Studies on kinetics and mechanism of oxidation of D-sorbitol and D-mannitol by cerium (IV) in aqueous micellar sulfuric acid media

Article abstract of DOI:10.1002/kin.20332

The kinetics and mechanism of cerium(IV) oxidation of hexitols, i.e. D-sorbitoL and D-mannitoL, in aqueous sulfuric acid media have been studied in the presence and absence of surfactants. Under the kinetic conditions, [S] _t [Ce(IV)]_T , where [S]_T is the total substrate (D-sorbitol or D-mannitol) concentration, the overall process shows a first-order dependence on [Ce(IV)]_T and [S]_T. The process is acid catalyzed and inhibited by [HSO₄^-]. From the [HSO₄^-] dependence, it has been noted that the both Ce(SO₄)²⁺ and Ce(SO₄)₂ have been found kinetically active. The different rate constants in the presence and absence of surfactants have been estimated with the activation parameters. N-cetylpyridinium chloride has been found to retard the oxidation process of hexitols, whereas sodium dodecyl sulfate has been found to accelerate the rate process. All these findings including the micellar effects have been interpreted in terms of the proposed reaction mechanism and partitioning behavior of the kinetically active different species of Ce(IV) between the aqueous and pseudomicellar phase.

Full text of DOI:10.1002/kin.20332

Studies on Kinetics and
Mechanism of Oxidation of
D-Sorbitol and D-Mannitol
by Cerium(IV) in
Aqueous Micellar Sulfuric
Acid Media
ASIM K. DAS, MONIRUL ISLAM, RUHIDAS BAYEN
Department of Chemistry, Visva Bharati University, Santiniketan 731 235, India
Received 23 September 2007; revised 14 February 2008; accepted 20 February 2008
DOI 10.1002/kin.20332
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The kinetics and mechanism of cerium(IV) oxidation of hexitols, i.e. D-sorbitol and
D-mannitol, in aqueous sulfuric acid media have been studied in the presence and absence of
surfactants. Under the kinetic conditions, [S]T ꢀ [Ce(IV)]T , where [S]T is the total substrate
(D-sorbitol or D-mannitol) concentration, the overall process shows a first-order dependence
on [Ce(IV)]T and [S]T . The process is acid catalyzed and inhibited by [HSO−4 ]. From the
[HSO−4 ] dependence, it has been noted that the both Ce(SO4)2+ and Ce(SO4)2 have been
found kinetically active. The different rate constants in the presence and absence of surfactants
have been estimated with the activation parameters. N-cetylpyridinium chloride has been
found to retard the oxidation process of hexitols, whereas sodium dodecyl sulfate has been
found to accelerate the rate process. All these findings including the micellar effects have been
interpreted in terms of the proposed reaction mechanism and partitioning behavior of the
kinetically active different species of Ce(IV) between the aqueous and pseudomicellar phase.
ꢁ
C
2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 445–453, 2008
tually, Ce(IV) is not so stable in aqueous HClO4 and
HNO3 media [1,2]. During the studies on kinetic and
mechanistic aspects of Ce(IV) oxidation of different
types of both organic and inorganic substrates in aque-
ous H2SO4 media, the major problem arises from the
standpoint of identification of kinetically active Ce(IV)
species [5]. Ce(IV) can exist as a mixture of different
types of sulfato species such as Ce(SO4)2+, Ce(SO4)2,
Ce(SO4)23− , and HCe(SO4)3− in aqueous H2SO4 me-
dia. Generally, from the bisulfate dependence of rate at
INTRODUCTION
Because of high stability, both kinetically and thermo-
dynamically [1,2] and easy availability, ceric sulfate
has been widely used in synthetic [3,4] and mechanis-
tic studies [1,2,5–10] in aqueous H2SO4 media. Ac-
Correspondence to: A. K. Das; e-mail: ak das3@yahoo.com.
Contract grant sponsor: Visva Bharati University (Central
University), Santiniketan, India.
c
ꢀ
2008 Wiley Periodicals, Inc.

446
DAS, ISLAM, AND BAYEN
fixed [H+], attempts [9–12] have been made to iden-
tify the kinetically active Ce(IV) species. Because of
so many interdependent equilibria involving Ce(IV),
SO24−, HSO−4 , and [H+], e.g. Ce(IV)–HSO4−–H+; SO24−
–HSO−4 –H+, it is very very difficult [13] to compute
the actual concentration of [HSO−4 ] and [H+] under
the experimental conditions. In fact, so many approx-
imations are required to compute [HSO−4 ] and [H+]
and it leads to the uncertainty to identify the kinet-
ically active Ce(IV) species from the dependence of
rate on [HSO−4 ] and [H+]. In fact, several conflict-
ing results are presented in the literature. Hintz and
Johnson [14] have reported the reactivity order,
Ce(SO4)2+ ꢀ Ce(SO4)2 ꢀ Ce(SO4)23− in the oxida-
tion of cyclic alcohols. In the oxidation of reducing
sugars by Ce(IV) in aqueous sulfuric acid media, there
is also a conflict among the workers [15,16] regarding
the kinetically active Ce(IV) species.
