Autocatalyzed oxidation of d-glucitol by alkaline copper (III) periodate complex: A kinetic and mechanistic approach

Article abstract of DOI:10.1002/poc.4146

An autocatalyzed oxidation of d-glucitol (DG) by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.06 mol dm^?3 was studied spectrophotometrically. An autocatalysis was observed by one of the products formed, that is, Cu (II). A 1:2 stoichiometry (DG : DPC) exhibited reaction between the DG and DPC in an aqueous alkaline medium. The reaction was of first order in [DPC] when [DPC] < < [DG], while the order with respect to [DG] and [OH^?] was less than unity, whereas periodate had retarding effect on the rate of reaction. Ionic strength had a negligible effect on the rate of reaction. The main reaction products were identified by the spot tests and spectroscopic analysis. The product, Cu (II), catalyzed the reaction with a fractional order. A composite mechanism involving uncatalyzed and autocatalyzed reaction paths was proposed. The activation parameters with respect to slow step of the mechanism and also the thermodynamic quantities were determined and discussed.

Full text of DOI:10.1002/poc.4146

Received: 25 June 2020
DOI: 10.1002/poc.4146
Revised: 31 August 2020
Accepted: 16 September 2020
R E S E A R C H A R T I C L E
Autocatalyzed oxidation of D-glucitol by alkaline copper
(III) periodate complex: A kinetic and mechanistic
approach
Shreekant M. Patil | Atmanand M. Bagoji
Sharanappa T. Nandibewoor
| Santosh B. Konnur |
Department of Studies in Chemistry,
Abstract
Karnatak University, Dharwad, India
An autocatalyzed oxidation of D-glucitol (DG) by diperiodatocuprate (III)
(DPC) in aqueous alkaline medium at a constant ionic strength of 0.06 mol
dm−3 was studied spectrophotometrically. An autocatalysis was observed by
one of the products formed, that is, Cu (II). A 1:2 stoichiometry (DG : DPC)
exhibited reaction between the DG and DPC in an aqueous alkaline medium.
The reaction was of first order in [DPC] when [DPC] < < [DG], while the
order with respect to [DG] and [OH−] was less than unity, whereas periodate
had retarding effect on the rate of reaction. Ionic strength had a negligible
effect on the rate of reaction. The main reaction products were identified by
the spot tests and spectroscopic analysis. The product, Cu (II), catalyzed the
Correspondence
Sharanappa T. Nandibewoor, Department
of Studies in Chemistry, Karnatak
University, Dharwad 580003, India.
Email: stnandibewoor@yahoo.com
reaction with
a fractional order. A composite mechanism involving
uncatalyzed and autocatalyzed reaction paths was proposed. The activation
parameters with respect to slow step of the mechanism and also the thermody-
namic quantities were determined and discussed.
K E Y W O R D S
autocatalysis, D-glucitol, diperiodatocuprate (III), kinetics, mechanism, oxidation
1 | INTRODUCTION
good oxidants in alkaline medium as given below. And
these are used for the analysis of several organic com-
The study of the metals in their highest oxidation state
has fascinated many researchers in the current years.
Such transition metals can be stabilized by chelating with
suitable bidentate or polydentate ligands. Metal chelate
complexes have various of interactions that affect physi-
cal, chemical, and biological behavior. For example, Cu
(II) and Zn (II) chelates influence the possible therapy for
Alzheimer's disease, as copper and zinc are linked with
the neurotoxicity of amyloid-beta peptide.[1–3]
pounds.[7] The kinetics of self-decomposition of these
complexes was studied in some details.[8] DPC is an
excellent oxidant due to its restricted solubility and stabil-
ity in aqueous medium. The reactivity of a few alcohols
with DPC[9] is reported by Movius. The characterization,
structural determination, and synthesis of DPC have
been reported.[10] Copper periodate complexes in their
+3 oxidation state have been widely used in the examina-
tion of several organic compounds.[11] The oxidation
reactions by DPC studies are already under use[12] Com-
plexes of copper have occupied a major role in the bio-
chemistry.[13] In the copper (II) catalyzed oxidation of
Metal chelates such as diperiodatocuprate (III)
(DPC),[4] diperiodatonickelate (IV) (DPN)[5] (reaction(i)),
and diperiodatoargentate (III) (DPA)[6] (reaction (ii)) are
J Phys Org Chem. 2020;e4146.
