Mechanism of uncatalyzed and osmium(VIII) catalyzed oxidation of L-alanine by Copper(III) periodate complex in aqueous alkaline medium

Article abstract of DOI:10.1080/15533174.2011.556408

The kinetics of oxidation of the L-alanine (L-ala) by diperiodatocuprate(III) (DPC) was carried both in the absence and presence of osmium(VIII) catalyst in alkalinemedium at constant ionic strength of 0.01 mol dm^-3 spectrophotometrically.The involvement of free radicals was observed in both the reactions. The oxidation products in both the cases were acetaldehyde and Cu(II), identified by spot test and spectroscopic studies. The stoichiometry is the same in both cases; that is, [L-ala]:[DPC] = 1:2. The reaction was first order in [DPC] and has negative fractional order in [OH-] in both the catalyzed and uncatalyzed cases. The order in [osmium(VIII)] was unity. A mechanism involving the formation of a complex between L-ala and DPC in case of uncatalyzed reaction and a mechanism involving the formation of a complex between L-alanine and osmium(VIII) in case of catalyzed reaction were proposed. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (Kc) was also calculated for catalyzed reaction at different temperatures. The activation parameters with respect to slow step of themechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for uncatalyzed and catalyzed reactions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2011.556408

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Mechanism of Uncatalyzed and Osmium(VIII)
Catalyzed Oxidation of L-alanine by Copper(III)
Periodate Complex in Aqueous Alkaline Medium
a
a
a
Shekappa D. Lamani , Tegginamat M. Veeresh & Sharanappa T. Nandibewoor
a
P.G. Department of Studies in Chemistry , Karnatak University , Dharwad, India
Published online: 22 Apr 2011.
To cite this article: Shekappa D. Lamani , Tegginamat M. Veeresh & Sharanappa T. Nandibewoor (2011) Mechanism
of Uncatalyzed and Osmium(VIII) Catalyzed Oxidation of L-alanine by Copper(III) Periodate Complex in Aqueous
Alkaline Medium, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:4, 394-404, DOI:
10.1080/15533174.2011.556408
To link to this article: http://dx.doi.org/10.1080/15533174.2011.556408
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:394–404, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.556408
Mechanism of Uncatalyzed and Osmium(VIII) Catalyzed
Oxidation of L-alanine by Copper(III) Periodate Complex
in Aqueous Alkaline Medium
Shekappa D. Lamani, Tegginamat M. Veeresh, and Sharanappa T. Nandibewoor
P.G. Department of Studies in Chemistry, Karnatak University, Dharwad, India
Copper(III) is an intermediate in the copper(II) catalyzed oxi-
The kinetics of oxidation of the L-alanine (L-ala) by diperioda- dation of amino acids by peroxydisulphate.[ The oxidation
6]
tocuprate(III) (DPC) was carried both in the absence and pres- reaction usually involves the copper(II)-copper(I) couple, and
ence of osmium(VIII) catalyst in alkaline medium at constant ionic
[7,8]
such aspects are detailed in different reviews.
The use of
−3
strength of 0.01 mol dm spectrophotometrically. The involvement
of free radicals was observed in both the reactions. The oxidation
products in both the cases were acetaldehyde and Cu(II), identi-
diperiodatocuprate(III) (DPC) as an oxidant in alkaline medium
is new and restricted to a few cases due to its limited solubility
fied by spot test and spectroscopic studies. The stoichiometry is and stability in aqueous medium. DPC is a versatile one-electron
the same in both cases; that is, [L-ala]:[DPC] = 1:2. The reac- oxidant for various organic compounds in alkaline medium and
tion was first order in [DPC] and has negative fractional order
[9]
its use as an analytical reagent is now well recognized. Copper
−
in [OH ] in both the catalyzed and uncatalyzed cases. The order
complexes have occupied a major place in oxidation chemistry
in [osmium(VIII)] was unity. A mechanism involving the forma-
tion of a complex between L-ala and DPC in case of uncatalyzed
due to their abundance and relevance in biological chemistry.[
10]
reaction and a mechanism involving the formation of a complex When the copper(III) periodate complex is the oxidant, and
between L-alanine and osmium(VIII) in case of catalyzed reaction multiple equilibria between different copper(III) species are in-
were proposed. The reaction constants involved in the different
steps of the mechanisms were calculated for both reactions. The
catalytic constant (Kc) was also calculated for catalyzed reaction at
different temperatures. The activation parameters with respect to
volved, it would be interesting to know which of the species is
the active oxidant.
Enzymatic dehydrogenation of amino acids by flavoenzymes
slow step of the mechanisms were computed and discussed for both has attracted considerable attention in recent years. Amino acids
the cases. The thermodynamic quantities were also determined for have been oxidized by a variety of oxidizing agents.[ The
11]
uncatalyzed and catalyzed reactions.
oxidation of amino acids is of interest as the oxidation products
differ for different oxidants.[
12,13]
The study of amino acids
Keywords diperiodatocuprate(III), kinetics, L-alanine, Os(VIII)
becomes important because of their biological significance and
selectivity towards the oxidant to yield different products. L-
alanine [L-ala] chemically is (2S)-2-aminopropanoic acid. It
is found primarily in poultry, beef, pork, and fish. Almost all
animal based protein sources are rich in L-ala. The contraction
of muscle results in increased L-ala levels within the body. As
an amino acid, L-ala is used by the body as a building block of
protein. L-ala plays a major role in transferring nitrogen from
tissue sites in the body, to the liver. It is also used by the body
catalysis, oxidation
INTRODUCTION
In recent years, the study of highest oxidation state tran-
sition metals has intrigued many researchers. Transition met-
als in a higher oxidation state can be stabilized by chela-
tion with suitable polydentate ligands. Metal chelates, such
[
1]
[2]
as diperiodatocuprate(III), diperiodatoargentate(III), and
[14]
to draw upon blood sugar as an energy source.
[3]
diperiodatonickelate(IV) are good oxidants in a medium with
an appropriate pH value. Periodate and tellurate complexes of
copper in its trivalent state have been extensively used in the
Transition metals are known to catalyze many oxidation-
reduction reactions since they involve multiple oxidation states.
The use of transition metal ions, such as osmium, ruthenium,
and irridium, either alone or as binary mixtures, as catalysts in
[4]
analysis of several organic compounds. The kinetics of self-
decomposition of these complexes was studied in some detail.[
5]
[15]
various redox processes has attracted considerable interest.
The role of osmium(VIII) as a catalyst in some redox reactions
has been reviewed.[ Although the mechanism of catalysis
depends on the nature of the substrate, the oxidant, and exper-
imental conditions, it has been shown[ that metal ions act as
catalysts by one of these different paths such as the formation
16]
Received 13 August 2010; accepted 6 October 2010.
