
N
N
h
CH2CH3
CH3COO
d
c
g
a
h
15.44
138.27
124.00
122.58
44.04
e
f
g
d
25.82
35.41
c
b
39.71
39.51
39.30
174.46
a
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
ppm
200
150
100
50
15.24
16.43
40.93
39.51
128.30
118.93
136.81
173.63
250
24.35
35.52
137.27
44.01
122.02
123.57
Pure EMIM-acetate prepared in DMSO
0
ppm
Recovered EMIM-acetate after used in several pre-treatment analysis prepared in DMSO
Figure 2.11: Comparison of 13C-NMR between EMIM-acetate from recovered
EMIM-acetate after used in pre-treatment analysis
53
1.33
1.29
1.36
3.38
4.00
3.96
6.88
7.18
1.05
7.5
1.04
7.0
2.51
2.50
4.03
3.93
7.63
1.00
2.35
6.5
5.5
5.0
4.5
ppm
3.54
4.0
3.5
3.0
2.5
2.0
1.5
H-NMR of 1-Ethyl imidazole prepared in DMSO
118.84
16.33
136.79
128.50
40.97
16.30
1
6.0
135
130
125
120
115
110
105
100
95
90
85
80
75
ppm
70
65
60
55
50
45
40
35
30
13
C-NMR of 1-Ethyl imidazole prepared in DMSO
Figure 2.12: 1H-NMR and 13C-NMR of 1-Ethyl imidazole
54
25
20
15
10
1
H-NMR of acetic acid
13
C-NMR of acetic acid
Figure 2.13: 1H-NMR and 13C-NMR of Acetic acid (spectra taken from Sci-finder)
55
EMIM cation of pure EMIM-acetate
EMIM cation of purified EMIM-acetate
Figure 2.14: MS of EMIM cation
56
2.4 CONCLUSIONS
Dissolution of cellulose by using ionic liquids has received considerable attention.
In the dissolution of cellulose by ionic liquids, the anionic portion of the IL interact with
the proton of the free hydroxyl group of cellulose and deprotonates the cellulose. While,
the cationic portion of the IL, imidazolium and pyridinium, interacts with the hydroxyl
group of the cellulose through n to π interaction. Participation of both the cation and
anion participation in the process is very essential. When the cationic portion of the IL is
larger the solubility decreases within a given mass of IL due to reduction of the effective
active anion. This was observed with OMIM-Cl and OBIM-Cl. These ILs have a long
linear alkyl chain attached to the nitrogen atoms of the imidazolium ring which causes a
decrease in Avicel solubility. The functionalization of the cation portion plays an
important role as well. When the cation part is appended by alkene substituents such as
ILs 1-3 and 13-15 moderately high solubility of cellulose was observed. This is due to the
enhanced π - π interaction contributed by both the aromatic ring and the substituents.
When the IL is substituted with an alkane group, a dramatic decrease of solubility was
observed. This was seen on ILs 4, 6 and 10. Moreover, a decrease in dissolution was also
observed in ILs appended with a hydroxyl group such as IL 11. This hydroxyl moiety
substituent increases the acidity of the IL but decreases the basicity.
The anionic portion of the IL defines its ability for hydrogen-bond basicity
characteristic. ILs paired with monocarborxylate anion (formate, acetate and propionate)
and some with chloride anion (EMIM-Cl, AMPyr-Cl, BMPyr-Cl and HEMPyr-Cl) have
high dissolution of Avicel cellulose. The size of the anion likewise can affect the
solubility of Avicel with the IL. For instance, comparing ILs 11 and 12, the latter IL
57
being paired with acetate anion significantly decreased the dissolution as compared to IL
11.
The effect of isomer of the IL showed that the dissolution process can be affected
by the position of the substituents with respect to the nitrogen atom of the pyridinium
cation or the substituents attached to said atom. Regarding the substituent position in the
pyridinium cation, low solubility of cellulose was seen if the methyl substituent of the IL
is at ortho-position but if at methyl group is at meta or para-postion, moderate to high
dissolution of Avicel was observed. Meanwhile, the substituents attached to the nitrogen
atom, this was the same finding as to functionalization of cation that increased in
solubility can be observed by the increased of π – π interaction in both the cation and
anion portion of the IL.
Lastly, the structural composition of the ILs are important in describing its
over-all solubility with Avicel cellulose. Higher solubility of cellulose can be achieved
with proper tuning of the cation and anion of synthesized ionic liquids.
2.5 BIBLIOGRAPHY
1. Pinkert, A., K. N. Marsh, et al. “Ionic Liquids and Their Interaction with Cellulose”,
Chemical Reviews, 2009, 109(12): 6712-6728
2. Dadi, A. P.; Varanasi, A.; Schall, C. A. “Enhancement of cellulose saccharification
kinetics using an ionic liquid pretreatment step”, Biotechnology and Bioengineering
2006, 95(5), 904-910
3. Cao, Y. et. al.. “ Room temperature ionic liquids (RTILs): A new and versatile
platform for cellulose processing and derivatization”, Chemical Engineering Journal,
58
2009, 147(1), 13-21.
4. Cuissinat, C.; Navard, P.; Heinze, T. “ Swelling and dissolution of cellulose, Part V:
cellulose derivatives fibres in aqueous systems and ionic liquids”, Cellulose, 2008,
15(1), 75-80
5. Swatloski R. P; et. al., “Dissolution of cellulose [correction of cellose] with ionic
liquids’, Journal of the American Chemical Society, 2002, 124(18), 4974-5
6. Zavrel M.; et. al., “High-throughput screening for ionic liquids dissolving
(ligno-)cellulose”, Bioresource technology, 2009, 100(9), 2580-7
7. Heinze, T. et. al., “Ionic Liquids as reaction Medium in Cellulose Functionalization”
Macromolecular Bioscience, 2005, 5, 520-525.
8. Samyam, I.P and Schall, C. A., “Saccharification of ionic liquid pretreated biomass
with commercial enzyme mixtures”, Bioresource Technology, 2010, 101, 3561-6
9. Fukaya, Y. et. al., “Cellulose dissolution with polar ionic liquids under mild conditions:
required factors for anions”, Green Chemistry, 2008, 10(1), 44-46.
10. Liebert, T. and Heinze, T., “Interaction of Ionic Liquids with polysaccharides 5.
Solvents and Reaction media for the modification of cellulose”, Bioresources, 2008,
3(2), 576-601
11. Zhang, H., et. al., “1-Allyl-3-methylimidazolium Chloride Room Temperature Ionic
Liquid: A New and Powerful Nonderivatizing Solvent for Cellulose”
Macromolecules, 2005, 38, 8272-8277
12. Kilpeläinen, I., et. al., “Dissolution of Wood in Ionic Liquids”, J. Agric. Food
Chem., 2007, 55, 9142-9148
13. Dadi, A. P.; Varanasi, A.; Schall, C. A., Varanasi, S., “ Mitigation of Cellulose
59
Recalcitrance to Enzymatic Hydrolysis by Ionic Liquid Pretreatment’, Applied
Biochemistry and Biotechnology, 2007, 37-140(1-12), 407-21
14. Chiappe, C. and D. Pieraccini, “Ionic liquids: solvent properties and organic
reactivity “, Journal of Physical Organic Chemistry, 2005, 18(4): 275-297
15. Plechkova, N. and Seddon, K, “Application of ionic liquids in chemical industry’,
Chemical Society reviews, 2007, 123-150
60
PART TWO
Evaluation of solvation properties of imidazolium
and pyridinium based ionic liquids
61
CHAPTER 3
CHARACTERIZATION OF IONIC LIQUID SOLVATION PROPERTIES USING
ABRAHAM SOLVATION PARAMETER MODEL BY INVERSE GAS
CHROMATOGRAPHY
3.1 INTRODUCTION
3.1.1 Solvation properties of ionic liquid using gas-liquid chromatography
Ionic liquid exhibits a plethora of unique physicochemical and solvation
properties. Their unique characteristics have attracted interest among researchers.
Various methods of examining properties of compounds were developed using liquid
chromatography and gas chromatography. But, gas chromatographic analysis is a
technique widely used in determination of solution properties because it showed a much
better measurement of physicochemical properties (4). Several parameters and techniques
have been developed to provide quantitative information that is related to the solvation
properties of ILs. In this study, among the different methods of analyses of solvation
properties, different pyridinium and imidazolium-based ionic liquids were examined by
using Abraham solvation parameter model by inverse gas chromatography. This
quantitative assessment of ILs solvation characteristic will explain clearly the results
observed in the study of cellulose dissolution.
62
3.1.1.1 Kovats retention index system
One method for the analysis of solvation properties is the concept of Kovats
retention index. This is a model based on gas-liquid chromatography where retention
times are measured and then converted into system-independent constants measured at
constant temperature (3, 4). The data derived varies with individual chromatographic
systems (i.e., column length, film thickness, column diameter, carrier gas velocity and
pressure) and can be used to compare columns from different analytical laboratories.
Linear n-alkanes are used as standard substances where each one is assigned 100 times its
carbon number. Homologous series of alkanes are used as reference compounds because
of their low polarity and freedom from H-bonding. For a member of homologous series
the logarithm of adjusted retention time is linearly related to the given temperature of the
column. This provides an information relating adjusted retention times to a fixed point of
the retention index scale (5). Furthermore, measurement using retention index is an
accurate method that exhibits high reproducibility with changing of temperature. The
retention index represented by the symbol I is calculated by the logarithmic scale of the
adjusted retention time or net retention volume of both the solute studied and the standard
substances or the n-alkanes, as shown in equation 3.1.
I = 100n + 100 (log Rx – log Rn)
(3.1)
(log Rn+1 – log Rn)
In the equation, R is the retention time or retention volume, n is the number or
carbon atom of n-alkane before solute X and n+1 is the number of carbon after solute X
63
(4-6). This system is combined with other solvation models in assessment of numerous
interactions that is related to retention mechanism (3).
3.1.1.2 Rohrschneider’s and McReynolds phase constants
Rohrschneider-McReynolds system was the first widely used approach for the
characterization of gas chromatography (GC) stationary phases (5). This was first
discovered by Rohrschneider in the mid 1960’s and was modified three years later by
McReynolds. The model provides an approach for the evaluation of retention indices (I)
under isothermal condition (3, 5). The system assumes that the intermolecular
interactions are additive and the contribution of different individual interactions. Each
probe molecules represents a specific interaction with the stationary phase (13). The
measurement of retention indices of the representative solutes are measured by taking
the difference between retention indices values of representative solute and a squalane
stationary phase which is used as a non-polar reference phase. Thirteen solutes were
initially used for characterization of stationary phase properties. However, only five are
commonly used to represent individual interactions identified with coefficients (X’, Y’,
Z’, U’, S’). These are; benzene (X’) which measures the dispersion interactions with a
weak proton acceptor and induction properties; Butanol (Y’) which measures orientation
properties of both proton donors and proton acceptors; 2-Pentanone (Z’) which measures
orientation properties with a proton acceptors but not proton donor properties;
Nitropropane (U’) which measures weak proton acceptor capabilities and pyridine (S’)
which measures strong proton acceptors with weak orientation properties but no proton
donor capabilities. Each of the representative solute coefficients, were paired with the
64
solvent coefficients a, b, c, d, e that are related to the properties of five probes shown in
equation 3. 2.
∆I = aX’ + bY’ + cZ’ + dU’+ eS’
(3.2)
The McReynolds approach suffers from unreliable deficiencies. Several solutes
(i.e., benzene, nitropropane and 2-pentanone) are too volatile and often elute with the
dead volume. The use of squalene as a stationary phase has poor thermal stability and
oxidative stability (13). The method was also ignores the contribution of the interfacial
adsorption as retention mechanism. If using polar phases, the retention index of n-alkane
are strongly retained and dominated by interfacial adsorption instead of true gas-liquid
partitioning (14). Thus, the resulting retention index becomes irreproducible and cannot
be included into solvation properties anymore. Another problem of the RohrschneiderMcReynolds approach is the retention of each solutes is not dictated by one single
interaction. These can express several interactions simultaneously. Hence, the method
will suffer difficulty in characterizing solvents accurately (3, 5).
3.1.1.3 Abraham’s solvation parameter model
To correlate the interaction of the solute to the stationary phase solvent, a more
feasible method must be implemented. The limitation of the Rohrschneider-McReynolds
system was overcome by Abraham and co-workers in 1993 (6). In their work, they have
examined a broad range of solutes. The model has been extensively used to characterize
the liquid or gas phase interactions between solutes and liquid phases. The solvation
parameter model provides a general tool to assign the contribution of individual
intermolecular interactions and cavity formation to equilibrium processes in
65
chromatography. Moreover, this model can be described as a linear free energy
relationship that involves a general approach for characterizing the contribution of
solvent-solute interaction and solvent-solvent interactions to equilibrium properties.
Transfer of the solute from the gas phase involves three steps. First, the cavity of suitable
size is constructed. This process depends on the forces that hold together the solvent
molecules. Second, the solvent reorganizes itself in the cavity into an equilibrium
position around the solute. Finally, the solute is inserted into the cavity and various
solute-solvent interactions occur. The model utilizes a large number of probes which can
undergo several interactions with the stationary phase depending on their structural
properties. Each solute molecule is defined with all of its possible interactions. Five
established parameters were used to describe the properties of the solute which they are
known as solute descriptors (E, S, A, B, L). E is the measure of molar excess refraction
calculated from the solute’s refractive index. S is the measure of solute dipolarity /
polarizability. A is the solute hydrogen-bond donating ability. B is solute hydrogen-bond
accepting ability. And L is the measure of gas-hexadecane partition coefficient at 298 K.
The equation 3.3 is given as:
log k = c + eE + sS + aA + bB + lL
(3.3)
The lower cases (e, s, a, b, l) are the coefficients that describe the stationary phase
and they are called the system constants. System constant e is the measure of n-π or π- π
interaction; s is the solvent dipolarity/polarizability measurement; a is a measure of
hydrogen bond basicity; b is the solvent’s hydrogen-bond acidity measurement; l is the
dispersion or cohesive interaction of the solvent. The coefficient c is the intercept or
phase ratio. All these solute descriptors and system constant are equal to log of the
66
retention factor (k).
The system constant is obtained by multiple linear regression
analysis (MLRA) of the solute descriptors and retention factor. The value of system
constant is dependent on the temperature of the column. It was observed that the polar
interaction generally increases at lower temperatures (3, 5, 6, 12, 14).
In this study, the evaluated solvation properties of ILs will aid in understanding
on the solubility of cellulose experiments.
3.2 EXPERIMENTAL
3.2.1 MATERIALS
3.2.1.1 Probe molecules used in inverse gas chromatography analysis
Different probe molecules were selected and used in the analysis of various ILs
using the solvation parameter model. These include: acetic acid, methyl caproate,
naphthalene and propionic acid which were purchased from Supelco (Bellefonte, PA,
USA). Bromoethane, butyraldehyde, ethyl acetate, and 2-nitrophenol were purchased
from Acros Organics (Morris Plains, NJ, USA). 1-Butanol, N, N- dimethylformamide, 2propanol, and toluene were purchased from Fisher Scientific (Fairlawn, NJ, USA). 2Chloroaniline, cyclohexanone, and 1-pentanol were purchased from Aldrich (Milwaukee,
WI, USA) and p-cresol, m-xylene, o-xylene, and p-xylene were purchased from Fluka
(Steinheim, Germany). Cyclohexanol was purchased from J.T. Baker (Phillipsburg, NJ,
USA); ethylbenzene from Eastman Kodak Company (Rochester, NY, USA); and
acetophenone, aniline, benzaldehyde, benzene, benzonitrile, benzyl alcohol, 1bromohexane, 1- bromooctane, 1-chlorobutane, 1-chlorohexane, 1-chlorooctane, 1,2dichlorobenzene, 1,4-dioxane, 1-iodobutane, nitrobenzene, 1-nitropropane, 1-octanol,
67
octyldehyde, 2-pentanone, phenetole, phenol, propionitrile, pyridine, pyrrole, and 1decanol were purchased from Sigma–Aldrich (St. Louis, MO, USA). All probe molecules
were used as received. Methylene chloride was purchased from Fisher Scientific
(Fairlawn, NJ, USA). Table 3.1 shows the solute descriptors of the 46 probe molecules
used in this study.
3.2.2 METHODS
3.2.2.1 Instrumentation
All gas chromatographic analyses were performed on HP 5890 GC equipped with
a flame ionization detector (FID) connected to a HP 3396 integrator. The temperatures of
the detector and injector port were set at 250 ºC and 200 ºC, respectively. Helium was
used as the carrier gas with inlet pressure flow rate adjusted to 1 mL/min. The chart speed
of the integrator was maintained at 0.2 cm/min.
3.2.2.2 Static coating technique
For inverse gas chromatography (IGC) analysis, the untreated fused silica
capillary tubing capillary column, 5 m x 0.25-mm I.D., obtained from Supelco
(Bellefonte, PA, USA) was used and coated with the different ILs. The IL was coated on
the inner wall of capillary column using the static coating technique. This was done by
first making sure that both ends of the capillary column were flat to ensure there will be
no air to initiate a leak. Plastic tubing was then attached to both ends. One end of the
column was assigned for the introduction of the IL into the inner walls of the column
(this was the “head” of the column) and the other end with plastic tubing was clamped at
68
the end of the coating experiment. ILs were prepared at concentrations of 0.25% (w/v) in
dichloromethane and injected into the capillary column by attaching a syringe to the
“head” of the column and allowing the IL solution to flow to the other end. About 1 mL
of the coating solution IL was introduced into the column by gently pressing the plunger
and then, carefully removing the syringe in the “head” side of the column. Then the head
side of the column was immediately attached to the plastic tubing attached to a vacuum
assembly and the entire column immersed into a water bath set at the boiling temperature
of the solvent. Once the vacuum was turned on, the solvent in an IL solution was slowly
removed leaving only the ionic liquid coated on the inner wall. The coating was said to
be finished by observing the evaporation interface. Initially when the column was filled
with IL solution it appeared as yellow gold but as the solvent is removed from the
vacuum, the column appears to be dark brown. This can be better observed when light
was directed into the column while keeping the room dark.
The coated column was removed from the water bath and mounted into the GC.
Before doing the actual IGC experiments, the column was conditioned initially at 30 ºC
and ramped to 100 ºC at 0.5 ºC / min and held for 60 minutes at 100 ºC. The efficiency of
the column was measured using naphthalene, which was introduced into the column at a
temperature of 100 ºC. To ensure that the coated IL has not changed during the
chromatographic study, the retention time of naphthalene at 100 ºC was recorded for each
column before and after evaluating all probe molecules at three column temperatures.