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© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/poc.4146

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PATIL ET AL.
various amino acids by peroxydisulfate involves copper
(III) as an intermediate[14] compound. DPC is a versatile
one-electron oxidant and involves multiple equilibria
between different copper (III) species. Hence, it has
intrigued many researchers to know as to which of the
active species of the copper (III) is involved in the
reaction.
by DPC, the present study has been taken up. The title
reaction represents a full mechanistic and kinetic oxida-
tion of DG by DPC in alkali media to establish the opti-
mum conditions affecting such oxidation reaction as
mentioned in reaction (iii), to understand more about the
active species of the reactants in these media, and finally
to determine the plausible oxidation mechanism on the
D-glucitol (DG) is a sugar alcohol having sweet taste,
which is slowly metabolized in the human body. It can
be obtained by changing the aldehyde group of glucose to
a hydroxyl group. Prunes (cut portions) of apples, pears,
and peaches contain most of the glucitol compounds.[15]
It is converted to fructose by sorbitol-6-phosphate
2-dehydrogenase. DG is an isomer of mannitol, another
sugar alcohol; the two differ only in the orientation of the
hydroxyl group on β-carbon.[16]
basis of the observed kinetic and spectral studies were
taken up. By understanding the mechanism, the reactiv-
ity of DG towards DPC was interpreted and understood.
2 | EXPERIMENTAL
2.1 | Materials and reagents
In earlier report[17] on DPC oxidation, periodate and
alkali had shown retarding effect; however, in the present
study, we have obtained entirely different kinetic obser-
vations. Literature survey revealed that the mechanisms
of autocatalysis are scanty.[18] In view of the observed
study of autocatalysis by Cu (II) in the oxidation of DG
All chemicals used were of reagent grade and double dis-
tilled water was used throughout the work. A solution of
D-glucitol (Sigma-Aldrich) was prepared by dissolving an
appropriate amount of recrystallized sample in double
distilled water. The copper (III) periodate complex was
prepared by standard procedure.[19] Existence of copper

PATIL ET AL.
3 of 11
(III) complex was verified by its UV-vis spectrum, which
showed an absorption band with maximum absorption at
416 nm. The aqueous solution of copper (III) was stan-
dardized by iodometric titration and gravimetrically by
the thiocyanate[20] method. The copper (II) solution was
prepared by dissolving the known amount of copper sul-
fate (BDH) in distilled water. Periodate solution was pre-
pared in hot water and used after keeping it for 24 h. Its
concentration was ascertained iodometrically[21] at neu-
tral pH by phosphate buffer. Because periodate is present
in excess in DPC, the possibility of oxidation of DG by
periodate in alkaline medium at 25ꢀC was tested. The
progress of the reaction was followed iodometrically.
However, it was found that there was no significant reac-
tion under the experimental conditions. KOH and KNO3
were employed to maintain the required alkalinity and
ionic strength respectively in reaction solutions.