Address correspondence to Sharanappa T. Nandibewoor, P.G. De-
partment of Studies in Chemistry, Karnatak University, Dharwad-580
17]
0
03, India. E-mail: stnandibewoor@yahoo.com
394

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION
395
of complexes with reactants, oxidation of the substrate itself, or
through the formation of free radicals. Osmium(VIII) catalysis
in redox reactions involves several complexes, different oxi-
dation states of osmium, etc. The authors have observed that
osmium(VIII) catalyzes the oxidation of L-ala by DPC in alka-
line medium in micro amounts. In order to understand the active
species of oxidant and catalyst, and to propose the appropriate
mechanisms, the title reaction is investigated in detail in view of
various mechanistic possibilities. An understanding of mecha-
nism allows chemistry to be interpreted and hence understood
and predicted.
EXPERIMENTAL
FIG. 1. Spectroscopic changes occurring in the oxidation of L-alanine by
Materials and Reagents
◦
−5
−4
,
diperiodatocuprate(III) at 25 C, [DPC] = 5.0 × 10 , [L-ala] = 4.0 × 10
All chemicals were of reagent grade, and double distilled wa-
−
−3
[
OH ] = 0.004 and I = 0.01 mol dm with scanningtime interval of: (1) 0.5,
ter was used throughout the work. A solution of L-alanine (S.D (2) 1.0, (3) 1.5, (4) 2.0, and (5) 2.5 minutes.
Fine Chem.) was prepared by dissolving an appropriate amount
of recrystallised sample in double distilled water. The purity of
KOH, KIO4, and Os(VIII) catalyst. The progress of reaction was
followed spectrophotometrically at 415 nm by monitoring the
decrease in absorbance due to DPC with the molar absorbency
index, ‘ε’ taken as 6230 ± 100 dm mol cm in both cat-
alyzed and uncatalyzed reactions. It was verified that there is a
negligible interference from other species present in the reaction
mixture at this wavelength. The spectroscopic changes during
the reaction are shown in Figure 1. It is evident from the figure
that the concentration of DPC in terms of absorbance of DPC
decreases at 415 nm.
◦
the L-ala sample was checked with its m.p. 312 C (Lit. m.p.
◦
3
14 C). The required concentration of L-ala was made from
its stock solution. The osmium(VIII) solution was prepared by
3
−1
−1
−
3
dissolving OsO4oxide (Johnson Matthey) in 0.50 mol dm
[18]
NaOH. The concentration was ascertained
by determining
the unreacted [Fe(CN)64 with standard Ce(IV) solution in an
acidic medium. KNO3 and KOH (BDH) were used to main-
tain ionic strength and alkalinity of the reaction, respectively.
The copper(III) periodate complex was prepared by standard
procedure.[ The aqueous solution of copper(III) was standard-
ized by iodometric titration and gravimetrically by thiocyanate
method.[ The copper(II) solutions were prepared by dissolv-
ing a known amount of copper sulphate (BDH) in distilled water.
Periodate solution was prepared by weighing out the required
−
19]
The pseudo first-order rate constants, (‘kU or kC’), in both the
cases were determined from the log (absorbance) versus time
plots. The plots were linear up to 80% completion of reaction
20]
(for uncatalyzed and catalyzed) in Figure 2. The orders for var-
ious species were determined from the slopes of plots of log
amount of sample in hot water and used after keeping it for
(
[
kU or kC) versus respective concentration of species except for
DPC] in which non-variation of ‘kU or kC’ was observed as
21]
2
4 h. Its concentration was ascertained iodometrically[ at neu-
tral pH maintained using phosphate buffer. Since periodate is
present in excess in DPC, the possibility of oxidation of L-ala by
2
◦
periodate in alkaline medium at 25 C was tested. The progress
1.8
1.6
1.4
1.2
of the reaction was followed iodometrically. There was no sig-
nificant reaction under the experimental conditions employed
compared to the DPC oxidation of L-ala. The pH of the medium
in the solution was measured by (ELICO (LI613) pH meter.
(5)
(4)
(3)
1.01
(
2)
0
.8
.6
.4
.2
0
Kinetics
0
The kinetic measurements were performed on a Varian
CARY 50 Bio UV–vis spectrophotometer. The kinetics was fol-
lowed under pseudo first-order condition where [L-ala] > [DPC]
(1)
0
0
◦
both in uncatalyzed and catalyzed reaction at 25 ± 0.1 C, unless
0
0.5
1
1.5
2
specified. In the absence of catalyst, the reaction was initiated
by mixing the DPC to L-ala solution, which also contained re-
quired concentration of KNO3, KOH, and KIO4. The reaction
in the presence of catalyst was initiated by mixing DPC to L-ala
Time (min)
FIG. 2. First order plots for the oxidation of Os(VIII) catalyzed L-alanine by
diperiodatocuprate(III) in aqueous alkaline medium. [diperiodatocuprate(III)]
5
−3
solution, which also contained required concentration of KNO3, × 10 (mol dm ): 1) 1.0, 2) 3.0, 3) 5.0, 4) 8.0, and 5) 10.0.

396
S. D. LAMANI ET AL.
expected to the reaction condition. The rate constants were re-
TABLE 1
−
−
producible to within ± 5%. Regression analysis of experimental Effect of [DPC], [L-ala], [IO ] and [OH ] on the oxidation of
4
data to obtain regression coefficient r and the standard deviation
s, of points from the regression line, was performed with the
Microsoft office Excel-2003 program.
L-alanine by diperiodatocuprate(III) in alkaline medium at
◦
−3
25 C, I = 0.01 mol dm
(
A) Effect of temperature
2
2
−2
RESULTS AND DISCUSSION
10 k1
10 K1
10 K2
−
1
−3
3
−1
Temperature (K)
(s
)
(mol dm
)
(dm mol
)
Stoichiometry and Product Analysis
2
3
3
3
98
03
08
13
4.2
5.4
6.0
7.6
1.2
1.1
0.9
0.5
2.7
3.3
3.5
4.4
Different sets of reaction mixtures containing varying ratios
of DPC to L-ala in the presence of constant amount of OH ,
−
KNO3 and KIO4 in uncatalyzed reaction and a constant amount
Os(VIII) in catalyzed reaction were kept for 2 h in a closed
vessel under nitrogen atmosphere. The remaining concentration
of DPC was estimated by spectrophotometrically at 415 nm.
The results indicate that 1:2 stoichiometry, as given in Eq. (1).
(B) Thermodynamic activation parameter for the oxidation of L-
alanine by diperiodatocuprate(III) in aqueous alkaline medium
Activation parameters using k1
Values
Os(VIII)
CH3 CH COO- + 2 [Cu(OH) (H IO ) ] + H O
3-
CH CHO + 2Cu(OH)
2
3
6
2
2
3
2
#
−1
)
ꢀ
ꢀ
ꢀ
H (kJ mol
25 ± 2
−184 ± 20
80 ± 3
NH2
2-
+ NH3 + CO
+
H
2
+
+ 4H
IO
3
6
#
−1
−1
S (JK mol )
[
1]
#
−1
G (kJ mol )
The stoichiometric ratio in both the cases suggests that the
main product was acetaldehyde, which was identified by spot
log A
4.6 ± 0.2
test[ and confirmed by its IR(KBr) spectrum showing a car- (C) Thermodynamic quantities using K1 and K2
22]
−1
−1
bonyl stretching at 1729 cm and -CH stretching at 2928 cm .