In aqueous-micellar media, the different sulfato
complexes of Ce(IV) are expected to be partitioned
in different ways. This partitioning behavior may be
helpful to identify the kinetically reactive species [16–
19]. This idea promoted us to undertake the work to
identify the active Ce(IV) species. In fact, the micel-
lar effect can be treated as a reliable probe to identify
the reactive species. This approach has been exten-
sively utilized [20] in the present author’s laboratory
to characterize the reactive species for the oxidation of
different substrates by chromic acid.
N-Cetylpyridinium chloride (CPC; SRL), sodium do-
decyl sulfate (SDS; SRL), HClO4 (AR; SRL), and all
other chemicals used were of the highest purity avail-
able commercially.
Procedure and Kinetic Measurements
The rate of disappearance of Ce(IV) was followed in
aqueous H2SO4 media under the conditions, [S]T ꢀ
[Ce(IV)]T (where S stands for the substrates, i.e., hex-
itols such as D-sorbitol and D-mannitol) at different
temperatures. The reaction was initiated by mixing the
thermally preequilibrated solution taken at the desired
conditions. Ce(IV) solution was added to the reac-
tion vessel to initiate the process. The progress of the
reaction was monitored [6] by withdrawing aliquots
(5.0 mL) of the reaction mixture at different time in-
tervals, quenching the reaction by adding excess stan-
dard Mohr’s solution prepared in about 1.0 mol dm−3
H2SO4, and the unreacted Fe(II) was back-titrated
against the standard Ce(IV) solution using ferroin as an
indicator. The pseudo-first-order rate constants (kobs
were evaluated from the slopes of the plots of log(V
)
∞
– Vt ) versus time t, where Vt and V denote the titer
∞
values of the standard Ce(IV) solution required in the
back titration at time (t) and infinity, respectively. Av-
erage values of at least two independent determinations
of kobs were taken for the analysis. All the data except
those for log[Ce(IV)]t versus t were analyzed by the
linear least-squares methods where appropriate. Errors
associated with the reported rate constants and activa-
tion parameters were estimated as usual [22].
A few kinetic runs were carried out after bubbling
purified dinitrogen and compared with those taken un-
der air, and the results were found to be the same. Thus
the dissolved oxygen does not have any effect on the
rate constant. Similar observation has also been noted
by earlier workers [23].
The present work also aims to flourish the appli-
cability of cerate oxidimetry in organic synthesis un-
der two-phase oxidation [21]. In fact, Ce(IV)-sulfato
species is hydrophilic whereas the organic substrates
are hydrophobic and this produces a hydrophobic–
hydrophilic barrier in the oxidation of organic com-
pounds by Ce(IV). Oxidation in aqueous micellar me-
dia may be helpful to overcome the hydrophobic–
hydrophilic barrier.
EXPERIMENTAL
Product Analysis and Stoichiometry
The hexitols (D-sorbitol and D-mannitol) are oxidized
to the corresponding aldohexoses, which are detected
and confirmed by spot tests by using the reagent so-
lution prepared by dissolving 4 g of urea and 0.2 g of
stannous chloride in 10 mL 40% sulfuric acid under the
heating condition [24]. One drop of the final solution
containing the oxidized product of hexitol was treated
with about 15 drops of the reagent solution in a hard
glass test tube and heated for a prolonged time. Then,
the color of the resultant solutions appeared red. This
color indicated the formation of aldohexoses. The same
observation was observed by using the authentic sam-
ple of aldohexoses. Our results conform to the findings
Materials and Reagents
The standard Ce(IV) stock solution in aqueous H2SO4
media was prepared. The free acid content of the so-
lution was determined by titration with a standard
NaOH solution after separation of Ce(IV) as insol-
uble Ce(III) oxalate, formed by the addition of an
excess of Na2C2O4. Ce(III)-salt solution was pre-
pared from the corresponding stock solution of Ce(IV)
after the treatment with H2O2, and the excess of
H2O2 was decomposed by boiling. Stock solutions of
D-sorbitol (AR; SRL, India) and D-mannitol (AR; SRL)
were freshly prepared and stored in a refrigerator.
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STUDIES ON KINETICS AND MECHANISM OF OXIDATION OF D-SORBITOL AND D-MANNITOL
447
of previous workers [25]. The overall stoichiometry of
the reaction may be represented as
RCH2OH + 2Ce(IV) → RCHO + 2Ce(III) + 2H+
(1)
where R is HOCH2(CHOH)−4 .
It may be pointed out that the product RCHO is
itself oxidizable, and it may be further oxidized to
aldonic acid (RCOOH). To detect the aldonic acid,
the dinapthol sulfuric acid test [24] was carried out.
