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CHAPTER -3
te
OXIDATION OF SUGARS
BY
Es
VANADIUM (V)
IN AQUEOUS SULPHURIC
ACID
55
The study of saccharides has special importance due to their
multidimensional physical, biological and industrial relevance [1, 2, 3, 4]. The
behaviour of electrolytes in aqueous carbohydrates and carbohydrates containing
small quantity of ions which are present in body fluids has became subject of
interest [5, 6, 7]. Simple saccharides have received attention due to their ability to
protect biological macro molecules in addition to their importance to
pharmaceutical and food [8].
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r
The molecular interaction of sugars in solutions plays an important role in
governing the mechanism of any system. The aqueous solutions of sugar have been
used by many workers in studying the solute – solvent interaction in aqueous and
mixed solvent system including studies related to viscosity of the medium [9, 10,
11, 12, 13, 14, 15]. The solvent – solvent interaction produced in solvent mixture
can effect solute – solvent interaction and preferential solvation [16].
te
Solvent plays an important role in many chemical processes. Organic
liquids are characterised by several properties that make them suitable for
dissolving and providing reaction media for various type of solutes or reactant [17].
During recent past workers have shown considerable interest in explaining the role
Es
of solvent properties like preferential solvation on reaction rates [18, 19, 20, 21].
The study of the oxidation of organic compounds by vanadium (V) has an
importance due to role of vanadium in relation to the insuline – mimetic act and
catalytic activities [22, 23, 24]. The study of oxidation mechanism of compounds
by vanadium (V) has also an importance in the studies concerning possible role of
transient ions of chromium and manganese on certain oxidation reactions by both
chromic acid and potassium permanganate [25]. The kinetics of oxidation of sugars
have been carried out in both acidic and alkaline media using such oxidants as
transition metal ions, inorganic acids, organometalic complexes and enzymes due
to there biological importance [26].
Kinetics of oxidation of sugars by vanadium (V) in sulphuric acid,
perchloric and hydrochloric acid solutions has been subject of research [27]. These
studies are not related to the medium effect on rate of reaction. The present study is
therefore undertaken to study the effect of medium mainly viscosity on rate of
oxidation of sugars by vanadium (V) in sulphuric acid.
56
3.1 OXIDATION OF SUGARS BY VANADIUM (V)
Oxidation of carbohydrates by transition metal ions vanadium (V),
chromium (VI), thallium (III), manganese (VII), cerium (IV) and colloidal MnO2
are of especial interest due to there application in biological sciences [28]. The
oxidation of sugars by vanadium (V) has special importance due to there biological
relevance and application in oxidation reaction by chromium / potassium
permanganate [25, 27]. In the higher acid concentration range (> 4.5 mol dm-3) the
following active species and equilibrium have been reported.
+ 2H+
+
[V(OH)2(HSO4)2]+
2HSO4-
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VO2+
…(3.1)
The vanadium (V) is amphoteric [29] and at lower acid concentration (pH
≥ 1.0) exist in a form of pervanadyl ion VO2+. The ion VO2+ may be in hydrated
form in lower concentration range.
te
fast
VO3-
+
2H+
VO2+
H2 O
…(3.2)
The results of these studies have revealed that in some cases the mechanism
Es
was proposed on the basis of the formation of intermediate complex between
substrate and the oxidant while in some cases the mechanism were proposed on the
basis of formation of free radical in the oxidation process. All these studies have
reported that the oxidation of sugars shows first order dependence on vanadium
(V), H+ ion and HSO4- ion.
The effect of sulphuric acid concentration on rate of oxidation has both acid
independent and dependant path, depending upon the concentration range. The plot
between kobs and [H2SO4] has non linear nature but the rate increases with the
increase of sulphuric acid concentration. The various explanations have been
proposed for the justification of the effect of acid concentration on rate of reaction.
3.2 EXPERIMENTAL
All the solutions were prepared using the chemical mentioned in the list of
chemicals and by the methods described in the chapter 2. The studies were carried
57
out according to the experimental methods with the instrument mentioned in the
chapter 2.
The rate constants were calculated by using the rate expression under
pseudo first order condition.
3.3 RESULTS
In the study, the kinetics of oxidation of glucose, fructose and sucrose by
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vanadium (V) in aqueous sulphuric acid medium has been studied. The
experimental values of rate constant obtained under experimental conditions at
different concentration of the reactant species are presented below.