The efficiency was measured and calculated using the following equation 3. 4:
69
N = 5.54
tr
2
(3.4)16
w1/2
L
Where, N is the efficiency or number of plates; tr is the retention time of the
analyte (naphthalene), w1/2 is the width at half height of the analyte and L is the length of
the column. Nearly all columns had more than 1000 plates per meter except for 1hydroxyethyl-3-methy
pyridinium
chloride,
EMIM-aspartate
and
1-ally-3-vinyl
imidazolium chloride which possessed maximum theoretical plates of only 600 plates per
meter. This is likely due to the polarity of the compound. The mentioned ILs are too polar
to be dissolved in methylene chloride. So, methanol (0.1-0.3 mL) was added to the
solution. The drop in the efficiency is due to the added methanol that functions as a cosolvent. There is a big possibility that after coating, there is a minimal amount of
methanol that remains inside the wall of the capillary column which can affect the even
and smooth coating of the IL.
3.2.2.3 Inverse gas chromatographic analysis
All probe molecules (Table 3.1) dissolved in methylene chloride were injected
individually to the column which was set to isothermal temperatures 30 ºC, 70 ºC and
100 ºC. Some probes that have low boiling point (i.e., benzene, ethyl acetate,
bromoethane) and low interaction with the stationary phase eluted the same time as the
solvent and some probes (i.e., 2-nitrophenol, p-cresol, phenol) that have high boiling
point and strong interaction with the stationary phase have retention time more than three
hours. These types of these probes were obviously not included in the linear regression
70
analysis. Methane was used to determine the dead volume at each isothermal temperature.
To quantitatively evaluate each property of the column, the retention time of analytes that
eluted from the column were input for statistical calculation and multiple linear
regression analysis (MLRA) using the program Analyze-It (Microsoft, USA).
71
Table 3.1: List of probe molecules and their corresponding solute descriptors used
in the solvation parameter model
Probe molecules
Acetic acid
Acetophenone
Aniline
Benzaldehyde
Benzene
Benzonitrile
Benzyl alcohol
Bromoethane
1-Bromooctane
1-Butanol
Butyraldehyde
2-Chloroaniline
1-Chlorobutane
1-Chlorohexane
1-Chlorooctane
p-Cresol
Cyclohexanol
Cyclohexanone
1,2-Dichlorobenzene
N,N-DMF
1,4-Dioxane
Ethyl Acetate
Ethyl benzene
1-Iodobutane
Methyl Caproate
Naphthalene
Nitrobenzene
1-Nitropropane
1-Octanol
Octylaldehyde
1-Pentanol
2-Pentanone
Phenetole/ Ethylphenylether
Phenol
Propionitrile
Pyridine
Pyrrole
Toluene
m-Xylene
o-Xylene
p-Xylene
2-Propanol
2-Nitrophenol
1-Bromohexane
Propionic acid
1-Decanol
E
0.265
0.818
0.955
0.820
0.610
0.742
0.803
0.366
0.339
0.224
0.187
1.033
0.210
0.201
0.191
0.820
0.460
0.403
0.872
0.367
0.329
0.106
0.613
0.628
0.067
1.340
0.871
0.242
0.199
0.160
0.219
0.143
0.681
0.805
0.162
0.631
0.613
0.601
0.623
0.663
0.613
0.212
1.015
0.349
0.233
0.191
S
0.65
1.01
0.96
1.00
0.52
1.11
0.87
0.40
0.40
0.42
0.65
0.92
0.40
0.40
0.40
0.87
0.54
0.86
0.78
1.31
0.75
0.62
0.51
0.40
0.60
0.92
1.11
0.95
0.42
0.65
0.42
0.68
0.70
0.89
0.90
0.84
0.73
0.52
0.52
0.56
0.52
0.36
1.05
0.40
0.65
0.42
72
A
0.61
0.00
0.26
0.00
0.00
0.00
0.33
0.00
0.00
0.37
0.00
0.25
0.00
0.00
0.00
0.57
0.32
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.37
0.00
0.37
0.00
0.00
0.60
0.02
0.00
0.41
0.00
0.00
0.00
0.00
0.33
0.05
0.00
0.60
0.37
B
0.44
0.48
0.41
0.39
0.14
0.33
0.56
0.12
0.12
0.48
0.45
0.31
0.10
0.10
0.10
0.31
0.57
0.56
0.04
0.74
0.64
0.45
0.15
0.15
0.45
0.20
0.28
0.31
0.48
0.45
0.48
0.51
0.32
0.30
0.36
0.52
0.29
0.14
0.16
0.16
0.16
0.56
0.37
0.12
0.45
0.48
L
1.750
4.501
3.934
4.008
2.786
4.039
4.221
2.620
5.090
2.601
2.270
4.674
2.722
3.777
4.772
4.312
3.758
3.792
4.518
3.173
2.892
2.314
3.778
4.130
3.844
5.161
4.557
2.894
4.619
4.361
3.106
2.755
4.242
3.766
2.082
3.022
2.865
3.325
3.839
3.939
3.839
1.764
4.760
4.130
2.290
5.628
3.3 RESULTS AND DISCUSSION
3.3.1 CHARACTERIZATION OF PURE AND MIXED IONIC LIQUID
STATIONARY PHASES USING THE ABRAHAM SOLVATION
PARAMETER MODEL
The solvation properties of the synthesized imidazolium and pyridinium based ILs
were analyzed using the Abraham solvation parameter model by inverse gas
chromatography. Inverse gas chromatography is a useful technique in characterizing
different compounds. It is an extension of conventional gas chromatography in which the
immobilized compounds were evaluated. The stationary phase or immobilized
compounds into the inner wall of the column were characterized by injecting numerous
probe molecules into the column one at a time. The retention time of these probe
molecules based on its interaction with the stationary phase were plotted and examined
the properties of the coated compound (15). One advantage of this technique is the
characteristics of each compounds can be determined at different temperature and
assessed the system constant at different temperatures. The system constants of the nine
imidazolium chloride ILs were evaluated at 40 ºC, 70 ºC and 100 ºC. The measured
system constants were all statistically sound as revealed by the correlation coefficient (r2),
Fisher F-statistic and the standard deviation. The ILs were grouped according to
structure/functionality and the dominant characteristics observed were r reported. The
four main groups were: a) imidazolium chloride based ILs; b) EMIM based ILs; c)
pyridinium based ILs and d) binary stationary phases as compared to the neat IL.
73
3.3.1.1 IMIDAZOLIUM-BASED IONIC LIQUIDS
The first group are ILs with various substituents on the imidazolium cation
coupled to chloride anion. The system constants are presented in Table 3.2 and their
structures are given in Table 3.3. It has been reported that the most dominant interaction
of the ILs is the hydrogen-bond basicity value or the a – term (7, 11). Since all of these
ILs are paired with the chloride anion, their hydrogen-bond basicity values were similar.
Moreover, the high measured hydrogen-bond basicity of ILs paired with chloride
is due to its strong ability to accept a proton because it is the most coordinating halide (8).
The hydrogen-bond acidity or the b – term has a negative value for some ILs at
some temperatures. This is due to the limited solutes that eluted from the column.
Because all the ILs that were synthesized have relatively high hydrogen bond property.
Thus most probe molecules either eluted near the solvent front or interact longer to the
stationary phase at an allowed given time thereby decreasing the number of probe
molecules for evaluation.
ILs 1-5 are alkyl functionalized compounds. Different linear alkyl group
substituents were attached to the nitrogen atoms of the imidazolium ring cation and
paired with the chloride anion. The foremost interaction for comparing these ILs is the
dispersion interaction or the l – term. Among these ILs, 1-octyl-3-methyl imidazolium
chloride or IL 4 has the highest measured l – term. As expected IL 1 or 1-ethyl-3-methyl
imidazolium chloride was the lowest calculated l – value. The dispersion interaction of IL
4 is slightly higher that IL 5. The order of dispersion interaction of these alkyl
functionalized ILs in decreasing sequence is IL 4 > IL 5 > IL 3 > IL 2 > IL 1.
74
ILs 6 and 7 were alkene functionalized compounds. The alkene group was
attached at one of the nitrogen atom of the imidazolium ring cation as in the case of IL 6
(1-allyl-3-methyl imidazolium chloride). Alternatively both nitrogen atoms of the
imidazolium ring cation were attached with an alkene groups as in the case of IL 7 (1vinyl-3-methyl imidazolium chloride). Both of these ILs were paired with chloride anion.
The system constants that could best distinguish these ILs is the e – term or the n - π or π
- π interaction. IL 7 is predicted to have a higher measured e – value because of the vinyl
substituent. But, IL 6 posses higher n to π interaction. The possible reason was when
these ILs were prepared IL 7 did not dissolved completely with methylene chloride
compared to IL 6. As a result, the coated stationary phase (IL 7) will have a poor coated
capillary column that could possibly interfere with the partitioning of most solutes. Thus,
could lower the measured retention factor and calculated system constants.
ILs 8 and 9 were the ether functionalized compounds. An ether group was
attached to the nitrogen atom of the imidazolium ring cation and coupled with chloride
anion. The primary system constant that would describe these ILs is the n -π or π - π
interaction or the e – value. IL 9 was observed to have greater e – value due to its higher
electron donating ability compared to IL 8.
75
values obtain from literature (20)
-3.19 (0.17)
-4.11 (0.46)
-4.28 (0.35)
9. 1-methoxyethyl-3-methyl imidazolium chloride (MEMIM-Cl)
40ºC
70ºC
100ºC
a
-3.27 (0.09)
-3.39 (0.11)
-3.59 (0.16)
8. 1-methoxymethyl-3-methyl imidazolium chloride (MMMIM-Cl)
40ºC
70ºC
100ºC
-3.10 (0.27)
-3.52 (0.26)
-3.81 (0.27)
-3.30 (0.17)
-3.41 (0.11)
-3.39 (0.08)
-3.57 (0.36)
-3.62 (0.31)
-3.74 (0.20)
-2.93 (0.31)
-3.05 (0.24)
-2.97 (0.23)
-3.0950
-2.8410
-3.0990
-2.83 (0.24)
-3.04 (0.23)
-3.45 (0.21)
-3.37 (0.15)
-3.47 (0.21)
-3.64 (0.26)
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
Intercept
40ºC
70ºC
100ºC
7. 1- allyl-3-vinyl imidazolium chloride (AVIM-Cl)
6. 1-allyl-3-methyl imidazolium chloride (AMIM-Cl)
5. 1- octyl-3-butyl imidazolium chloride (OBIM-Cl)
4. 1-octyl-3-methyl imidazolium chloride (OMIM-Cl)
3. 1-hexyl -3-methyl imidazolium chloride (HMIM-Cl)
2. 1-butyl -3-methyl imidazolium chloridea (BMIM-Cl)
1. 1-ethyl-3-methyl imidazolium chloride (EMIM-Cl)
IONIC LIQUIDS
System constants
0.39 (0.12)
0.94 (0.29)
0.88 (0.21)
0.29 (0.08)
0.41 (0.08)
0.46 (0.12)
0.25 (0.12)
0.46 (0.13)
0.57 (0.17)
0.36 (0.17)
0.72 (0.16)
0.82 (0.18)
0
0
0.06 (0.06)
0.10 (0.17)
0.25 (0.18)
0.40 (0.15)
0.35 (0.17)
0.38 (0.16)
0.29 (0.13)
0.2370
0.2910
0.4080
0.52 (0.15)
0.54 (0.14)
0.53 (0.12)
e
76
2.54 (0.17)
2.43 (0.32)
2.38 (0.28)
2.21 (0.09)
2.20 (0.09)
2.16 (0.12)
2.17 (0.14)
2.11 (0.15)
1.99 (0.18)
2.33 (0.22)
2.38 (0.18)
2.25 (0.18)
2.22 (0.13)
2.07 (0.11)
1.85 (0.08)
2.26 (0.24)
1.89 (0.23)
1.65 (0.19)
2.20 (0.23)
1.84 (0.21)
1.56 (0.19)
2.2470
2.0070
1.8260
2.32 (0.19)
2.24 (0.18)
2.13 (0.17)
s
6.29 (0.28)
6.11 (0.41)
5.66 (0.39)
5.05 (014)
4.67 (0.10)
4.30 (0.10)
5.68 (0.21)
5.28 (0.18)
4.82 (0.19)
5.90 (0.32)
5.87 (0.22)
5.51 (0.24)
7.09 (0.25)
6.21 (0.16)
5.33 (0.11)
7.63 (0.53)
6.31 (0.35)
5.48 (0.24)
6.88 (0.46)
5.67 (0.32)
4.72 (0.31)
7.0300
5.2300
4.8600
6.03 (0.31)
5.53 (0.29)
5.24 (0.29)
a
-0.34 (0.23)
0.32 (0.42)
0
0.23 (0.09)
0.12 (0.13)
0
0.25 (0.19)
0
0
0
0
0
-0.36 (0.18)
-0.30 (0.14)
-0.23 (0.11)
-0.50 (0.29)
0
0
-0.40 (0.28)
0.02 (0.26)
-0.15 (0.21)
-0.3580
-0.3200
-0.1210
0
-0.25 (0.23)
0
b
0.40 (0.03)
0.35 (0.09)
0.29 (0.05)
0.44 (0.02)
0.31 (0.02)
0.23 (0.03)
0.55 (0.04)
0.41 (0.03)
0.31 (0.04)
0.45 (0.05)
0.31 (0.04)
0.24 (0.04)
0.73 (0.04)
0.62 (0.02)
0.51 (0.01)
0.76 (0.07)
0.63 (0.06)
0.54 (0.03)
0.58 (0.07)
0.49 (0.49)
0.43 (0.03)
0.6270
0.4450
0.3920
0.40 (0.03)
0.30 (0.03)
0.27 (0.03)
l
0.99 (0.09)
0.97 (0.16)
0.97 (0.13)
0.99 (0.06)
0.99 (0.06)
0.99 (0.08)
0.99 (0.11)
0.98 (0.11)
0.98 (0.11)
0.98 (0.11)
0.98 (0.14)
0.98 (0.12)
0.99 (0.08)
0.99 (0.07)
1.00 (0.05)
0.98 (0.13)
0.98 (0.15)
0.99 (0.11)
0.98 (0.12)
0.98 (0.13)
0.98 (0.10)
0.97
0.98
0.98
0.98 (0.11)
0.98 (0.11)
0.98 (0.09)
r2
Table 3.2: System constants of the imidazolium chloride-based IL stationary phases at three temperatures
16
16
15
20
21
21
24
22
18
15
22
18
19
22
21
16
18
18
17
17
16
15
22
23
16
16
15
no. of
probes
179
61
55
520
446
380
240
191
139
103
152
109
252
564
949
80
95
167
98
97
93
100
87
89
Fisher constants
Table 3.3: Imidazolium-based ILs analyzed using solvation parameter model and
their corresponding structures
Number
Imidazolium chloride ionic liquids
Structures
1-ethyl-3-methyl imidazolium chloride
N
N
1
Cl-
(EMIM-Cl)
1-butyl-3-methyl imidazolium chloride
N
N
2
Cl-
(BMIM-Cl)
1-hexyl-3-methyl imidazolium chloride
N
N
3
Cl-
(HMIM-Cl)
1-octyl-3-methyl imidazolium chloride
N
N
4
Cl-
(OMIM-Cl)
1-octyl-3-butyl imidazolium chloride
N
N
5
Cl-
(OBIM-Cl)
1-allyl-3-methyl imidazolium chloride
N
N
6
Cl-
(AMIM-Cl)
1-allyl-3-vinyl imidazolium chloride
N
N
7
Cl-
(AVIM-Cl)
1-methoxymethyl-3-methyl
N
8
O
N
Cl-
imidazolium chloride (MMMIM-Cl)
O
1-methoxyethyl-3-methyl imidazolium
N
9
N
Cl-
chloride (MEMIM-Cl)
77
3.3.1.2 EMIM-BASED IONIC LIQUIDS
These ILs include various anions coupled to the EMIM cation. The anion
component plays a major role in describing the property of the IL (7, 10, 11) such as the
hydrogen – bond basicity or a – term system constant. In this group of ILs, the hydrogen
bond acidity or b – term has negative values for some compounds at some temperature.
This was explained in detail in section 3.3.1.1. Table 3.4 presents the calculated system
constants of the EMIM-based ILs at three different temperatures. Their structures are
shown in Table 3.5.
ILs 1-3 are the EMIM cation paired with monocarboxylate anion. These ILs
include EMIM-formate, EMIM-acetate, and EMIM-propionate. All three compounds
showed a high hydrogen-bond basicity value. The anionic portion of the IL yielded high
hydrogen-bond basicity (a-value). This can be explained through the concept of acid –
base strength pair. Weak acids such as carboxylates have strong conjugate bases. The
chain length of the anion increases the hydrogen-bond basicity of the IL. This trend also
follows the increasing pKa values of these acids of the anion: formic acid, 3.74; acetic
acid, 4.76; propanoic acid, 4.88. Hence, among the carboxylate ILs, the EMIMpropionate possesses the highest hydrogen-bond basicity (7.04 ± 0.54, observed at 70 ºC).
Dispersion interaction (l) showed the opposite effect. EMIM–formate has the highest l –
value and the EMIM-propionate was observed to have the lowest dispersion interaction.
The EMIM-formate IL was not characterized at 100 ºC since the compound is
thermally unstable. This was discussed in section 5.3.1.6.
ILs 5 and 6 are EMM cations paired with the dicarboxylate anion. This includes
EMIM succinate and EMIM aspartate. Comparing the two ILs, EMIM-aspartate (6.39 ±
78
0.33, observed at 70 ºC) possesses a larger a – value than EMIM-succinate (6.17 ± 0.31,
observed at 70 ºC). Looking at their structures in Table 3.5, they differ by the presence of
amine group on EMIM-aspartate. Amines are known to act as a good base and the
presence of this group will enhance the proton acceptor ability of the IL. Therefore, the
strengthening of hydrogen-bond basicity of the EMIM-aspartate will likely occur.
ILs 8 and 9 are examples of the EMIM cation paired with haloacetate anions,
trichloroacetate and trifluoroacetate. The anions are analogues of acetic acid in which the
three hydrogen atoms of the methyl group have all been replaced by chlorine or fluorine
atoms. The substitution of these atoms increases the acidity of the conjugate acids of the
bases which is evident with pKa values. The pKa of trichloroacetic acid is 0.70 and the
pKa of trifluoroacetic acid is 0.30. It will be expected then that the measured hydrogenbond basicity of EMIM-trichloroacetate (5.95 ± 0.31, observed at 70 ºC) is the more than
EMIM-trifluoroacetate (4.32 ± 0.16, observed at 70 ºC).
