Micellar catalysis on pentavalent vanadium ion oxidation of D-sorbitol in aqueous acid media: A kinetic study

Article abstract of DOI:10.1007/s10953-008-9304-0

Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the concentrations of D-sorbitol, vanadium(V), H⁺ and HSO₄ ^- . These observations remain unaltered in the presence of externally added surfactants. The effects of the cationic surfactant (i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to different extents. SDS and TX-100 can be used as catalysts in the production of D-glucose from D-sorbitol.

Full text of DOI:10.1007/s10953-008-9304-0

J Solution Chem (2008) 37: 1321–1328
DOI 10.1007/s10953-008-9304-0
Micellar Catalysis on Pentavalent Vanadium Ion
Oxidation of D-Sorbitol in Aqueous Acid Media:
A Kinetic Study
Bidyut Saha · Kiran M. Chowdhury · Jayashree Mandal
Received: 19 February 2008 / Accepted: 20 April 2008 / Published online: 10 July 2008
© Springer Science+Business Media, LLC 2008
Abstract Vanadium(V) oxidation of D-sorbitol shows a first-order dependency on the con-
centrations of D-sorbitol, vanadium(V), H+ and HSO4−. These observations remain unal-
tered in the presence of externally added surfactants. The effects of the cationic surfactant
(i.e., CPC), anionic surfactant (i.e., SDS) and neutral surfactant (i.e., TX-100) have been
studied. CPC inhibits the reactions whereas SDS and TX-100 accelerate the reaction to dif-
ferent extents. SDS and TX-100 can be used as catalysts in the production of D-glucose
from D-sorbitol.
Keywords Kinetics · Vanadium · D-sorbitol · Micelle · SDS · CPC · TX-100
1 Introduction
The special properties of surfactants are important in a wide variety of applications in chem-
istry, biology, engineering, material science and other areas. These molecules are said to
be amphipathic, i.e. they have distinct hydrophilic (polar) and hydrophobic (non polar) re-
gions [1]. The polar regions, called the head group, may be either neutral, cationic, anionic
or zwitterionic. The hydrophobic tail has one or more chains of varying length, composed
usually of a hydrocarbon. Surfactants dissolve completely in water at very low concentra-
tions, but above a certain level, the critical micelle concentration (CMC), the molecules
form globular aggregates called micelles. Micelles vary in size and shape but are commonly
rough surfaced spheres with aggregation numbers on the order of 50–100. The presence of
micelles can have marked effects on chemical reactions. Reaction rates can be either acceler-
ated or decelerated, depending on the chemical system, the type of the surfactant, and other
factors, such as pH, ionic strength, etc. The effect of surfactants on reaction kinetics is often
called micellar catalysis. Reactions with in-situ separation have great potential because of
the possibilities to improve conversion and selectivity. Micellar systems seem well suited
B. Saha ( ) · K.M. Chowdhury · J. Mandal
ꢀ
Department of Chemistry, The University of Burdwan, Golapbag, Burdwan 713104, WB, India
e-mail: b_saha31@rediffmail.com

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J Solution Chem (2008) 37: 1321–1328
for various separation [2] and catalytic processes [3, 4]. For catalytic processes micellar so-
lutions provide a way for other synthesis routes in an aqueous medium. Large amounts of
glucose are produced every year industrially. Here we report a method for glucose produc-
tion using micelles as catalysts, although it is not a feasible route from an economical point
of view. The purpose of this work is a generic investigation into the elucidation of catalytic
mechanisms. We previously reported that micelles have effects on the rate of reaction [5–
11]. The kinetics of oxidation of D-sorbitol by vanadium(V) was described [12] previously.
Here we report micellar catalysis of pentavalent vanadium ion oxidation of D-sorbitol in
aqueous acidic media.
2 Experimental
2.1 Materials
A stock solution of D-sorbitol (A.R., SRL) was freshly prepared by direct weigh-
ing of the sample and stored in a refrigerator. Sodium dodecyl sulfate (SDS) (A.R.,
SRL), N-cetylpyridinium chloride (CPC) (A.R., SRL), 4-(1,1,3,3-tetramethylbutyl)phenyl-
polyethylene glycol (TX-100) (A.R., SRL), H2SO4 (A.R., E. Merck), ammonium meta-
vanadate (A.R., SRL) and all other chemicals used were of the highest purity available
commercially.
2.2 Measurements
The solutions were prepared in doubly distilled water. Ammonium metavanadate was dis-
solved in sulfuric acid. The acid concentration of the stock vanadium(V) solution was taken
as the difference between the amount initially added and amount consumed by reaction (1).
NH4VO3(aq) + 2H+ → NH4+ + VO2+ + H2O(l)
(1)
The vanadium(V) solution is quite stable and was standardized against a freshly prepared
standard solution of ferrous ammonium sulfate, to a barium diphenyl ammonium sulfonate
end point in the presence of phosphoric acid. Solutions of the oxidant and reaction mix-
tures containing known quantities of the substrate (S) (i.e., D-sorbitol) (under the condi-
tions [S]T ꢀ [V(V)]T), acid and other necessary chemicals were separately thermostatted
( 0.1◦C). The reaction was started by mixing the requisite amounts of the oxidant with
the substrate. The concentration of unreacted vanadium(V) at different time intervals was
determined tritrimetrically [13] by using a standard Mohr’s solution in the presence of bar-
ium diphenylamine sulfonate as the redox indicator. The H+ concentration was varied by
keeping [HSO−4 ] constant ([H2SO4] + [NaHSO4] = [HSO−4 ]) and the [HSO−4 ] was varied
by keeping [H+] constant ([H2SO4] + [HClO4] = [H+]).
2.3 Product analysis
D-sorbitol was oxidized to glucose as confirmed by spot tests [14], whereas vanadium(V)
was reduced to vanadium(IV). A drop of the oxidized reaction mixture was treated with ten
drops of the reagent solution (0.4 g urea and 0.2 g SnCl2 were dissolved by heating with
10 mL of 40% sulfuric acid) in a microcrucible, heated for a minute over a microburner and
allowed to cool. A blue color appeared on cooling. This is the test for aldose. Glucose was