3.3.1 Dependence of rate on initial [oxidant]
The effect of [Vanadium (V)] on the reaction rate was studied at constant
te
concentration of sulphuric acid, sugars and temperature. The values of rate constant
kobs are summarized in Table 3.1 in the concentration range of vanadium (V) used
in the study, the rate constant kobs was independent of the [vanadium (V)]. These
observation are in agreement with a first order dependence on [vanadium (V)]T and
Es
the reaction follows a first order rate law given by equation 3.3.
-d[vanadium (V) ] /dt
=
kobs [vanadium (V)]T
…(3.3)
Table 3.1 Variation o f rate with initial [ Vanadium (V)] at 298 K
[Sugars ] = 0.04 mol dm-3
[H2SO4 ] =
S.No.
2.0 mol dm-3
[Oxidant] mol dm-3
105 kobs ( sec-1 )
Fructose
Sucrose
1
0.002
17.1
9.0
2
0.003
17.2
9.1
3
0.004
17.0
9.2
4
0.005
17.3
9.1
5
0.006
17.2
9.2
58
In the synopsis of the work three sugars namely glucose, fructose and sucrose were
proposed for the kinetic study. During the study when the reaction was started
under similar conditions of the concentration of sulphuric acid, concentration of
substrate (fructose and sucrose) and temperature, it was notice that the rate of
reaction for glucose was many times smaller than the rate of oxidation of other two
sugars. Hence the kinetic study of the glucose in the context of all range of
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concentration were not possible under similar experimental condition used for other
two sugars namely fructose and sucrose.
3.3.2 Dependence of rate on initial [Substrate]
The effect of initial [sugars] on rate of reaction was investigated in the
concentration range 0.04 mol dm-3 to 0.09 mol dm-3. The values of rate constant for
te
both the sugars are presented in Table 3.2.
Table 3.2 Variation of rate with initial [Substrate] at 298 K
[Vanadium (V)] = 0.004 mol dm-3
Es
[H2SO4] = 2.0 mol dm-3
[Substrate] mol dm-3
S. No.
105 kobs ( sec-1)
Fructose
Sucrose
1
0.04
1.6
0.8
2
0.05
2.1
1.1
3
0.06
2.5
1.3
4
0.07
2.9
1.6
5
0.08
3.2
1.7
6
0.09
3.7
1.9
59
3.3.3 Dependence of rate on initial [H2SO4]
In aqueous sulphuric acid concentration the rate constant were measured at
different concentration of sulphuric acid at constant concentration of substrate and
oxidant. The results are given in Table 3.3.
Table 3.3 Variation of rate with initial [H2SO4] at 298 K
[Sugars ] = 0.04 mol dm-3
S. No.
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[ Vanadium(V)] = 0.004 mol dm-3
[H2SO4 ] mol dm-3
105 kobs ( sec-1 )
Fructose
Sucrose
1.0
9.1
2.2
2
1.5
17.1
3.7
3
2.0
25.4
5.5
te
1
2.5
33.5
7.3
5
3.0
42.2
9.2
Es
4
3.4 DISCUSSION
The results shown in table 3.1 to 3.3 were used to analyse the effect of
various reactant on rate of oxidation of sugars. The pseudo first order rate at
constant [oxidant] and [H2SO4], increased with increasing [sugars]. The plot
between [sugars] and kobs is shown in Fig 3.1, for both the substrates. The plots are
linear and the linearity coefficient is > 0.98. The rate constant is increased with
increasing [H2SO4]. The plot between [H2SO4] and the rate constant were also
linear for both the sugars. The representative plots are given in Fig 3.2.