EMIM-thiocynate or IL 5 is one of the unique ionic liquids in this group of
EMIM-based ILs. One distinct characteristic of the thiocyante anion is it has negative
charge which can be in either sulfur or nitrogen as shown in equation 3.5.
S
C
N C S
N
(3.5)
Furthermore, thiocyante is considered a psuedohalide because its reactions are the
as same halides, but still the behavior of the IL is different towards solvation parameter
analysis. Hydrogen-bond basicity was 3.87 ± 0.20
(observed at 70 ºC) is its most
predominating interaction influenced by the anion part of the IL.
79
Like EMIM-thiocyanate, EMIM-ethyl sulfate or IL 4 is also individually
characterized since its solvation characteristics are distinct for the other EMIM-based ILs.
Firstly, the acidity of the conjugate acid, sulfovinic acid, is very high, pKa = - 3.71.
Secondly, the same as the EMIM-formate, the IL is unstable at 100 ºC, discussed in
section 5.3.1.6. And thirdly, the structure of the compound would not fit into to ILs in
this EMIM group. The hydrogen-bond basicity, (4.27 ± 0.35 measured at 70 ºC) is also
the most dominant property of EMIM-ethyl sulfate.
80
EMIM-propionate
EMIM-ethylsulfate
EMIM-thiocyanate
EMIM-succinate
EMIM-aspartate
EMIM-trifluoroacetate
40ºC
70ºC
100ºC
EMIM-trichloroacetate
40ºC
70ºC
100ºC
2.
3.
4.
5.
6.
7.
8.
9.
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
EMIM-acetate
1.
40ºC
70ºC
100ºC
IONIC LIQUIDS
EMIM-formate
-3.24 (0.17)
-3.40 (0.27)
-3.52 (0.18)
-3.08 (0.12)
-3.22 (0.12)
-3.12 (0.27)
-3.37 (0.24)
-3.94 (0.26)
-4.50 (0.22)
-2.82 (0.24)
-3.43 (0.24)
-3.63 (0.26)
-3.13 (0.13)
-3.41 (0.16)
-3.64 (0.27)
-2.94 (0.33)
-3.33 (0.36)
-2.89 (0.31)
-3.37 (0.28)
-4.12 (0.39)
-2.73 (0.32)
-3.61 (0.30)
-4.19 (0.41)
-3.20 (0.10)
-3.95 (0.29)
System constants
Intercept
0.31 (0.13)
0.56 (0.17)
0.64 (0.12)
0.14 (0.09)
0.17 (0.09)
0.20 (0.18)
0.44 (0.15)
1.02 (0.17)
0.88 (0.10)
0.29 (0.13)
0.56 (0.15)
0.67 (0.16)
0.45 (0.10)
0.54 (0.11)
0.68 (0.16)
0.41 (0.16)
0.40 (0.18)
0.21 (0.20)
0.39 (0.18)
0.94 (0.27)
0.10 (0.21)
0.74 (0.21)
0.98 (0.28)
-0.18 (0.14)
0.78 (0.17)
e
2.30 (0.15)
2.24 (0.22)
2.15 (0.15)
2.12 (0.11)
2.03 (0.12)
2.04 (0.20)
2.33 (0.19)
2.36 (0.21)
2.52 (0.14)
2.16 (0.20)
2.22 (0.21)
2.02 (0.20)
2.28 (0.13)
2.25 (0.15)
1.99 (0.20)
2.23 (0.20)
2.27 (0.25)
2.57 (0.29)
2.68 (0.30)
2.14 (0.34)
2.28 (0.30)
2.14 (0.23)
2.14 (0.36)
1.90 (0.08)
1.73 (0.19)
s
b
l
-0.62 (0.36)
-0.67 (0.38)
0.47 (0.44)
-0.54 (0.37)
0.25 (0.34)
0.52 (0.47)
0.45 (0.06)
0.35 (0.04)
0.32 (0.05)
0.50 (0.06)
0.39(0.04)
0.32 (0.06)
81
6.30 (0.23)
5.95 (0.31)
5.26 (0.21)
4.77 (0.17)
4.32 (0.16)
4.16 (0.20)
6.46 (0.32)
6.41 (0.32)
6.07 (0.21)
6.41 (0.33)
6.17 (0.31)
5.42 (0.27)
4.12 (0.18)
3.87 (0.20)
3.46 (0.24)
0
0
0
0.32 (0.15)
0.23 (0.16)
0
0
0
0.26 (0.21)
-0.29 (0.25)
0
0
0.44 (0.18)
0.38 (0.20)
0.53 (0.26)
0.51 (0.04)
0.37 (0.04)
0.27 (0.03)
0.56 (0.03)
0.46 (0.02)
0.30 (0.05)
0.45 (0.03)
0.29 (0.03)
0.26 (0.02)
0.48 (0.04)
0.37 (0.04)
0.30 (0.04)
0.49 (0.03)
0.40 (0.03)
0.33 (0.04)
4.49 (0.38)
-0.20 (0.23)
0.48 (0.06)
4.27 (0.35)
-0.25 (0.27)
0.42 (0.07)
THERMALLY UNSTABLE
7.11 (0.53)
7.04 (0.54)
6.17 (0.52)
6.87 (0.55)
6.60 (0.33)
6.43 (0.55)
4.38 (0.13)
0.70 (0.10)
0.53 (0.02)
6.38 (0.27)
0
0.47 (0.04)
THERMALLY UNSTABLE
a
0.98 (0.12)
0.98 (0.15)
0.99 (0.09)
0.99 (0.09)
0.99 (0.09)
0.97 (0.14)
0.98 (0.12)
0.98 (0.12)
0.99 (0.06)
0.98 (0.12)
0.98 (0.12)
0.98 (0.10)
0.99 (0.10)
0.98 (0.11)
0.97 (0.10)
0.98 (0.12)
0.97 (0.13)
0.97 (0.15)
0.97 (0.15)
0.96 (0.18)
0.97 (0.16)
0.98 (0.14)
0.96 (0.19)
1.00 (0.04)
0.99 (0.11)
r2
Table 3.4: System constants of the EMIM-based IL stationary phases at three temperatures
24
19
18
28
26
20
16
15
13
18
17
15
24
23
16
18
18
16
16
15
16
16
15
13
14
no. of probes
223
106
175
336
325
96
126
106
209
114
125
95
258
194
71
104
72
61
75
40
57
89
39
449
138
Fisher constants
Table 3.5: EMIM-based ionic liquids analyzed using solvation parameter model and
their corresponding structures
Number
EMIM-based ionic liquids
Structures
1
EMIM-formate
N
N
2
EMIM-acetate
N
N
3
EMIM-propionate
N
N
4
EMIM-ethylsulfate
N
N
5
EMIM-thiocyanate
N
N
HCOO-
CH3COO-
CH3CH2COO-
CH3CH2SO4-
SCN -
O
6
N
N
EMIM-succinate
O
OOO
7
O
EMIM-aspartate
N
O-
N
-
O
8
EMIM-trifluoroacetate
N
N
9
EMM-trichloroacetate
N
N
82
CF3COO -
CCl3COO -
NH2
3.3.1.3 PYRIDINIUM-BASED IONIC LIQUIDS
In this group of ILs, the nitrogen atom of the pyridinium ring cation was attached
with different functional groups and was paired with chloride or acetate anion. Table 3.6
presents the calculated system constants of these ILs and in Table 3.7 their structures are
shown.
3.3.1.3.1 EFFECT OF CATIONS
The cation of ILs 1, 2 and 3 have different substituents attached to the nitrogen
atom of the pyridinium ring cation and all were paired with chloride anion. In IL 1 and 3,
an allyl and alkane group, respectively, is attached to the nitrogen atom of the pyridinium
ring. The hydrogen bond basicity of these ILs are the same. However, the dispersion
interaction or l - term showed a slight difference. As expected, IL 3 has a higher
dispersion interaction value than in IL 1 because of the presence of a longer alkyl chain,
(butyl vs. propyl). Comparing IL 2 to ILs 1 and 3, the decreased basicity value and
increased hydrogen bond acidity or the b – term was pronounced. This is due to the
presence of hydroxyl group of IL 2 which is a strong proton donating group.
3.3.1.3.2 EFFECT OF ANIONS
The system constants of 1-butyl-3-methyl pyridinium chloride, IL 3 and its
acetate analogue, IL 4 were compared. Hydrogen-bond basicity of IL 3, 5.74 ± 0.24, is
greater than IL 4, 5.60 ± 0.23. The higher a – value which influenced by the anionic
portion of the IL can be explained through the concept of acid – base strength pair where
weak acids have strong conjugate bases. Acetic acid and hydrochloric acid are the
83
conjugate acids of acetate and chloride anions. The pKa values of the acids of the anion
are: acetic acid, 4.76; hydrochloric acid, -8.00. The expected result is that IL 4 with
acetate anion will have greater IL 3 with chloride. But what was observed is the reverse.
The possible reason was when IL 4 was prepared for coating solution it is not completely
miscible with dichloromethane. Methanol was added as co-solvent that affects the
evaluation of the properties of the coated stationary phase. This was explained in the
latter part of section 3.3.1.1. Hence, the opposite observation was seen.
84
4. 1-butyl- 3- methyl pyridium acetate (BMPyr-Ac)
40ºC
70ºC
100ºC
40ºC
70ºC
100ºC
-4.20 (0.32)
-4.09 (0.21)
-3.75 (0.20)
-2.66 (0.29)
-3.10 (0.19)
-3.49 (0.25)
-3.37 (0.28)
-6.13 (0.35)
-5.55 (0.21)
2. 1-hydroxyethyl-3- methyl pyridium chloride (HEMPyr-Cl)
40ºC
70ºC
100ºC
3. 1-butyl- 3- methyl pyridium chloride (BMPyr-Cl)
-2.80 (0.34)
-2.93 (0.19)
-4.02 (0.39)
System constants
Intercept
40ºC
70ºC
100ºC
1. 1-allyl- 3- methyl pyridium chloride (AMPyr-Cl)
IONIC LIQUIDS
-0.37 (0.13)
0.26 (0.16)
0.54 (0.12)
0.43 (0.14)
0.44 (0.13)
0.61 (0.16)
-0.24 (0.14)
0.22 (0.19)
0.80 (0.12)
0.40 (0.17)
0.57 (0.12)
0.85 (0.23)
e
85
2.77 (0.17)
2.29 (0.21)
1.79 (0.16)
2.186 (0.21)
1.98 (0.17)
1.99 (0.21)
1.20 (0.22)
2.70 (0.25)
1.94 (0.19)
2.25 (0.24)
1.95 (0.15)
2.15 (0.31)
s
7.43 (0.31)
5.60 (0.23)
4.81 (0.22)
6.59 (0.40)
5.74 (0.24)
5.46 (0.30)
3.26 (0.21)
5.00 (0.19)
4.42 (0.13)
6.27 (0.49)
5.23 (0.23)
5.67 (0.44)
a
-1.75 (0.19)
0
0
-0.60 (0.26)
-0.17 (0.21)
0
-0.56 (0.23)
0.86 (0.36)
1.79 (0.22)
-0.48 (0.27)
-0.19 (0.35)
0
b
0.83 (0.06)
0.60 (0.03)
0.45 (0.03)
0.51 (0.06)
0.46 (0.03)
0.38 (0.04)
0.69 (0.05)
0.62 (0.04)
0.37 (0.02)
0.45 (0.06)
0.35 (0.03)
0.33 (0.05)
l
0.99 (0.08)
0.99 (0.10)
0.99 (0.07)
0.98 (0.12)
0.98 (0.12)
0.98 (0.13)
0.97 (0.11)
0.99 (0.12)
1.00 (0.06)
0.98 (0.12)
0.98 (0.09)
0.96 (0.14)
r2
Table 3.6: System constants of the pyridinium based IL stationary phases at three temperatures
15
16
15
17
20
19
17
17
12
16
17
14
no. of probes
208
181
145
92
163
105
83
151
286
81
141
44
Fisher constants
Table 3.7: Pyridinium-based ionic liquids analyzed using solvation parameter model
and their corresponding structures
Number
1
2
Pyridinium-based ionic liquids
Structures
1-Allyl-3-Methyl Pyridium Chloride
(AMPyr-Cl)
N
Cl-
N
1-Hydroxyethyl-3-Methyl Pyridium Chloride
(HEMPyr-Cl)
Cl-
HO
3
1-Butyl-3-Methyl Pyridium Chloride
(BMPyr-Cl)
4
1-Butyl-3-Methyl Pyridium Acetate
(BMPyr-Ac)
N
Cl-
N
86
CH3COO-
3.3.2 EFFECT OF IONIC LIQUID STATIONARY-PHASE COMPOSITION ON
THE RETENTION FACTOR OF ANALYTES
Retention factor is the ratio of time an analyte (tr) spends time in the stationary
phase subtracted to the dead time (tm) (Equation 3.6). Dead time is the retention time
required by an unretained solute to travel through the column which do not sorb in the
stationary phase (17).
k = tr – tm / tm
(3.6)
3.3.2.1 IMIDAZOLIUM-BASED IONIC LIQUID
3.3.2.1.1 Alkyl-functionalized ILs
Table 3.8 lists the retention factors of selected probe molecules on alkyl
functionalized IL stationary phases. Good proton donor solutes such as alcohols (1octanol, 1-pentanol and 1-butanol) were tenaciously retained on the strong hydrogen
bond basic stationary phases. This was attributed to the anionic portion of the IL which is
responsible for the overall hydrogen bond basicity characteristic. Whereas, the cationic
portion of the IL influenced the dispersion interaction due to the long alkyl chain
appended in the nitrogen atoms of the imidazolium ring. This explains the high retention
factor of long linear chain alcohol like 1-octanol. These observations were pronounced in
stationary phases, HMIM-Cl, OMIM-Cl and OBIM-Cl ILs where cationic moiety were
substituted with long alkyl chains.
87
3.3.2.1.2 Alkene-functionalized ILs
The retention factor of selected probe molecules on AMIM-Cl and AVIM-Cl are
presented in Table 3.9. These alkene functionalized ILs demonstrated hydrogen bond
basicty or a - term from the chloride anion and nonbonding or π interaction or e – term
from the cationic portion of the IL. Carboxylic acids (i.e., acetic acid, propionic acid),
amines (1-chloroaniline, aniline) and pyrrole showed long interaction of these solutes in
both stationary phases because of its ability to donate proton. Aromatic compounds (i.e.,
benzonitrile, cyclohexanol, and nitrobenzene) which are capable of undergoing n - π or ππ interaction demonstrated modest retention factors as well.
3.3.2.1.3 Ether-functionalized ILs
The retention factor of different probe molecules on ether functionalized ILs
stationary phases, MEMIM-Cl and MMMIM-Cl are shown in Table 3.10. The main
interactions demonstrated by these ILs were hydrogen-bond basicity imparted by the
anion and n - π or π - π interactions due to the cationic portion of the IL. Between the two
ILs, solutes exhibited higher retention factors in MEMIM-Cl because of its higher
basicity and n and π electron interactions than MMMIM-Cl (Table 3.2). As expected,
amines (i. e. aniline and chloroaniline) which are good proton donor solutes demonstrated
high retention. Meanwhile, aromatic compounds (i.e., acetophenone, benzonitrile,
benzaldehyde, naphthalene and nitrobenzene) that are capable of undergoing n and π
interactions showed increased interaction in the same IL.
88
Table 3.8: Retention factors obtained at 70 ºC for selected probes in EMIM-Cl,
HMIM-Cl, OMIM-Cl and OBIM-Cl stationary phases
Probes
EMIM-Cl
HMIM-Cl
OMIM-Cl
OBIM-Cl
Acetophenone
11.82
25.69
24.17
24.54
Benzonitrile
11.26
23.24
18.89
20.53
1-Butanol
5.35
15.62
13.68
14.59
Nitrobenzene
19.92
46.07
41.75
42.62
1-Nitropropane
1.23
2.10
1.51
1.69
1-Octanol
19.70
169.62
298.59
299.47
1-Pentanol
7.88
27.93
31.29
31.79
2-Propanol
1.33
3.21
2.07
2.48
89
Table 3.9: Retention factors obtained at 70 ºC for selected probes in AMIM-Cl and
AVIM-Cl stationary phases
Probes
AMIM-Cl
AVIM-Cl
Acetic acid
248.74
111.66
Aniline
306.08
164.20
Benzonitrile
8.86
8.38
1-Butanol
4.16
3.64
2-Chloroaniline
301.23
187.62
Cyclohexanol
15.71
14.85
Nitrobenzene
17.26
15.78
1-Nitropropane
0.91
0.86
1-Octanol
14.76
22.74
1-Pentanol
6.68
6.58
Pyrrole
52.88
29.48
2-Propanol
1.19
0.84
Propionic acid
294.05
148.99
1- Decanol
39.99
63.28
90
Table 3.10: Retention factors obtained at 70 ºC for selected probes in
MEMIM-Cl and MMMIM-Cl stationary phases
Probes
MEMIM-Cl
MMMIM-Cl
Acetophenone
8.30
4.68
Aniline
299.70
43.56
Benzaldehyde
5.34
2.80
Benzonitrile
7.24
4.58
1-Butanol
3.04
1.60
2-Chloroaniline
272.68
57.35
Cyclohexanol
10.81
5.93
Naphthalene
8.87
4.68
Nitrobenzene
12.82
9.05
1-Octanol
12.20
6.44
1-Pentanol
4.23
2.27
91
3.3.1.2 EMIM-BASED IONIC LIQUIDS
3.3.1.2.1 Monocarboxylic acid-based ILs
Table 3.11 presents the retention factors of various probe molecules on
monocarboxylic acid-based IL stationary phases. These ILs have the same cation, EMIM
and different monocarboxylic acid anions. As mentioned previously in the literature (7, 9,
10), the anionic portion of the IL largely controls the basicity or proton accepting ability
characteristics. Good proton donating solutes such as 1-octanol, 1-pentanol, 1-butanol
and cyclohexanol showed extensive interaction with the stationary phases.
3.3.1.2.2 Dicarboxylic acid-based ILs
Shown in Table 3.12 are the retention factors of selected solutes on dicarboxylic
acid based IL stationary phases. The high retention factor of solutes such as pyrrole, 1octanol and 1-decanol was influenced by its inherent characteristic to donate protons to
the stationary phases with strong hydrogen bond basic
3.3.1.2.3 Haloacetic acid-based ILs
Retention factors of several analytes in haloacetic acid-based stationary phases are
presented in Table 3.13. The dominant characteristic of these ILs were their strong
hydrogen bond basicity. It allows strong interaction of good proton donating solutes such
as alcohols (i.e., cyclohexanol, 1-octanol), amines (i.e., aniline) and pyrrole with EMIMtrichloroacetate and EMIM-trifluoroacetate stationary phases.