[20]
Thermodynamic
quantities
Values from
K1
Values from
K2
Ammonia was identified by Nessler’s reagent. CO2 was qual-
itatively detected by bubbling N2 gas through the acidified reac-
tion mixture and passing a liberated gas through a tube contain-
−1
ꢀ
ꢀ
ꢀ
H (kJ mol
)
−42.4 ± 2.0
−178 ± 10
12 ± 0.3
20.3 ± 0.8
114 ± 5
ing limewater. The aldehyde was confirmed by preparing its 2,
−1
−1
S (JK mol
G298 (kJ mol
)
)
23]
4
-DNP derivative.[ The metal product Cu(II) was identified
−1
−14.8 ± 0.8
by UV-vis spectra. The reaction product did not undergo further
oxidation under the present kinetic conditions.
−
3
strength of 0.01 mol dm in both the cases of catalyzed and
uncatalyzed reaction. In case of catalyzed and uncatalyzed re-
action, the L-ala concentration was varied in the range of 1.0 ×
Reaction Orders
As the diperiodatocuprate(III) oxidation of L-alanine in al-
kaline medium proceeds with a measurable rate in the absence
of Os(VIII), the catalyzed reaction is understood to occur in
parallel paths with contributions from both the catalyzed and
uncatalyzed paths. Thus, the total rate constant (kT) is equal to
the sum of the rate constants of the catalyzed (kC) and uncat-
alyzed (kU) reactions, so kC = kT – kU.Hence, the reaction orders
have been determined from the slopes of log kCversus log (con-
centration) plots by varying the concentrations of L-ala, alkali,
periodate, and Os(VIII) catalyst in turn while keeping all other
concentrations and conditions constant. The order in DPC was
unity between the concentrations was varied in the range of 1.0
−4
−3
−3
◦
10
to 1.0 × 10 mol dm at 25 C while keeping other re-
actant concentrations and conditions constant. The kC and kU
values increased with the increase in concentration of L-ala in-
dicating an apparent less than unit order dependence on [L-ala]
(
Table 1 and 3). The effect of alkali on the reaction has been
studied for both the cases in the range of 0.001 to 0.01 mol dm
at constant concentrations of L-ala, DPC and periodate at a con-
stant ionic strength of 0.01 mol dm in uncatalyzed reaction
and at concentration of Os(VIII) in catalyzed reaction. The rate
constants decreased with increase in alkali concentration (Table
−3
−3
1
and 3), indicating negative fractional order dependence of rate
−
5
−4
−3
×
10 to 1.0 × 10 mol dm at fixed L-ala, KOH and KNO3
on alkali concentration.
in both the cases uncatalyzed and catalyzed reactions. Linearity
of the plots of log [absorbance] versus time up to 80% comple-
tion of the reaction indicates a reaction order of unity in [DPC]. Effect of Periodate
This was also confirmed by varying [DPC], and did not result
The effect of increasing concentration of periodate was
in any change in rate constants, kU (Table 1) and kC (Table 3). studied by varying the periodate concentration from 1.0 ×
−
5
−4
−3
The effect of L-ala on the rate of reaction was studied at constant 10 to 1.0 × 10 mol dm keeping all other reactant
concentrations of alkali, DPC, and periodate at a constant ionic concentrations constant. The added periodate had no effect on

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION
397
TABLE 2
Effect of temperature on k1, K1 and K2 for the oxidation of L-alanine by diperiodatocuprate(III) in aqueous alkaline medium
3
−1
)
1
0 k (s
U
05 [DPC] (mol dm−3
)
10 [L-ala] (mol dm
4
−3
)
10 [IO ] (mol dm
5
−
−3
)
10 [OH ] (mol dm )
2
−
−3
Found
Calculated
1
4
1
3
5
7
.0
.0
.0
.0
4.0
4.0
4.0
4.0
4.0
5.0
5.0
5.0
5.0
5.0
0.4
0.4
0.4
0.4
0.4
3.5
3.4
3.2
3.3
3.4
3.2
3.2
3.2
3.2
3.2
1
0.0
5.0
5.0
5.0
5.0
5.0
1.0
2.0
4.0
6.0
10.0
5.0
5.0
5.0
5.0
5.0
0.4
0.4
0.4
0.4
0.4
0.89
1.6
3.2
5.0
6.7
0.86
1.7
3.2
4.8
6.8
5
5
5
5
5
.0
.0
.0
.0
.0
4.0
4.0
4.0
4.0
4.0
1.0
3.0
5.0
8.0
10.0
0.4
0.4
0.4
0.4
0.4
3.4
3.5
3.2
3.4
3.2
3.2
3.2
3.2
3.2
3.2
5
5
5
5
5
.0
.0
.0
.0
.0
4.0
4.0
4.0
4.0
4.0
5.0
5.0
5.0
5.0
5.0
0.1
0.2
0.4
0.8
1.0
4.2
3.5
3.2
2.8
2.4
3.9
3.7
3.2
2.9
2.4
the rate of reaction (Table 1 and 3) in catalyzed and uncatalyzed or L-ala alone with acrylonitrile did not induce any poly-
reactions.
merization under the same conditions. Initially added acry-
lonitrile decreased the rate of reaction, indicating free radical
participation.
Effect of Added Products
The externally added products, aldehyde, and copper(II)
(
CuSO4) did not have any significant effect on the rate of the
Effect of Temperature
The influence of temperature on the rate of reaction was
studied for uncatalyzed reaction at 25, 30, 35, and 40 C. The
rate constants, (k1), of the slow step of Scheme 1 were obtained
from the slopes and the intercepts of the plots of 1/ku versus 1/[L-
ala] plots at four different temperatures. The values are given
in Table 1 and were used to calculate the activation parameters.
The energy of activation corresponding to these constants was
evaluated from the Arrhenius plot of log k1 versus 1/T (r ≥
0.9997, S ≤ 0.011) and other activation parameters obtained are
reaction in both the cases.
◦
Effect of Ionic Strength (I) and Dielectric Constant (D)
It was found that ionic strength (using KNO3) and dielectric
constant of the medium (using t-butyl alcohol and H2O) had
no significant effect on the rate of reaction in both the cases of
uncatalyzed and catalyzed reactions.