2.2 | Kinetic measurements
Kinetic measurements were carried out by using a Peltier
accessory for temperature control attached to Varian
CARY 50 Bio UV-vis Spectrophotometer connected with
a
rapid kinetic accessory (Varian, Victoria-3170,
Australia). For pH measurement, an Elico pH meter
model LI 120 was used. Kinetic runs were performed
under pseudo-first order ([DG] > [DPC] at 25
0.1ꢀC)
conditions. The required amount previously thermostat
solution of DG and DPC was used to initiate the reaction,
to which required concentrations of KNO3, KOH, and
KIO4 were also added to maintain the conditions of the
reaction. The progress of the reaction was studied spec-
trophotometrically at 416 nm, by recording the decrease
in the absorbance due to DPC with the molar absorbancy
index, ε = 6,231 100 dm3 mol−1 cm−1. The negligible
interference of other species present was observed in the
reaction mixture at this wavelength. The log (Abs) versus
time plots were used to calculate the pseudo-first-order
rate constants, kobs, and they were linear up to 30% com-
pletion of the reactions under the range of [OH−] used.
Above 30% completion of the reaction, a nonlinearity was
due to the autocatalysis, by copper (II) and the rate
constants were reproducible about 5%. During the
kinetics, a constant (5.0 × 10−4 mol dm−3) concentration
of KIO4 was used throughout the study unless otherwise
stated.
The total [OH−] and [IO4−] were calculated by the
consideration of previously present ions in the DPC solu-
tion and that additionally added. No effect of added car-
bonate was observed on the rate of reaction. The spectral
change of reaction progression has been shown in
Figure 1A, in which decrease in [DPC] at 416 nm during
the reaction was observed. The autocatalyzed oxidation
of Cu (II) is also shown in Figure 1B. Microsoft 2007
Excel program was used for regression analysis of experi-
mental data, standard deviation 'S' and regression coeffi-
cient 'r' of the points.
3 | RESULTS
3.1 | Stoichiometry and analysis of the
product
Different sets of reaction mixtures containing varying
ratios of DPC to DG in the presence of constant amount
of OH−, KNO3, and KIO4 were kept for 4 h in a closed
vessel under nitrogen atmosphere. The unreacted DPC
was estimated spectrophotometrically at 416 nm. The
results indicated a 1:2 stoichiometry (DG : DPC) is as
given in Equation (1).
FIGURE 1 (A) Spectroscopic changes of diperiodatocuprate
(III) (DPC) during the reaction period in the Cu (II) autocatalyzed
oxidation of D-glucitol (DG) by DPC at 298 K (scanning interval
30 s). (B) Autocatalysis of Cu (II) on oxidation of DG by alkaline
DPC at 298 K at various [Cu (II)] × 106 (a) 2, (b) 5, (c) 8, and
(d) 10 mol dm−3

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PATIL ET AL.
The main reaction product was isolated by acidifying
3.2 | Reaction orders
the reaction mixture followed by ether and ethyl acetate
extraction. Each extract was dehydrated with anhydrous
Na2SO4 and decanted; the solvent was removed by evapo-
ration. The residue was recrystallized from warm glacial
acetic acid. The main reaction product was identified as
glucose that was confirmed by spot test and its molecular
ion peak at 180 amu in ESI-Mass spectrum (Figure S1a),
product also confirmed by 1H-NMR spectrum
(Figure S1b). Another product Cu (II) was identified by
its UV-vis spectrum (Figure S1c). The reaction products
did not undergo further oxidation under the present
kinetic conditions.
The log kobs versus log concentration plots were used to
find the order of reaction with respect to [DG], [OH−],
and [IO4−]. These orders were obtained by varying the
concentrations of DG, alkali, and periodate in turn while
keeping all other concentrations and conditions constant.