92
3.3.1.2.4 EMIM- thiocyanate
The retention factors of numerous solutes on the EMIM-thiocyante stationary
phase are shown in Table 3.14. Alcohol compounds like 1-octanol, 1-decanol, amines and
pyrrole exhibited high retention factors due to extensive interaction with the stationary
phase of IL hydrogen bond basicity. Also, the solvent’s property to interact via n - π and
π - π interaction properties (Table 3.4), allows strong interaction to aromatic compounds
(i.e., acetophenone, benzaldehyde, benzonitrile, naphthalene, and nitrobenzene).
3.3.1.2.5 EMIM- ethylsulfate
Table 3.15 shows the measured retention factors of a number of solutes on the
EMIM-ethylsulfate stationary phase. The hydrogen bond basicity property of the solvent
showed long interaction of analytes like aniline and pyrrole which are intrinsically good
proton donating solutes. The IL also has the ability to undergo interaction by means of n π or π - π interaction. This interaction defines the modest retention factor of aromatic
solutes such as acetophenone, benzonitrile, naphthalene and nitrobenzene.
93
Table 3.11: Retention factors obtained at 40 ºC for selected probes in
EMIM-formate, EMIM-acetate and EMIM-propionate stationary phases
Probe molecules
EMIM-formate
EMIM-acetate
EMIM-propionate
Acetophenone
23.58
72.42
67.09
Benzonitrile
16.92
63.25
62.56
1-Butanol
8.17
57.45
45.10
Cyclohexanol
40.85
269.79
214.57
Nitrobenzene
37.10
122.69
122.10
1-Octanol
93.30
584.45
461.38
1-Pentanol
17.05
102.60
82.76
2-Propanol
1.80
10.96
8.56
94
Table 3.12: Retention factors obtained at 70 ºC for selected probes in
EMIM-aspartate and EMIM-succinate stationary phases
Analyte
EMIM-aspartate
EMIM-succinate
Acetophenone
5.24
11.70
Benzonitrile
4.97
10.26
1-Butanol
2.82
7.41
Cyclohexanol
10.07
28.13
1,2-Dichlorobenzene
1.36
2.50
N,N-DMF
2.52
4.92
Naphthalene
8.04
12.97
Nitrobenzene
9.60
18.95
1-Octanol
9.46
39.66
1-Pentanol
3.76
11.07
Pyrrole
58.78
96.09
2-Propanol
0.76
1.78
1-Decanol
19.81
96.24
95
Table 3.13: Retention factors obtained at 70 ºC for selected probes in EMIMtricholoroacetate and EMIM-trifluoroacetate stationary phases
Probe molecules
EMIM-trichloroacetate
EMIM-trifluoroacetate
Acetophenone
11.47
18.90
Aniline
328.73
128.09
1-Butanol
5.47
3.66
Cyclohexanol
20.46
14.52
Cyclohexanone
1.31
2.98
1,2-Dichlorobenzene
2.80
3.13
Naphthalene
13.08
16.26
Nitrobenzene
20.54
25.07
1-Nitropropane
1.12
1.80
1-Octanol
31.96
28.78
1-Pentanol
8.76
6.18
Phenetole/ Ethylphenylether
1.56
2.62
Pyridine
0.65
1.27
Pyrrole
71.31
30.05
2-Propanol
1.58
0.88
96
Table 3.14: Retention factors obtained at 70 ºC for selected probes in
EMIM-thiocyanate stationary phase
Probe molecules
EMIM-thiocyanate
Acetophenone
22.767
Aniline
157.974
Benzaldehyde
12.910
Benzonitrile
15.150
1-Butanol
1.820
2-Chloroaniline
180.628
Cyclohexanol
8.962
Cyclohexanone
3.060
1,2-Dichlorobenzene
3.293
N,N-DMF
11.398
Naphthalene
22.102
Nitrobenzene
30.451
1-Nitropropane
1.617
1-Octanol
10.560
Octylaldehyde
1.195
1-Pentanol
3.214
Penelope/ Ethylphenylether
2.797
Propionitrile
0.617
Pyridine
1.444
Pyrrole
19.470
p-Xylene
0.459
2-Propanol
0.500
1-Decanol
30.632
97
Table 3.15: Retention factors obtained at 70 ºC for selected probes in EMIMethylsulfate stationary phase
Probe molecules
EMIM-ethyl sulfate
Acetophenone
15.66
Aniline
129.13
Benzaldehyde
8.89
Benzonitrile
13.59
1-Bromooctane
0.84
1-Butanol
1.70
Cyclohexanol
8.16
Cyclohexanone
1.75
1,2-Dichlorobenzene
3.43
N,N-DMF
5.88
Naphthalene
16.51
Nitrobenzene
22.69
1-Nitropropane
1.41
1-Octanol
11.24
Octylaldehyde
0.72
1-Pentanol
2.66
Phenetole/ Ethylphenylether
1.82
Pyrrole
25.20
98
3.3.1.3 PYRIDINIUM-BASED IONIC LIQUIDS
3.3.1.1 EFFECT OF CATION TYPE
Table 3.16 shows the retention factors for different probe molecules to the
pyridinium-based ILs. The characteristic of the IL to be exhibit cohesive which is
influenced by the cationic component of the IL from the alkyl chain attached in the
nitrogen atom of the pyridinium ring. This explains the high retention factor of aromatic
probe molecules (i.e. acetophenone, benzonitrile, naphthalene and nitrobenzene) in
BMPyr-Cl and AMPyr-Cl stationary phases.
Meanwhile, retention factors of alcohols and pyrrole showed a dramatic decreased
on the HEMPyr-Cl stationary phase when compared to the other two ILs in Table 3.6.
This was caused by the hydroxyl group suspended in the alkyl chain in the nitrogen atom
of the pyridinium cation. This significantly increases the hydrogen bond acidity
characteristic of the stationary phase (Table 3.6). For example, the retention factor of 1octanol is 116.15 in BMPyr-Cl, decreased to 28.69 in AMPyr-Cl and further lowers to
1.36 in HEMPyr-Cl. Aromatic compounds such as acetophenone, benzonitrile,
naphthalene and nitrobenzene demonstrated low retention factors as influenced by a
notable decrease in n - π or π - π interaction of the HEMPyr-Cl against AMPyr-Cl and
BMPyr-Cl (Table 3.6). For instance, in the case of naphthalene probe molecule, the
retention factor on BMPyr-Cl is 36.11 then decreased to 20.44 in AMPyr-Cl and showed
the lowest interaction on HEMPyr-Cl with a calculated retention value of 1.38.
99
3.3.1.2 EFFECT OF ANION TYPE
In Table 3.17, the retention factors of several probe molecules are presented for
the BMPyr-Cl and BMPyr-Ac stationary phases. The inherent ability of the alcohol
compounds to donate protons, explains the high retention characteristic of cyclohexanol,
1-octanol, 1-pentanol and 1-decanol. Intrinsically, pyrrole showed the same property as
alcohol, and thus explains the extended interaction with the stationary phases. Aromatic
compounds exhibited higher retention factors in BMPyr-Cl than BMPyr-Ac. This can be
explained by the higher ability of the said stationary phase to interact via n - π or π interaction (Table 3.6). For example, the retention factor of acetophenone is 24.16 in
BMPyr-Cl and decreased to 16.54 in BMPyr-Ac.
100
Table 3.16: Retention factors obtained at 70 ºC for selected probes in BMPyr-Cl,
AMPyr-Cl, HEMPyr-Cl stationary phases
Probe molecules
BMPyr-Cl
AMPyr-Cl
HEMPyr-Cl
Acetophenone
24.16
15.44
1.04
Benzonitrile
22.88
13.05
0.68
Cyclohexanol
48.04
22.63
0.45
Naphthalene
36.11
20.44
1.38
Nitrobenzene
41.96
23.76
1.36
1-Octanol
116.15
28.69
1.62
1-Pentanol
20.43
9.41
0.16
Pyrrole
110.15
77.68
1.12
1-Decanol
273.79
69.36
7.65
101
Table 3.17: Retention factors obtained at 70 ºC for selected probes in BMPyr-Cl and
BMPyr-Ac stationary phases
1-butyl-3-methyl
1-butyl-3-methyl
pyridinium chloride
pyridinium acetate
Acetophenone
24.16
16.54
Benzonitrile
22.88
11.01
1-Butanol
11.51
4.32
Cyclohexanol
48.04
21.09
1,2-Dichlorobenzene
7.83
3.46
Naphthalene
36.11
26.34
Nitrobenzene
41.96
26.60
1-Octanol
116.15
60.02
1-Pentanol
20.43
9.48
Phenetole/ Ethylphenylether
2.95
1.34
Pyrrole
110.15
51.60
Probe molecules
102
3.3.3. EFFECT OF STATIONARY PHASE COMPOSITION ON THE
CHROMATOGRAPHIC SELECTIVITY OF IONIC LIQUIDS
Chromatographic selectivity or separation factor is a thermodynamic factor that
measures the relative retention of two substances which is determined at constant
experimental conditions. This includes the same stationary phase or mobile phase
composition (in liquid chromatography). It is also a measure of peak to peak position of
any two analytes and mathematically calculated as the ratio of two retention factors (k)
for any two peaks in the chromatogram (6). The effect of stationary phases on the
separation factor or selectivity of various solute pairs were analyzed by grouping the ILs
based on structure and functionality.
3.3.3.1 IMIDAZOLIUM-BASED IONIC LIQUIDS
3.3.3.1.1 Alkyl-functionalized ILs
The selectivity of several analyte pairs at 70 ºC on different alkyl functionalized
ILs is presented in Table 3.18. It can be seen that the selectivity between aromatic solute
pairs was highest on the OMIM-Cl stationary phase. This can be explained by the higher l
– term or dispersion forces of the said IL. For example, between homologous alcohol
pairs, such as the analyte pair of 1-octanol and 1-pentanol; the calculated separation
factors were 2.50 in EMIM-Cl to 6.07 in HMIM to 9.42 in OBIM-Cl and 9.54 in OMIMCl.
103
3.3.3.1.2 Alkene-functionalized ILs
In Table 3.19, the effect of AMIM-Cl and AVIM-Cl stationary phases on the
selectivity of selected analyte pairs at 70 ºC is shown. It can be seen that due to the high
measured l – term of AVIM-Cl compared to AMIM-Cl (Table 3.2) greater selectivity of
all analyte pairs in AVIM-Cl stationary phase was observed. For example, between
homologous analyte pair of alcohol such as 1-decanol and 1-octanol, the measured
selectivity of 1-decanol and 1-octanol was 2.71 in AMIM-Cl and then increased to 2.78
on the AVIM-Cl stationary phase.
3.3.3.1.3 Ether-functionalized ILs
Table 3.20 lists the separation factor of different analyte pairs on etherfunctionalized ILs. Analyte pairs showed better selectivity on MEMIM-Cl than
MMMIM-Cl due to the n – π or π – π interaction and hydrogen-bond basicity of the
former IL. The n – π or π – π interaction are characteristic between aromatic pairs like
benzonitrile and cyclohexanone. In MMMIM-Cl, the selectivity is 5.35 to 9.11 in
MEMIM-Cl. Between alcohols such as, 1-octanol and 1-pentanol pair, the selectivity is
highest in MEMIM-Cl, 2.88 than in MMMIM-Cl, 2.84 influenced by the higher a – value
of former IL compared to the later IL.
104
Table 3.18: Effect of EMIM-Cl, HMIM-Cl, OMIM-Cl and OBIM-Cl stationary
phases on the selectivity of selected analyte pairs at 70 ºC
Analyte pairs
EMIM-Cl
HMIM-Cl
OMIM-Cl
OBIM-Cl
Acetophenone / Benzonitrile
1.05
1.11
1.28
1.20
1,2 Dichlorobenzene / Cyclohexanone
3.01
3.19
4.39
4.07
Cyclohexanol / Naphthalene
1.21
1.72
2.26
1.80
Nitrobenzene / Benzonitrile
1.77
1.98
2.21
2.08
1-Octanol / 1-Pentanol
2.50
6.07
9.54
9.42
Cyclohexanol / 1-Pentanol
2.21
2.36
2.53
2.34
Aromatic / Aromatic
Alcohol / Alcohol
105
Table 3.19: Effect of AMIM-Cl and AVIM-Cl stationary phases on the selectivity of
selected analyte pairs at 70 ºC
Analyte pairs
AMIM-Cl
AVIM-Cl
Aniline / Acetic acid
1.23
1.47
2-Chloroaniline / Propionic acid
1.02
1.26
1-Pentanol / 1-Butanol
1.60
1.81
1-Butanol / 2-Propanol
3.49
4.32
1-Decanol / 1-Octanol
2.71
2.78
1-Decanol / Cyclohexanol
2.55
4.26
Acetophenone / Benzonitrile
1.09
1.20
1,2 Dichlorobenzene / Cyclohexanone
2.01
2.06
Naphthalene / Pyridine
13.39
13.99
Phenetole / Pyridine
1.56
1.80
Amine / Carboxylic acid
Alcohol / Alcohol
Aromatic / Aromatic
106
Table 3.20: Effect of MEMIM-Cl and MMMIM-Cl stationary phases on the
selectivity of selected analyte pairs at 70 ºC
Analyte pair
MEMIM-Cl
MMMIM-Cl
Naphthalene / Benzonitrile
1.22
1.02
Benzaldehyde / 1,2 Dichlorobenzene
3.34
2.34
1,2 Dichlorobenzene / Phenetole
1.94
1.64
1,2 Dichlorobenzene / Cyclohexanone
2.01
1.39
Benzonitrile / Cyclohexanone
9.11
5.35
1-Octanol / 1-Pentanol
2.88
2.84
1-Octanol / Cyclohexanol
1.13
1.09
Aromatic / Aromatic
Alcohol / Alcohol
107
3.3.3.2 EMIM-BASED IONIC LIQUIDS
3.3.3.2.1 Monocarboxylic acid-based ILs
The selectivity of different analyte pairs on monocarboxylic acid based ILs are
shown in Table 3.21. All of the analyte pairs showed increased separation factors on an
EMIM-formate stationary phase due to its higher n – π or π – π interactions. The
measured selectivity on EMIM-propionate is 1.46 to 1.68 in EMIM-acetate and 1.99 in
EMIM-formate for the analyte pair of 1,2-dichlorobenzene and 1-nitropropane. This is
also evident in aromatic compounds like acetophenone and benzonitrile, nitrobenzene
and benzonitrile, and naphthalene and benzonitrile analyte pairs. The homologous series
of alcohol pairs such as 1-pentanol and 1-butanol; and 1-octanol and 1-butanol showed
increased selectivity on the EMIM-formate stationary phase. This observation may be
explained by the high observed cohesive forces of EMIM-formate compared to EMIMacetate and EMIM-propionate (Table 3.4).
3.3.3.2.2 Dicarboxylic acid-based ILs
Table 3.22 presents the selectivity of several analyte pairs of two dicarboxylic
acid-based ILs stationary phases. All of the analyte pairs exhibited greater separation
factors on the EMIM-succinate IL. The pair of aromatic compounds such as;
acetophenone and benzonitrile, nitrobenzene and naphthalene, and benzonitrile and 1, 2dichlorobenzene showed an increase in selectivity by more than 100 % in EMIMsuccinate stationary phase. For example between nitrobenzene and naphthalene, the
measured selectivity is 1.19 on EMIM-aspartate to 1.46 on EMIM-succinate or an
enhancement of 123 % in separation factor. As to alcohol analyte pairs, they showed the
108
same selectivity behavior. The homologous series of alcohols like 1-pentanol and 1butanol showed an increase in selectivity in EMIM-succinate, 1.50 as to EMIM-aspartate,
1.33.
3.3.3.2.3 Haloacetic acid-based ILs
Table 3.23 lists the selectivity of several analyte pairs on stationary phases
comprising the EMIM cation paired with haloacetate-based anions. Between several
alcohol pairs and aromatic pairs, selectivity was greater in EMIM-trifluoroacetate
compared to EMIM-trichloroacetate. An increase of more than 100% in separation factor
was observed. For instance, solute pairs of 1-decanol and pyrrole, the separation factor of
1.06 in EMIM-tricholoroacetate was observed and increased to 2.90 or augmented by
274 % on the EMIM-trifluroacetate stationary phase. For aromatic pairs, the improved
selectivity was seen on EMIM-trifluoroacetate stationary phase, like between acetone and
1, 2-dichlorobenzene analyte pairs. In EMIM-trichloroacetate the measured separation
factor was 4.09 to 6.05 or 148 % improvement in selectivity EMIM-trifluoroacetate.
3.3.3.2.4 EMIM- thiocyanate
In Table 3.24, the effect of EMIM thiocyanate stationary phase on the selectivity
of different analyte pairs is presented. This IL was individually categorized because of
the uniqueness in its structure and properties as explained in section 3.3.1.2. Compared to
the measured solvation properties as to other ILs (Table 3.4), the hydrogen-bond basicity
and cohesive interaction were comparable to other EMIM-based ILs. So the selectivity
between good-proton donor solutes, like amines (2-chloroaniline and aniline) and
109
alcohols (i.e. 1-butanol and 2-propanol; and 1-decanol and 1-octanol) showed high
selectivity. High separation selectivity was also observed between aromatic pairs like
pyridine and p-xylene; nitrobenzene and naphthalene among others.
3.3.3.2.5 EMIM- ethylsulfate
The effect of EMIM-ethylsulfate stationary phase on the selectivity of selected
analyte pairs at 70 ºC is presented in Table 3.25. As mentioned previously in section
3.3.1.2, this IL has unique properties such as the conjugate acid of ethylsulfate which is
sulfovonic acid. Sulfovonic acid is a very acidic compared to the conjugate acid of other
ILs and the structure of the anion does not fit into other EMIM ILs. Thus, the evaluation
of its interaction was separated the other ILs in this group. From Table 3.4, it shows that
the basicity was almost the same as other ILs in this group. This can explain the high
selectivity of good proton donor solute pairs of aniline and pyrrole; 1-pentanol and 1butanol and 1-octanol and cyclohexanol in term of basicity characteristic. The
comparable n - π or π - π interaction of EMIM-ethylsulfate to other EMIM-based ILs can
describe the high selectivity of aromatic pairs like 1, 2-dichlorobenzene and 1nitropropane; and acetophenone and benzonitrile.
