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

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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

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

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

−

3

dissolving OsO4oxide (Johnson Matthey) in 0.50 mol dm

[18]

NaOH. The concentration was ascertained

by determining

the unreacted [Fe(CN)6⁴with 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

◦

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

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

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)

CH₃CH COO^-+ 2 [Cu(OH) (H IO ) ] + H O

3-

CH CHO + 2Cu(OH)

2

3

6

2

3

2

#

−1

)

ꢀ

H (kJ mol

25 ± 2

−184 ± 20

80 ± 3

NH₂

2-

⁺^N^H3 + CO

+

H

2

+

+ 4H

IO

3

6

#

−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

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

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

◦

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

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

4.0

5.0

0.4

3.5

3.4

3.2

3.3

3.4

3.2

1

0.0

5.0

1.0

2.0

4.0

6.0

10.0

5.0

0.4

0.89

1.6

3.2

5.0

6.7

0.86

1.7

3.2

4.8

6.8

5

.0

4.0

1.0

3.0

5.0

8.0

10.0

0.4

3.4

3.5

3.2

3.4

3.2

5

.0

4.0

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 ) ] + CH₃CH COO

Complex(C₁)

2

3

6 2

NH₂

Complex(C₁)

.

k₁

2-

CH₃CH + Cu(OH) + 2H IO + CO₂

2

3

6

slow

NH₂

.

3

-

fast

CH₃CH + [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^-

^H^C^O3

-

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

-

CH₃CH COO + [OsO (OH) ]

-

Complex

(C₂)

4

2

^N^H2

.

CH₃CH + Cu(OH) + 2 H IO +

2

3 6

3

-

slow

k₂

2-

Complex (C ) + [Cu(OH) (H IO )]

2

3

6 2

2

-

^N^H2

CO₂+ [OsO (OH) ]

4

2

.

fast

2-

3

-

CH₃CH + [Cu(OH) (H IO ) ] + H O

CH₃CHO + Cu(OH)

+ 2 H IO

2

3

6 2

2

3

6

+

^N^H2

fast

Fast

+ NH₄

+

-

NH₄+ OH

NH OH

4

CO + OH^-

^H^C^O3

-

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

−1

mol dm

)

(mol dm

)

(mol dm

)

(mol dm

)

(mol dm

)

(s

)

(s

)

Found

Calculated

1

3

5

8

.0

4.0

1.0

2.0

4.0

6.0

10.0

4.0

5.0

1.0

3.0

5.0

8.0

10.0

5.0

0.4

0.1

0.2

0.4

0.6

1.0

0.4

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

2.8

2.9

3.3

2.9

2.5

2.3

2.1

1.2

2.5

3.1

8.3

14.0

2.5

0.72

1.4

2.6

3.7

5.6

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

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

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

−

_m_a_i_n_s_p_e_c_i_e_s_a_r_e_e_x_p_e_c_t_e_d_t_o_b_e_H₃_I_O₆₂−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 ²KC

−

(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

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

ꢀ

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

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

O

OH

I

(

Cu

O

I

O

HO

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

^C^H3

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

_C_H₃₋_C_H₍_N_H₂₎_C_O_O_H₊_O_H− ꢁ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

[30]

=

+

[9]

observed in earlier work.

kU

k1K1K2[L-ala]

K1K2[L-ala]

k1

MECHANISM OF UNCATALYZED AND OSMIUM(VIII) CATALYZED OXIDATION

401

-

-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

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

2

1

0

.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

-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

^C^H3 CH

OH

O

−

[

L-ala] and [OH ] (Table 1) were varied at four different tem-

C

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)

0²k1

10 k

2

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

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)

0²k1

10 k

2

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

7

6

5

4

REFERENCES

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

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

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

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

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

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

^[^O^s⁽^V^I^I^I⁾^]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

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. 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

[

1

(

Similarly rate equation for uncatalyzed reaction can be derived.

Article Doi

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

DOI: 10.1080/15533174.2011.556408

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Article abstract of DOI:10.1080/15533174.2011.556408

Full text of DOI:10.1080/15533174.2011.556408

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