Best combination of promoter and micellar catalyst for the rapid conversion of sorbitol to glucose

Article abstract of DOI:10.1016/j.saa.2013.11.068

Kinetic data for oxidation of D-sorbitol to glucose by hexavalent chromium in aqueous medium and aqueous surfactant medium (SDS, TX-100) have been reported. Effect of promoter such as PA, bipy and phenanthroline on the reaction has been investigated. The reaction is performed under pseudo first order condition with an excess of substrate over the oxidant. The reaction is first order with respect to substrate and oxidant. The micelles have a catalytic effect on the reaction. Combination of phen and TX-100 produces almost twelve times increase in rate of oxidation.

Full text of DOI:10.1016/j.saa.2013.11.068

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 204–208
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Best combination of promoter and micellar catalyst for the rapid
conversion of sorbitol to glucose
⇑
Kakali Mukherjee, Aniruddha Ghosh, Rumpa Saha, Pintu Sar, Susanta Malik, Bidyut Saha
Homogeneous Catalysis Laboratory, Department of Chemistry, The University of Burdwan, Golapbag, Burdwan 713104, WB, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Picolinic acid, 2,20-bipyndine and 1,10-phenanthroline promoted Cr(VI) oxidation of
D-sorbitol to glucose
ꢀ
ꢀ
The reaction is carried out in aqueous
media.
Toxic hexavalent chromium is
completely reduced to trivalent
chromium.
in aqueous micellar media is shown here. The anionic surfactant (SDS) and neutral surfactant (TX-100)
accelerate the rate of reaction. Combination of phen and TX-100 is the best choice for chromic acid
oxidation of D
-sorbitol to glucose in aqueous media although 2,20-bipyridine is best promoter in absence
of micellar catalyst.
ꢀ
ꢀ
The reaction can be carried out very
rapidly.
PA, bipy, phen are used as promoters
to accelerate the rate in micellar
media.
ꢀ
Combination of phen and TX-100
catalyzes the oxidation of D-sorbitol
most.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 August 2013
Received in revised form 31 October 2013
Accepted 10 November 2013
Available online 20 November 2013
Kinetic data for oxidation of D-sorbitol to glucose by hexavalent chromium in aqueous medium and
aqueous surfactant medium (SDS, TX-100) have been reported. Effect of promoter such as PA, bipy and
phenanthroline on the reaction has been investigated. The reaction is performed under pseudo first order
condition with an excess of substrate over the oxidant. The reaction is first order with respect to substrate
and oxidant. The micelles have a catalytic effect on the reaction. Combination of phen and TX-100
produces almost twelve times increase in rate of oxidation.
Keywords:
Oxidation
Sorbitol
Ó 2013 Elsevier B.V. All rights reserved.
Glucose
Micellar catalyst
Promoter
Introduction
metabolism processes [1]. Sugars and their derivatives play an
important role in the chemistry of chromium in the environment
Carbohydrates are important biochemical compounds as they
are the major sources of energy for living organism for vital
[2,3] and in the mechanism of chromium-induced cancer [4]. As
oxidation of carbohydrates is widely studied under the field of
organic chemistry [5], the present research has been conducted
to study the oxidation of sorbitol which is a sugar alcohol with
Cr(VI) as an oxidizing agent in sulphuric acid medium. Sorbitol is
a sugar alcohol which can be obtained by the reduction of glucose.
⇑
Corresponding author. Fax: +91 0342 2530452.
E-mail address: b_saha31@rediffmail.com (B. Saha).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.11.068

K. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 204–208
205
2.8
2.7
2.6
2.5
2.4
0
5
10
15
time
20
25
30
Fig. 1. plot of ꢁlnA vs time at regular time interval (3 min).
Fig. 2a. Scanned absorption spectra of the reaction in absence of promoter at
regular time interval (3 min). [D-sorbitol]T = 100 ꢂ 10ꢁ4 mol dmꢁ3
, [Cr(VI)]T =
5 ꢂ 10ꢁ4 mol dmꢁ3, [H2SO4] = 0.5 mol dmꢁ3, Temp = 35 °C.
Table 1
kobs and half life of the reaction in presence and absence of promoter and non
functional micellar catalyst.
Promoter
Micellar catalyst 104 ꢂ kobs (sꢁ1) t1/2 (h)
(mol dmꢁ3
)
(mol dmꢁ3
)
None
None
0.0025 None
0.0025 None
1.717 0.001 1.121
2.483 0.0006 0.775
6.183 0.001 0.311
5.917 0.0006 0.325
0.030 0.005 64.16
Picolinic acid (PA)
2,20-Bipyridine (bipy)
1,10-Phenanthroline (phen) 0.0025
None
None
None
CPC
SDS
0.01 3.433 0.001 0.561
TX-100 0.01 3.483 0.001 0.553
0.005 TX-100 0.01 3.583 0.0001 0.537
Picolinic acid (PA)
0.0075
0.01
0.0125
0.0150
4.633 0.0005 0.415
5.817 0.0007 0.331
6.767 0.0004 0.284
7.450 0.0002 0.258
2,20-Bipyridine (bipy)
0.005 TX-100 0.01 10.22 0.002 0.188
0.0075
0.01
0.0125
0.0150
13.95 0.0005 0.138
16.02 0.0003 0.120
19.00 0.0001 0.101
19.33 0.0004 0.099
1,10-Phenanthroline (phen) 0.0025 TX-100 0.01 7.367 0.002 0.261
0.005
12.77 0.0007 0.151
13.62 0.0006 0.141
15.90 0.001 0.121
20.33 0.0008 0.094
0.01 4.117 0.003 0.467
4.951 0.0009 0.388
5.283 0.0002 0.364
5.412 0.0006 0.356
6.270 0.001 0.307
0.01 11.80 0.005 0.163
13.40 0.009 0.144
13.98 0.006 0.138
16.31 0.002 0.118
18.20 0.004 0.106
0.01 4.612 0.0006 0.417
6.910 0.0005 0.278
Fig. 2b. Scanned absorption spectra of the reaction mixture at regular time interval
0.0065
0.0075
0.01
0.005 SDS
0.0065
0.0075
0.01
0.0125
0.005 SDS
0.0065
0.0075
0.01
(1 min).
[D-sorbitol]T = 100 ꢂ 10ꢁ4 mol dmꢁ3
,
[Cr(VI)]T = 5 ꢂ 10ꢁ4 mol dmꢁ3
,
[H2SO4] = 0.5 mol dmꢁ3, [bipy]T = 25 ꢂ 10ꢁ4 mol dmꢁ3, Temp = 35 °C.
Picolinic acid (PA)
hexitols are more resistant to oxidation than are the familiar hex-
oses [9]. So we choose chromic acid as oxidizing agent as the other
Cr(VI) containing agent like pyridinium chloro chromate (PCC),
pyridinium dichromate (PDC), etc. are not soluble in water. Again
by this reaction toxic and carcinogenic hexavalent chromium
[10–12] is completely reduced to nontoxic trivalent chromium.
But for large scale production of organic compound it is very much
essential to know the velocity of the reaction. The catalytic effect of
surfactants over a certain concentration called critical micellar
concentration has been previously reported [13–18]. Surfactant
entrapped water molecule provides unique microenvironments
for interactions and reactions, as a result of which attention has
been drawn to the effect of micelles on the nature and rates of
reactions. Addition of surfactants above CMC creates two phases
in the reaction medium. One is aqueous phase and the other is
micellar phase. When the effective concentration of reactive spe-
cies is greater in micellar phase then surfactants behave as positive
catalyst. In this work the effects of anionic micelle sodiumdodecyl
sulphate (SDS) and neutral micelle Triton-X-100 (TX-100) on the
reaction rate are shown. Both of them accelerate the reaction rate.
Rate of the reaction is further increased when we use some pro-
moter in combination with the surfactants. Picolinic acid (PA), 2,
2,20-Bipyridine (bipy)
0.0125
1,10-Phenanthroline (phen) 0.0025 SDS
0.005
[Cr(VI)]T = 5 ꢂ 10–4 mol dmꢁ3
,
[H2SO4]T = 0.5 mol dmꢁ3
,
[D-sorbitol]T = 100 -
ꢂ 10ꢁ4 mol dmꢁ3, Temp = 35 °C.
It is 60% as sweet as sucrose and is used as a sugar substitute for
diabetics. It is a major intermediate for the production of fuels from
biomass resources. Sorbitol can be oxidized to its corresponding
aldohexose by employing different type of oxidants such as transi-
tion metal ions [6,7], inorganic acids, complex ions and hydrogen
peroxide [8]. Present work describes how fast the terminal (pri-
mary) alcohol group of sorbitol can be oxidized by chromic acid
to an aldehyde to yield glucose. Our aim is to perform the reaction
in aqueous media and to accelerate the rate of the reaction as