3.3 | Effect of [DPC]
The concentration of DPC was varied in the range of
1.0 × 10−4 to 1.0 × 10−3 mol dm−3, and the fairly constant
TABLE 1 Effects of [DPC], [DG], [OH], and [IO4−] on autocatalyzed oxidation of D-glucitol (DG) by diperiodatocuprate (III) (DPC) at
25ꢀC, I = 0.06 mol dm−3
[DPC] × 104
[DG] × 103
[IO4−] × 104
[OH−] × 102
kobs × 103
kcal × 103
(mol dm−3
)
(mol dm−3
)
(mol dm−3
)
(mol dm−3
)
(s-1)
(s−1
1.94
1.94
1.94
1.94
1.94
0.86
1.73
1.94
2.25
3.31
3.10
2.28
1.94
0.78
0.49
0.32
0.61
1.12
1.94
2.60
)
1.0
5.0
5.0
5.0
5.0
5.0
3.0
4.0
5.0
6.0
8.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1.0
4.0
1.94
1.92
1.95
1.93
1.95
0.91
1.81
2.00
2.52
3.13
3.21
2.60
2.00
0.82
0.53
0.32
0.57
1.07
2.00
2.94
3.0
1.0
4.0
5.0
1.0
4.0
8.0
1.0
4.0
10.0
5.0
1.0
4.0
1.0
4.0
5.0
1.0
4.0
5.0
1.0
4.0
5.0
1.0
4.0
5.0
1.0
4.0
5.0
0.5
4.0
5.0
0.8
4.0
5.0
1.0
4.0
5.0
3.0
4.0
5.0
5.0
4.0
5.0
1.0
0.5
5.0
1.0
1.0
5.0
1.0
2.0
5.0
1.0
4.0
5.0
1.0
6.0
Bold Numbers indicates particular concentration was varied.

PATIL ET AL.
5 of 11
concentrations constant. It was found that periodate had
retarding effect on the rate of reaction. The order with
respect to [periodate] was negative less than unity
(i.e., −0.26) (Table 1) (r ≥ 0.901, S ≤ 0.005).
3.7 | Effect of ionic strength (i) and
dielectric constant of the medium (D)
The addition of KNO3 at constant [DPC], [G-glucitol],
[OH−], and [IO4−] was found that increasing ionic
strength had negligible effect on the rate of the reaction.
Dielectric constant of the medium, D, was varied by vary-
ing the t-butyl alcohol and water percentage. The
D values were calculated using the equation D = Dw
Vw + DB VB, where Dw and DB are dielectric constants of
pure water and t-butyl alcohol, respectively, and Vw and
VB are the volume fractions of components water and t-
butyl alcohol, respectively, in the total mixture. The
decrease in dielectric constant of the reaction medium
had no effect on the rate of reaction.
FIGURE 2 First order plots for the oxidation of D-glucitol
(DG) by diperiodatocuprate (III) (DPC) in aqueous alkaline
medium at 298 K. {[DPC] × 104 (mol dm−3): (a) 0.1, (b) 0.3; (c) 0.5,
(d) 0.8, and (e) 1.0}
kobs values indicated that order with respect to [DPC] was
unity (Table 1). This was also confirmed by linearity of
the plots of log [Absorbance] versus time (r ≥ 0.956,
S ≤ 0.006) up to 30% completion of the reaction
(Figure 2).
3.8 | Effect of initially added products
3.4 | Effect of [D-glucitol]
The initially added product, copper (II), was studied in
the range 2.0 × 10−6 to 2.0 × 10−5 mol dm−3 when all
other reactant concentrations were kept constant
(Table 2). The initially added Cu (II) enhanced the rate of
reaction with an order + 0.22 (Figure 3). However, the
other product glucose did not have any significant effect
on the rate of the reaction.
The effect of DG on the rate of reaction was studied at
constant concentrations of alkali, DPC, and periodate at
a constant ionic strength of 0.06 mol dm−3. The substrate,
DG, was varied in the range of 3.0 × 10−3 to
8.0 × 10−3 mol dm−3. The kobs values were increased with
an increase in the concentration of DG. The order with
respect to [DG] was found to be less than unity (i.e., 0.22)
(Table 1) (r ≥ 0.978, S ≤ 0.003).