110
Table 3.21: Effect of EMIM-formate, EMIM-acetate and EMIM-propionate
stationary phases on the selectivity of selected analyte pairs at 40 ºC
Analyte pairs
EMIM-formate
EMIM-acetate
EMIM-propionate
1,2-Dichlorobenzene / 1-Nitropropane
1.99
1.68
1.46
1-Bromooctane / 2-Propanol
1.18
0.53a
0.30 a
Acetophenone / Benzonitrile
1.39
1.14
1.07
Naphthalene / Benzonitrile
1.48
1.26
1.31
Nitrobenzene / Benzonitrile
2.19
1.94
1.95
Cyclohexanol / 1-Butanol
5.00
4.70
4.76
1-Pentanol / 1-Butanol
2.09
1.79
1.84
1-Octanol / Cyclohexanol
2.28
2.17
2.15
1-Octanol / 1-Butanol
11.42
10.17
10.23
Aromatic / Aromatic
Alcohol / Alcohol
a
By definition, the value of the separation factor should be greater than unity. However, some analytes
exhibited reversal of elution order making it impossible to report integers greater than unity for all
stationary phase.
111
Table 3.22: Effect of EMIM-aspartate and EMIM-succinate stationary phases on
the selectivity of selected analyte pairs at 70 ºC
Analyte pairs
EMIM-aspartate
EMIM-succinate
1.97
2.08
Acetophenone / Benzonitrile
1.05
1.14
Nitrobenzene / Naphthalene
1.19
1.46
Benzonitrile / 1,2-Dichlorobenzene
3.66
4.10
1-Pentanol / 1-Butanol
1.33
1.50
1-Butanol / 2-Propanol
3.72
4.17
1-Decanol / Cyclohexanol
1.97
3.42
Benzonitrile / N,N-DMF
Aromatic / Aromatic
Alcohol / Alcohol
112
Table 3.23: Effect of EMIM-trichloroacetate and EMIM-trifluoroacetate stationary
phases on the selectivity of selected analyte pairs at 70 ºC
EMIM
EMIM
trichloroacetate
trifluoroacetate
1-Decanol / Pyrrole
1.06
2.90
N,N-DMF / 2-Propanol
2.81
10.63
Cyclohexanone / 1-Nitropropane
1.16
1.65
Acetophenone / Benzonitrile
1.12
2.14
2-Chloroaniline / Aniline
1.07
1.11
Acetophenone / 1,2 Dichlorobenzene
4.09
6.05
Nitrobenzene / Benzonitrile
2.00
2.84
1-Pentanol / 1-Butanol
1.60
1.69
1-Octanol / 1-Cyclohexanol
1.56
1.98
1-Butanol / 2-Propanol
3.46
4.15
Analyte pairs
Aromatic / Aromatic
Alcohol / Alcohol
113
Table 3.24: Effect of EMIM thiocyanate stationary phase on the selectivity of
selected analyte pairs at 70 ºC
Analyte pairs
EMIM thiocyanate
1,2-Dichlorobenzene / Cyclohexanone
1.08
Benzaldehyde / N,N-DMF
1.13
Phenetole / 1-Nitropropane
1.73
Cyclohexanone / Octylaldehyde
2.56
Pyridine / Propionitrile
2.34
Acetophenone / Benzonitrile
1.50
2-Chloroaniline / Aniline
1.14
Benzonitrile / Benzaldehyde
1.17
Nitrobenzene / Naphthalene
1.38
Phenetole / Pyridine
1.94
Naphthalene / Pyrrole
1.14
Pyridine / p-Xylene
3.15
1-Pentanol / 1-Butanol
1.77
1-Octanol / Cyclohexanol
1.18
1-Butanol / 2-Propanol
3.64
1-Decanol / 1-Octanol
2.90
Aromatic / Aromatic
Alcohol / Alcohol
114
Table 3.25: Effect of EMIM-ethylsulfate stationary phase on the selectivity of
selected analyte pairs at 70 ºC
Analyte pair
EMIM ethyl sulfate
1-Nitropropane / 1-Bromooctane
1.68
N,N-DMF / 1,2-Dichlorobenzene
1.71
Cyclohexanone / Octylaldehyde
2.44
Aromatic / Aromatic
Acetophenone / Benzonitrile
1.15
Aniline / Pyrrole
5.12
Benzonitrile / Benzaldehyde
1.53
1,2-Dichlorobenzene / Phenetole
1.88
Nitrobenzene / Naphthalene
1.37
1,2-Dichlorobenzene / 1-Nitropropane
2.43
Alcohol / Alcohol
1-Pentanol / 1-Butanol
1.56
1-Octanol / Cyclohexanol
1.38
115
3.3.3.3 PYRIDINIUM-BASED IONIC LIQUIDS
3.3.3.3.1 EFFECT OF CATIONS
Table 3.26 presents the effect of stationary phase on the selectivity of selected
analyte pairs at 70 ºC on BMPyr-Cl, AMPyr-Cl and HEPyr-Cl stationary phases. It is
shown that the selectivity is altered by the specific functional groups attached to the
cation part of the IL. The high dispersion interaction and hydrogen bond acidity of
HEMPyr-Cl, showed significant increase in the selectivity between alcohol pairs. For
example the selectivity of 1-decanol and cyclohexanol increased from 3.06 on AMPyr-Cl
to 5.70 on the BMPyr-Cl and further increased to 16.98 on HEMPyr-Cl IL. For aromatic
analyte pairs, the selectivity was reversed, for example between nitrobenzene and
acetophenone. The measured separation factor is 1.74 in BMPyr-Cl then went down to
1.54 in AMPyr-Cl and reduced more to 1.31 in HEMPyr-Cl. Moreover, certain solute
pairs exhibited reversal of elution order. Examples are selectivity for analyte pairs of
cyclohexanol and naphthalene, cyclohexanol and acetophenone and cyclohexanol and
nitrobenzene.
3.3.3.3.2 EFFECT OF ANIONS
Selectivity of selected analytes at 70 ºC on BMPyr-Cl and BMPyr-Ac presented
in Table 3.27. Interesting behavior was observed in the separation of these two ILs. The
alteration of the anion influenced the selectivity of analytes significantly. The separation
factor between aromatic compounds was higher on the BMPyr-Cl IL. For example the
measured separation factor of an analyte pair like nitrobenzene and naphthalene, is 1.01
in BMPyr-Ac and increases to 1.16 in BMPyr-Cl. This can attributed to the higher n - π
116
or π - π interaction of the later IL (Table 3.6). However, the selectivity was reversed
between alcohols. For instance, the analyte pair of 1-decanol and 1-octanol, the
separation factor in BMPyr-Cl is 2.36 and significantly increases to 3.66 in BMPyr-Ac.
This can be explained by the increased in acidity and dispersion interaction properties of
BMPyr-Ac stationary phase.
117
Table 3.26: Effect of BMPyr-Cl, AMPyr-Cl and HEMPyr-Cl stationary phases on
the selectivity of selected analyte pairs at 70 ºC
Analyte pairs
BMPyr-Cl
AMPyr-Cl
HEMPyr-Cl
Cyclohexanol / Naphthalene
1.33
1.11
0.33a
Naphthalene / Acetophenone
1.49
1.32
1.32
Nitrobenzene / Acetophenone
1.74
1.54
1.31
Cyclohexanol / Acetophenone
1.99
1.47
0.43a
Cyclohexanol / Nitrobenzene
1.15
0.95a
0.33a
1-Octanol / Cyclohexanol
2.42
1.27
3.59
Cyclohexanol / 1-Pentanol
2.35
2.41
2.88
1-Decanol / Cyclohexanol
5.70
3.06
16.98
1-Decanol / 1-Octanol
2.36
2.42
4.73
Aromatic / Aromatic
Alcohol / Alcohol
a
By definition, the value of the separation factor should be greater than unity. However, some analytes
exhibited reversal of elution order making it impossible to report integers greater than unity for all
stationary phase.
118
Table 3.27: Effect of BMPyr-Cl and BMPyr-Ac stationary phases on the selectivity
of selected analyte pairs at 70 ºC
Analyte pair
BMPyr-Cl
BMPyr-Ac
1,2-Dichlorobenzene / Phenetole
2.65
2.58
Nitrobenzene / Naphthalene
1.16
1.01
1,2 Dichlorobenzene / Phenetole
2.65
2.58
Pyrrole / Nitrobenzene
2.63
1.94
1-Pentanol / 1-Butanol
1.78
2.20
1-Decanol / 1-Octanol
2.36
3.66
1-Octanol / Cyclohexanol
2.42
2.85
Aromatic / Aromatic
Alcohol / Alcohol
119
3.4 CONCLUSION
The remarkable properties of ionic liquids showed a greater dimension in
chemical processes. The solvation of properties of various ionic liquids were examined
using the Abraham solvation parameter model. The anionic component of the IL largely
determines its hydrogen bond basicity (a). All ILs that are paired with chloride anion
exhibited a high a-value. The highest measured hydrogen-bond basicity was OMIM-Cl at
6.31 ± 0.35. High basicity was also observed with ILs paired with monocarboxylate
anions like formate, acetate and propionate. While, the cationic portion of the IL accounts
for the majority of the n-π or π-π interaction. This is due to the aromatic pyridinium or
imidazolium ring. Functionalization of this component could significantly decrease the
hydrogen-bond basicity as in HEMPyr-Cl. Furthermore, the increase in the n - π or π - π
(e) interaction was observed with the alkene and ether-functionalized imidazolium ILs.
While, the dispersion interaction (l-value) characteristics can be attributed to both ions
but appears dominated by the cationic component of the IL. This was seen with OMIMCl and OBIM-Cl both having the highest l – value among all the examined ILs. The
measured dipolarity/polarizability (s) system constant in all ILs were almost the same at
each temperature.
The solvation properties of the ILs explain trends in the retention characteristic
and selectivity of various analytes. The dominant interactions that were observed among
the ILs were hydrogen-bond basicity, cohesive forces and nonbonding and π interactions.
The strong interaction of solutes that are good proton donors like alcohols or amines
which mostly have high calculated retention factor was influenced by the hydrogen-bond
basicity capability of the IL. The high retention characteristic of aromatic compounds on
120
the other hand, can be explained by the ILs capability to undergo n - π or π - π interaction.
The ILs with high dispersion parameter, showed high retention of alcohols with long
alkyl chains such as 1-octanol or 1-decanol.
On the concept of separation selectivity, this was also influenced by the ILs
solvation characteristic. The higher basicity and cohesive forces of ILs results in better
separation selectivity between several alcohols and aromatic analyte pairs.
3.5 BIBLIOGRAPHY
1. Wasserscheid, P. and Welton, T.; “Ionic Liquids in Synthesis”, 2008, Wiley-VCH
2. Pinkert, A., K. N. Marsh, et al. “Ionic Liquids and Their Interaction with Cellulose”,
Chemical Reviews, 2009, 109(12): 6712-6728
3. Yao, C.; Anderson, J. L., “Retention characteristics of organic compounds on molten
salt and ionic liquid-based gas chromatography stationary phases”, Journal of
Chromatography, A, 2009, 1216(10), 1658-1712
4. Berthod, A.; et. al., “Determination and use of Rohrschneider-McReynolds constants
for chiral stationary phases used in capillary gas chromatography”, Analytical
Chemistry, 1995, 67(5), 849-57
5. Poole, C. “The Essence of Chromatography”, 2003
6. Abraham, M., “Scales of Solute Hydrogen-bonding: Their Construction and
Application to Physicochemical and Biochemical Process”, Chemical Society
Reviews, 1993, 72-83
7. Anderson, J. L., et. al., “Characterizing Ionic Liquids On the Basis of Multiple
121
Solvation Interactions”, Journal of the American Chemical Society, 2002, 124(47),
14247-14254
8. Lancaster, N. Llewellyn, et. al, “Nucleophilicity in Ionic Liquids. 2. Cation Effects on
Halide Nucleophilicity in a Series of Bis (trifluoromethylsulfonyl) imide Ionic
Liquids”, Journal of Organic Chemistry, 2002, 67(25), 8855- 8861
9. Zhao, Q. and Anderson, J L.,”Highly selective GC stationary phases consisting of
binary mixtures of polymeric ionic liquids”. J. Sep Sci, 2009, 33, 1-9
10. Baltazar, Q. Q.; et. al. “ Binary ionic liquid mixtures as gas chromatography
stationary phases for improving the separation selectivity of alcohols and aromatic
compounds”, Journal of Chromatography A, 2008, 1182(1), 119-127
11. Anderson, J. L. and Armstrong, D.W., “High-Stability Ionic Liquids. A New Class of
Stationary Phases for Gas Chromatography “, Anal. Chem, 2003, 75, 4851-4858
12. Poole, C.; and Poole, S.; “Chemometric evaluation of the solvent properties of liquid
organic salts”, Journal of Chromatography A, 2008, 1184, 254-280
13. Koel, M., “Ionic Liquids in Chemical Analysis”, 2009, CRC Press
14. Abraham, M. H., et. al, “Classification of stationary phases and other materials by
gas chromatography”, Journal of Chromatography A, 1999, 842, 79-114
15. Lloyd, D. R., et. al., “Inverse Gas Chromatography”, ACS Symposium Series, 1988
16. Skoog, D., and Leary, J.J., “Principles of Instrumental Analysis’, 1992, Saunders
College Publishing
17. McNair, H. M. and Miller, J. M., “Basic Gas Chromatography”, 1998, John Wiley
and Sons, Inc.
122
PART THREE
Binary mixture of ionic liquids as gas
chromatography stationary phases
123
CHAPTER 4
EVALUATION OF SOLVATION PROPERTIES OF PURE AND BINARY
MIXTURE GAS CHROMATOGRAPHIC STATIONARY PHASES IONIC
LIQUIDS
4.1 INTRODUCTION
The structural tunability of ionic liquids allows them to be tailored-made for a
specific application. The performance of ionic liquids in the dissolution of cellulose were
analyzed and in great detail in chapter 2. Recent study by Fukaya and co-workers (1)
found that EMIM-acetate and phosphite based ILs can dissolve large amounts of
cellulose. Thus, it is interesting to study the characteristics of these ILs and their mixtures
through the application of the solvation parameter model using inverse gas
chromatography.
4.2 EXPERIMENTAL
4.2.1 MATERIALS
4.2.1.1 Probe molecules used in inverse gas chromatography analysis
Probe molecules for the evaluation of pure ILs, Section 3.2.1.1 and the binary
mixture were the same.
124
4.2.2 METHODS
4.2.2.1 Instrumentation
The condition of HP 5890 GC equipped with a flame ionization detector (FID)
connected to a HP 3396 integrator that was used for gas chromatographic analysis was
the same as for ILs evaluated in Section 3.2.2.1.
4.2.2.2 Static coating technique
The static coating of the capillary column procedure in Section 3.2.2.3 was
followed.
4.2.2.3 Inverse gas chromatographic analysis
The procedure in section 3.2.2.3 for the inverse gas chromatography analysis was
the same.
4.3 RESULTS AND DISCUSSION
4.3.1 COMPARISON OF SOLVATION PROPERTIES BETWEEN PURE AND
BINARY MIXTURE IONIC LIQUIDS
Comparing the hydrogen-bond basicity or a – value between the neat EMIMacetate and 1, 3-dimethyl imidazolium phosphite (DMIM-phosphite), the EMIM-acetate,
6.60 ± 0.33 observed at 70 ºC, possesses a slightly higher proton accepting ability than
DMIM-phosphite, 5.80 ± 0.13. This is presented in Table 4.1 and their structure in Table
125
4.2. This is anticipated since the conjugate acid of acetate is weaker than conjugate acid
of phosphite. The pKa values of conjugate acids, acetic acid and phosphonic acid were
4.75 and < -3.00 respectively (2). Thus, these values clearly showed that the EMIMacetate is more basic than DMIM-phosphite. On the other hand, the binary mixture, 90%
/ 10% mixture, the yielded slightly higher hydrogen-bond basicity as to 50% / 50%. From
the results, the basicity trend was generated which is as the amount of the EMIM-acetate
was increased in the stationary phase, the hydrogen bond basicity increases. This is
observation is true at 70 ºC and 100 ºC. However, at 40 ºC, the said trend was not
followed. This could be due to the partitioning of most analytes via adsorption
mechanism. The analytes partition on the surface of the stationary phase instead into the
bulk of the said phase (3). Studies found that interfacial adsorption leads to linear change
of system constants and increase importance at lower temperature. (4, 5). Graph of
correlation of hydrogen bond basicity to percent of EMIM-acetate is presented in Figure
4.1
Meanwhile, the dispersion interaction (l – value) system constant shows an
interesting trend. The 50% / 50% mixture of the stationary phase gave the highest
dispersion interaction, 0.43 ± 0.04, followed by the 90% / 10% mixture (0.40 ± 0.04) then
the neat EMIM-acetate, 0.39 ± 0.04 and the lowest is the neat DMIM-phosphite, 0.35 ±
0.02. All these values were observed at 70 ºC. The other system constants remained
unchanged.