However, no positive test [24] for aldonic acid was
noticed in the reaction mixture. The test was carried
out by treating a little amount of the final reaction
mixture with a few drops of β,βꢂ-dinaphthol solution
in concentrated sulfuric acid and then heated for 1 h
in a water bath at 85◦C. It did not show any char-
acteristic green fluorescence of aldonic acid. The ab-
sence of aldonic acid is also reasonable because of the
much higher concentration of RCH2OH than that of
RCHO.
Figure 1 Effect of [substrate]T on k for the Ce(IV) oxi-
dation of the reaction in aqueous H2SO4 media. [H2SO4]
obs
= 0.5 mol dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3
,
(A): [D-mannitol]T = (10–50) × 10−3 mol dm−3, [CPC]T
= 2 × 10−2, T = 35◦C. (B) [D-mannitol]T = (10–
50) × 10−3 mol dm−3, T = 35◦C. (C) [D-sorbitol]T = (10–
40) × 10−3 mol dm−3, T = 35◦C. (D) [D-sorbitol]T = (10–
30) × 10−3 mol dm−3, [SDS]T = 2 × 10−2 mol dm−3, T =
35◦C. (E) [D-sorbitol]T = (10–30) × 10−3 mol dm−3, T =
40◦C.
Dependence on [HSO−4 ]
For variations in [HSO4−] (in the range 0.5–1.75 mol
dm−3) at fixed [H+] and [S]T, the composition of the
mixture, [H2SO4] + [HClO4] = [H+] = 1.75 mol dm−3
(ignoring the dissociation of HSO−4 ), was varied [26].
In such experiments, [HSO−4 ] shows the overall rate-
retarding effect. The [HSO−4 ] dependence (cf. Figs. 2
and 3) can be expressed from the experimental fit in
the following forms:
RESULTS AND DISCUSSION
Dependence on [Ce(IV)]T
Under the kinetic conditions, [S]T ꢀ [Ce(IV)]T (where
[S]T is [D-mannitol]T and [D-sorbitol]T, i.e. hexitols)
in aqueous sulfuric acid media, the rate of disappear-
ance of cerium(IV) shows a first-order dependence
on [cerium(IV)]. The pseudo-first-order rate constants
(kobs) are obtained from the plot ln[Ce(IV)]t versus
t (time) as usual. In the presence of both surfactants,
i.e. CPC and SDS, the same rate dependence pattern
has been found.
p
kobs[HSO−4 ] = n +
(4)
[HSO−4 ]
Thus the dependence is given by
d ln[Ce(IV)]
−
= kobs
(2)
dt
Dependence on [Substrate]T
From the plot of kobs versus [S]T (Fig. 1), it has been
shown that a strict first-order dependence on [S]T is
maintained throughout the range of concentration used.
The rate of dependence can be presented as follows:
Figure 2 The plot of kobs× [HSO−4 ]versus [HSO4−]−1 to
explain the effect of [HSO−4 ] on k
for the Ce(IV) oxi-
obs
dation of D-sorbitol and D-mannitol in aqueous H2SO4 me-
kobs = ks[S]T
(3)
dia. I = [H2SO4] + [HClO4] = 1.75 mol dm−3, [Ce(IV)]T
= 1 × 10−3 mol dm−3, [HSO4−] = (0.5–1.75) mol dm−3
,
T = 35◦C. (A) [D-mannitol]T = 2 × 10−2 mol dm−3, (B) [D-
sorbitol]T = 1 × 10−2 mol dm−3, [SDS]T = 2 × 10−2 mol
In the presence of both CPC and SDS surfactants,
the same first-order dependence pattern has been
found.
dm−3
.
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448
DAS, ISLAM, AND BAYEN
Effect of Temperature
The rate constants (ks(w)) have been determined at
different temperatures, and the activation parameters
(ꢀH=, ꢀS=) have been computed as usual by using
the Eyring equation [29]. The activation parameters are
presented in Table II.
Dependence on the Cationic Surfactant
(CPC) and the Anionic Surfactant (SDS)
In the case of both hexitols, the cationic surfactant N-
cetylpyridinium chloride (CPC) has been found (Fig. 4)
to retard the rate process and the rate levels off at
higher CPC concentration, whereas the anionic sur-
factant sodium dodecyl sulfate (SDS) has been found
(Fig. 5) to accelerate the rate process and it attains a
limiting value at higher SDS concentration.
Figure 3 The plot of k
versus [HSO−4 ] to explain the
obs
effect of [HSO−4 ] in the presence and absence of surfactant on
obs for the Ce(IV) oxidation of D-sorbitol and D-mannitol in
k
aqueous H2SO4 media. I = [H2SO4] + [HClO4] = 1.75 mol
dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3, [HSO−4 ] = (0.5–
1.75) mol dm−3, T = 35◦C; (A) [D-mannitol]T = 2 × 10−2
mol dm−3, (B) [D-sorbitol]T = 1 × 10−2 mol dm−3, [SDS]T
= 2 × 10−2 mol dm−3
.