3.9 | The study of polymerization
3.5 | Effect of [alkali]
The intervention of free radicals in the reaction was exam-
ined as follows. The reaction mixture, to which a known
quantity of acrylonitrile monomer initially added, was kept
The effect of increase in concentration from 0.5 × 10−2 to
6.0 × 10−2 of alkali on the reaction was studied at con-
stant concentrations of G-glucitol, DPC, and periodate at
a constant ionic strength of 0.06 mol dm−3 at 298 K. The
rate constants increased with increase in alkali concen-
trations (Table 1), indicating fractional order (i.e., 0.5)
dependence of rate on alkali concentration (r ≥ 0.918,
S ≤ 0.008).
TABLE 2 Effects of added product [Cu (II)] on oxidation of
D-glucitol (DG) by diperiodatocuprate (III) (DPC) at 298 K,
I = 0.06 mol dm−3
[Cu (II)] × 106 (mol dm−3
)
kobs × 103 (s−1
)
2.0
5.0
8.0
10
6.08
6.66
7.45
8.41
9.22
9.72
3.6 | Effect of [periodate]
The effect of concentration of periodate was studied by
varying the periodate concentration from 5.0 × 10−5 to
5.0 × 10−4 mol dm−3 keeping all other reactant
15
20

6 of 11
PATIL ET AL.
[alkali], and [IO4−]. The rate constants were found to
increase with the increase in temperature. The rate con-
stants (k) of the slow step of Scheme 1 were obtained
from the slopes and intercepts of 1/kobs versus 1/[DG],
1/kobs versus [H3IO62−], and 1/kobs versus 1/[OH−] plots
at four different temperatures, and these were used to
calculate the activation parameters (Table 3A). The
energy of activation corresponding to these constants was
evaluated from the Arrhenius plot of log k versus 1/T
(r ≥ 0.9987, S ≤ 0.011), and other activation parameters
obtained are tabulated in Table 3B.
4 | DISCUSSION
FIGURE 3 Order plot of 3 + log kobs against 5 + log [Cu (II)]
The [Cu (HIO6)2(OH)2][7–23] has been reported as
water-soluble copper (III) periodate complex in an
aqueous alkaline medium. However, studies at a higher
pH range employed showed that periodate is unexpected
for 2 h in an inert atmosphere. On diluting the reaction
mixture with methanol, a white precipitate was formed,
indicating the intervention of free radicals in the reaction.
The blank experiments of either DPC or G-glucitol alone
with acrylonitrile did not induce any polymerization under
the same conditions as those induced for reaction mixture.
Initially added acrylonitrile decreased the rate of reaction
indicating free radical intervention, which is the case in
the earlier work.[22] Such type of free radical intervention
is observed in earlier works.[4,6]
4−
to exist as HIO6 (as present in the complex) as is clear
from its involvement in the multiple equilibria[24]
(Equations 2–4) depending upon pH of the solution.
−
Periodic acid exists as H4IO6 at pH 7 and as H5IO6 in
acid medium. Thus, in the present study in alkaline
2−
6
3−
6
medium, H3IO
and H2IO
are found to be as main
active species. Periodate dimerizes[4] at higher concentra-
tion. However, in the present kinetic conditions, the for-
mation of this kind of species is negligible. Thus, [Cu
(H3IO6) (H2IO6)]2− is the soluble copper (III) periodate
complex in the employed pH conditions, also supported
by the earlier work.[25]
3.10 | Effect of temperature (T)
The rate of reaction was measured for every 5 K raise in
the temperature (298, 303, 308, 313/K) at varying [DG],
SCHEME 1 Mechanism of oxidation of
D-glucitol (DG) by diperiodatocuprate
(III) (DPC)

PATIL ET AL.