126
-2.73 (0.32)
-3.61 (0.30)
-4.19 (0.41)
-3.38 (0.23)
-3.42 (0.27)
-3.75 (0.17)
-3.37 (0.26)
-3.22 (0.23)
-3.74 (0.14)
-3.14 (0.29)
-3.19 (0.10)
-3.66 (0.16)
EMIM-Acetate (90%) / DMIM-Phosphite (10%)
40ºC
70ºC
100ºC
EMIM-Acetate (50%) / DMIM-Phosphite (50%)
40ºC
70ºC
100ºC
Dimethyl Imidazolium Phosphite (DMIM-Phosphite)
40ºC
70ºC
100ºC
System constants
Intercept
Ethyl-methyl Imidazolium Acetate (EMIM-Acetate)
40ºC
70ºC
100ºC
IONIC LIQUIDS
0.36 (0.18)
0.46 (0.07)
0.73 (0.10)
0.09 (0.17)
0.32 (0.16)
0.28 (0.08)
0.04 (0.15)
0.40 (0.17)
0.32 (0.10)
0
0.74 (0.21)
0.98 (0.28)
e
127
2.19 (0.22)
1.88 (0.09)
2.00 (0.13)
2.49 (0.20)
2.00 (0.20)
2.37 (0.13)
2.62 (0.18)
2.29 (0.22)
2.51 (0.15)
2.28 (0.30)
2.14 (0.23)
2.13 (0.36)
s
6.81 (0.44)
5.80 (0.13)
5.50 (0.19)
7.77 (0.38)
6.20 (0.27)
5.57 (0.18)
7.57 (0.35)
6.43 (0.31)
5.59 (0.21)
6.87 (0.55)
6.60 (0.33)
6.43 (0.55)
a
-0.23 (0.27)
0
0
-0.40 (0.27)
-0.21 (0.27)
0.35 (0.16)
-0.40 (0.25)
0
0.30 (0.20)
-0.54 (0.37)
0.25 (0.34)
0.52 (0.47)
b
stationary phases mixtures at three temperatures
0.47 (0.07)
0.35 (0.02)
0.25 (0.02)
0.56 (0.06)
0.44 (0.04)
0.32 (0.02)
0.55 (0.05)
0.40 (0.04)
0.29 (0.02)
0.50 (0.06)
0.39 (0.04)
0.32 (0.06)
l
0.98 (0.11)
1.00 (0.06)
0.99 (0.08)
0.98 (0.15)
0.98 (0.14)
0.99 (0.06)
0.98 (0.13)
0.98 (0.15)
0.99 (0.08)
0.97 (0.16)
0.98 (0.14)
0.96 (0.19)
r2
15
17
18
20
20
15
20
19
15
16
16
15
no. of probes
Table 4.1: System constants of pure EMIM-acetate and 1, 3-dimethyl imidazolium phosphite (DMIM-phosphite) and binary
98
541
236
118
142
305
134
118
208
57
89
39
Fisher constants
Table 4.2: EMIM-acetate and DMIM-phosphite used as binary mixture analyzed
using solvation parameter model and their corresponding structures
Ionic liquids
Structures
N
N
EMIM-acetate
CH3COO-
O
N
N
DMIM-phosphite
P
-
O
OCH3
H
128
7.90
7.65
Hydrogen bond basicity (a)
7.40
7.15
6.90
40 ºC
6.65
70 ºC
6.40
100 ºC
6.15
5.90
5.65
5.40
0
50
90
100
% EMIM- Acetate
Figure 4.1: Correlation between stationary phase weight percentage of
EMIM-Acetate and DMIM Phosphite and the resulting hydrogen bond basicity
NOTE: Data point at 0% is the pure DMIM-Phosphite
129
4.3.2 COMPARISON OF RETENTION FACTOR OF ANALYTES BETWEEN
PURE AND BINARY MIXTURE IONIC LIQUIDS
Variation on the retention factors of several solutes as influenced by the
composition of the stationary phase is shown in Table 4.3. Alcohols exhibited a
significant increase in the retention factor between pure EMIM-acetate and DMIMphosphite. More than a 200% increase was observed for some alcohols and aromatic
compounds. For example, the retention factor of 1-butanol, 1-octanol, 1-pentanol, 1decanol, acetophenone, nitrobenzene and pyrrole, increased by 240%, 250%, 220%,
265%, 295%, 281% and 209%, respectively, on pure EMIM-acetate compared to pure
DMIM-phosphite. Meanwhile, the interaction of these same probe molecules on the
binary mixture stationary phases 90 % / 10% and 50% / 50% EMIM-acetate / DMIMphosphite ILs were very slightly higher at 90 % / 10% mixture. This was not surprising
since the measured a-value of the binary mixtures agrees with the assessed property
(Table 4.1)
On the other hand, the calculated system constant of pure and binary mixture
stationary phases (Table 4.1), showed noticeable changes in the dispersion forces or the
l – value. The 50% / 50% mixture demonstrated the highest measured l – value followed
by 90%/10% mixture then the pure EMIM-acetate and the lowest was the pure DMIMphosphite. The effect of this property was pronounced in solutes that have the strong
ability for undergoing dispersion interactions such as 1-octanol and 1-decanol, due to the
long appended long alkyl chain. For example, the calculated retention factor of 1-octanol
is highest in 50% / 50% mixture, 77.62 then decreased to 64.08 in 90%/10% mixture
130
furthered lower to 63.25 in pure EMIM-acetate and lowest retention factor in pure
DMIM-phosphite, 25.26.
4.3.3 COMPARISON OF CHROMATOGRAPHIC SELECTIVITIES BETWEEN
PURE AND BINARY MIXTURE IONIC LIQUIDS
Selectivity between analytes in pure EMIM-acetate and DMIM-phosphite and
their binary mixture measured at 70 ºC is presented in Table 4.5. The evaluated cohesive
forces or the l – term (Table 4.1) influenced the selectivity significantly. The 50/50 binary
mixture of EMIM-acetate and DMIM-phosphite which showed the largest measured
dispersion interaction demonstrated the highest separation factor for homologous alcohol
compounds. For example, between 1-decanol and 1-butanol, the measured selectivity in
DMIM-phosphite was 14.10 then increased to 15.61 in EMIM-acetate then further
increased to 16.60 in 90/10 mixture of EMIM-acetate/DMIM-phosphite and showed
greatest separation factor of 18.49 in 50% / 50% mixture. However, alteration in
selectivity was seen between aromatic pairs. In the case of naphthalene and acetophenone,
the selectivity was 1.02 with the 90% / 10% binary mixture, 1.03 in 50% / 50% mixture,
and then increased to 1.07 in EMIM-acetate and showed the highest separation ratio in
DMIM-phosphite stationary phase, 1.69.
131
Table 4.4: Retention factors obtained at 70 ºC for selected probes on four different
IL stationary phases varying the weight percentages of EMIM-acetate and DMIMphosphite stationary phases
EMIM acetate / DMIM phosphite (% w/w)
Probe molecules
EMIM-acetate
90 / 10
50/50
DMIM-phosphite
Acetophenone
14.94
12.22
11.31
5.07
1-Butanol
10.43
8.99
10.00
4.35
Cyclohexanone
1.38
1.17
1.16
0.68
1,2-Dichlorobenzene
2.98
2.57
2.53
1.56
N,N-DMF
5.33
4.78
4.16
2.74
Naphthalene
15.93
12.48
11.70
8.58
Nitrobenzene
22.40
20.53
19.31
7.97
1-Octanol
63.25
64.08
77.62
25.26
1-Pentanol
17.02
14.52
15.14
7.74
Phenetole
1.46
1.39
1.45
0.86
Pyrrole
150.64
104.16
105.39
72.09
2-Propanol
2.58
2.06
2.36
1.29
1-Decanol
162.81
149.26
184.94
61.38
132
Table 4.5: Effect of neat EMIM-acetate, DMIM-phosphite and their binary mixture
stationary phases on the selectivity of selected analyte pairs at 70 ºC
Analyte pairs
EMIM-acetate
90 / 10
50/50
DMIM-phosphite
Naphthalene / Acetophenone
1.07
1.02
1.03
1.69
Pyrrole / Nitrobenzene
6.72
5.07
5.46
9.05
Cyclohexanol / Nitrobenzene
1.73
1.73
1.74
2.06
1-Decanol / 1-Pentanol
9.56
10.28
12.21
7.93
1-Octanol / Cyclohexanol
1.63
1.80
2.31
1.54
1-Decanol / Butanol
15.61
16.60
18.49
14.10
1-Octanol / 2-Propanol
24.49
31.07
32.83
19.54
Aromatic / Aromatic
Alcohol / Alcohol
133
4.4 CONCLUSION
The measured system constants of binary mixtures of stationary phases are
comparable to the system constants in its pure form, DMIM-phosphite and EMIM-acetate.
Hydrogen-basicity of the pure EMIM-acetate and DMIM-phosphite and binary mixture
revealed that as the amount of EMIM-acetate in the stationary phase increases, the
hydrogen bond basicity property increases. However, the said trend was not followed at
40 ºC due to increased in partitioning of analytes through interfacial adsorption.
Dispersion interaction illustrated that the 50% / 50% binary mixture showed
highest l – value while the pure DMIM-phosphite was the lowest. This said property
explained the high calculated retention factor of 1-octanol and 1-decanol probe molecules
due to the ability of the said compounds not only to donate a proton but have pronounced
cohesive forces. This is attributed to the long linear alkyl chain of these analytes.
On the concept of separation selectivity, higher selectivity were observed on the
binary mixture, 50% / 50% and 90% / 10% compared to pure ILs.
4.5 BIBLIOGRAPHY
1. Fukaya, Y. et. al., “Cellulose dissolution with polar ionic liquids under mild conditions:
required factors for anions”, Green Chemistry, 2008, 10(1), 44-46.
2. Morrison, R.T. and Boyd, R. N., “Organic Chemistry”, 1992, Prentice-Hall, Inc.
3. McNair, H. M. and Miller, J. M., “Basic Gas Chromatography”, 1998, John Wiley
and Sons, Inc.
4. Li, Q.; Poole, C. F. “Influence of interfacial adsorption on the system constants of the
134
solvation parameter model in gas-liquid chromatography”, Chromatographia (2000),
52(9/10), 639-647
5. Poole, C. “The Essence of Chromatography”, 2003
135
PART FOUR
Correlation of solvation properties to
cellulose dissolution
136
Chapter 5
INFLUENCE OF EVALUATED SOLVATION PROPERTIES AND
STRUCTURAL COMPOSITION OF
IONIC LIQUIDS TO THE DISSOLUTION OF CELLULOSE
5.1 INTRODUCTION
In Chapters 3 and 4, the solvation properties of several ionic liquids were
evaluated using the Abraham solvation parameter model. The two most significant
system constants related in this study appear to be the hydrogen bond basicity (a) and
dispersion interactions (l). The basicity characteristics is largely attributed to the anionic
portion of the IL. The dispersion interactions are largely imparted by the cationic portion
of the IL. The measured hydrogen bond basicity of the examined ILs ranged from 3.50
(EMIM-thiocyanate) to 6.50 (EMIM-propionate), both measurements observed at 100 ºC.
The assessed l – value is from 0.23 (1-methoxymethyl-3-methyl imidazolium chloride) to
0.54 (1-octyl-3-methyl imidazolium chloride), under the same temperature. The
correlation of the two system constants were examined and are calculated by obtaining
their ratio (a / l). This ratio can then be related to the results from cellulose dissolution
experiments.
In this research, the influence of the hydrogen bond basicity and dispersion
interaction to the solubility of different imidazolium and pyridinium-based ILs were
137
investigated. Some of the results in the solubility experiment were obtained from a
collaborator in the Chemical and Environmental Engineering Department at The
University of Toledo and from a labmate.
5.2 RESULTS AND DISCUSSION
5.2.1 Imidazolium-based ionic liquids
The solubility of Avicel appears to be greater when the ratio of hydrogen basicity
and dispersion interactions is 18 or higher, as shown in Table 5.1. This is true for ILs 1, 8
and 10. However, this is value is not followed in 1-allyl-3-methyl imidazolium chloride,
IL 6. The solubility of cellulose is only 10 % of the said IL even though the measured
ratio is 23.
Lower cellulose dissolution was observed when the ratio was 11 or lower. This
was observed in ILs 3, 4, 5. This decrease could be explained by the increase in
dispersion interaction because of the long linear substituents attached to the cationic
portion of these ILs.
Thus, in this set of ILs, it can be deduced that when the a – value, observed at 100
ºC is higher than 5.00 and the l – value is lower than 0.40, greater solubility of cellulose
is achieved.
5.2.2 EMIM-based ionic liquids
The hydrogen bond basicity is an important system constant in this set of ILs. The
dispersion interactions have less influence in the solubility of cellulose with some ILs.
138
For example, EMIM-propionate has an l – value of more 0.50, shown in Table 5.2, but
still exhibited moderate solubility of Avicel (22-26 %) where in the previous section it
was revealed that l – value lower than 0.4 can give a higher solubility of cellulose.
From the calculated ratio of hydrogen bond basicity to dispersion interaction,
values greater than 19 results in improve solubility. This is true with EMIM-acetate and
EMIM-propionate which both demonstrate high cellulose dissolution. However, even
though the calculated ratio for EMIM-aspartate, EMIM-trichloroacetate and EMIMsuccinate is more than 18, these ILs dissolve a lower amount of cellulose. This
observation cannot be influenced by dispersion interaction since the l – values of these
ILs were low compared to EMIM-acetate and EMIM-propionate. A possible reason could
be the size of the anion since in the dissolution process both the cation and anion were
interacting as a pair to disrupt the extensive hydrogen bond network of cellulose. The
bigger or bulkier anion could be harder for the IL to penetrate within the cellulose to
effectively disrupt the hydrogen bonding.
On the other hand, the solubility measurement of EMIM-formate and EMIMethylsulfate can still be examined even the solvation property of these compounds cannot
be measured at 100 ºC.
Thus, what can be inferred in this set of ILs is that when the a – value is greater
than 6.00 (measured at 100 º) and the l – value is lower than 0.40 (measured at 100 º), it
cannot assure of great solubility.
139
5.2.3 Pyridinium-based ionic liquids
The calculated ratio presented in Table 5.3 for these set of ILs range from 11 – 17.
All of the examined ILs exhibited high solubility. A hydrogen-bond basicity value greater
than 4.00, measured at 100 ºC, correlated with a good solubility of Avicel. When the
dispersion interaction or the l – value was 0.45, a relatively higher solubility of Avicel
was observed.
Comparing ILs 3, 1-butyl-3-methyl pyridinium chloride, to IL 4, its acetate
analogue anion, showed that the ability to dissolve cellulose is relatively similar. The
slight enhancement of solubility in IL 3 could be attributed to the lower l – value, 0.38
compared to IL 4, 0.45.
In this set of ILs it can be deduced that the solubility of cellulose is greater when
the a – value is 4.00 or higher and the l – value is 0.45 or lower.
140
Table 5.1: Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of imidazolium-based ILs
1.
System constants
a
l
IONIC LIQUID
1-ethyl-3-methyl imidazolium chloride
40ºC
70ºC
100ºC
2.
4.
5.
6.
7.
8.
9.
Solubility of Avicel
6.03
5.53
5.24
0.40
0.30
0.27
15.25
18.41
19.39
13 - 16 %
7.03
5.23
4.86
0.63
0.45
0.39
11.21
11.75
12.40
25% *1
40ºC
70ºC
100ºC
6.88
5.67
4.72
0.58
0.49
0.43
11.90
11.53
11.02
did not dissolve
40ºC
70ºC
100ºC
7.63
6.31
5.48
0.76
0.63
0.54
10.04
9.96
10.24
did not dissolve
40ºC
70ºC
100ºC
7.09
6.21
5.33
0.73
0.62
0.51
9.74
10.08
10.35
did not dissolve
40ºC
70ºC
100ºC
5.90
5.87
5.51
0.45
0.31
0.24
13.07
18.82
22.83
10% *2
40ºC
70ºC
100ºC
5.68
5.28
4.82
0.54
0.41
0.31
10.43
12.92
15.33
8% **
40ºC
70ºC
100ºC
5.05
4.67
4.30
0.44
0.31
0.23
11.34
14.99
18.48
20 % **
40ºC
70ºC
100ºC
6.29
6.11
5.66
0.40
0.35
0.29
15.59
17.35
19.68
25% **
1-butyl -3-methyl imidazolium chloride
40ºC
70ºC
100ºC
3.
Ratio
a /l
1-hexyl -3-methyl imidazolium chloride
1-octyl-3-methyl imidazolium chloride
1- octyl-3-butyl imidazolium chloride
1-allyl-3-methyl imidazolium chloride
1- allyl-3-vinyl imidazolium chloride
1-methoxymethyl imidazolium chloride
1-methoxyethyl imidazolium chloride
* values obtained from literature
** values obtained from collaborator
141
Table 5.2: Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of EMIM-based ILs
1.
2.
3.
4.
5.
6.
7.
8.
9.
System constants
a
l
Ratio
a/l
40ºC
70ºC
100ºC
4.86
0.59
6.65
0.48
thermally unstable
8.28
13.71
40ºC
70ºC
100ºC
6.87
6.60
6.43
0.50
0.39
0.32
13.82
16.80
20.31
20 - 25 %
40ºC
70ºC
100ºC
7.11
7.04
6.17
0.45
0.35
0.32
15.67
20.32
19.20
22 - 26 %
40ºC
70ºC
100ºC
4.49
0.48
4.27
0.42
thermally unstable
9.36
10.21
40ºC
70ºC
100ºC
4.12
3.87
3.46
0.49
0.40
0.33
8.32
9.68
10.40
did not dissolve**
40ºC
70ºC
100ºC
6.41
6.17
5.42
0.48
0.37
0.30
13.29
16.68
17.99
8%***
40ºC
70ºC
100ºC
6.46
6.41
6.07
0.45
0.29
0.26
14.38
22.28
22.93
7%***
40ºC
70ºC
100ºC
4.77
4.32
4.16
0.56
0.46
0.30
8.54
9.36
13.66
did not dissolve***
40ºC
70ºC
100ºC
6.30
5.95
5.26
0.51
0.37
0.27
12.36
15.92
19.21
8%***
IONIC LIQUID
EMIM-formate
Solubility of Avicel
20 - 25 %
EMIM-acetate
EMIM-propionate
EMIM-ethylsulfate
did not dissolve**
EMIM-thiocyanate
EMIM-succinate
EMIM-aspartate
EMIM-trifluoroacetate
EMIM-trichloroacetate
** values obtained from collaborator
*** values obtained from labmate
142
Table 5.3: Correlation of hydrogen bond basicity and dispersion interaction
system constant to cellulose dissolution of Pyridinium-based ILs
System constants
IONIC LIQUID
1.
2.
3.
4.
Ratio
a/l
Solubility with
Avicel
0.45
0.35
0.33
13.87
16.46
17.18
19 - 21 %
3.26
5.00
4.42
0.69
0.62
0.37
4.74
8.03
11.84
15 - 18 %
40ºC
70ºC
100ºC
6.59
5.74
5.46
0.51
0.46
0.38
12.93
12.53
14.48
16 - 19 %
40ºC
70ºC
100ºC
7.43
5.60
4.81
0.83
0.60
0.45
8.96
9.40
10.74
12 - 15 %
a
l
40ºC
70ºC
100ºC
6.27
5.83
5.67
1-hydroxylethyl-3- methyl pyridium chloride
40ºC
70ºC
100ºC
1-allyl- 3- methyl pyridium chloride
1-butyl- 3- methyl pyridium chloride
1-butyl- 3- methyl pyridium acetate
143
5.3 BIBLIOGRAPHY
1. Swatloski R. P; et. al., “Dissolution of cellulose [correction of cellose] with ionic
liquids’, Journal of the American Chemical Society, 2002, 124(18), 4974-5
2. Wu, J., “Homogeneous acetylation of cellulose in a new ionic liquid”,
Biomacromolecules, 2004, 5(2), 266-268
144
PART FIVE
Thermophysical properties of imidazolium and
pyridinium-based ionic liquids
145
CHAPTER 6
ONSET COLUMN BLEED TEMPERATURE OF SYNTHESIZED IONIC
LIQUIDS
6.1 INTRODUCTION
Understanding the thermophysical properties of an IL is important before
performing any chemical analyses. It defines the interval temperature where the IL is still
suitable to be used as a solvent (1). For instance, when an IL is used in separation
analysis as a stationary phase, the maximum allowable operating temperature of the
solvent is helpful in determining the lifetime of the column (2, 3). Examination of
thermal stability can be performed in several ways. Firstly, a small amount of IL can be
sealed in the capillary and then the temperature is gradually increased. The
decomposition occurs when discolorization of an IL occurs as visually observed (2, 4).