Dependence on the Products and Other
Factors
Under the kinetic condition, the effect of organic prod-
Dependence on [H+]
uct and Ce(III) (up to 1.0 × 10−3 mol dm−3) was
To explore the dependence of kobs on [H+] (in the range
0.5–1.5 mol dm−3) at fixed [HSO−4 ], the composition
of the mixture [H2SO4] + [NaHSO4] = [HSO−4 ] =
1.5 mol dm−3 was varied, assuming [H+] ≈ [H2SO4].
It has been found that the reactions are catalyzed by
[H+] (Table I). Because of the existence of so many
proton-dependent equilibria among the reactants, the
exact computation of [H+] and quantitative interpreta-
tion of [H+] dependence are very much complicated.
Because of this complexity [27,28] in the present sys-
tem, no attempt has been made to explain the [H+]
dependence quantitatively from the proposed reaction
mechanism. However, the qualitative observation is in
agreement with the fact that the Ce(IV) oxidation re-
action in aqueous H2SO4 media is catalyzed by [H+]
[9,27]. On protonation, positive charge on the Ce(IV)-
sulfato species increases and it facilitates the electron
transfer toward the Ce(IV) center. This factor may be
one of the contributing factors for the observed acid
catalysis [9,27].
Figure 4 Effect of [CPC]T on k for the Ce(IV) oxida-
obs
tion of D-sorbitol and D-mannitol in aqueous H2SO4 media.
[CPC]T = (0–8) × 10−2 mol dm−3, [H2SO4] = 0.5 mol
dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3, T = 35◦C. (A)
k
obs versus [CPC]T plot, [D-sorbitol]T = 3 × 10−2 mol dm−3
,
(B) kobs versus [CPC]T plot, [D-mannitol]T = 6 × 10−2 mol
dm−3
.
Table I Effect of [H+] on kobs for Ce(IV) Oxidation of D-Sorbitol and D-Mannitol in Aqueous Acid Media
104 × k (s−1
)
obs
[H+](mol dm−3
)
[D-Sorbitol] = 2 × 10−2 mol dm−3 T = 35◦C
[D-Mannitol] = 4 × 10−2 mol dm−3 T = 35◦C
0.50
0.75
1.00
1.25
1.50
0.80
1.40
1.70
2.10
2.60
1.00
1.50
1.90
2.40
2.90
Experimental condition: [Ce(IV)]T = 1 × 10−3 mol dm−3, I = [NaHSO4] + [H2SO4] = 1.5 mol dm−3
.
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STUDIES ON KINETICS AND MECHANISM OF OXIDATION OF D-SORBITOL AND D-MANNITOL
449
Table II Kinetic Parameters and Some Representative Rate Constants for the Ce(IV) Oxidation of D-Sorbitol and
D-Mannitol in the Presence and Absence of Surfactants at Different Temperatures
102 × k
102 × k
102 × k
s(W)
s(SDS)
s(CPC)
Substrate
D-sorbitol
Temp. (◦C)
(dm3 mol−1 s−1
)
(dm3 mol−1 s−1
)
(dm3 mol−1 s−1
)
30
35
40
45
2.0 0.10
3.2 0.16
4.5 0.25
–
–
4.0 0.2
–
2.3 0.15
–
6.3 0.31 ꢀH= = 58.5 3.0 kJ mol−1
ꢀS= = –90 10 J k−1 mol−1
1.6 0.08
D-mannitol
30
35
40
45
–
–
2.0 0.15
3.0 0.2
4.2 0.21
2.7 0.12
–
1.5 0.08
–
ꢀH= = 48 3.0 kJ mol−1
ꢀS= = –124 12 J k−1 mol−1
Experimental conditions. For D-sorbitol: [Ce(IV)]T = 1 × 10−3 mol dm−3, [CPC]T = 2 × 10−2 mol dm−3, [SDS]T = 2 × 10−2 mol dm−3
[H2SO4] = 0.5, mol dm−3, [D-sorbitol] = (10–40) × 10−3 mol dm−3, T = 30◦C; [D-sorbitol] = (10–40) × 10−3 mol dm−3, T = 35◦C;
,
[D-sorbitol] = (10–30) × 10−3 mol dm−3, T = 40◦C; [D-sorbitol] = (10–25) × 10−3 mol dm−3, T = 45◦C. For D-mannitol: [Ce(IV)]T = 1 × 10−3
mol dm−3, [CPC]T = 2 × 10−2 mol dm−3, [SDS]T = 2 × 10−2 mol dm−3, [H2SO4] = 0.5 mol dm−3, [D-mannitol] = (10–60) × 10−3 mol dm−3
T = 30◦C; [D-mannitol] = (10–50) × 10−3 mol dm−3, T = 35◦C; [D-mannitol] = (10–40) × 10−3 mol dm−3, T = 40 ◦C; [D-mannitol] =
(10–30) × 10−3 mol dm−3, T = 45◦C.
,
Mechanism of the Reaction
Under the present experimental conditions, there was
no spectrophotometric and kinetic evidence (strict first-
order dependence on the substrate concentration) in
favor of the intermediate complex formation between
Ce(IV) and the substrate. In fact, in aqueous H2SO4
media, complexation of organic substrate with Ce(IV)-
sulfato species is a rare possibility [5,6,21,30–33].