Test for Free Radicals (Polymerization Study)
The involvement of free radicals, for both uncatalyzed and tabulated in Table 2.
catalyzed reactions was tested. The reaction mixture was mixed
with acrylonitrile monomer initially added, and was kept for studied for catalyzed reaction at 25, 30, 35, and 40 C. The rate
h in an inert atmosphere. On diluting the reaction mix- constants, (k2), of the slow step of Scheme 2 were obtained from
The influence of temperature on the rate of reaction was
◦
2
ture with methanol, a white precipitate was formed, indicat- the slopes and the intercepts of the plots of [Os(VIII)]/kCversus
ing the involvement of free radicals in both catalyzed and 1/[L-ala] plots at four different temperatures. The values are
uncatalyzed reactions. The blank experiments of either DPC given in Table 3. The activation parameters for the rate

398
S. D. LAMANI ET AL.
K1
4
-
3-
-
[
Cu(OH) (H IO )(H IO )]
+ H O
[Cu(OH) (H IO ) ] + OH
2 3 6 2
2
3
6
2
6
2
K2
3
-
-
[
Cu(OH) (H IO ) ] + CH3 CH COO
Complex(C1)
2
3
6 2
NH2
Complex(C1)
.
k1
2-
CH3 CH + Cu(OH) + 2H IO + CO2
2
3
6
slow
NH2
.
3
-
fast
CH3 CH + [Cu(OH) (H IO ) ] + H O
CH CHO + Cu(OH) +
2
3
6 2
2
3
2
+
2-
NH2
+ NH4
2H IO6
3
+
-
fast
Fast
NH4 + OH
NH OH
4
CO + OH-
HCO3
-
2
SCH. 1. Detailed scheme for the oxidation of L-alanine by alkaline diperiodatocuprate(III).
determining step were obtained by the least square method of and ‘x’ the order of the reaction with respect to [Os(VIII)]. In
plot of log k2 versus 1/T and are presented in Table 4.
the present investigations, x values for the standard run were
found to be unity. Then the value of KC is calculated using the
equation,
Effect of [Os(VIII)]
−7
The [Os(VIII)] concentration was varied from 5.0 × 10
−6
−3
to 5.0 × 10 mol dm range, at constant concentration of
diperiodatocuprate(III), L-ala, alkali, and ionic strength. The
order in [Os(VIII)] was found to be unity from the linearity of
the plots of kC versus [Os(VIII)].
kT − kU
kC
C
K = [
=
(where, k − k = k ) [3]
T
U
C
x
Os(VIII)
[Os(VIII)]x
The values of KC were evaluated for [Os(VIII)] catalyst at
different temperatures and found to vary at different tempera-
Catalytic Activity
It has been pointed out by Moelwyn-Hughes[24] that in pres- tures. Further, plots of log KC versus 1/T were linear and the
ence of the catalyst, the uncatalyzed and catalyzed reaction values of energy activation and other activation parameters with
proceed simultaneously, so that
reference to catalyst were computed. These results are summa-
rized in Table 5.
x
kT = kU + KC[Os(VIII)]
[2]
The water-soluble copper(III) periodate complex is
reported[ to be [Cu(HIO6)2(OH)2] . However, in aqueous
25]
7−
Here kT is the observed pseudo first order rate constant in the alkaline medium at high pH as employed in this study, perio-
4−
presence [Os(VIII)] catalyst, kU the pseudo first–order rate con- date is unlikely to exist as HIO6 (as present in the complex)
stant for the uncatalyzed reaction, KC the catalytic constant, as is evident from its involvement in the multiple equilibria[
26]
K1
K3
4
-
3-
-
[
Cu(OH) (H IO ) (H IO )] + H O
[Cu(OH)
2
(H
3
IO
6
)
2
]
+ OH
2
3
6
2
6
2
2
-
CH3 CH COO + [OsO (OH) ]
-
Complex
(C2)
4
2
NH2
.
CH3 CH + Cu(OH) + 2 H IO +
2
3 6
3
-
slow
k2
2-
Complex (C ) + [Cu(OH) (H IO )]
2
2
3
6 2
2
-
NH2
CO2 + [OsO (OH) ]
4
2
.
fast
2-
3
-
CH3 CH + [Cu(OH) (H IO ) ] + H O
CH3 CHO + Cu(OH)
+ 2 H IO
2
3
6 2
2
2
3
6
+
NH2
fast
Fast
+ NH4
+
-
NH4 + OH
NH OH
4
CO + OH-
HCO3
-
2
SCH. 2. Detailed scheme for the Os(VIII) catalyzed oxidation of L-alanine by alkaline diperiodatocuprate(III).

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION
399
TABLE 3
−
Effect of [DPC], [L-ala], [IO4], [OH ], and [Os(VIII)] on the osmium(VIII) catalyzed oxidation of L-alanine by DPC in alkaline
◦
−3
medium at 25 C, I = 0.01 mol dm
1
02kC (s−1
)
5
4
5
2
−
7
2
3
1
(
0 [DPC]
10 [L-ala]
10 [IO4]
10 [OH ]
10 [Os(VIII)]
10 kT
10 kU
−
3
−3
−3
−3
−3
−1
−1
mol dm
)
(mol dm
)
(mol dm
)
(mol dm
)
(mol dm
)
(s
)
(s
)
Found
Calculated
1
3
5
8
.0
.0
.0
.0
4.0
4.0
4.0
4.0
4.0
1.0
2.0
4.0
6.0
10.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1.0
3.0
5.0
8.0
10.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.1
0.2
0.4
0.6
1.0
0.4
0.4
0.4
0.4
0.4
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
8.0
5.0
8.0
10.0
30.0
50.0
2.9
3.5
2.5
2.3
2.5
2.3
2.1
0.73
1.4
2.5
3.9
5.5
3.0
2.9
2.9
2.8
2.9
3.3
2.9
2.5
2.3
2.1
1.2
2.5
3.1
8.3
14.0
2.5
2.5
2.5
2.5
2.5
0.72
1.4
2.6
3.7
5.6
2.5
2.5
2.5
2.5
2.5
3.1
2.9
2.6
2.4
2.0
1.3
2.6
3.3
8.4
14.5
2.7
2.8
2.7
2.5
3.4
3.2
3.3
3.4
1
0.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.82
1.5
2.8
4.4
6.2
3.5
3.2
2.8
2.6
2.4
3.8
3.2
2.8
2.5
2.3
1.5
2.8
3.4
8.6
0.89
1.6
3.2
5.0
6.7
3.8
3.5
3.2
3.4
3.2
4.2
3.5
3.2
2.8
2.4
3.2
3.2
3.2
3.2
3.2
14.0
(
4)–(6) depending on the pH of the solution.
and periodate shows no effect on the rate. The result of decrease
in rate of reaction with increase in alkalinity (Table 1) can be
explained in terms of a prevailing equilibrium of formation of
−
+
+
+
H5IO6 ꢁꢂ H4IO6 + H
[4]
[5]
[6]
3−
4−
[Cu(OH)2(H3IO6)2)] from [Cu(OH)2(H3IO6)(H2IO6)] hy-
−
2−
H4IO ꢁꢂ H3IO6 + H
6
drolysis as given below.
H3IO2 ꢁꢂ H2IO6 + H
−
3−
6
−
4−
Periodic acid exists as H5IO6 and as H4IO6 around pH 7.