60
4
y = 40.571x + 0.0295
R2 = 0.9956
A
3.5
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3
2
B
te
10 5 k o b s (sec -1)
2.5
Es
1.5
1
y = 21.714x - 0.0114
R2 = 0.9823
0.5
0
0
0.02
0.04
0.06
[Sugars] mol dm -3
A Fructose
B Sucrose
Fig 3.1
61
0.08
0.1
y = 16.52x - 7.58
R2 = 0.9998
45
A
40
la
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35
25
te
105 kobs (sec-1)
30
20
15
Es
y = 3.52x - 1.46
R2 = 0.9983
B
10
5
0
0
0.5
1
1.5
2
[H2SO4] mol dm -3
A Fructose
B Sucrose
Fig 3.2
62
2.5
3
3.5
These results confirm that the order of reaction with respect to substrate is
one in the sulphuric acid medium. The reaction rate was accelerated with the
increase in the sulphuric acid concentrations. The very high concentrations of
sulphuric acid were not used to avoid the undesirable solvent effect such as
viscosity, dielectric constant etc in the kinetic measurement because we have
proposed to study the effect of solvent related to the viscosity of the medium on
rate of oxidation. The solvent effect related to the viscosity can be studied only at
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constant acid concentration to eliminate the catalytic effect of the acid. It results
that the oxidation of glucose would not be carried out by changing the
concentration of reactant according to experimental conditions.
The results of the study of the kinetics of the oxidation of two sugars
reported above namely fructose and sucrose could be summarized as below(i) The reactions have a first order dependence on vanadium (V), confirmed by the
te
experimental data which was independent of the initial vanadium (V)
concentration.
(ii) The reactions are acid catalyzed and the catalytic effect increases with
increasing concentration of sulphuric acid.
Es
(iii) The reaction rates have linear dependence on concentration of sulphuric acid.
The plot between concentration of sulphuric acid and rate constant indicates the
order of the reaction nearly unity with respect to sulphuric acid concentration.
(iv) The order with respect to the substrate concentration is also one for both the
sugars. The linear plot of rate constant against substrate concentration passing
through the origin is an indication of second order kinetics, first order with respect
to sugar and first order with respect to vanadium.
(v) The addition of substrate to the solution of vanadium results in a shift in the
absorbance wave length measured in the spectrophotometric study, which is an
indication of the intermediate complex formation between vanadium (V) and
substrate. Similar shift was also noted on increasing the acid concentration which is
indication of protonation equilibria between various vanadium (V) species in
sulphuric acid.
(vi) The reaction mixture on partial oxidation polymerizes the acrylonitrile with in
few minutes, indicating the presence of free radical in the progress of the reaction.
63
(vii) It is well established by earlier worker that the [V(OH)3HSO4]+ is kinetically
active species of vanadium in aqueous sulphuric acid [30].
3.5 MECHANISM
On the basis of the above facts and experimental results the mechanism for
the oxidation of sugars by vanadium(V) in aqueous sulphuric acid medium has
been proposed by considering the complex ion and free radical formation as given
VO2
+
ROH
+ H3 O
+
+
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in scheme I
+
HSO4
K1
-
[V(OH)3HSO4]+
K2
[V(OH)3HSO4]+
..(3.4)
(R-OH-X)+
..( 3.5)
te
Intermediate complex
Where X represent the species [V(OH)3HSO4]+
k
+
R-OH˙+ VO2+ + 2H2O + 2H2SO4+ HSO4- ..(3.6)
(R-OH-X)
Es
slow Free radical
R-OH˙
fast
+ V(V)
V(IV)
+
H+
+ Product
..(3.7)
Scheme I
According to scheme I the overall reaction rate is given by equation 3.8.
Rate
=
k K1K2 [R-OH]T [H+] [V(V)] [HSO4-]
...(3.8)
k K1K2 [R-OH]T [H+] [V(V)]T [HSO4-]
Rate
=
...(3.9)
-
+
[1+K1H ] [HSO4 ]
When the values of K1 [H+] [HSO4-] is less than one rate equals to
Rate
= k K1K2 [R-OH]T [H+] [V(V)]T [HSO4-]
64
..(3.10)
The above mechanism is in agreement with the experimental results and
mechanism proposed for oxidation of glucose [31].
3.6 DEPENDENCE OF REACTION RATE ON VISCOSITY OF THE
MEDIUM
The reaction rate obtained on the basis of viscosity approach can be
compared with the increase in the rate with increase in concentration of the
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substrate. The comparison shows that the graph between viscosity of the medium
and concentration of the substrate has a considerable importance. The graph
between concentration and viscosity of the substrate in aqueous solutions at 298 K
Es
te
are given in Fig 3.3, 3.4 and 3.5.