However, there may be a weak association between
the substrate and Ce(IV)-sulfato species as shown in
Scheme 1.
Here the complex (C1) may undergo deprotonation
with the transfer of one electron from the substrate to
Ce(IV)-sulfato species at the rate-determining step to
give Ce(III) and free radical (C2) that participates at the
faster steps to give the aldohexose product. The forma-
tion of free radical is evident through the acrylonitrile
polymerization test. Considering the very small value
of K1, Scheme 1 leads to the following rate law:
Figure 5 Effect of [SDS]T on k for the Ce(IV) oxida-
obs
tion of D-sorbitol and D-mannitol in aqueous H2SO4 me-
dia. [SDS]T = (0–6) × 10−2 mol dm−3, [H2SO4] = 0.5 mol
dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3, T = 35◦C. (A) k
obs
;
versus [SDS]T plot, [D-mannitol]T = 4 × 10−2 mol dm−3
(B) k versus [SDS]T plot, [D-sorbitol]T = 3 × 10−2 mol
dm−3obs
.
investigated and no effect was observed. The kobs val-
ues remained unchanged when the reactions were car-
ried out under nitrogen atmosphere or in the presence
of light.
−d[Ce(IV)]/dt = 2f k1K1[Ce(IV)]T[S]T (5)
or
kobs = 2f k1K1[S]T
Acrylonitrile Polymerization Test
= ks[S]T
(6)
Acrylonitrile was added to the reaction mixture under
nitrogen atmosphere, and the solution became viscous,
indicating the generation of free radicals.
A similar rate law may also be obtained by considering
the fact that the substrate is directly oxidized by Ce(IV)
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DAS, ISLAM, AND BAYEN
Scheme 1 Oxidation of hexitols (i.e. D-sorbitol and D-mannitol) by Ce(IV) in aqueous media.
Scheme 2 Direct interaction between the hexitols (S) and Ce(IV).
in a bimolecular step. In this case, the interaction may
occur at the transition state as shown in Scheme 2.
When the K1 value is very small then it is not possi-
ble to discriminate between Schemes 1 and 2. Forma-
tion of complex or compact association of the reactants
at the preequilibrium step and rigid stereochemical ori-
entation of the reactants in the activated complex for the
electron transfer are supported by the highly negative
values of entropy of activation (ꢀS=) (cf. Table II).
Here, Ce(IV) actually denotes the kinetically active
Ce(IV) species and f gives the fraction of total Ce(IV)
kinetically active. This aspect will be discussed later.
ous sulfuric acid media has been studied by different
workers [35,36]. The important equilibria (considering
up to tris-sulfato species) proposed by Hardwick and
Robertson [35] are
Ce4+ + HSO−4
Ce(SO4)2+ + H+; Q1 = 3500
ꢀ
ꢁ
(7)
Ce(SO4)2+ + HSO−4
Ce(SO )2 + HSO−
Ce(SO4)2 + H ; Q2 = 200
+
ꢀ
ꢁ
(8)
Ce(SO4)23− + H+; Q3 = 20
ꢀ
ꢁ
4
4
(9)
The equilibrium constants (Q1, Q2, Q3) are given at
25◦C and at ionic strength 2 mol dm−3. These values
determined by Hanna and Sarac [30] are 8600, 500,
and 10. Bugaenko and Kuan-Lin [36] have suggested
the following equilibrium (10) instead of equilibrium
(9):
[HSO−4 ] Dependence and Kinetically
Active Ce(IV) Species
Ce(IV) center is relatively labile [34]; the relevant
equilibria involving Ce(IV) and [HSO−4 ] in aqueous
H2SO4 media are important to explain the bisulfate
dependence. The nature of Ce(IV) species in aque-
−
Ce(SO )2 + HSO−
HCe(SO4)3
(10)
ꢀ
ꢁ
4
4
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Table III Kinetic Parameters for the Oxidation of
D-Sorbitol and D-Mannitol by Monosulfato (i.e. k5 path)
and bis-sulfato (i.e. k6 path) Species by Ce(IV)
The value of this equilibrium constant has been found
in the range 5–8 by different workers [11,37,38]. The
above equilibrium may be considered to arise due
to protonation of different Ce(IV)-sulfato complexes,
and the extent of protonation depends on the H+
concentration−.
102 × k5
104 × k
6
(mol2 dm−6 s−1
)
(mol dm−3 s−1
)
Substrate
D-Sorbitol
k5(W)
k5(SDS)
k
k
6(SDS)
6(W)
The [HSO4 ] dependence at fixed [H+] can be ex-
plained by considering the simultaneous participation
of both the mono- and bis-sulfato species of Ce(IV).