7 of 11
TABLE 3 Effects of temperature on Cu (II) autocatalyzed oxidation of D-glucitol (DG) by diperiodatocuprate (III) with respect to slow
step of Scheme 1
Temperature (K)
k × 103 (s−1
)
A
298
1.13
1.66
2.05
3.26
303
308
313
B
Parameters
ΔH# (kJ mol−1
ΔS# (J K−1 mol−1
)
64
2
1
)
−60
82
2
ΔG# (kJ mol−1
)
C
Temperature (K)
K1 × 10 (dm3 mol−1
4.7 0.2
)
K2 × 105 (mol dm−3
5.7 0.3
)
K3 × 10−3 (dm3 mol−1
3.8 0.1
)
298
303
308
313
D
6.5 0.4
2.4 0.06
6.0 0.3
8.1 0.6
1.8 0.03
8.8 0.4
11.1 0.7
0.88 0.02
9.9 0.5
Thermodynamic quantities
ΔH (kJ mol−1
ΔS (J K-1 mol−1
ΔG298 (kJ mol−1
Values from K1
45.4 0.6
Values from K2
−91.4 2.0
−390 20
Values from K3
49.9 0.7
)
)
166
4
237 15
)
−3.8 0.1
24.2 0.9
−20.4 0.8
Note: (A) Effect of temperature; (B) activation parameters; (C) effect of temperature to calculate K1, K2, and K3; and (D) thermodynamic
quantities using K1, K2, and K3.
The results obtained in the present study were
entirely different from the earlier work on DPC oxida-
tion.[26] Further kinetic studies were made in order to
check the active species of DPC in such alkaline media. It
was observed that the reaction exhibited an order of neg-
ative fraction with respect to [IO4−], less than unit order
in DG and alkali concentrations (Table 1). In view of the
retarding effect of periodate, the active species of DPC
have been proposed as [Cu(H2IO6)(H2O)2], which was
also observed in earlier report,[25] and the mechanism
befitting the obtained results was proposed (Scheme 1).In
aqueous alkaline medium, a diaquomonoperiodato cop-
per (III) complex (MPC) (in Equation 5) was produced
due to substitution of bidentate ligand [H3IO62−] of DPC

8 of 11
PATIL ET AL.
SCHEME 2 Mechanism of
autocatalysis by Cu (II) in the oxidation
of D-glucitol (DG) by diperiodatocuprate
(III) (DPC)
by water molecules, and its formation was important in
the present study. The kinetics and mechanistic study of
oxidation by silver (III) and nickel (IV) periodate com-
plexes[27,28] also reported the similar form of complexes.
equilibrium to bind DG to MPC species to form a
complex (C1).[6] Then, this complex (C1) decomposed
in a slow step to form a free radical derived from
DG. This free radical species further reacted with
The inverse fractional order in [IO4−] might be also
due to this reason. Such types of equilibria have been
well noticed in literature.[12] Also the spectra of Cu
(III) periodate complex were dependent on [OH−], and
the absorption becomes almost constant, indicating the
predominance of one species, presumably [Cu(H2IO6)
(H2O)2]. Because of this and the fact that rate is a
function of [OH−] (less than unit order), the main oxi-
dant species is [Cu(H2IO6)(H2O)2], and its formation
equilibrium (6) is important in the reaction. The less
than unit order in [DG] presumably resulted from the
another molecule of MPC species in a fast step to yield
the products such as D-glucose, Cu (II), and periodate.
Similar type of reaction mechanism was observed in
the earlier work.[6] On this basis, the detailed mecha-
nistic pathway involving MPC species for the oxidation
of DG is shown in Scheme 1:
The Michaelis–Menten plot proved the complex for-
mation between DPC and DG, which explains the less
than unit order dependence on [DG]. Such a complex
between a substrate and an oxidant has been observed in
other studies.[29]
-d½DPCꢁ
kK1K2K3½DGꢁ½OH-ꢁ½DPCꢁ
Â
Ã
Â
Ã
rate =
=
H3IO6 + K1 ½OH-ꢁ H3IO6 + K1K2½OH-ꢁ + K1K2K3½DGꢁ½OH-ꢁ
2-
2-
dt
ð7Þ
rate
kK1K2K3½DGꢁ½OH-ꢁ
Â
Ã
Â
Ã
kobs
=
=
:
H3IO6 + K1½OH-ꢁ H3IO6 + K1K2½OH-ꢁ + K1K2K3½DGꢁ½OH-ꢁ
2-
2-
½DPCꢁ
formation of a complex (C1) between the oxidant and
DG prior to the formation of the products. K3 is the
composite equilibrium constant comprising the
Scheme 1 leads to the rate law 7
The rate law can be rearranged into the
following form, which is suitable for verification.