65
2.5
y = 0.7116x + 0.8858
R2 = 0.9842
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r
2
te
Viscosity poise
1.5
Es
1
0.5
0
0
0.2
0.4
0.6
0.8
1
[ Fructose] m ol dm -3
T= 298 K
Fig 3.3
66
1.2
1.4
1.6
y = 4.645x - 1.0723
R2 = 0.9893
6
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5
3
Es
Viscosity poise
te
4
2
1
0
0
0.2
0.4
0.6
0.8
[ Sucrose] m ol dm
T= 298 K
Fig 3.4
67
1
-3
1.2
1.4
1.6
2.5
y = 0.9337x + 0.774
R2 = 0.9888
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2
te
Viscosity poise
1.5
Es
1
0.5
0
0
0.2
0.4
0.6
0.8
1
[ Glucose] m ol dm -3
T= 298 K
Fig 3.5
68
1.2
1.4
1.6
In the measurement of the viscosity the effect of other reactant, oxidant and acid
has not considered because the concentration of these reactants have constant
magnitude. Thus the viscosity of the substrate in aqueous medium can be taken as
the viscosity of the reaction media as an experimental purpose. This assumption has
been used in order to asses the effect of viscosity on the rate of reaction of the
medium.
A simple way of obtaining the relationship between viscosity of the medium
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and rate of reaction is careful study of rate of reaction with change of concentration
of the substrate used in the determination of the viscosity of the medium.
The plots between viscosity and rate of reaction are shown in Fig. 3.6 and
Fig. 3.7. It is seen that for both the substrates the cures are linear in nature. For both
the substrate it has been found that the values of rate constant obtained
experimentally are in reasonable agreement with the relation obtained between
Es
te
concentration and viscosity of the substrate.
69
y = 0.0009x - 0.001
R2 = 0.9655
0.0009
0.0008
la
r
0.0007
0.0005
te
k o b s (s e c - 1 )
0.0006
0.0004
Es
0.0003
0.0002
0.0001
0
0
0.5
1
1.5
Viscosity poise
Fructose
T= 298 K
Fig 3.6
70
2
2.5
y = 7E-05x - 9E-06
R 2 = 0.9668
0.0004
0.00035
la
r
0.0003
0.0002
te
k ob s (s e c - 1 )
0.00025
Es
0.00015
0.0001
0.00005
0
0
1
2
3
Viscosity poise
Sucrose
T=298 K
Fig 3.7
71
4
5
6
y = 0.0007x - 0.0002
0.0009
R2 = 0.9739
0.0008
la
r
0.0007
0.0006
te
k o bs (se c -1)
0.0005
Es
0.0004
0.0003
0.0002
0.0001
0
0
0.2
0.4
0.6
0.8
[ Fructose] mol dm
Fig 3.8
72
1
-3
1.2
1.4
1.6
0.0004
y = 0.0003x - 8E-05
R2 = 0.9809
0.00035
la
r
0.0003
te
k o b s (s e c - 1 )
0.00025
0.0002
Es
0.00015
0.0001
0.00005
0
0
0.2
0.4
0.6
0.8
1
[ Sucrose] mol dm -3
Fig 3.9
73
1.2
1.4
1.6
In acidic solutions the moment H3O+ ion loses its proton to a neighbouring
water molecule it itself transforms into water molecule. However the time taken in
the transfer process is about 10-14 sec. While the time of H3O+ ion wait for its
adjacent water molecules to reorient is about 2.4×10-13 sec. [32]. The contribution
towards viscosity by the H+ ions can be considered negligible and the contribution
of sugars mainly at higher concentration is responsible for the increase in viscosity
in aqueous solutions.
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Spectroscopic studies have shown that the hydration of saccharides depends
upon the hydroxyl group, the hydrogen bonding sites and the relative position of
the hydroxyl groups in the carbohydrate molecules [33]. In purely aqueous
solutions mono and disaccharides have structure – maker character as observed
from viscometric measurement [34].
In our study the following linear relations are applicable for fructose (Fig.
te
3.3 and Fig. 3.8)
η
=
+ 0.8858
0.0007 [S]
Es
kobs
= 0.7116 [S]
-
0.0002
…(3.11)
…(3.12)
These equations can be rearranged and equation (3.11) can be divided by equation
(3.12).