[
Cu(OH)2(H3IO6)(H2IO6)] + H2O
Thus, under the conditions employed in alkaline medium, the
K
1
ꢁ [Cu(OH) (H IO ) ] + OH−
3
−
main species are expected to be H3IO62−and H2IO63−. At higher
ꢂ
2
3
6 2
[27]
concentrations, periodate also tends to dimerise.
However,
formation of this species is negligible under the conditions em-
ployed for this study. Hence, at the pH employed in this study, Because of this reaction and the observation that the kU or kC
the soluble copper(III) periodate complex exists as diperioda- values are inversely related to the hydroxyl ion concentration
2−
tocuprate(III), [Cu(H3IO6)2(OH)2] , a conclusion also sup- with fractional order in OH concentration, the main oxidant
[
28]
3−
ported by earlier work.
species is likely to be [Cu(OH)2(H3IO6)2] and its formation
[
1,28]
In most of the reports
tards and OH increases the rate of the reaction. However, in
on DPC oxidation, periodate re- by the above equilibrium is important in the present study.
−
[29]
It is known that L-ala exists in the form of Zwitterion
the present kinetic study, entirely different kinetic observations in aqueous medium. In highly acidic medium, it exists in the
−
have been obtained. In this study, OH retards the rate of reaction protonated form, whereas in highly basic medium it exists as

400
S. D. LAMANI ET AL.
TABLE 4
Thermodynamic activation parameters for the osmium(VIII)
TABLE 5
Values of catalytic constant (K ) at different temperatures and
C
catalyzed oxidation of L-alanine by DPC in aqueous alkaline
medium with respect to the slow step of Scheme 2
activation parameters calculated using K values
C
Temperature
98
10 2 KC
−
(A) Temperature effect
2
303
308
2.5
3.5
−
2
−2
Temperature
K)
10 5k2
10 K1
10 K3
3
−1 −1
−3
3
−1
(
(dm mol
s
)
(mol dm
)
(dm mol
)
4.3
3
13
−1
Ea (kJ mol
5.3
2
3
3
3
98
03
08
13
3.3
3.8
4.7
5.7
1.6
1.4
0.8
0.5
3.4
3.9
5.8
6.6
)
37.8
35.2
−159.6
84.1
5.0
#
−1
−1
ꢀ
ꢀ
ꢀ
H (kJ mol
)
#
−1
S (kJ mol )
#
−1
)
G (kJ mol
log A
(
B) Activation parameters (Scheme 2)
Activation parameters using k2
Values
The probable structure of the complex is given by
#
−1
)
ꢀ
ꢀ
ꢀ
H (kJ mol
25.2 ± 0.4
−56.5 ± 5
42.5 ± 2
#
−1
−1
S (JK mol )
4
-
#
−1
0
O
G (kJ mol
O
log A
C) Thermodynamic quantities using K1 and K3
Thermodynamic quantities Values from K1 Values from K3
10.3 ± 0.4
HO
HO
O
O
O
OH
OH
OH
I
(
Cu
O
I
O
HO
OH
OH
ꢀ
ꢀ
ꢀ
H (kJ mol−1)
S (JK mol
G298 (kJ mol
−55.0 ± 3.0
−218 ± 20
11.6 ± 0.1
36.3 ± 2.0
170 ± 18
NH2
CH
−1
−1
)
−1
CH3
C
)
−15.6 ± 0.9
O
Spectroscopic evidence for the complex formation between
oxidant and substrate was obtained from UV-vis spectra of
the anionic form according to the following equilibria.
−4
−5
−
L-ala = (4.0 × 10 ), DPC = (5.0 × 10 ), [OH ] = 0.004
−3
(
mol dm ) and a mixture of both. A hypsochromic shift of
aqueous
about 8 nm from 247 nm of L-ala to 239 nm of mixture of
DPC and L-ala and a hyperchromicity at 239 nm was observed.
A Lineweaver-Burk plot also indicated the complex formation
between DPC and L-ala, which explains the less than unit or-
der dependence on [L-ala]. Such a type of complex between a
substrate and an oxidant has been observed in other studies.[
The rate law for Scheme 1 could be derived as
+
−
CH3−CH(NH2)COOH ꢁꢂ CH3−CH(NH ) COO
3
basic
CH3 − CH(NH2)COOH + OH− ꢁꢂ CH3
−
−
CH(NH2)COO H2O
+
31]
The less than unit order in [L-ala] presumably results from
formation of a complex(C1) between the DPC species and L-ala
prior to the formation of the products. This complex(C1) decom-
poses in a slow step to form a free radical derived from L-ala.
This free radical species further reacts with another molecule
of DPC in a fast step to form the products aldehyde, Cu(II) and
periodate as given in Scheme 1.
−
d[DPC]
k1K1K2[L-ala]
Rate =
=
[7]
[8]
−
dt
[OH ] + K1 + K1K2[L-ala]
k1K1K2[L-ala]
kU =
−
[
OH ] + K1 + K1K2[L-ala]
Since Scheme 1 is in accordance with the generally well-
accepted principle of non-complementary oxidations taking
place in sequence of one-electron steps, the reaction between
the substrate and oxidant would afford a radical intermediate.
The free radical scavenging experiment revealed such a possi-
bility (see infra). This type of radical intermediate has also been
which explains all the observed kinetic orders of different
species.
The rate law (8) can be rearranged to Eqn (9), which is
suitable for verification.
−
1
[OH ]
1
1
[30]
=
+
+
[9]
observed in earlier work.
kU
k1K1K2[L-ala]
K1K2[L-ala]
k1

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION
401
-
-3
-3
occurs via an inner-sphere mechanism. This conclusion is sup-
[
OH ] X 10 mol dm
(
ꢀ
8
)
[35,36]
ported by earlier observations.
A high negative value of
0
2 4
6
10
12
#
−1
−1
1
1
1
4
2
0
8
6
4
2
0
4.5
4
ꢀS (–184 JK mol ) suggests that intermediate complex is
more ordered than the reactants.[
37]
Osmium(VIII) is known to form different complexes at
3
3
2
2
1
1
0
0
.5
.5
.5
.5
−[38]
2−
−
−
different OH
concentrations, such as [OsO4(OH)2]
ꢀ
ꢀ
3−
and [OsO5(OH)] . At higher concentration of OH ,
3
−
[OsO (OH)] is significant. At lower concentrations of OH ,
5
as employed in the present study, and since the rate of oxi-
−
dation increased with increase in [OH ], it is reasonable that
2−
[OsO4(OH)2] was operative and its formation is important
in the reaction. To explain the observed orders, the following
Scheme 2 is proposed for osmium(VIII) catalyzed reaction.
The reaction between the diperiodatocuprate(III) complex
and L-alanine in alkaline medium in the presence of os-
mium(VIII) catalyst has the stoichiometry 1:2 (L-ala:DPC) with
a first order dependence on [DPC] and [Os(VIII)]. Based on
these experimental results, a mechanism is proposed for which
all the observed orders in each constituent such as [oxidant],
0
2
4
6
8
10
12
-
3
3
-1
(
)
1
/[L-ala] X 10 dm mol
ꢀ
FIG. 3. Verification of rate law (8) in the form of (9) for the oxidation of
L-alanine by diperiodatocuprate(III) at 25 C K.
