Volume 4, Issue 6, November-December 2015
ISSN No.: 2319-7536
Available Online at www.gpublication.com/crbps
©Genxcellence Publication 2015-19, All Rights Reserved
RESEARCH PAPER
Effect of Cationic Micellar System on the Oxidation of Pentose Sugar by Chloramine–T: A
Kinetic Study
Sunanda Dhoke and Ram Krishna Shrivastava *
Department of Chemical Sciences, Chandra Shekhar Azad Govt. Post Graduate College, Sehore, India, PIN- 466001
* Department of Chemical Sciences, Institute for Excellence in Higher Education, Bhopal, India, PIN-462042
Abstract
The effect of a cationic surfactant i.e. Cetyl Trimethyl Ammonium Bromide (CTAB) on the oxidation of pentose sugar i.e. D-Arabinose by
sodium salt of p- toluene sulphonamide (Chloramine-T) has been studied in acetic acid medium at 313 K. The catalytic effect of CTAB
has been observed on the rate of oxidation. The reaction is first order with respect to oxidant and fractional order to substrate
concentration. Various effects like solvent, salt, temperature and addition of reaction product etc. have been studied. Different
thermodynamic parameters have been computed and on the basis of findings and observations a suitable reaction mechanism has been
suggested.
Keywords
kinetics, mechanism, surfactant, oxidation, thermodynamic parameters
INTRODUCTION
The effect of surfactants and their tendency to form micelle
during chemical reactions are always an interesting field for
researchers. The catalytic activities of aqueous micelles play
a significant role on the rate of reactions occurring in
micellar system. Sodium salt of p- toluene sulphonamide
commonly known as Chloramine-T has been used as an
oxidizing agent by several workers.1-3 Earlier the work on
the oxidation of pentose sugars by Chloramine –T (CAT)
has received considerable attention.4-7 but literature survey
revealed that there are very scanty work on the oxidation of
D- Arabinose in acetic acid medium by CAT in micellar
system from the kinetic and mechanistic point of view.8-11
Therefore, present work on oxidation of D- Arabinose in the
presence of cetyl trimethyl ammonium bromide (CTAB) and
acetic acid has been taken for consideration.
MATERIALS AND METHOD
The obtained values were well supported by literature
values. All the chemicals were used of analytical grade of
purity. The stock solution of Chloramine -T and all other
solutions were prepared in deionized, doubly distilled water.
The Chloramine-T solution was standardized by iodometric
method and preserved in black painted bottle to avoid any
photochemical deterioration. Acetic acid was distilled over
chromic acid before use. To avoid any photochemical
decomposition the reaction vessels were also painted black.
RESULT AND DISCUSSION
In the presence and absence of cationic surfactant, the
kinetics of oxidation of D-Arabinose by Chloramine–T has
been studied in acetic acid medium. The reaction rates for
micellar catalysed oxidation depends on both sugar and
surfactant concentrations.
1. Effect of varying substrate concentration [DArabinose] : The dependence of rate constant on [DArabinose] was determined at different concentrations
of Arabinose from 02 x 10-3 to 14 x 10-3 mol dm -3 at
constant concentrations of other reactants at 313 K. The
plot of log k versus log [D-Arabinose] is linear (fig. 1)
indicating fractional order dependence in micellar
media.
CTAB was used as received but its purity was confirmed by
measuring its critical micelle concentration (CMC) by
plotting surface tension versus log [surfactant] and also
confirmed with the plot of specific conductance versus
[surfactant] using conductometric determination method.
2.
Table -1: AcOH = 20 % v/v , [CTAB] = 1.2 x 10-3 mol dm -3 , Temp. = 313 K
S.
[CAT] x 103
[D- Arabinose] x 103
In presence of [CTAB]
-3
No.
mol dm
mol dm -3
k1 x 103 min-1
1.
0.5
10.0
20.4
2.
0.8
10.0
21.4
3.