7

PATIL ET AL.
9 of 11
and intercepts of such plots lead to the values of K1, K2,
(A)
K3, and
k
as (4.67
0.2) × ,
10−1 mol dm−3
(5.7 0.3) × 10−5 mol dm−3, (3.8 0.1) × 10−3 dm−3 mol−1
and (1.7 0.1) × 10−2 s−1, respectively. The equilibrium
constant K1 was far greater than K2. This may be attrib-
uted to the greater tendency of DPC to undergo hydroly-
sis compared with the dissociation of hydrolyzed species
in alkaline medium. Using these constants, the rate con-
stants under varying conditions were calculated and com-
pared with observed rate constants. There was a
reasonable agreement between them (Table 1), which
fortifies the proposed mechanism.
The negligible effect of ionic strength and dielectric
constant of medium on the rate explains qualitatively the
reaction between neutral and negatively charged ions, as
seen in Scheme 1.
(B)
The thermodynamic quantities for the first, second,
and third equilibrium steps of Scheme 1 were evalu-
ated as follows. The [H3IO6 2−], [DG] and [OH−]
(as in Table 1) were varied at four different tempera-
tures. The plots of 1/kobs versus 1/[OH−], 1/kobs versus
1/[DG], and 1/kobs versus [H2IO63−] should be linear
(Figure 4). From the slopes and intercepts, the values
of K1 were calculated at different temperatures, and
these values are given in Table 3C. A van't Hoff's plot
was made for variation of K1 with temperature (log K1
vs. 1/T (r ≥ 0.9624, S ≤ 0.006), and the values of
enthalpy of reaction ΔH, entropy of reaction ΔS, and
free energy of reaction ΔG were calculated for the first
equilibrium step. These values are given in Table 3D.
A comparison of the latter values with those obtained
for the slow step of the reaction shows that these
values mainly refer to the rate limiting step,
supporting the fact that the reaction before rate deter-
mining step is fairly fast and involves low activation
energy.[30] In the same manner, K2 and K3 values were
calculated at different temperatures, and their
corresponding values of the thermodynamic quantities
are given in the Table 3D.
(C)
FIGURE 4 Verification of rate law 7 for the oxidation of DG
by diperiodatocuprate (III) (DPC). Plots of (A) 1/kobs versus 1/[DG],
(B) 1/kobs versus 1/[OH−], (C) 1/kobs versus [H3IO62−], at four
different temperatures (conditions as in Table 1). DG, D-glucitol
The values of ΔH# and ΔS# were both favorable for
electron transfer processes; the negative value of ΔS#
indicates that the complex (C1) is more ordered than the
reactants.[31] The observed modest activation energy and
sizeable entropy of activation supports, a complex state of
transition in the reaction.[32] Because Scheme 1 is in
accordance with the generally well-accepted principle of
noncomplementary oxidations taking place in sequence
of one-electron steps, the reaction between the substrate
and oxidant would afford a radical intermediate. A free
radical scavenging experiment revealed such a possibility.
This type of radical intermediate has also been observed
in the earlier work.[32,33] The independence of rate of
reaction on ionic strength[4] and dielectric constant of the
Â
Ã
Â
Ã
2-
2-
H3IO6
H3IO6
1
kobs
1
1
k
=
+
+
+
:
kK1K2K3½DGꢁ½OH-ꢁ kK2K3½DGꢁ kK3½DGꢁ
ð8Þ
According to Equation 8, other conditions being con-
stant, plots of 1/kobs versus 1/[OH−](r
0.9968,
S ≤ 0.014), 1/kobs versus 1/[DG] (r ≥ 0.9918, S ≤ 0.016),
and 1/kobs versus [H3IO62−] (r ≥ 0.9989, S ≤ 0.012) should
be linear and are found to be so (Figure 4). The slopes
≥

10 of 11
PATIL ET AL.
medium was due to the involvement of neutral species in
the rate determining step of Schemes 1 and 2.