Thus, the rate expression may be expressed as follows:
2.7
3.5
2.0
0.7
0.6
1.25
1.1
D-Mannitol 1.30
Experimental conditions. For D-sorbitol: [D-sorbitol]T
=
1 × 10−2 mol dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3, [HClO4] +
[H2SO4] = 1.75 mol dm−3, [HSO4−] = (0.5–1.75) mol dm−3, [SDS]T
ꢀ
ꢁ
−d[Ce(IV)]/dt = 2K1k1[S]T Ce(SO )2+
4
T
= 2 × 10−2 mol dm−3, T = 35◦C. For D-mannitol: [D-mannitol]T
=
2 × 10−2 mol dm−3, [Ce(IV)]T = 1 × 10−3 mol dm−3, [HClO4] +
[H2SO4] = 1.75 mol dm−3, [HSO4−] = (0.5–1.75) mol dm−3, [SDS]T
= 2.5 × 10−2 mol dm−3, T = 35◦C.
+ 2K2k2[S]T[Ce(SO4)2]T
(11)
where K1 is the equilibrium constant in the interaction
of Ce(SO4)+2 and substrates and k1 is the rate constant
for electron transfer within the complex; similarly K2
and k2 bear the significance for Ce(SO4)2.
taking k5
=
[S]T(k3[H+]2)/Q2Q3 and k6
=
[S]T(k4[H+])/Q3, at the fixed acid concentration.
K1
+
The plot of kobs[HSO4−] versus 1/[HSO−4 ] (cf Fig. 2)
indicates that Ce(SO4)2+ (i.e. k5 path) and Ce(SO4)2
(i.e. k6 path) are kinetically active in the reaction. The
composite rate constants k5 (the slope of the plot) and
k6 (the intercept of the plot) indicate the kinetic contri-
bution of Ce(SO4)2+ and Ce(SO4)2, respectively. For
both hexitols, the contribution of Ce(SO4)2) is negligi-
Ce(SO4)2+ + S
C1 + H
(12)
(13)
ꢀ
ꢁ
k1
C1 −→ Ce(III) + CO2 + C2(radical)
Then the radical RC•HOH (C2) experiences redox de-
composition at the faster steps as outlined in Scheme 1.
By considering the relative magnitudes of Q1, Q2,
and Q3, the concentration of Ce(SO4)2+ and Ce(SO4)2
can be reasonably expressed as follows:
bly small and the major active species is Ce(SO4)2+
.
Electron flow toward Ce(IV) center in Ce(SO4)2+ is
more favored than in Ce(SO4)2 because the Ce(IV)
center in Ce(SO4)2+ bears more positive charge. It
may be noted that under the experimental conditions,
Ce(SO4)2 is more predominant than Ce(SO4)2+, but
Ce(SO4)2+ is kinetically more active than Ce(SO4)2
[14,30,39–41]. These are shown in Table III. Here it is
noteworthy that both the k5 (due to Ce(SO4)2+) and k6
(due to Ce(SO4)2) paths are favored in the presence of
SDS (cf. Table III). These are also expected in the light
of the above discussion.
ꢀ
ꢁ
ꢂ
ꢃ ꢂ
ꢃ
Ce(SO4)2+ ≈ [Ce(IV)]T [H+]2 / Q2Q3[HSO−4 ]2
= f1[Ce(IV)]T
(14)
[Ce(SO4)2] ≈ {[Ce(IV)]T [H+]}/Q3[HSO4−]
= f2[Ce(IV)]T
(15)
By considering the species Ce(SO4)2+ and Ce(SO4)2 as
the kinetically active species, the [HSO−4 ] dependence
of rate can be explained by considering Eq. (17).
Interpretation of Micellar Effect
f = f1 + f2
(16)
ꢂ
ꢃ
= [H+]2/ Q2Q3[HSO4−]2 + [H+]/(Q3[HSO4−])
In the case of both hexitols, the anionic surfactant SDS
has been found to show the rate-accelerating effect
whereas the cationic surfactant CPC has been found
to show the rate-retarding effect. In both cases, after
a certain concentration of surfactant, the rate constant
attains a limiting value.
In the presence of the anionic surfactant SDS,
both the reactants, i.e. hexitols and Ce(SO4)2+, are
preferably partitioned in the stern layer of SDS (an
anionic surfactant), bearing the negatively charged mi-
cellar head groups and consequently the rate is accel-
erated.
(17)
Using relation (17) in Eq. (11), it reduces to Eq. (18).
ꢄꢂ
ꢃ
kobs
=
k3[H+]2 /(Q2Q3[HSO4−])
ꢅ
+ (k4[H+]/Q3 [S] /[HSO−4 ]
(18)
T
where k3 is 2K1k1 and k4 is 2K2k2
or, kobs[HSO−4 ] = {k5[HSO−4 ]−1 + k6}[S]T
(19)
International Journal of Chemical Kinetics DOI 10.1002/kin

452
DAS, ISLAM, AND BAYEN
Scheme 3 Partitioning of Ce(SO4)2+ and hexitols (i.e. D-sorbitol and D-mannitol) in the presence of anionic surfactant (D−,
i.e. SDS) and cationic surfactant (D+, i.e. CPC, S denotes the substrate in aqueous phase and S denotes the substrate in
w
M
micellar phase).
