The kinetics of picolinic acid (PA)-catalysed CrVI oxidation of organic sulphur compounds have been studied with several alkyl aryl sulphides and diphenyl sulphides in acetic acid–water mixtures. The PA-catalysed oxidation follows third-order kinetics, first order each in oxidant, sulphide, and catalyst, at constant [H+] and ionic strength. A good correlation exists btween log k2 and Hammett σ constants for both aryl methyl and diphenyl sulphides, and the reaction constants are negative. Steric congestion at the reaction centre, sulphur, has been revealed by studies with C6H5SR (R = Me, Et, Pr, Pri, and But). Three mechanisms are proposed to account for the observed experimental results. In aryl methyl sulphides the rate benefit (kcat–kuncat)/kuncat is the least for p-methoxyphenyl methyl sulphide ad the largest for p-nitrophenyl methyl sulphide and this is in accordance with the reactivity–selectivity principle.

Mechanism of picolinic-acid-catalysed chromium(VI) oxidation of alkyl aryl and diphenyl sulphides

TiO 2 photocatalyzed oxidation of aryl methyl sulfides results in the formation of sulfoxides as the major product with small amounts of sulfones and C-S bond cleaved products. Increase in the irradiation time leads to disproportionation reaction (irradiation time determines the composition of the product). However, TiO 2 acts as an effective photocatalyst for the oxidation of aryl methyl sulfoxides to give exclusively sulfones. Photoelectrochemical studies provide support for electron transfer to occur from sulfide to the hole.

Oxidation of aryl methyl sulfides and sulfoxides on irradiated TiO2

Photocatalyzed Oxidation of Triphenyl Derivatives of P, As, Sb & Bi and Reduction of Their Oxides.

Photoredox reactions of polypyridyl chromium(III) complexes with arylthioacetic acids in acetonitrile and aqueous media

Kinetics of oxidation of twenty six S-arylmercaptoacetic acids (SAMA) (I) by sodium perborate (PB) have been studied in acid medium. The product of oxidation is the corresponding thiophenol. The rate data of meta-and para-substituted acids have been correlated with DSP equations. While the para-compounds correlate well with σI and σR° values, the meta-compounds correlate well with σI and σ values. The reaction constants are negative and of smaller magnitudes. Further, the ortho-substituted acids show a good correlation with a triparametric equation involving Taft's σI and R° and Charton's steric parameter ν. There is a considerable steric contribution to the total ortho-substituent effect. Based on these observations, mechanism involving the formation of protonated arylsulfinylacetic acid intermediate, followed by an intramolecular rearrangement leading to the product thiophenol has been proposed. © 1995 John Wiley & Sons, Inc.

Oxidative cleavage of S‐arylmercaptoacetic acids by sodium perborate: Kinetic and correlation study

The rates of oxidation of phenylthioacetic acid (PTAA) and several substituted phenylthioacetic acids by potassium peroxodiphosphate (PP) in 50% (v/v) aqueous acetic acid have been studied in detail. The rate of oxidation is expressed as 








An analysis of the dependence of the rate on [H+] reveals that H3P2O is the active oxidizing species in the oxidation. The effect of ring substituents on the rate gives a ρ+ value of -0.45 ± 0.03 (r = 0.998, s = 0.02 at 40°C), pointing to the development of an electron-deficient center in the transition state. The results are discussed in terms of a mechanism involving the rate-determining formation of an intermediate between PP and phenylthioacetic acids, followed by the decomposition of the intermediate. These kinetic results are compared with those obtained in the oxidation of phenylthioacetic acids by peroxodisulfate.

Mechanism of oxidation of phenylthioacetic acids by potassium peroxodiphosphate

The kinetics of oxidation of triphenyl derivatives of group V elements Ph3M (M = P, As, Sb) by potassium peroxodisulfate have been investigated spectrophotometrically in 60% acetonitrile–40% water (v/v) mixture. The reaction follows second-order kinetics, first order in each reactant. Changes in the [H+] and ionic strength have negligible effect on the reaction rate. Addition of acrylonitrile fails to inhibit the rate. The results indicate a rate-determining nucleophilic displacement of the Ph3M molecule on the peroxide linkage. The relative rate order has been found to be Ph3P > Ph3Sb > Ph3As. This can be attributed to two conflicting trends.

K. Pitchumani

Papers

Mechanism of oxidation of phenylthioacetic acids by potassium peroxodiphosphate

Mechanism of oxidation of triphenylphosphine, triphenylarsine, and triphenylstibine by potassium peroxodisulfate