J Solution Chem (2008) 37: 1321–1328
1323
also detected by paper chromatography [15] using an authentic sample as the reference one.
Paper chromatography was effected using butan-1-ol-acetic acid-water (4:1:5 by volume)
as elutant by adding three sequential drops of silver nitrate, sodium hydroxide and sodium
thiosulfate solutions.
3 Result and Discussion
The reaction mixture had an excess of D-sorbitol to ensure that there was no appreciable
reduction of vanadium(V) by the product, if oxidizable, and it also maintains a pseudo-first-
order condition. The rate of disappearance of [V(V)]T shows a first-order dependence on
[V(V)]T and the pseudo-first-order rate constants (kobs) (= 2.303 slope) were calculated as
usual from the plot of log10[V(V)]T versus time (t). The rate shows a first-order dependence
on the substrate concentration, HSO−4 and H+ ion concentrations (cf., Figs. 1, 2 and 3) that
is slightly different from that reported in the Fandis and Kulshreshtha [12] work. Fadnis and
Kulshreshtha came to almost the same conclusion with respect to the order of the reaction
in [HSO−4 ] and [substrate]T. However, they reported no dependence on [H+]. Earlier studies
[16–18] have indicated that the form of the active vanadium(V) species depends on the acid
type and its concentration range. It has been established by earlier workers [16–19] that in
aqueous sulfuric acid media (≤4.5 mol·dm−3) the kinetically active species of vanadium(V)
is V(OH)3HSO+4 and the equilibrium leading to this active species is given by [16–21]
VO+2 + H3O+ + HSO4− ꢀ V(OH)3HSO+4
(2)
In the same way for results obtained in a higher acid concentration range (>4.5
mol·dm−3), the following equilibrium can be considered to be operative [22] for the for-
mation of the active species:
VO+2 + 2H+ + 2HSO4− ꢀ V(OH)2(HSO4)2+
(3)
The result can be explained by considering the proposed mechanism (Scheme 1) [21]
Rate = k3K1K2[S]T[H+][OX][HSO4−]
= k3K1K2[S]T[H+][OX]T[HSO4−]/(1 + K1[H+][HSO−4 ])
= k3K1K2[S]T[H+][OX]T[HSO4−](K1[H+][HSO−4 ] ꢁ 1)
Fig. 1 Dependence of k
on
obs
[D-sorbitol] for the
T
vanadium(V) oxidation of
◦
D-sorbitol at 35 C.
V
−3
−3
[V ] = 3 × 10 mol·dm
,
T
−3
[H SO ] = 2.0 mol·dm
.
2
4
−3
−3
,
A ([CPC] = 4.0×10 mol·dm
T
−3
[SDS] = 0 mol·dm
,
T
−3
[TX-100] = 0 mol·dm );
T
T
T
T
B ([CPC] = [SDS]
=
T
−3
[TX-100] = 0 mol·dm );
−3
C ([CPC] = 0 mol·dm
,
−3
[SDS] = 0 mol·dm
,
T
−2
−3
[TX-100] = 4×10 mol·dm );
T
T
T
−2
−3
,
D ([SDS] = 4×10 mol·dm
−3
[TX-100] = [CPC] = 0 mol·dm
)
T