The cationic species Ce(SO4)2+ is being repelled
by the positively charged micellar head groups of
CPC (a cationic surfactant), and consequently the rate
is retarded. This distribution pattern is illustrated in
Scheme 3.
the competition between Ox2+ and Na+ ions only, the
overall micellar-binding parameter (β) can be given by
Na+M
2[Ox2+
]
β = mNa + 2mOx
=
+
(21)
[Dn]
[Dn]
Scheme 3 actually represents the pseudophase ion
exchange model (PIE) [42,43], which is illustrated in
Scheme 4. In the PIE model, the micellar surface is
treated as a selective ion exchanger saturated with
the counterions. For SDS, the dipositive ion oxidant
Ce(SO4)2+ and the counterion Na+ will mutually com-
pete for micellar binding and the pseudophase ion-
exchange equilibrium (Kex) will be established.
This PIE model works well under conditions where
there is no ion-specific interaction and ion binding does
not perturb the micellar structure. The pseudophase
first-order-rate constant (kψ) is given by [43]
where [Dn] is the concentration of micellized surfac-
tant ion = [SDS]T – CMC.
It can be shown [43] that Y can be expressed in the
term of β as
ꢇ
ꢈ
2
(β − 2mOx)[Dn]
Y =
(22)
{[Na+]T − (β − 2mOx)[Dn]}
For SDS, the value of β is close to 0.7 0.1 [44] and
CMC of SDS is highly dependent on the electrolyte
concentration. The electrolytes reduce the CMC value
of SDS. The present kinetic studies were carried out
in strongly aqueous acidic media, and determination of
the CMC value under the present condition is a difficult
task. That is why it has not been possible to analyze
the kinetic data in a quantitative way and the results
have been interpreted in a qualitative way.
If Ce(SO4)2 is considered to be kinetically active
then this neutral species may be partly partitioned in
the Stern layer of the micelles of both types. The dis-
tribution of the reactants is shown in Scheme 5.
Thus if Ce(SO4)2 is considered kinetically active
then the rate process is expected to be accelerated
for both types of surfactants. From Schemes 3 and
5, it is evident that SDS can accelerate the rate pro-
cess by involving both Ce(SO4)2+ and Ce(SO4)2. On
the other hand, CPC can accelerate the rate process
by involving Ce(SO4)2 but inhibits the rate process
kW + kMKex/YF
kψ
=
(20)
1 + Kex/YF
ꢀ
ꢁ
ꢆ
2
Ox2M+ YF
[Na+W]
[Na+M]
where Kex
=
ꢀ
ꢁ ; Y =
Ox2W+
and
γW2 (Na+)
F =
γW(Ox2+
)
where Ox2+ is Ce(SO4)2+
.
The activity coefficient ratio γ2M(Na+)/(γM(Ox2+))
for the micellar pseudophase is assumed to be constant.
The overall micellar-binding parameter β neutralizes
the fraction of micellar head groups. By considering
Scheme 5 Partitioning of Ce(SO4)2 and hexitols (i.e. D-
sorbitol and D-mannitol) in the presence of both anionic and
cationic surfactant. D denotes the both types of surfactants.
S
denotes substrate in aqueous phase, and S denotes the
M
W
Scheme 4 Pseudophase ion exchange model.
substrate in micellar phase.
International Journal of Chemical Kinetics DOI 10.1002/kin

STUDIES ON KINETICS AND MECHANISM OF OXIDATION OF D-SORBITOL AND D-MANNITOL
453
by involving Ce(SO4)2+. The kinetic contribution of
Ce(SO4)2+ is more important than Ce(SO4)2. That is
why for CPC the overall rate-retarding effect is mani-
fested. It has been found so for hexitols (D-sorbitol and
D-mannitol).
18. Panigrahi, G. P.; Sahu, B. P. Int J Chem Kinet 1993, 25,
595.
19. Panigrahi, G. P.; Sahu, B. P. Int J Chem Kinet 1991, 23,
989.
20. Das, A. K. Coord Chem Rev 2004, 248, 81.
21. Skrzewski, J.; Cichacz, E. Bull Chem Soc Jpn 1984, 57,
271.
22. Lyons, L. A practical Guide to Data Analysis for Phys-
ical Science Students; Cambridge University Press:
Cambridge, UK, 1991.
23. Wells, C. F.; Husain, M. J Chem Soc A 1971, 380.
24. Feigl, F. Spot Tests in Organic Analysis, 5th ed.; El-
sevier: Amsterdam, the Netherlands, 1956; p. 391 and
358.
25. Rajeswar Rao, Y.; Saiprakash, P. K. Curr Sci 1978,
47(20), 763.