◦
−
2−
6
[
reductant], [OH ], [Os(VIII)] and [H3IO ] may be well ac-
−
According to equation (9), the plots of 1/kU versus [OH ] (r commodated.
≥
0.998, S ≤ 0.014) and 1/kU versus 1/[L-ala] (r ≥ 0.997, S
Anionic form of L-ala reacts with Os(VIII) active species
0.016) should be linear, which is the case as given in Figure to form a complex (C2), which further reacts with one mole of
≤
3. From the slopes and intercepts of such plots, the reaction DPC in a slow step to give the free radical of L-ala, Cu(II) with
−2
constants K1, K2and k1 were calculated as (1.2 ± 0.04) × 10
regeneration of catalyst, osmium(VIII). Further, this free radical
3
2
3
−1
mol dm , (2.7 ± 0.1) × 10 dm mol and (4.2 ± 0.1) × of L-ala reacts with one more molecule of DPC species in a fast
−2 −1
10
s respectively. The value of K1 is in good agreement step to yield the products, as given in Scheme 2.
[32]
with the literature. Using these constants, the rate constants
were calculated and the values agreed well with the experimental
values (Table 1).
The probable structure of the complex (C2) is given below:
3
-
The thermodynamic quantities for the first and second equi-
O
librium steps of Scheme 1 can be evaluated as follows. The
NH2
CH3 CH
OH
O
−
[
L-ala] and [OH ] (Table 1) were varied at four different tem-
C
O
O
OS
O
peratures. The plots of 1/kU versus 1/[L-ala] and 1/kU versus
O
OH
−
[
OH ] should be linear (Figure 3). From the slopes and in-
tercepts, the values of K1 and K2 were calculated at different
temperatures and these values are given in Table 2. The vant
Hoff’s plots were made for variation of K1 and K2 with temper-
ature (log K1 versus 1/T (r ≥ 0.9604, S ≤ 0.006), log K2 versus
Spectroscopic evidence for the complex formation between
catalyst and substrate was obtained from UV-Vis spectra of L-
1
ꢀ
/T (r ≥ 0.996, s ≤ 0.007) and the values of enthalpy of reaction
H, entropy of reaction ꢀS and free energy of reaction ꢀG,
−4
−7
−
ala (4.0 × 10 ), Os(VIII) (8.0 × 10 ), [OH ] = 0.004 mol
were calculated for the first and second equilibrium steps. These
−
3
dm ) and mixture of both. A hypsochromic shift of about 7
nm from 292 nm of L-alanine to 285 nm of mixture of Os(VIII)
and L-ala and a hyperchromicity at 285 nm, was observed. The
Lineweaver-Burk plot proved the complex formation between
Os(VIII) and L-ala, which explains less than unit order in [L-
ala]. The rate law for Scheme 2 could be derived as,
values are given in Table 2. A comparison of ꢀH value (20.3 ±
#
2
) from K2 with that of ꢀH (25.0 ± 2) of rate limiting step
supports that the second step of Scheme 1 is fairly fast since it
[
33]
involves low activation energy.
#
#
The moderate values of ꢀH and ꢀS were both favorable
for electron transfer processes. The value of ꢀS within the
range for a radical reaction has been ascribed
#
[34]
to the nature
−
d[DPC]
of electron pairing and unpairing processes and to the loss of
degrees of freedom upon the formation of rigid transition state.
The observed modest enthalpy of activation and a relatively low
value of the entropy of activation, as well as a higher rate con-
stant of the slow step, indicate that the oxidation presumably
Rate =
dt
k2K1K3[DPC][L-ala][Os(V III)]
=
−
−
[OH ] + K1 + K3[L-ala][OH ] + K1K3[L-ala]
[10]

402
S. D. LAMANI ET AL.
and found to be in reasonable agreement with each other, which
fortifies Scheme 2.
The thermodynamic quantities for the different equilibrium
steps in Scheme 2 can be evaluated as follows. The L-ala and
hydroxide ion concentrations (Table 3) were varied at different
temperatures. The plots of [Os(VIII)]/kC versus 1/[L-ala] (r ≥
−
0
≤
.9996,s ≤ 0.00134), [Os(VIII)]/kC versus [OH ] (r ≥ 0.9994,s
0.00086), should be linear, as shown in Figure 4. From the
slopes and intercepts, the values of K1 are calculated at different
temperatures. A vant Hoff’s plot was made for the variation of
K1 with temperature [i.e., log K1 versus 1/T (r ≥ 0.9992, s ≤
0
.1106)], and the values of the enthalpy of reaction ꢀH, entropy
of reaction ꢀS, and free energy of reaction ꢀG were calculated.
These values are also given in Table 4. In the same manner,
K3 values were calculated at different temperatures, and the
corresponding values of thermodynamic quantities are given in
FIG. 4. Verification of rate law (11) in the form of (12) for the Os(VIII) Table 4. A comparison of ꢀH value (36.3) from K with that of
3
◦
catalyzed oxidation of L-alanine by diperiodatocuprate(III) at 25 C.
#
ꢀ
H (25.2 ± 0.4) of rate limiting step, supports that the second
step of Scheme 2 is fairly slow since it involves high activation
energy.[
33]
Rate
=
DPC]
kC = kT − kU
Negligible effect of ionic strength and dielectric constant in
uncatalyzed and catalyzed reaction might be due to involve-
ment of neutral species in the reaction (Schemes 1 and 2). The
[
k2K1K3[L-ala][Os(V III)]
= [
OH ] + K1 + K3[L-ala][OH ] + K1K3[L-ala]
−
−
#
negative value of ꢀS suggests that the intermediate complex
[11]
[37]
is more ordered than the reactants.
The observed modest
enthalpy of activation and a higher rate constant for the slow
The rate law (11) can be rearranged to Eqn (12), which is suitable step indicate that the oxidation presumably occurs via an inner-
for verification
sphere mechanism. This conclusion is supported by an earlier
observation.[
36]
−
[
Os(VIII)]
[OH ]
The activation parameters evaluated for the catalyzed and
uncatalyzed reaction explain the catalytic effect on the reaction.
The catalyst Os(VIII) forms the complex (C2) with L-ala, which
enhances the reducing property of the substrate than that without
catalyst. Further, the catalyst Os(VIII) modifies the reaction path
by lowering the energy of activation. The Os(VIII) catalyzed
reaction, however, is reasonably fast in view of readiness of
Os(VIII) to act across the –COO bond.
