Kinetics and mechanism of oxygenation of aromatic sulfides and arylmercaptoacetic acids by peroxomonophosphoric acid

The oxygenation of aryl methyl sulfides and diaryl sulfides by peroxomonophosphoric acid in acetonitrile–water mixture follows an overall second-order kinetics, first-order in each reactant. The study of the influence of [H+] on the oxidation of phenyl methyl and diphenyl sulfides reveals that H2PO5− and HPO52− are the oxidising species in the oxidation process. In substituted phenyl methyl sulfides and diphenyl sulfides, the rate of oxygenation is accelerated by electron-donating substituents and retarded by electron-withdrawing groups, indicating the nucleophilic displacement by the sulfide sulfur on the peroxide oxygen. The negative ρ value obtained in the correlation analysis of rate constants with σ constants also shows the formation of a more positively charged sulfur species in the rate-limiting step. Studies with different alkyl phenyl sulfides (C6H5SR; R=Me, Et, Pri or But) indicate that the rate is retarded by bulky R groups. Similar kinetic results are also obtained in the peroxomonophosphoric acid oxidation of sodium phenylmercaptoacetate. On the basis of the kinetic studies, a common mechanism has been proposed.