26. Arcoleo, G.; Calvaruso, G.; Cavasino, F. P.; Sbriziolo,
C. Inorg Chem Acta 1977, 23, 227.
Origin of Acid Catalysis
The Ce(IV)-sulfato complexes may undergo protona-
tion in strong acid condition as follows:
Ce(SO4)2+ + H+
Ce(SO4)2 + H+
HCe(SO4)+2 + H+
HCe(SO4)
(23)
(24)
(25)
3+
ꢀ
ꢁ
+
ꢀ
HCe(SO4)2
ꢁ
2+
ꢀ
H2Ce(SO4)2
ꢁ
27. (a) Das, A. K. J Chem Res S 1996, 184; (b) J Chem Res.
M 1023.
The increase in the acid concentration would thus en-
hance the concentration of the protonated forms of
Ce(IV) species. With the increase in positive charge
on the Ce(IV) species, the electron transfer toward the
Ce(IV) center would take place more readily. This ex-
plains the origin of the acid catalysis [9] of Ce(IV)
oxidation in aqueous sulfuric acid media.
28. Saha, P. N.; Mondal, S. K.; Kar, D.; Das, M.; Das, A. K.;
Mohanty, R. K. J Chem Res S 1997, 364.
29. (a) Wynne-Jones, W. F. K.; Eyring, H. J Chem Phys
1935, 3, 492; (b) Glastone, S.; Laidler, K. J.; Eyring,
H. The Theory of Rate Processes; McGraw-Hill: New
York, 1941, p.196.
30. Hanna, S. B.; Sarac, S. A. J Org Chem 1977, 42,
2063.
31. Pottenger, C. R.; Johnson, D. C. J Polym Sci A-1 1970,
8, 301.
BIBLIOGRAPHY
1. Grant, D. J Inorg Nucl Chem 1964, 26, 337.
2. Grant, D.; Payne, D. S. Anal Chem Acta 1961, 25, 422.
3. Jwo Jing-Jer.; Noyes, R. M. J Chem Soc 1975, 97, 5422.
4. (a) Ho, T. L. Synthesis 1973, 347; (b) Galliani, G.;
Rindone, B.; Scolastico, C.; Synth Commun 1975, 5,
319.
5. Das, A. K. Coord Chem Rev 2000, 213, 307.
6. Das, A. K.; Das, M. J Chem Soc, Dalton Trans 1994,
589.
7. Das, A. K.; Das. M. Int J Chem Kinet 1995, 27, 7.
8. Sharma, J.; Singh, R. J Indian Chem Soc 1990, 67, 316.
9. Lakshmi, S.; Ranganathan, R. Int J Chem Kinet 1996,
28, 713.
10. Misra, S. K.; Gupta,Y. K. J Inorg Nucl Chem 1967, 29,
1643.
32. Das, A. K. D Sc thesis Visva Bharati University, Part II:
Ch. 1, 2002.
33. Richardson, W. H. In Oxidation in Organic Chemistry;
Wiberg, K. B. (Ed.); Academic Press: New York, 1965;
Ch. 4.
34. Wilkins, R. G. The Study of Kinetics and Mechanism
of Reactions of Transition Metal Complexes; Allyn and
Bacon: Boston, MA, 1974.
35. Hardwick, T. J.; Robertson, E. Can J Chem 1951, 29,
828.
36. Bugaenko, L. T.; Kuan-Lin H. Russ J Chem 1963, 8(11),
1299.
37. Grover, V. K.; Gupta, Y. K. J. Inorg Nucl Chem 1969,
31, 1403.
38. Das, A. K.; Mondal, S. K.; Kar, D. Indian J Chem A
1998, 37, 1102.
39. Dayal, R.; Bakore, G. V. Indian J Chem 1972, 10, 1165.
40. McAuley, A. J Chem Soc 1965, 4054.
41. Kar, D.; Mondal, S. K.; Das, M.; Das, A. K. J. Chem
Res S 1998, 394.
11. Misra, S. K.; Gupta, Y. K. J Chem Soc A 1970, 2918.
12. Sankhala, P. S.; Mehrotra, R. N. J Inorg Nucl Chem
1972, 34, 3781.
13. Das, A. K.; Mondal, S. K.; Kar, D.; Das, M. Inorg React
Mech 1999, 1, 169.
14. Hintz, H. L.; Johnson, D. C. J Org Chem 1967, 32, 556.
15. Mehrotra, R. N.; Amis, E. S. J Org Chem 1974, 39, 1788.
16. Kabir-ud-Din.; Ali, M. S.; Khan, Z. Int J Chem Kinet
2006, 38, 18.
42. Bunton, C. A.; Nome, F.; Quina, F. H.; Romsted, L. S.
Acc Chem Res 1991, 24, 357.
43. Dash, A. C.; Prusti, J.; Pradhan, J.; Das, P. K. J Chem
Soc, Faraday Trans 1990, 86, 507.
17. Kabir-ud-Din.; Ali, M. S.; Khan, Z. Colloid Polym Sci
2007, 284, 627.
44. Garnett, C. J.; Lambic, A. J.; Beck, W. H.; Liler, M.
J Chem Soc, Faraday Trans 1 1983, 79, 953.
International Journal of Chemical Kinetics DOI 10.1002/kin