The activation parameters for the uncatalyzed and Os(VIII)
catalyzed oxidation of some amino acids by DPC are summa-
rized in Tables 6 and 7. The entropy of activation for the title
reaction falls within the observed range. Variation in the rate
=
kC
k2K1K3[L-ala]
1
−
[OH ]
1
+
+
+
[12]
k2K3[l-ala]
k2K1
k2
According to Eq (12), the plots of [Os(VIII)]/kCversus 1/[L-ala]
and [Os(VIII)]/kCversus[OH ] were linear (Figure 4). From the
intercepts and slopes of such plots, the reaction constants K1,
−
−2
−3
K3 and k2 were calculated as (1.6 ± 0.02) × 10 mol dm
,
2
3
−1
5
3
−1
(
s
3.5 ± 0.2) × 10 dm mol (3.3 ± 0.1) × 10 dm mol
−1
, respectively. These constants were used to calculate the
rate constants and compared with the experimental kC values,
TABLE 6
Activation parameters for uncatalyzed reactions, oxidation of some amino acids (for isokinetic temperature)
02 k1
10 k
2
1
1
1
3
−1 −1
3
−1 −1
ꢀH#
ꢀ S#
(
dm mol
s
)
(dm mol
s
)
Amino acids
at T = 298 K
at T = 303 K
(J/K/mol)
(kJ/mol)
References
Vanilline
L-glutamic acid
L-valine
L-proline
L-alanine
3.7
4.2
13.1
13.1
38.0
29.0
25.0
−227
−238
−154
−181
−184
[31]
[42]
[43]
0.98
1.20
2.7
1.12
1.62
3.16
5.4
[44]
4.2
Present work

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION
403
TABLE 7
Activation parameters for Os(VIII) catalyzed reactions, oxidation of some amino acids (for isokinetic temperature)
02 k1
10 k
2
1
1
1
3
−1 −1
3
−1 −1
ꢀH#
ꢀ S#
(
dm mol
s
)
(dm mol
s
)
Amino acids
at T = 298 K
at T = 303 K
(J/K/mol)
(kJ/mol)
References
L-tryptophan
L-lysine
Vanilline
3.2
2.8
1.4
3.3
5.3
3.08
1.8
44.0
15.5
41.0
25.2
−30
−107
−25.7
−6.7
[45]
[46]
[47]
L-alanine
3.8
Present work
within the reaction series may be caused by change in the en- We have calculated the isokinetic temperature for uncatalyzed
thalpy or entropy of activation. Changes in rate are caused by and Os(VIII) catalyzed reaction. The values for β of uncatalyzed
#
#
1
changes in both ꢀH and ꢀS , but these quantities vary exten- reaction to be 325.5 K by plotting log k1 at 303 K versus log
#
#
sively in a parallel fashion. A plot of ꢀH versus ꢀS is linear k1 at 298 K (r ≥ 0.9865, s ≤ 0.007) and isokinetic temperature
according to the following equation:
for Os(VIII) catalyzed reaction to be 333.4 K by plotting log
1
k at 303 K versus log k2 at 298 K (r ≥ 0.9788, s ≤ 0.005), as
2
#
#
ꢀH = βꢀS + constant
in (Figure 5). The values of β for uncatalyzed (325.5 K) and
catalyzed (333.4 K) are higher than experimental temperature
β is called the isokinetic temperature; it has been asserted that (298 K). This indicates that the rate is governed by enthalpy of
#
#
[41]
apparently linear correlations of ꢀH with ꢀS are sometimes activation in both the cases. The linearity and the slope of the
misleading and the evaluation of β by means of the above equa- plot obtained may confirm that the kinetics of these reactions
[39]
[40]
tion lacks statistical validity. Exner advocates an alterna- follow a similar mechanism, as previously suggested.
tive method for the treatment of experimental data. If the rates
of several reactions in series have been measured at two tem-
peratures and log k2 (at T2) is linearly related to log k1 (at T1),
CONCLUSION
The comparative study of uncatalyzed and osmium(VIII) cat-
i.e., log k2 = a + b log k1, he proposes that β can be evaluated
alyzed oxidation of L-ala by diperiodatocuprate(III) was stud-
ied. Oxidation products were identified. Among the various
species of Cu(III) in alkaline medium, protonated DPC is con-
sidered to be the active species for the title reaction. Active
from the equation:
β = T1 T2(b − 1)/(T2 b − T1)
2−
species of Os(VIII) is found to be [OsO4(OH)2] . Activation
parameters were evaluated for both uncatalyzed and catalyzed
reactions with respect to slow step of reaction schemes. Catalytic
constants and activation parameters with respect to catalyst were
also computed. Isokinetic temperature for both uncatalyzed and
catalyzed reactions was also determined.
3
+ log k2
0
9
2
4
6
8
7.8
5
6
5
4
3
2
.8
.8
.8
.8
.8
8
7
6
5
4
4
4
REFERENCES
3
3
1
2
. Reddy, B; Sethuram, B.; Navaneeth Rao, T. Indian J. Chem. 1984, 23, 593.
. Kumar, A.; Kumar, P.; Ramamurthy, P. Polyhedron. 1999, 18, 773.
2
1
3. Shettar, R.S; Nandibewoor, S.T. J. Mol. Cat. A 2005, 234, 137.
4
5
6
. Niu, W.; Zhu, Y.; Hu, K.; Tong, C.; Yang, H. Int. J. Chem. Kinet. 1996, 28,
99.
. Rozovoskii, G.I.; Misyavichyus, A.K.; Prokopchik, A.Y. Kinet. Catal. 1975,
6, 337.
. Ramreddy, M.G.; Sethuram, B.; Navaneeth Rao, T. Indian J. Chem. 1978,
6, 313.
7. Karlin, K.D.; Gultneh, Y. In:Progress in Inorganic Chemistry; Lipard, S.J.
ed)., Wiley: New York, 1997, p. 220.
2
1
8
1.8
0.8
1
3
0
2
4
6
8
1
3
+ log k1
(
1
1
1
2
FIG. 5. Plot of log k at 303 K versus log k1 at 298 K and plot of log k at
8. Tolman, W.B. Acc. Chem. Res. 1997, 30, 227.
9. Kovat, Z. Acta. Chim. Hung. 1960, 22, 313.
3
03 K versus log k2 at 298 K for the isokinetic temperature (Tables 6 and 7).
For uncatalyzed (−ꢀ−): (1) L-glutamic acid; (2) L-valine; (3) L-proline; (4)
10. Kitajima, K.N.; Moro-oka, Y. Chem. Rev. 1994, 94, 737.
Vanilline; (5) L-alanine. For catalyzed (−ꢁ−): (1) L-lysine; (2) L-tryptophan; 11. Mahadevappa, D.S.; Rangappa, K.S.; Gowda, N.N.M.; Thimmegowda, B.
(
3) Vanilline; (4) L-alanine.
Int. J. Chem. Kinet. 1986, 60, 589. and reference therein.

404
S. D. LAMANI ET AL.
1
1
2. Mohanti, M.K.; Laloo, D. J. Chem. Soc., Dalton Trans. 1990, 311.
3. Balreddy, K.; Sethuram, B.; Navaneeth Rao, T. Indian J. Chem. 1981, 20A,
APPENDIX
According to Scheme 2,
3
95.
1
4. Rennie, J.M. Physical Exertion, Amino Acid and Protein Metabolism, and
Protein Requirements, Protein and Amino Acids; Washington DC: National
Academy Press, 1999, p. 243.