206
K. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 204–208
Fig. 3. Absorption spectrum of unpromoted and promoted reaction mixtures (after
completion of reaction): (a) [D-sorbitol]T = 100 ꢂ 10ꢁ4 mol dmꢁ3
, [Cr(VI)]T = 5 -
Fig. 2c. Scanned absorption spectra of the reaction mixture at regular time interval
ꢂ 10ꢁ4 mol dmꢁ3
,
[H2SO4] = 0.5 mol dmꢁ3
,
(b) [PA]T = 75 ꢂ 10ꢁ4 mol dmꢁ3
, (c)
(2 min). [D-sorbitol]T = 100 ꢂ 10ꢁ4 mol dmꢁ3
,
[Cr(VI)]T = 5 ꢂ 10ꢁ4 mol dmꢁ3
, [H2-
[bipy]T = 75 ꢂ 10ꢁ4 mol dmꢁ3, (d) [phen]T = 75 ꢂ 10ꢁ4 mol dmꢁ3, Temp = 35 °C.
SO4] = 0.5 mol dmꢁ3, [TX-100]T = 1 ꢂ 10ꢁ2 mol dmꢁ3, Temp = 35 °C.
Experimental section
Materials
D-sorbitol (AR, Qualigens), picolinic acid (AR, BDH), 2,20-bipy
(AR, MERCK), 1,10-phen (AR, Spectrochem, India), sodiumdodecyl
sulphate (AR, SRL), TX-100 (AR, SRL) and all other chemicals used
are of highest purity available commercially. Solutions are
prepared in doubly distilled water. Concentrations of above
reagents are as follows: [D-sorbitol] = 100 ꢂ 10ꢁ4 mol dmꢁ3
,
[Cr(VI)]T = 5 ꢂ 10ꢁ4 mol dmꢁ3, [H2SO4] = 0.5 mol dmꢁ3
.
Procedure and kinetic measurements
The reaction is initiated by mixing the requisite amount of the
oxidant with the reaction mixture. Progress of the reaction is mon-
itored by measuring the absorbance of Cr(VI) at different time
interval at 450 nm. The kinetics is monitored for 80% completion
of the reaction by spectrophotometric determination of the decay
of absorbance of chromium(VI) at 450 nm using a Bausch & Lomb
Spectronic-20 spectrophotometer. No other reactant or product
has any significant absorption at this wavelength. Pseudo first
order rate constants (kobs) are evaluated from the linear plot of
log[Cr(VI)]T vs time (t) (Fig. 1) and the half-life (t1/2) values
(Table 1) were also determined.
Fig. 2d. Scanned absorption spectra of the reaction mixture at regular time interval
(30 s). [D-sorbitol]T = 100 ꢂ 10ꢁ4 mol dmꢁ3
,
[Cr(VI)]T = 5 ꢂ 10ꢁ4 mol dmꢁ3
, [H2-
SO4] = 0.5 mol dmꢁ3
,
[TX-100]T = 1 ꢂ 10ꢁ2 mol dmꢁ3
,
[phen]T = 75 ꢂ 10ꢁ4
-
mol dmꢁ3, Temp = 35 °C.
20-bipyridine (bipy), 1, 10-phenanthroline (phen) are well known
as promoter for chromic acid oxidation of organic substances
[19–27]. Our present work will find out the best combination of
promoter and micellar catalyst in presence of which the reaction
occurs most rapidly. The overall stoichiometry of the reaction
may be presented as:
The scanned spectra indicates the gradual disappearance of
Cr(VI) and the appearance of Cr(III) at regular time interval. For
unpromoted and uncatalyzed reaction an isobestic point appears
near about 535 nm (Fig. 2a). The presence of a isosbestic point
indicates that two species (hexavalent chromium and trivalent
chromium) were in equilibrium and formation of a single discrete
species (trivalent chromium) during the reaction [30]. A shift in
isobestic point was observed for both promoted and catalyzed
reaction. In aqueous medium bipy was the best promoter as is evi-
dent from Table 1. For this reaction isobestic point appeared at
523 nm (Fig. 2b) and for TX-100 catalyzed reaction isobestic point
appeared at 523 nm (Fig. 2c). But the rate of the reaction was
fastest in presence of the combination of phen and TX-100 and
in this case isobestic point was observed at 526 nm (see Fig. 2d).
Under the experimental condition the color of the solution after
completion of the reaction is pale blue for unpromoted reaction
(kmax = 582 nm and kmax = 356 nm) and the corresponding transi-
3RCH2OH þ 2HCrOꢁ þ 8Hþ ! 3RCHO þ 2Cr3þ þ 8H2O
4
where
H
HO
H
OH
H
OH
R =
H
OH
CH2OH
.
The product of the reaction is glucose. It is detected and
confirmed by spot tests by using the reagent solution prepared
by dissolving 4 g of urea and 0.2 g of stannous chloride in 10 ml
40% sulfuric acid under heating condition [28,29]. The presence
of isosbestic points in both figures indicates that two species are
in equilibrium.
4
tion are A2g(F) ? 4T2g(F) and 523 nm for 4A2g(F) ? 4T1g(F) of Cr(III)