0.7116 [ S]
η - 0.8858
=
0.0007 [ S]
…(3.13)
kobs + 0.0002
Where [S] = fructose
kobs
= 0.0009 η - 0.0009
kobs
=
or
0.0009 (η - 1)
…(3.14)
The eq (3.14) is in agreement with the linear relation obtained in the graph η versus
kobs given by equation (3.15)
74
kobs
= 0.0009 η - 0.001
…(3.15)
The value of intercept 0.001 is nearly equal 0.0009.
In the same way the relation for sucrose obtained in the study can be taken
as actual relation between viscosity and kobs.
3.7 CONCLUSION
= 0.00007 (η - 0.12)
…(3.16)
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r
kobs
From the above discussion and analysis of the kinetic data it is concluded
that the value of rate constant for the solutes having structure maker character in
aqueous solutions is directly proportional to the viscosity of the solutions used in
te
the kinetic study. Further investigations in the light of influence of viscosity /
medium effect on rate of reaction are expected to be an important example as a
Es
model.
75
REFERENCES
1
Radha Rani Gupta
J. Indian Chem. Soc., 85 (2008)
and
176.
Mukhtar Singh
2
Polyhyderon, 25 (2006) 3581.
A. C. F. Ribeiro,
V. M. M. Lobo,
la
r
A. J. M. Valente,
S. M. N. Simoes,
A. J. F. N. Sobral,
M. L. Ramos,
and
H. D. Burrows
R. L. Putnam
J. Chem. Thermodyn., 25 (1993)
te
3
and
607.
J. Boerio - Goates
4
R. N. Goldberg
J. Biol. Chem., 264 (1989) 9897.
Es
and
Y. B. Tewari
5
S. K. Lomesh,
J. Indian Chem. Soc., 81 (2004)
Neelam Sharma
881.
and
Sushil Kumar
6
Shashi Kant,
Indian J. Chem. Soc., SecA 43
Pankaj Dogra
(2004) 2555.
and
Sushil Kumar
7
S. K. Lomesh,
J. Indian Chem. Soc., 83 (2006)
Pawan Jamwal
156.
and
Rakesh Kumar
8
J. Phys. Chem. (B), 104 (2000)
D. P. Miller
76
and
8876.
J. J. Depablo
9
R. Mathpal,
Monathshetefur
B. K. Joshi,
(2006) 375.
Chem.,
137
S. Joshi
and
N. D. Kandpal
D. Geeta
and
Indian J. Phys., 77 (2003) 525.
la
r
10
C. Rakkppan
11
P. C. Dey,
Monathshetefur Chemie., 134(6)
(2003) 797.
A. Muhamad,
M. A. Motin,
te
T. K. Biswas
and
E. M. Haque
12
N. Dash
Indian J. Chem., 34A (1995) 834.
Es
and
E. R. Patnaik
13
Indian J. Chem., 34A (1995) 462.
D. V. Jahangirdav,
B. R. Arbad,
M. P. Lokhande
and
S. C. Mehrotra
14
B. K. Sadhukhan,
Indian J. Chem., 22A (1983) 741.
D. K. Choudhary
and
K. S. Birdi
15
B. Behara,
Indian J. Chem., 22A (1983) 20.
B. Sahu,
S. Pradhan
and
77
K. Behra
16
C. Reichardt
Angew. Chem. Int. Ed (Eng.), 4
(1965) 29.
17
A. Thirumoorthi
J. Indian Chem. Soc., 87 (2010)
and
797.
K. P. Elango
D. S. Bhuvaneshwari
J. Indian Chem. Soc., 86 (2009)
and
233.
K. P. Elango
19
D. S. Bhuvaneshwari
Int. J. Chem. Kinet., 39 (2007)
and
657.
K. P. Elango
20
la
r
18
J. Mol. Liq., 143 (2008) 147.
D. S. Bhuvaneshwari
te
and
K. P. Elango
21
Z. Naturforsch, 63A (2008) 493.
D. S. Bhuvaneshwari
and
Es
K. P. Elango
22
23
D. C. Crans
J. Inorg. Biochem., 80 (2000)
123.