Secondly, thermogravimetric analysis (TGA) is another commonly used technique.
Thirdly, the IL can be used as a stationary phase in a GC capillary column and the
temperature gradually increased until column bleed occurs. This is indicated by the rising
of the baseline signal which indicates that the stationary phase starts to decompose. The
signal then flattens or produces a plateau that signifies that all the stationary phase has
decomposed or bled from the column. The recorded temperature in this method is usually
lower than using thermogravimetric and differential thermal analyzer (TG-DTA) because
the GC detector is more sensitive than visual observation (2).
146
Different imidazolium and pyridinium based IL and mixed stationary phases were
subjected to thermal stability analysis and their temperature ranges were compared. The
latter technique was used in the analysis described in this chapter.
6.2 EXPERIMENTAL
6.2.1 Methodology
The onset column bleeding temperature or thermal decomposition of ILs was
measured using GC. The column coated with different imidazolium and pyridiniumbased ILs were quickly conditioned using temperature programming, using a temperature
profile ranging from 30-100 ºC at 2.5 ºC/min ramp and held for 30 minutes at 100 ºC.
The helium flow rate was adjusted to 1 mL/min. Analysis was done by adjusting the
column temperature initially to 50 ºC and final temperature to 300 ºC and held for 15
minutes at 0.5 ºC/min ramp. The onset column bleeding occurs when the volatilization /
decomposition of the stationary phase occurs (2). This can be observed in the
chromatogram where the rising of the baseline signifies that the stationary phase starts
decomposing. IL completely volatilizes in the capillary column when a plateau effect was
observed. The reported temperature range of the onset column bleeding is between when
the baseline starts to rise until the plateau or signal flattens off. Figure 5.1 shows an
example of a chromatogram of onset column bleeding of stationary phase using gas
chromatography.
147
Stationary phase
completely decomposed
Stationary phase starts to
decomposed
Figure 6.1: Onset column bleeding analysis of stationary phases using gas
chromatography
148
6.3 RESULTS AND DISCUSSION
6.3.1 ONSET COLUMN BLEEDING TEMPERATURE OF IMIDAZOLIUM
BASED, PYRIDINIUM BASED AND BINARY MIXTURE IONIC LIQUID
STATIONARY PHASES
The thermal stability or column bleed onset temperature of the IL depends
primarily on the anion (6, 10, 18). According to Baranyai and co-workers (6) the
mechanism involves the dealkylation of the anion while the cation undergoes primarily
an alkyl migration or elimination reaction. Table 6.1 presents the onset bleed temperature
of neat and binary mixtures of ILs.
6.3.1.1 EFFECT OF CATION TYPE
First, the effect of cation on the IL’s onset column bleeding was analyzed. This is
observed with ILs 1-8 (Table 6.1) wherein these ILs are paired with the chloride anion.
ILs 3 and 4 demonstrated a moderately high on-set bleeding temperature. This is due to
the longer alkyl chain attached to the nitrogen atom of the imidazolium cation. This is
consistent with observations by Ngo and coworkers (8), in which the thermal stability is
improved by increasing the length of the alkyl substituents for linear series of the alkyl
unit.
IL 5 showed a greater onset column bleeding temperature than IL 6. This may be
due to the shape of the cation which is more asymmetric than IL 6. Between ILs 7-8, a
149
higher onset bleed temperature is observed with IL 7. This can be attributed to the larger
cation size of IL 7 than to IL 8.
ILs 18, 20, 22, 24 are examples of pyridinium chloride ILs with thermal stability
similar to the imidazolium chloride ILs. The slight increase in onset column bleed of IL
18 as compared to 24 was due to the longer alkyl chain substituents, butyl and propyl
respectively, on the pyridinium ring cation. IL 22 with an alkene side chain showed
appreciable onset bleeding temperature (130-142 ºC) due to extended delocalization of
the π electron of the alkene side chain. IL 20, which has hydroxyl group suspended at the
alkyl chain at the nitrogen of the ring, showed higher column bleed temperature as
compared to other pyridinium chloride ILs.
6.3.1.2 EFFECT OF ANION TYPE
The thermal stability of an IL is largely dominated by the anion (5). ILs
decomposes via SN1 or SN2 nucleophilic reactions (2, 9, 10). The increase in thermal
stability can originate from an increase in anion size, and/or a more delocalized negative
anion charge (5, 11). The imidazolium ILs 10 and 11 were in almost the same range with
a very slight increase in bleeding temperature of IL 11 because of the size of alkyl chain.
With a bigger anion size IL 13 exhibited a higher column bleeding temperature. IL 14
showed a slightly higher column bleed temperature compared to IL 15. In addition, IL 14
is a more symmetric anion which can lead to more stable intramolecular bonding and as a
result, a higher onset column bleed temperature (1, 12). Moderately high thermal stability,
however, was observed for ILs 16 compared to 17. This maybe due to the anion size of
IL 16 which is larger than IL 17.
150
Table 6.1 Onset column bleeding temperature of neat and binary ionic liquid
stationary phases
NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
STATIONARY PHASES
1-ethyl-3-methyl imidazolium chloride
1-hexyl -3-methyl imidazolium chloride
1-octyl-3-methyl imidazolium chloride
1- octyl-3-butyl imidazolium chloride
1-allyl-3-methyl imidazolium chloride
1- allyl-3-vinyl imidazolium chloride
1-methoxyethyl imidazolium chloride
1-methoxymethyl imidazolium chloride
EMIM-formate
EMIM-acetate
EMIM-propionate
EMIM-ethylsulfate
EMIM-thiocyanate
EMIM-succinate
EMIM-aspartate
EMIM-trichloroacetate
EMIM-trifluoroacetate
ON-SET BLEED TEMPERATURE
140-160 °C
145 -170 °C
180-205 ºC
185-200 ºC
170-185 ºC
140-150 ºC
105-120 ºC
105-115 ºC
not detected
145-160 ºC
145-165 °C
not detected
165-185 ºC
175-190 ºC
160-175 ºC
125-155 ºC
115-125 ºC
18
19
20
1-butyl- 3- methyl pyridium chloride
1-butyl- 3- methyl pyridium acetate
1-hydroxylethyl-3- methyl pyridium chloride
145-160 ºC
135-165 ºC
155-180 ºC
21
22
23
24
1-allyl- 4- methyl pyridium chloride
1-allyl- 3- methyl pyridium chloride
1-allyl- 2- methyl pyridium chloride
1-propyl- 3- methyl pyridium chloride
125-140 ºC
130-145 ºC
120-135 ºC
145-155 ºC
25
26
27
1,3-dimethyl imidazolium phosphite
50% EMIM-Acetate / 50% DMIM Phosphite
90% EMIM-Acetate / 10% DMIM Phosphite
115-125 ºC
155-170 ºC
150-175 ºC
151
6.3.1.3 Effect of isomer
It is interesting to observe the thermal stability changes of the IL that were varied
by the position of the methyl substituent in the cation. Among the isomeric ILs 21-23, IL
22 in which the methyl group is in meta-position relative to the nitrogen in the
pyridinium ring, possesses highest decomposition temperature among these ILs. IL 23,
where the methyl group is attached ortho to the nitrogen of the pyridinium ring, was
observed to have the lowest onset bleeding temperature. While, comparing IL 21 where
methyl is at para-position to IL 22, a slightly higher column bleed temperature was
observed with the latter IL.
6.3.1.4 Comparison between pyridinium chloride and pyridinium acetate
The on-set column bleed temperature of the 1-butyl-3-methyl pyridinium chloride
IL 18 is lower than its acetate analog, IL 19. As mentioned previously in section 5.3.1,
the decomposition of the anion is caused by an SN2 reaction (2, 9, 10). Comparing these
two ILs, aside from the decomposition by an SN2 reaction, the size of an anion illustrates
the said observation. The higher the onset column bleed temperature observed with
pyridinium acetate is due to bigger acetate anion than chloride.
6.3.1.5 Comparison between pure ILs and binary mixture stationary phases
The stability of the stationary phase was tested by comparing the neat ILs 10 and
25 to its mixture IL 26 and 27. The data given in Table 5.1 shows that the mixture 90% /
10% of the EMIM-acetate / DMIM-phosphite, IL 27, showed the highest on-set column
152
bleeding temperature. It was followed by the 50 % / 50 % mixture, IL 26, then with the
pure EMIM-acetate, IL 10, and lowest is the pure DMIM-phosphite, IL 25.
6.3.1.6. Thermally unstable ionic liquids
EMIM-fomate and EMIM-sulfate were not analyzed for thermal stability because
they are unstable at higher temperature. As reported by Fukaya (12), EMIM-formate
showed relatively poor thermal stability because of decarboxylation.
For EMIM-sulfate, the decomposition happens over time when the column was
set to temperatures higher than 80 ºC. A study was done by Fernandez and co-workers (5),
where they have observed the stability of EMIM-sulfate at different temperatures. They
have reported that when this IL is exposed to a temperature higher than 80 ºC, the IL
slowly decomposes over time.
6.4 CONCLUSION
Ionic liquids had a remarkable impact in chemical processes and industries. The
thermal decomposition or the onset column bleeding temperature of several ILs was
measured using GC. It is important to understand the thermal stability property of the
solvent because it determines its useful operating temperature range. In the ILs that were
examined it revealed that the onset column bleeding temperature depends on the over-all
structural composition of the cation and anion components. Increasing the linear alkyl
chain substituent in the cationic portion increases the on-set column bleed temperature.
This was seen in OMIM-Cl and OBIM-Cl ILs. While, the ability of the anion portion of
the IL to delocalized its negative charge likewise control the said property. ILs like
153
EMIM-succinate and EMIM-aspartate which have highly delocalized anion resulted to
high thermal stability. Meanwhile, the on-set column bleeding of binary mixture
stationary phases of 90% / 10% EMIM-acetate / DMIM-phosphite and the 50% / 50%
mixture showed higher thermal stability than the pure EMIM-acetate and DMIMphosphite.
6.5 BIBLIOGRAPHY
1. Chiappe, C. and D. Pieraccini, “Ionic liquids: solvent properties and organic
reactivity “, Journal of Physical Organic Chemistry, 2005, 18(4): 275-297
2. Yao, C.; Anderson, J. L., “Retention characteristics of organic compounds on molten
salt and ionic liquid-based gas chromatography stationary phases”, Journal of
Chromatography, A, 2009, 1216(10), 1658-1712
3.
Zhao, Q. and Anderson, J L.,”Highly selective GC stationary phases consisting of
binary mixtures of polymeric ionic liquids”. J. Sep Sci, 2009, 33, 1-9
4.
Furton, K. G.; Poole, C. F. “Solute-solvent interactions in liquid alkylammonium 4toluenesulfonate salts studied by gas chromatography”. Analytical Chemistry, 1987,
59(8), 1170-6.
5.
Fernandez, A.; et. al., “ Thermophysical properties of 1-ethyl-3-methylimidazolium
ethylsulfate and 1-butyl-3-methylimidazolium methylsulfate ionic liquids”. Journal
of Chemical & Engineering Data, 2007, 52(5), 1979-1983
6.
Baranyai, K. J.; et.al. “Thermal Degradation of Ionic Liquids at Elevated
Temperatures”, Australian Journal of Chemistry, 2004, 57(2), 145-147
7.
Plechkova, N. and Seddon, K, “Application of ionic liquids in chemical industry’,
154
Chemical Society reviews, 2007, 123-150
8. Ngo, H. L., et.al, “Thermal properties of imidazolium ionic liquids”,
Thermochimica Acta, 2000, 357-358, 97-102
9.
Fox, D. M., et. al., “Flammability, thermal stability, and phse change
characteristics of several trialkylimidazolium salt”, Green Chemistry, 2003, 5, 724727
10. Poole, C. “The Essence of Chromatography”, 2003
11. Hasse, B.; et.al. “Viscosity, Interfacial Tension, Density, and Refractive Index of
Ionic Liquids [EMIM][MeSO3], [EMIM][MeOHPO2], [EMIM][OcSO4], and
[BBIM][NTf2] in Dependence on Temperature at Atmospheric Pressure”. Journal of
Chemical & Engineering Data, 2009, 54(9), 2576-2583
12. Fukaya, Y. et. al., “Cellulose dissolution with polar ionic liquids under mild
conditions: required factors for anions”, Green Chemistry, 2008, 10(1), 44-46
13. Awad, W. H. et. al., “Thermal degradation studies of alkyl-imidazolium salts and
their application in nanocomposites.” Thermochimica Acta, 2004, 409(1), 3-11
155
APPENDIX A
1
H-NMR of the synthesized imidazolium based and
pyridinium based ILs
Accompanying Chapter 2 Section 2.2.2.1
156
IMIDAZOLIUM-BASED ILs
3.85
EMIM-Br
N
Br-
1.00
1.07
9.0
1
8.5
8.0
DMSO
2.50
water
4.22
4.18
9.24
7.83
7.82
7.73 7.73
4.21
4.20
1.42
1.39
1.40
N
2.12
7.5
7.0
6.5
6.0
5.5
5.0
ppm
4.5
3.24
3.15
4.0
3.5
3.0
2.5
2.0
1.5
1.0
H-NMR (600 MHz, DMSO): δ=1.404 (3H, t, 7.2 Hz), δ=3.854 (3H, s), δ=4.201 (2H, q,
7.2 Hz), δ=7,732 (1H, s), δ=7.824 (1H, s), δ=9.241 (1H, s).
3.85
EMIM-formate
N
N
1.38
4.21
4.20
4.19
7.84
7.83
7.75
7.74
9.57
8.60
8.59
1.42
1.40
3.86
HCOO-
2.50
8.61
4.17
DMSO
water
1.00
13
1
12
11
10
0.77
9
2.01
8
2.083.25
7
6
ppm
5
4
2.99
3
2
1
0
-1
H-NMR (400 MHz, DMSO): δ =1.405 (3H, q, 2Hz), δ=3.856 (3H, t, 2Hz), δ=4.180 (2H,
q, 2Hz), δ=7.745 (1H, d, 1.6Hz), δ=7.836 (1H, d, 1.6Hz), δ=9.573 (1H, s)
157
1.55
EMIM acetate
N
CH3COO-
4.21
4.20
7.85
7.76
DMSO
1.00
10.0
1
1.13
9.5
9.0
8.5
8.0
2.50
4.22
4.19
9.92
1.41
1.38
1.40
3.86
N
2.34 3.55
7.5
7.0
6.5
6.0
5.5
ppm
5.0
4.5
4.0
3.41
3.5
3.0
2.5
2.0
1.5
1.0
H-NMR (600 MHz, DMSO): δ=1.396 (3H, t, 7.2 Hz), δ=1.552 (3H, s), δ=3.862 (3H, s),
δ=4.205 (2H, q, 7.2 Hz), δ=7.759 (1H, s), δ=7.852 (1H, s), δ=9.924 (1H, s).
3.87
EMIM-propionate
N
N
1.00
10.0
1
1.08
9.5
9.0
8.5
8.0
2.48 3.34
7.5
7.0
6.5
6.0
5.5
5.0
ppm
4.5
4.0
2.21
3.5
3.0
2.5
0.88
0.85
1.41
1.38
1.83
1.79
2.50
2.50
4.23
4.20
10.06
7.87
7.78
4.22
4.21
1.81
1.80
1.39
0.87
CH3CH2COO-
2.0
3.29
1.5
3.17
1.0
0.5
H-NMR (600 MHz, DMSO) δ=0.866 (3H, t, 7.8 Hz), δ=1.395 (3H,t, 7.8 Hz), δ=1.81
(2H, q, 7.2 Hz), δ=3.870 (3H, s), δ=4.214 (2H, q, 7.2 Hz), δ=7.780 (1H, s), δ=7.874 (1H,
s) δ=10.062 (1H, s).