K. Mukherjee et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 204–208
207
appears at much lower energy due to favored metal to ligand
charge transfer. Vacant p⁄ orbitals of promoters favored metal to
ligand charge transfer.
Results
TEM images of blank TX-100 micelle and Cr(VI) loaded TX-100
micelle are taken (Fig. 4). From Fig. 4(a) it can be said that TX-100
micelle is roughly spherical in aqueous acid media. After the addi-
tion of Cr(VI) the presence of small holes are seen in the micellar
surface. So we can say that Cr(VI) is incorporated inside the
micelle.
Discussion
Effect of non functional micellar catalyst on reaction rate
In case of promoted reaction the active oxidants Cr(VI)-PA
(Scheme S2), Cr(VI)-bipy (Scheme S3), Cr(VI)-phen (Scheme S4)
form ternary complex with D-sorbitol. This complex then under-
goes a redox decomposition in the rate limiting step. Most of the
micellar mediated reactions occur either inside the Stern layer or
at the interfacial junctional region of Stern and Guoy Chapman
layer. SDS micelle has an aggregation number around sixty and is
roughly spherical in shape. TX-100 is larger in size than SDS. Non-
ionic surfactant TX-100 has larger core compared to SDS. So the
largest active oxidant Cr(VI)-phen complex interact best with the
TX-100 micelle (Fig. 5). There is also hydrophobic interaction
between the active oxidants and the micelles. On the other hand
the negative charges on the SDS micelles are partially neutralized
in presence of excess H+. So lesser no of active oxidant come in con-
tact with the SDS Stern layer due to coulombic attraction. So the
steric factor and hydrophobic interaction play the dominant role
and the rate of oxidation is fastest in presence of the combination
of phen and TX-100. The different number of polar components
Fig. 4. TEM image of (a) blank TX-100 micelle in presence of acid (b) TX-100 micelle
in presence of Cr(VI) and acid.
species (Fig. 3a). In case of promoted reaction color of the final
solution is pale violet kmax = 579 nm for PA, (Fig. 3b) kmax = 546 nm
for bipy (Fig. 3c) and kmax = 554 nm for phen (Fig. 3d). In the over-
night spectrum (Fig. 3) of promoted reactions a blue shift is seen
4
for A2g(F) ? 4T2g(F) transition due to the presence of strong field
ligands. A charge transfer band appeared for unpromoted and pro-
moted reaction. But for promoted reaction charge transfer band
(a)
(b)
Fig. 5. Schematic representation of partitioning of substrate and active oxidant [AO+ = Cr(VI) promoter complex in a (a) anionic surfactant (b) nonionic surfactant.
Table 2
A comparative study of different conditions used in sorbitol to glucose.
Entry
Oxidant
Reference
Condition
104 kobs
(sꢁ1
Half life
(h)
)
1
2
3
[KMnO4] = 5 ꢂ 10ꢁ4 mol dmꢁ3
[VV] = 3 ꢂ 10ꢁ3 mol dmꢁ3
[31]
[7]
Present work
[sorbitol] = 5 ꢂ 10ꢁ4 mol dmꢁ3, pH = 11, [KNO3] = 0.2 mol dmꢁ3
,
15.7
5.9
20.33
0.123
0.327
0.094
[sorbitol] = 6 ꢂ 10ꢁ2 mol dmꢁ3, [SDS] = 2 ꢂ 10ꢁ2 mol dmꢁ3, [H+] = 2 mol dmꢁ3
[Cr(VI)] = 5 ꢂ 10ꢁ4 mol dmꢁ3
[sorbitol] = 0.01 M, [phen] = 0.01 mol dmꢁ3, [TX-100] = 0.01 mol dmꢁ3

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(CH2–CH2–O) attached with TX-100 also better interacts with the
substrate D-sorbitol which contains a large no of polar group.
The phenomenon of maximum rate-acceleration effect by combi-
nation of TX-100 and phen in the oxidation rate of D-sorbitol by
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Acknowledgement
Thanks to CSIR, New Delhi for providing financial helps in the
form of project and fellowship.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.11.068.
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