G. R. Wilsky,
J. Inorg. Biochem., 85 (2001) 33.
A. B. Goldfine,
P. J. Kostyniak,
J. H. McNeil,
L.Q. Yang,
H. R. Khan
and
D. C. Crans
24
R. Wever
Adv. Inorg. Chem., 35 (1990) 81.
and
K. Kustin
25
T. A. Turney
Oxidation
78
Mechanism,
Butterworths
London,
(1965)
102.
26 (i)
L. F. Sala,
J. Chem. Soc. Perkin Trans., 2
A. F. Cirelli
(1977) 685.
and
R. M. de Lederkren
M. Gupta,
J. Chem. Soc. Perkin Trans., 2
S. K. Saha
(1988) 1781.
and
la
r
(ii)
P. J. Banerjee
(iii)
J. Barek,
A. Berka
and
Collect. Czech. Chem. Commun.,
47 (1982) 2466.
(iv)
te
A. Pokorna- Hladikova
S. Signorella,
New J. Chem., 20 (1996) 989.
L. Ciullo,
R. Lafarga
Es
and
L. F. Sala
(v)
K. K. Gupta
Carbohyrd. Res., 71 (1979) 71.
and
S. N. Basu
(vi)
E. O. Odebummi
Nigerian J. Sci., 33 (1999) 133.
and
R. Marufu
(vii)
S. Gregory- Neyhart
J. Am. Chem. Soc., 117(5) (1995)
and
1463.
R. R. Thorp
(viii)
K. Michael
The Biochemical J., 124 (1971)
and
801.
J. Harold
79
(ix)
H. Shanker
Carbohydr. Res., 211 (1991) 235.
and
S. Bihari
27(i)
A. Kumar
J. Org. Chem., 40 (1975) 1248.
and
R. N. Mehrotra
(ii)
K. K. Sen Gupta,
Carbohydr. Res., 139 (1986) 185.
and
la
r
S. Sen Gupta
S. K. Mandal
(iii)
P. O. I. Virtanen,
Acta Chem. Scand., A40 (1986)
S. Kurkisuo,
200.
H. Nevala
te
and
S. Pohjola
(iv)
P. O. I. Virtanen
Acta Chem. Scand., B42 (1988)
and
411.
Es
R. Lindroos- Heinanen
(v)
Z. Khan
Int. J. Chem. Kinet., 31 (1999)
and
409.
Kabir- Ud- Din
(vi)
Z. Khan,
Carbohydr. Res., 339 (2004) 133.
P.S. S. Babu
and
Kabir- Ud- Din
28(i)
S. Signorella,
J. Chem. Soc. Dalton Trans.,
M. Rizotto,
(1996) 1607.
V. Daier,
C. Frascaroli,
D. Pdopoli,
D. Martino,
A. Bousseksou
80
and
L. F. Sala
(ii)
Z. Khan,
Colloid and Surf. A Physico
P. Kumar
Chem. Eng. Aspets., 248 (2004)
and
25.
Kabir- ud- Din
P. Kumar
Carbohydr.
and
1365.
Z. Khan
29
S. Yamada,
M. Tanaka
(2005)
835.
K. K. Sen Gupta,
Carbohydrate Res., 315 (1999)
te
30
340
J. Inorg. Nucl. Chem., 37 (1975)
S. Funahashi
and
Res.,
la
r
(iii)
B. A. Begum
70.
and
B. B. Pal
Bidyut Saha,
Int. Chem. Kinet., 40 (2008) 282.
Es
31
Sucharita Sarkar
and
Kiran M. Chowdhury
32
John O’ M Bockris
Modern Electrochemistry vol(1)
and
(1977) 487.
Amulya K. N. Reddy
33(i)
R. K. Schmidt,
J. Am. Chem. Soc., 118 (1996)
M. Karplus
541.
and
J. W. Brady
(ii)
M. J. Tait,
J. Soln. Chem., 1 (1972) 131.
A. Suggett,
F. Frank,
S. Abbett
81
and
P. A. Quickenden
(iii)
A. Suggett,
J. Soln. Chem., 5 (1976) 17.
S. Abbett
and
P. J. Lillford
(iv)
M. D. Danford
J. Am. Chem. Soc., 84 (1962)
34
T. C. Bai,
la
r
3965.
Fluid
(2005) 171.
C. C. Huang,
W. W. Yao
and
Es
te
C. W. Zhu
Phase
82
Equilibria,
232