158
3.84
EMIM-CF3COO
N
CF3COO-
1.12
9.0
8.5
8.0
2.12
7.5
1.39
2.50
3.85
4.20
7.79
7.71
7.70
9.16
1.00
1
4.18
4.19
1.41
1.40
1.40
N
7.0
6.5
6.0
5.5
5.0
ppm
4.5
3.25
4.0
3.16
3.5
3.0
2.5
2.0
1.5
1.0
H-NMR (600 MHz, DMSO) δ=1.404 (3H, t, 7.8 Hz), δ=3.841 (3H, s), δ=4.186 (2H, q,
7.2 Hz), δ=7.705 (1H, s), δ=7.780 (1H, s), δ=9.157 (1H, s)
ESI-MS {CF3COO-} = 113 u
159
EMIM-succinate
O
N
3.87
N
O
O-
4.23
4.21
7.89
7.80
10.25
1.39
1.37
1.99
1.38
O
1.00
1.15
10.0
9.5
9.0
8.5
8.0
2.31
7.5
7.0
6.5
6.0
5.5
5.0
4.5
2.50
4.24
4.20
DMSO
3.49
4.0
2.33
3.5
3.0
2.5
2.0
3.41
1.5
ppm
1
H-NMR (600 MHz, DMSO) δ=1.381 (3H, t, 7.2 Hz), δ=1.991 (2H, s), δ=3.874 (3H, s),
δ=4.220 (2H, q, 7.2Hz), δ=7.800 (1H, s), δ=7.892 (1H, s) δ=10.248 (1H, s)
ESI-MS= {-OOCCH2CH2COO-} = 116 u
160
EMIM-aspartate
O
3.86
O
O-
N
N
1.40
O-
1.41
1.39
4.23
4.19
2.50
DMSO
9.75
7.82
7.74
4.22
4.20
water
1.00
12
1
11
10
2.22
9
8
7
6
2.23 3.35
0.63
4
3
5
ppm
0.59
0.573.36
2
1
0
-1
H-NMR (600 MHz, DMSO) δ=1.398 (3H, t, 7.2 Hz), δ=1.681-1.722 (1H, m), δ=2.248
(2H, d, 14.4 Hz), δ=3.035 (2H, d, 10.2 Hz), δ=3.864 (3H, s), δ=4.210 (2H, q, 7.2 Hz),
δ=7.736 (1H, s), δ=7.821 (1H, s), δ=9.748 (1H, s)
ESI-MS= {-OOCCH2 NH2CHCOO-} = 131 u
161
NH2
3.85
DMIM-phosphite
O
N
N
P
-
O
OCH3
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
2.50
7.93
5.07
9.34
3.29
3.24
7.74
H
5.0
4.5
4.0
3.5
3.0
2.5
ppm
1
H-NMR (200 MHz, DMSO) δ=3.261 (3H, d, 11.6 Hz), δ=3.851 (6H, s), δ=5.607 (1H, s),
δ=7.728 (1H, s), δ=7.735 (1H, s), δ=9.333 (1H, s)
O
N
N
P
3.63
3.86
EMIM-phosphite
-
O
OCH3
9.0
8.5
8.0
1.40
1.44
1.36
4.22
4.19
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
2.50
4.26
9.5
4.15
5.09
7.91
9.49
7.86
7.76
3.27
3.21
H
3.5
3.0
2.5
2.0
1.5
1.0
ppm
1
H-NMR (200 MHz, DMSO) δ= (3H, t, 1.2 Hz), δ=3.241 (3H, d, 8.6, Hz), δ=3.857 (3H,
s), δ=4.207 (2H, q, 1.8Hz), δ=5.093 (1H, s), δ=7.765 (1H, d, 1.4 Hz), δ=7.858 (1H, d, 1.6
Hz), δ=9.489 (1H, s)
162
4.60
HMIM-Br
N
N
1.00
14
13
1
12
11
2.07
10
9
7
ppm
6
1.55
2.52
2.50
2.48
2.243.38
8
1.76
4.92
4.94
4.90
8.51
8.51
10.06
8.59
1.57
1.98
1.76
1.74
Br-
6.01 2.83
5
4
3
2
1
0
-1
H-NMR (400 MHz, DMSO) δ=3.261 (3H, t, 3.2 Hz), δ=1.741-1.765 (2H, m), δ=1.976
(6H, s), δ=4.603 (3H, s), δ=6.800 (2H, t), δ=8.506 (1H, d, 1.2 Hz), δ=8.585 (1H, d, 1.6
Hz ), δ=10.047 (1H, s)
N
N
CH3COO-
1.00
13
12
11
1
10
8
6
ppm
5
4
4.88
3
2
0.82
1.76
1.78
1.91 3.15
7
0.86
4.17
4.19
1.99
9
4.16
7.76
9.56
7.84
0.84
1.24
3.87
1.66
HMIM-Ac
5.80
2.85
1
0
-1
H-NMR (600 MHz, DMSO) δ=0.838 (3H, t, 10.2 Hz), δ=1.242 (6H, s), δ=1.660
(3H, s), δ=1.773 (2H, d, 10.2 Hz), δ=3.866 (3H, s), δ=4.175 (3H, t, 11.4 Hz), δ=7.765
(1H, d, 2.4 Hz), δ=7.842 (1H, d, 2.4 Hz), δ=9.556 (1H, s)
163
PYRIDINIUM-BASED ILs
2.97
EMPyr-Br
Br-
1.00
12
1
11
10
9
1.07 2.15
8
7
1.19
5.71
5.43 5.71
5.42
5.17
5.14
1.06 2.10
6.08
6.07
6.06
6.10
7.95
7.93
9.71
9.70
8.42 8.41
8.39
8.00
7.27
N
1.08
6
3.22
5
ppm
4
3
2
1
0
-1
H-NMR (600 MHz, CDCl3) δ=1.708 (3H, t, 7.2 Hz), δ=2.637 (3H, s), δ=5.010 (2H, q,
7.8 Hz), δ=7.998 (1H, t, 7.8 Hz), δ=8.232 (1H, d, 7.8 Hz), δ=9.413 (1H, d, 3 Hz) δ=9.592
0.97
2.62
(1H, s)
PMPyr-Cl
1.04
9.0
8.5
8.0
2.14
7.5
7.0
6.5
6.0
5.5
5.0
3.30
4.5
4.0
3.5
3.0
2.5
-0.05
2.09
2.06
4.93
4.90
7.27
8.23
8.22
8.01
8.00
7.99
9.47
9.46
1.04
9.5
2.08
2.07
9.60
0.98
0.96
4.92
N
2.20
2.0
3.18
1.5
1.0
0.5
0.0
ppm
1
H-NMR (600 MHz, CDCl3) δ=0.971 (3H, t, 7.8 Hz), δ=2.086 (2H, q, 7.2Hz), δ=2.617
(3H, s), δ=4.916 (2H, t, 7.2 Hz), δ=7.997 (1H, d, 6.6 Hz ), δ=8.227 (1H, d, 7.8 Hz),
δ=9.461 (1H, d, 6Hz), δ=9.602 (1H, s)
164
Cl-
1.87
1.86
4.81
4.80
HEMPyr-Cl
Cl-
2.49
N
1.00
8.5
5.49
5.47
5.42
5.39
6.11
6.10
6.09
6.07
6.06
7.90
7.89
0.97
0.97
8.0
7.5
7.0
6.5
1.03
6.0
2.12
5.5
3.15
5.0
4.5
4.0
3.5
3.0
4.04
2.5
2.0
ppm
1
H-NMR (600 MHz, D2O) δ=2.492 (3H, s), δ=3.997 (2H, t, 4.8Hz), δ=4.609 (2H, t, 4.8
Hz), δ=7.891 (1H, t, 14.4Hz), δ=8.339 (1H, d, 8.4Hz), δ=8.592 (1H, d, 6 Hz), δ=8.644
(1H, s)
2.94
B(2)MPyr-Cl
7.25
Chloroform-d
-0.02
0.98
N
Cl-
1.00
12
1
11
10
1.08 1.08
9
8
1.92
1.91
1.90
1.53
1.52
1.50
1.49
4.99
4.98
4.97
7.25
7.97
7.85
7.84
8.32
8.30
9.95
9.94
0.99
water
8.33
1.00
8.34
8.32
8.60
8.59
8.64
5.12
5.13
HO
2.16
7
6
5
ppm
4
3.19
2.13 2.20
3
2
3.18
1
0
-1
H-NMR (600 MHz, CDCl3) δ=0.938 (3H, t, 7.2 Hz), δ=1.390 (3H, t, 7.8Hz), δ=1.500-
1.550 (2H, m), δ=1.849-1.920(2H, m), δ=2.959 (3H, s), δ=4.999 (2H, t, 7.8 Hz), δ=7.866
(1H, d, 7.8 Hz), δ=7.992 (1H, t, 7.2 Hz), δ=8.326 (1H, t, 1.2 Hz), δ=9.963 (1H, d, 6 Hz)
165
2.54
B(3)MPyr-Cl
0.83
N
1.03
12
1
11
10
1.04
9
8
1.94
1.92
1.90 1.91
1.31
1.30
1.29
1.26
4.86
4.84
chloroform
7.27
8.18
8.17
7.97
7.96
7.95
9.35
9.52
4.85
0.84
0.82
Cl-
2.13
7
6
5
ppm
3.26
4
3
2.15
2.12
2
3.13
1
0
-1
H-NMR (200 MHz, CDCl3) δ=0.829 (3H, t, 7.2 Hz), δ=1.275-1.314 (2H, m), δ=1.928-
2.079 (2H, m), δ=1.898-1.936 (2H, m), δ=2.540 (3H, s), δ=4.848 (2H, t, 7.8 Hz),
δ=7.956-7.969 (1H, t, 1.2 Hz), δ=8.176 (1H, d, 7.8 Hz), δ=9.349 (1H, s, 6 Hz), δ=9.518
(1H, s, 6 Hz)
2.61
B(4)MPyr-Cl
N
1
11
10
9
8
6
5
ppm
0.91
3
2
-0.06
1.35
1.33 1.34
1.37
1.95
1.97
4
1.94
4.88
4.89
7
4.87
7.85
7.86
7.25
12
0.88
Chloroform-d
9.45
9.46
0.89
Cl-
1
0
H-NMR (600 MHz, CDCl3) δ=0.924 (3H, t, 6.0 Hz), δ=1.337-1.398 (2H, m), δ=1.950-
2.000 (2H, m), δ=2.627 (3H, s), δ=4.897 (2H, t, 7.2 Hz), δ=7.877 (1H, d, 6.0 Hz),
δ=9.471 (1H, d, 5.4 Hz)
166
-1
2.97
A(2)MPyr-Cl
N
1.00
12
1
11
10
8
1.07 2.15
7
1.19
5.71
5.43 5.71
5.42
5.17
5.14
1.06 2.10
9
6.08
6.07
6.06
6.10
7.95
7.93
8.39
8.00
9.71
9.70
8.42 8.41
7.27
Cl-
6
1.08
3.22
5
ppm
4
3
2
1
0
-1
H-NMR (600 MHz, CDCl3) δ=2.967 (3H, s), δ=5.155 (1H, d, 13.8Hz), δ=5.425 (1H, d.
10.2 Hz), δ=5.710 (2H, d, 6.6 Hz), δ=6.048-6.104 (1H, m), δ=7.939 (1H, d, 7.8 Hz),
δ=8.003 (1H, t, 8.2 Hz), δ=8.407 (1H, t, 6.6 Hz), δ=9.697 (1H, s)
3.36
A(3)MPyr-Cl
2.50
DMSO
N
5.24
5.23
8.0
7.5
7.0
6.5
6.0
5.45
5.43
8.5
6.18
6.17
6.16
6.15
6.14
6.13
8.10
8.08
8.07
9.0
8.48
8.47
9.01
8.92
8.91
Cl-
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
ppm
1
H-NMR (600 MHz, DMSO) δ=3.357 (3H, s), δ=5.238 (2H, d, 4 Hz), δ=5.395 (1H, d.
11.6 Hz), δ=5.439 (1H, d, 6.8 Hz), δ=6.131-6.148 (1H, m), δ=8.083 (1H, t, 4.4 Hz),
δ=8.447 (1H, d, 5.2 Hz), δ=8.915 (1H, d, 5.2 Hz), δ=9.005 (1H, s)
167
1.5
2.61
A(4)MPyr-Cl
N
5.26
5.25
6.18
6.17
6.15
6.13
6.12
6.11
2.50
2.50
5.43
8.02
8.96
8.03
8.98
Cl-
13
1
12
11
10
9
8
7
6
ppm
5
4
3
2
1
0
-1
H-NMR (600 MHz, CDCl3) δ=2.591 (3H, s), δ=5.260 (2H, d, 6.0Hz), δ=5.392 (2H, d,
7.8 Hz), δ=6.110-6.180 (1H, m), δ=8.030 (1H, d, 6.0Hz), δ=8.970 (1H, d, 12.0 Hz)
1.64
N
1.03
9.0
8.5
1
4.61
1.05
8.0
4.58
8.06
8.45
8.43
9.07
8.98
8.97
1.04
2.27
7.5
7.0
6.5
6.0
5.5
5.0
CH3COO-
0.00
1.52
4.60
4.59
1.54
2.50
EMPyr-Ac
4.5
ppm
4.08
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
H-NMR (600 MHz, DMSO) δ=1.536 (3H, t, 7.2Hz), δ=1.638 (3H, s), δ=4.496 (2H, q,
7.2Hz), δ=8.059 (1H, t, 7.2Hz), δ=8.441 (1H, d, 7.8Hz), δ=8.978 (1H, d, 6.0 Hz),
δ=9.071 (1H, s)
168
1.87
1.86
4.81
4.80
A(2)MPyr-Ac
CH3COO-
1.00
1
5.49
5.47
5.42
5.39
6.11
6.10
6.09
6.07
6.06
7.90
7.89
8.34
8.32
0.97
0.97
8.0
7.5
7.0
6.5
6.0
1.03
2.12
5.5
5.0
ppm
3.15
4.5
4.0
3.5
3.0
2.5
4.04
2.0
H-NMR (600 MHz, D2O) δ=1.867 (3H, s), δ=2.491 (3H, s), δ=5.123 (2H, d. 4.8 Hz),
δ=5.483 (2H, d, 10.2 Hz), δ=6.069-6.089 (1H, m), δ=7.897 (1H, d, 4.8 Hz), δ=8.331 (1H,
d, 7.2 Hz), δ=8.600 (1H, d, 3.0 Hz), δ=8.640 (1H, s)
1.90
2.52
4.80
A(3)MPyr-Ac
1.00
1.04
8.5
1.06
8.0
1.00
7.5
7.0
6.5
6.0
CH3COO-
5.52
5.50
5.44
5.42
5.16
5.15
N
6.13
6.11
6.10
6.08
6.07
8.5
7.93
7.92
7.91
1.00
8.66
8.63
8.62
8.37
8.35
8.60
8.59
8.64
5.12
5.13
2.49
N
1.07
2.10
5.5
3.70
5.0
4.5
4.0
3.5
3.0
2.5
5.64
2.0
1.5
ppm
1
H-NMR (600 MHz, D2O) δ=1.904 (3H, s), δ=2.519 (3H, s), δ=5.151 (2H, d, 6.0 Hz),
δ=5.430 (2H, d, 6.0 Hz), δ=6.084-6.101 (1H, m), δ=7.932 (1H, t, 13.8 Hz), δ=8.359 (1H,
d, 7.8 Hz), δ=8.621 (1H, d, 6.0 Hz), δ=8.662 (1H, s)
169
2.68
0.00
7.27
A(4)MPyr-Ac
1.87
1.22
11
1
10
9
7
5.53
5.51
5.67
5.62
6.12
6
5.59
5.68
8
6.11
6.15
7.83
7.85
9.33
9.34
12
CH3COO-
1.21
N
5
ppm
4
3
2
1
0
-1
H-NMR (600 MHz, CDCl3) δ=1.215 (3H, s), δ=2.680 (3H, s), δ=5.518 (2H, d, 9.6 Hz),
δ=5.679 (2H, d, 6.6 Hz), δ=6.116-6.144 (1H, m), δ=7.840 (1H, d, 6.6 Hz), δ=9.337 (1H,
d, 6.6 Hz)
BMPyr-Ac
2.39
N
1.03
13
1
12
11
10
9
1.02
8
2.04
7
6
ppm
5
2.94
3.00
4
3
1.90
2
0.68
0.72
1.14
1.12
1.16
1.18
1.79 1.77
4.60
4.63
7.86
7.84
8.08
8.10
7.88
8.98
9.00
9.07
4.62
1.58
0.70
4.21
CH3COO-
1.88
2.71
1
0
-1
H-NMR (600 MHz, CDCl3) δ=0.700 (3H, s), δ=1.12-1.18 (2H, m), δ=1.580 (3H, s),
δ=1.756-1.790 (2H, m), δ=4.210(3H, s), δ=4.621 (2H, t, 8.0 Hz), δ=7.863 (1H, t, 8.0 Hz),
δ=8.903 (1H, d, 8.0 Hz), δ=8.991 (1H, d, 8 Hz), δ=9.074 (1H, s)
170
2.50 2.50
2.49
3.35
3.33
HEPyr-Ac
N
9.0
1.05
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
2.25
2.37
4.5
4.0
1.67
1.65
3.85
1.00
4.60
4.59
8.06
1.04
8.45
8.94
8.93
8.84
HO
1.60
3.5
3.0
2.5
2.0
1.5
ppm
1
H-NMR (600 MHz, DMSO) δ=1.621 (3H, s), δ=3.822 (2H, d, 4.8 Hz), δ=4.571 (2H, t,
5.4 Hz), δ=8.032 (1H, d, 6.6 Hz), δ=8.426 (1H, d, 7.8 Hz), δ=8.466 (1H, d, 6.0 Hz),
δ=8.909 (1H, s)
171
CH3COO-
Appendix B
1
H-NMR of the Alternative Route on the Synthesis of
EMIM-acetate
Accompanying Chapter 2 Section 2.2.2.1.4
172
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
ppm
-0.01
1.37
3.95
7.79
4.22
4.16
9.18
7.71
4.20
4.18
1.42
1.39
2.50
1.41
3.35
3.85
Using CH2Cl2 as co-solvent
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
ppm
173
4.5
4.0
2.50
1.37
1.36
3.09
3.88
4.22
9.0
4.17
7.81
9.23
7.72
4.21
4.19
1.42
1.38
1.40
1.85
3.85
1.84
Using THF as co-solvent
3.5
3.0
2.5
2.0
1.5
1.0
0.0
Appendix C
1
H-NMR and 13C-NMR Analysis of the recovered EMIM-acetate after
Pre-treatment analysis
Accompanying Chapter 2 Section 2.3.4
174
BATCH 1
2.21
9.0
8.5
8.0
1.54
1.39
1.37
7.76
7.67
1.00
4.17
4.16
9.19
3.82
2.48
3.39
EMIM-Ac
Purified 1
1
H-NMR
2.40
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.61
3.19 3.29
3.5
3.0
2.5
2.0
1.5
ppm
39.93 39.51
136.96
37.09
46.18
124.91
123.31
16.06
EMIM-Ac
Purified 1
13
C-NMR
250
200
150
100
ppm
175
50
0
1.46
1.42
4.20
8.66
7.43
7.36
4.18
4.15
1.44
3.82
1.90
3.83
4.80
4.79
EMIM-Ac
Purified 2
1
H-NMR
1.00
2.06
8.5
8.0
7.5
2.39
7.0
6.5
6.0
5.5
5.0
ppm
4.5
3.61
4.0
4.79
3.5
3.0
2.5
3.20
2.0
1.5
135.65
35.72
123.56
121.97
44.88
14.63
EMIM-Ac
Purified 2
13
C-NMR
250
200
150
100
ppm
176
50
0
2.04
8.5
8.0
7.5
2.17
7.0
6.5
6.0
5.5
5.0
ppm
4.5
1.46
4.18
4.16
4.15
7.43
7.36
8.66
1.00
1.44
1.43
3.82
1.90
4.80
4.79
EMIM-Ac
Purified 3
1
H-NMR
3.24
4.0
3.97
3.5
3.0
2.5
2.84
2.0
1.5
135.67
35.73
123.58
121.99
44.88
14.63
EMIM-Ac
Purified 3
13
C-NMR
250
200
150
100
ppm
177
50
0
40.14
39.93
44.31
250
11
10
200
9
8
2.303.51
7
6
ppm
150
ppm
178
5
4
100
3
2
50
1
15.48
12
39.51
13
2.39
39.30
123.78
122.17
1.00
35.81
137.10
1.60
4.17
9.62
1.42
1.38
2.50
2.50
4.21
4.19
7.81
7.73
1.40
3.85
BATCH 2
EMIM-Ac
S1
1
H-NMR
3.59
0
-1
EMIM-Ac
S1
13
C-NMR
0
250
200
5
ppm
4
150
ppm
179
3
100
2
1
50
15.24
6
24.35
7
1.31
3.97
6.86
7.18
1.41
1.32
2.50
4.20
4.19
7.80
7.80
7.62 7.72
2.41 3.46
16.43
123.57
8
35.52
44.01
122.02
9
40.93
39.51
137.27
10
2.39
128.30
11
1.00
118.93
136.81
173.63
12
9.44
1.40
3.85
1.66
EMIM-Ac
S26
1
H-NMR
4.98
0
-1
EMIM-Ac
S26
13
C-NMR
0