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J Solution Chem (2008) 37: 1321–1328
Fig. 2 Dependence of k
on
obs
−
[HSO ] for the vanadium(V)
4
◦
oxidation of D-sorbitol at 25 C.
V
−3
−3
[V ] = 3 × 10 mol·dm
,
T
−3
−3
−3
[D-sorbitol] = 60×10 mol·dm
,
T
[HClO ]+[H SO ] = 4.0 mol·dm
4
2
4
Fig. 3 Dependence of k
on
obs
+
[H ] for the vanadium(V)
◦
oxidation of D-sorbitol at 25 C.
V
−3
−3
[V ] = 3 × 10 mol·dm
,
T
−3
−3
[D-sorbitol] = 60×10 mol·dm
,
T
−3
[NaHSO ]+[H SO ] = 4.5 mol·dm
4
2
4
where [S]T and [OX]T stand for the total substrate and oxidant concentrations, respectively:
[S]T = [D-sorbitol]T and [OX]T = [V(V)]T.
The pseudo-first-order rate constants, kobs, in the presence of varying concentrations of
different types of surfactants like sodium dodecyl sulfate (SDS, a representative anionic
surfactant), N-cetylpyridinium chloride (CPC, a representative cationic surfactant) and TX-
100 (a neutral surfactant) are presented in Table 1.
The data reveal that SDS and TX-100 accelerate the rate, whereas CPC decreases the rate.
Rate acceleration is higher in the case of SDS than for TX-100. Previously we made this type
of observation for Cr(VI) oxidation reactions [5–7] and recently for the V(V) oxidation of
D-glucose [22]. This can be explained by Scheme 2 [8] and Scheme 3.
The substrate is partitioned in the Stern layer of the micellar phase. SDS is an anionic
surfactant, such that electrostatic attraction between the positively charged [V(OH)3HSO4]+
species and negatively charged micellar head group causes the active oxidant
[V(OH)3HSO4]+ to go easily into the Stern layer of the micelle (Scheme 3). The reaction
proceeds in both micellar and aqueous media. The observed rate acceleration is due to the re-
action being favored in the micellar phase where both the active oxidant and the substrate are
preferably accumulated. In the case of TX-100, the active oxidant also enters the Stern layer
of the micelles but the amount is less compared to SDS because TX-100 is a neutral surfac-
tant so that there is no electrostatic attraction. CPC is a cationic surfactant and consequently,
due to the electrostatic repulsion between the positively charged V(OH)3HSO+4 species and
positively charged micellar head group (Scheme 3), the active oxidant, V(OH)3HSO+4 , does
not penetrate the Stern layer of the micelle. The reaction occurs only in aqueous media,

J Solution Chem (2008) 37: 1321–1328
1325
Scheme 1 Vanadium(V) oxidation of D-sorbitol
Scheme 2 Partitioning of the
reactive species between the
aqueous and micellar phases
which is depleted in substrate concentration. From the above observation it can be con-
cluded that SDS and TX-100 can be used as catalysts in the production of D-glucose from
D-sorbitol.
To interpret the observed kinetic data, the applicability of the pseudo-phase kinetic model
proposed by Menger and Portnoy [23] may be considered. This model considers the parti-
tioning of one reactant between the aqueous and micellar phases, and leads to the following
rate equation,
kobs = (kw + kmKB[Dn])/(1 + KB[Dn])
(4)

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J Solution Chem (2008) 37: 1321–1328
◦
Table 1 Some representative pseudo-first-order rate constants (k ) at 35 C for the vanadium(V) oxidation
obs
−3
3
V
−3
of D-sorbitol under different conditions: 10 [V ] = 3.0 mol·dm [H SO ] = 2.0 mol·dm
T
2
4
3
3
2
2
4
−1
(s )
10 [D-sorbitol]
10 [CPC]
10 [SDS]
10 [TX-100]
T
10 k
T
T
−3
T
obs
−3
−3
−3
(mol·dm
)
(mol·dm
)
(mol·dm
)
(mol·dm
)
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
90
90
90
90
90
90
90
90
90
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
02
03
04
05
06
07
08
09
10
02
03
04
05
06
07
08
09
10
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
00
02
03
04
05
06
07
08
09
10
00
00
00
00
00
00
00
00
00
5.9
6.5
7.5
8.0
8.5
9.1
9.5
10
10.3
5.0
6.1
6.5
7.1
7.6
7.8
8.2
8.5
8.7
8.3
8.0
7.6
7.0
6.8
6.4
5.5
5.0
4.0
where kw and km are the first-order rate constants in the aqueous and micellar phases, re-
spectively, and include the concentration of the other reactant in these pseudo-phases. KB
is the binding constant of the partitioned reactant with the micelles; [Dn] is the concen-
tration of the micelles and is related to the stoichiometric concentration of the surfactant,
[D]T, the critical micellar concentration, cmc, and the aggregation number, N. That is,
[Dn] = ([D]T − cmc)/N. Equation 4 leads to
1/(kw − kobs) = 1/(kw − km) + (N/KB){1/([D]T − cmc)}{1/(kw − km)}
(kw − kobs)/(kobs − km) = P = (KB/N)[D]T − (KB/N)(cmc)
(5)
(6)
To deal with Eqs. 5 and 6 one requires the knowledge of the cmc, which is not available
under the present kinetic conditions.

J Solution Chem (2008) 37: 1321–1328
1327
Scheme 3
Acknowledgements We thank Burdwan University for financial support and Prof. Asim K. Das, Visva-
Bharati University, WB, India for his helpful discussions and our parents for their dedication.

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J Solution Chem (2008) 37: 1321–1328
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