5 | AUTOCATALYSIS
The autocatalysis by one of the products, Cu (II), is inter-
esting. The first order in [DPC] and less than unity in
[DG] are observed. The apparent less than unit order in
Cu (II) ion may be attributed to complex formation
between DG and Cu (II). The complex C2 is then subse-
quently involved in the interaction with MPC. These
steps are shown in Scheme 2, which will form a part of
Scheme 1. The plot of 1/kobs versus 1/[Cu (II)] was linear,
and a hypsochromic shift of Cu (II) from 765 to 757 nm
in the presence of DG is the confirmation for complex
formation between DG and Cu (II).
FIGURE 5 The plot of [DG]/kauto versus 1/[Cu (II)]. DG,
D-glucitol
According to Equation 12, the plot of [DG]/kauto ver-
sus 1/[Cu (II)] should be linear (R2 > 0.992, S<0.0219)
and is found to be so (Figure 5). The slope and intercept
of such plot lead to the values of K4 and ka as
The rate law for autocatalyzed oxidation of DG by
DPC is given by Equation 9
5.023 × 105 dm3 mol−1 and 10.1 × 102 dm3 mol−1 s−1
,
respectively.
Â
Ã
kaK4 ½DGꢁ½DPCꢁ Cu2 +
À
Â
ÃÁ
rate =
,
ð9Þ
1 + K4 Cu2 + ð1 + K4 ½DGꢁ Þ
6 | CONCLUSIONS
Among the various species of DPC, mono-
periodatocuprate (III) (MPC), [Cu(H2IO6)(H2O)2] is con-
sidered as active species among various species of DPC
for the title reaction. The results demonstrate that in car-
rying out this reaction, the role of pH in the reaction
medium is crucial. Autocatalysis by one of the products,
Cu (II) is observed, and a composite rate law is obtained.
Rate constant of slow step and other equilibrium con-
stants involved in the mechanism are evaluated, and acti-
vation parameters with respect to slow step of reaction
or
Â
Ã
kaK4 ½DGꢁ Cu2 +
rate
½DPCꢁ
Â
Ã
Â
Ã
kauto
=
=
:
1 + K4 Cu2 + ½DGꢁ + K4 Cu2 + + K4 ½DGꢁ
ð10Þ
2
Thus, when [Cu2+] is initially present, a composite
scheme involving steps of Schemes 1 and 2 operates
Â
Ã
kaK4 ½DGꢁT Cu2 +
kK1K2K3½DGꢁ½OH− ꢁ
T
Â
Ã
Â
Ã
Â
Ã
Â
Ã
kgross = kobs + kauto kgross
=
+
:
H3IO62− + K1½OH− ꢁ H3IO26− + K1K2½OH− ꢁ + K1K2K3½DGꢁ½OH− ꢁ 1 + K4 Cu2 + ½DGꢁ + K4 Cu2 + + K4 ½DGꢁ
2
ð11Þ
On rearranging kauto part of Equation 11,
we get,
are computed. The overall mechanistic sequence
described here is consistent with product studies and
kinetic studies.
½DGꢁ
1
½DGꢁ
1
ka
K4 ½DGꢁ
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
Â
Ã
Â
Ã
=
+
+
+
: ð12Þ
kaK4 Cu2 +
ka Cu2 +
kauto
ka

PATIL ET AL.
11 of 11
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ORCID
Atmanand M. Bagoji https://orcid.org/0000-0001-5660-
8427
Sharanappa T. Nandibewoor https://orcid.org/0000-
0003-2340-2275
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