1.0
10.0
23.2
4.
1.2
10.0
24.8
5.
1.5
10.0
25.3
6.
1.0
02.0
16.2
7.
1.0
05.0
21.4
8.
1.0
10.0
23.2
34
Sunanda Dhoke et al, Current Research in Biological and Pharmaceutical Sciences, 4 (6) November-December 2015,34-37
1.0
1.0
12.0
14.0
24.0
25.1
3.0
log [CAT] x 103 mol dm-3
log k x 103 mol dm-3
9.
10.
2.5
2.0
1.5
1.0
0.5
0.0
1.70
1.90
2.10
2.30
3
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0. 0
2.50
0
5
10
-3
2. Effect of varying oxidant concentration [CAT] : To
find out the order with respect to [CAT] the rate constant
were determined at different concentrations ranging from
0.5 x 10-3 to 1.5 x 10-3 mol dm -3 at constant concentration of
other reactants at 313K. It was found that the values of rate
constant were independent of the initial concentrations of
20
25
30
35
40
time
log [D-Arabinose] x 10 mol dm
Fig 1 The plot of log k versus log [D- Arabinose]
15
Fig 2 Plot of log [CAT] versus time
CAT that indicating the order of reaction with respect to
[CAT] is first order, which is well evident by the graph
between log [CAT] and time (fig. 2 ) which is linear. The
effect of varying oxidant concentration is well demonstrated
by fig 3 and fig 4 also.
Table -2: [D- Arabinose] = 10 x 10-3 mol dm -3, AcOH = 20 % v/v, [CAT] = 1.0 x 10-3 mol dm -3, Temp. = 313 K
S. No.
[CTAB] x 103 mol dm -3
1.
2.
3.
4.
5.
6.
7.
0.0
0.4
0.6
0.8
1.0
1.2
1.4
In presence of [CTAB]
k1 x 103 min -1
08.3
11.8
13.0
16.2
19.3
23.2
26.2
Fig 1 Plot of log (a-x) versus time for
oxidant variation
1.4
k x 10-3 min -1
1.2
1
log [CAT]
30
0.8
0.6
Fig 2 Plot of Rate Constant
versus [CAT]
25
20
15
10
0.4
5
0.2
0
5
0
0
5
10 15 20 25 30 35 40 45 50
Time
Fig 3 Plot of log [CAT] versus time
3. Effect of varying surfactant concentration [CTAB] :
To observe the catalytic effect of CTAB, the reaction was
carried out at different concentrations of the surfactant i.e.
CTAB and it is found that the reaction rate was increases
with the increase in the surfactant concentration up to
certain limits. The pre-micellar catalysis is due to the fact
8
10
12
15
[CAT] x 10 -3 mol dm-3
Fig 4 Plot of Rate Constant versus [CAT]
that small aggregates of surfactant molecules exist below the
CMC and that start the catalyzing the reaction.12 The
behaviour is in accordance with the micellar catalysis of
organic reactions of anion neutral molecule type. With
increasing concentration of CTAB the relative concentration
of organic substrate and ionic reactants in the stern layer of
35
Sunanda Dhoke et al, Current Research in Biological and Pharmaceutical Sciences, 4 (6) November-December 2015,34-37
the micelle increase rapidly. This behaviour is also
analogous to the Hill model accommodates the plot of log
[kobs - ko/km – kobs] versus log[CTAB] which is linear13-14
with slope value indicating positive co-operativity i.e.
induced interaction of additional substrate molecule due to
the interaction of the micelle with the first substrate
molecule. Hence, the reaction has been found to be
catalyzed by addition of CTAB.
4. Effect of initially added probable product [p-TS] : The
effect of addition of probable reaction product was studied
and found that the rate of reaction decreases on the addition
of p-TS suggest that a pre equilibrium step involving a
process in which p-TS is one of the product.
5. Dependence on [Hg(OAc)2] : The effect of [Hg(OAc)2]
was observed in the sufficient range and was found to be
negligible effect on the reaction rate.