−
d[DPC]
3−
Rate =
= k2[C] [Cu(OH)2(H3IO6)2]
[A-1]
[A-2]
dt
1
5. Das, A.K. Coord. Chem. Rev. 2001, 213, 307.
k2K1K3[L-ala] [DPC]f[Os(VIII)]
=
16. (a) Agrawal, M.C.; Upadhyay, S.K.J . Sci. Ind. Res. 1983, 42, 508;
−
[
OH ]
(b) Hugar, G.H.; Nandibewoor, S.T. Transition Met Chem. 1994, 19,
3
−
[
DPC]T = [DPC]f + [Cu(OH)2(H3IO6)2]
[A-3]
2
15.
ꢀ
ꢁ
−
1
7. Veerasomaiah, P; Bal Reddy, K.; Sethuram, B.; Navaneeth Rao, T. Indian
J. Chem. 1987, 26A, 402.
K1[DPC]
[OH ] + K1]
[DPC]T = [DPC]f +
= [DPC]f
−
−
[
OH ]
[OH ]
1
8. Saxena, O.C. Microchem J. 1967, 12, 609.
19. Murthy, C.P.; Sethuram, B.; Navaneeth Rao, T. Z. Phys. Chem. 1981, 262,
[A-4]
3
36.
2
0. Jeffery, G.H.; Bassett, J.; Mendham, J.; Denny, R.C. Vogel’s Textbook of
Quantitative Chemical Analysis, 5 edn.; ELBS Longman: Essex UK,
Where [DPC]T and [DPC] refer to total and free DPC concen-
trations, respectively. The free DPC is given by
th
1
996, p. 455.
2
2
1. Panigrahi, G.P.; Misro, P.K. Indian J. Chem. 1977, 15A, 1066.
2. Feigl, F. Spot Tests in Organic Analysis; Elsevier: New York, 1975,
p. 58.
−
[
DPC]T[OH ]
[
DPC]f =
[A-5]
−
[
OH ] + K1
2
3. Vogel, A.I. A Text Book of Practical Organic Chemistry Including Quan-
titative Organic Analysis, 3rdEd; ELBS Longman: Essex UK,, 1973, p.
−
Similarly total [OH ] can be calculated by
3
32.
2
2
2
2
2
2
3
3
4. Moelwyn-Hughes, E.A. Kinetics of Reactions in Solutions; Oxford Univer-
sity Press: London, 1947, p. 297.
5. Reddy, K.B.; Sethuram, B.; Navaneeth Rao, T. Z. Phys. Chem. 1987, 268,
−
−
3−
[
OH ]T = [OH ]f + [Cu(OH)2(H3IO6)2]
K [DPC]
−
1
=
[OH ]f +
7
06.
−
[
OH ]
6. Bailar, J.C.; Emeleus, H.J.; Nyholm, S.R.; Trotman-Dikenson, A.F. Com-
prehensive Inorganic Chemistry; Pergamon Press: Oxford, 1975, p. 1456.
7. Sethuram, B. Some Aspects of Electron Transfer Reactions Involving Or-
ganic Molecules; Allied Publishers (P) Ltd.: New Delhi, 2003, p. 78.
8. Kiran, T.S.; Hiremath, D.C.; Nandibewoor, S.T. Z. Phys. Chem. 2007, 221,
In view of low concentration of DPC used,
−
−
5
01.
[OH ]T = [OH ]f
[A-6]
9. Chang, R. Physical Chemistry with Applications to Biological Systems;
Macmillan: New York, 1981, p. 326.
0. Chougale, R.B.; Hiremath, G.A.; Nandibewoor, S.T. Polish. J. Chem. 1997,
Similarly
7
1, 1471.
1. Hiremath, D.C.; Kiran, T.S.; Nandibewoor, S.T. Int. J. Chem. Kinet. 2006,
9, 236.
[
L-ala]T = [L-ala]f + [C]
3
=
[L-ala]f + K3[L-ala] [Os(VIII)]
3
2. Kulkarni, S.D.; Nandibewoor, S.T. Transition Met Chem 2006, 31, 1034.
3. Rangappa, K.S.; Raghavendra, M.P.; Mahadevappa, D.S.; Chennegouda,
D. J. Org. Chem. 1998, 63, 531.
3
In view of low concentration of [Os(VIII)] is used,
3
4. Walling, C. Free Radicals in Solutions; Academic Press: New York, 1957,
p. 38.
[L-ala]f = [L-ala]T
[A-7]
[A-8]
3
3
3
5. Moore, F.M.; Hicks, K.W. J. Inorg. Nucl. Chem. 1976, 38, 381.
6. Farokhi, S.A.; Nandibewoor, S.T. Tetrahedron 2003, 59, 7595.
7. Vemulapalli, G.K. Physical Chemistry; Prentice-Hall, Inc.: England Cliffs,
N.J, U.S.A, 1997, p. 734.
[
Os(VIII)]T = [Os(VIII)f + [C]
= [Os(VIII) + K3[L-ala] [Os(VIII)]
f
=
[Os(VIII)] {1 + K3[L-ala]}
f
38. Kamble, D.L.; Nandibewoor, S.T. J. Phys. Org. Chem. 1998, 11, 171.
rd
[Os(VIII)]T
3
9. Lewis, E.S. Investigations of Rates and Mechanisms of Reactions, 3 edn.;
[
Os(VIII)] = 1
f
New York: Wiley, 1974, p. 415.
0. Exner, O. Collect Czech Chem Commun 1972, 37, 1425.
1. Leffler, J.E. J. Org. Chem.1955, 20, 1202.
2. Shettar, R.S.; Shetti, N.P.; Nandibewoor, S.T. Oxidn. Commun. 2008, (In
press).
+ K3[L-ala]
4
4
4
Substituting eqn (A-5), (A-6), (A-7) and (A-8) in eqn (A-2)
and omitting the T and f subscript s, we get
4
3. Deganatti, B.A; Shetti, N.P.; Nandibewoor, S.T. Transition Met. Chem.
−
d[DPC]
2
009, 34, 143.
Rate =
= [
4
4
4. Hiremath, M.I; Nandibewoor, S.T. Russ. J. Phys. Chem. 2006, 80, 1178.
5. Shetti, N.P.; Hosamani, R.R.; Nandibewoor, S.T. Res. Lett. Inorg. Chem.
dt
k2 K1 K3[DPC] [L-ala] [Os (VIII)]
2
008, 10, 1155.
6. Hiremath, D.C.; Kiran, T.S.; Nandibewoor, S.T. Catalysis Letters. 2008,
22, 144.
7. Kiran, T.S.; Hiramath, D.C.; Nandibewoor, S.T. Ind. Eng. Chem. Res. 2008,
Communicated).
−
−
OH ] + K1 + K3[L-ala][OH ] + K1K3[L-ala]
A-9]
4
4
[
1
(
Similarly rate equation for uncatalyzed reaction can be derived.