6. Effect of varying solvent concentration : The effect of
changing solvent composition the reaction rate was studied
by varying the concentration of methanol. The rate constant
decreases with the increase of the solvent concentration.
This may be due to the possible interaction of negative ion
and dipole interaction.
7. Effect of salt concentration : The effect of changing salt
concentration on the reaction rate was also studied by
varying the concentration of salt.
8. Test for free radical : The generation of free radicals
during the course of oxidation was confirmed by adding
acrylamide solution, no precipitate was found in the reaction
mixture which indicates that there is no free radical are
found in the reaction mechanism.
9. Effect of varying temperature and Activation
parameters : The effect of temperature on reaction rate was
studied in the temperature range of 303K to 323K. From
Arrhenius plot the values of activation energy (Ea*) was
calculated while the value of entropy of activation (ΔS*),
enthalpy of activation(ΔH*), free energy of activation(ΔG*),
and frequency factor (log Pz) were computed from Eyring
equation. The higher negative value of entropy of activation
in the presence of CTAB indicates that more ordered
activated complex is formed. The high positive value of
enthalpy of activation and free energy of activation indicates
that
the
transition
state
is
highly
solvated.
Table 3
Energy of Activation
(Ea*)
Entropy of Activation
(ΔS*)
Enthalpy
Activation(ΔH*)
64.33 KJ mol -1
-108.71 J mol -1K-1
61.72 KJ mol -1
Stoichiometry and Product Analysis : following
stoichiometry was found –
CHO–(CHOH)3–CH2OH + 2CH3C6H4SO2NClNa + 2H2O
COOH – (CHOH)3 – CH2OH + 2CH3C6H4SO2NH2
+ HCOOH + 2Na + + 2ClThe products of oxidation were analyzed by HPLC and spot
test.
Reaction Mechanism : On the basis of information and
findings from experimental work the following probable
reaction scheme has been proposed which is very consistent
with the most of the experimental results Oxidation in presence of surfactant KD
Dn + S
DnS
km
Products
DnS + RNCl
kw
S + RNCl
Products
Where D is surfactant molecule, DnS is substrate- surfactant
micelle, RNCl- is oxidant species and KD, km and kw are the
constants.
The rate equation for this scheme can be given by -
-
𝑑𝑑 [𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − ]
𝑑𝑑𝑑𝑑
=
𝑑𝑑 [𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − ]
𝑑𝑑𝑑𝑑 [𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − ]
=
n
{𝐾𝐾𝐾𝐾
[ D]
𝐾𝐾𝐾𝐾
n
+𝑘𝑘𝑘𝑘
K
D } {[𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − ][𝑆𝑆]}
KD + [ D ]
[ D]
+𝑘𝑘𝑘𝑘
KD + [ D ]
Free
energy
Activation(ΔG*)
of
95.74 K J mol -1
kobs
Frequency
(log Pz)
factor
2.099 x 107 mol
dm -3 sec -1
-1
{km[ D ]n + kw.KD}[ S ]
=
KD + [ D ]n
kobs
km[ D ]n + kw.KD
=
S
KD + [ D ]n
Where kobs is first order rate constant.
𝑑𝑑 [𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 − ]
= 𝑘𝑘 𝑜𝑜𝑜𝑜𝑜𝑜 (𝑎𝑎 − 𝑥𝑥)
𝑑𝑑𝑑𝑑
CONCLUSION
The oxidation of D-Arabinose by CAT is a surfactant
catalyzed reaction studied at 313K. On the basis of study of
various effects and changes in concentrations of reactants
during the course of reaction, it can be said that the cationic
micelle of CTAB is an effective catalyst for the oxidation of
D–Arabinose by Chloramine-T in acetic acid medium. The
effects of solvent polarity and ionic strength suggest that the
participation of an ion and a neutral molecule in the
mechanistic steps.
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