KINETICS AND MECHANISM OF PERBORATE OXIDATION OF ORGANIC SULFIDES

The perborate oxidation of organic sulphides to sulphoxides is first order in perborate. It is first order with respect to diethyl and diphenyl sulphides, and the rate increases linearly with [MeSPh]. In highly acidic medium the oxidation exhibits first order dependence on [acid]. The oxidation is inhibited by NaCl and enhanced by increase in solvent polarity. Metaborate has no influence on the oxidation rates. The rates of oxidation by hydrogen peroxide, and hydrogen peroxide with metaborate are about two-third of the perborate oxidation rates. Electron-releasing groups accelerate and electron-withdrawing groups retard the oxidation. In the oxidation of diethyl sulphide attack of protonated perboric acid on sulphide and in methyl phenyl sulphide (i) attack of protonated perboric acid on sulphide, and (ii) breakdown of protonated perboric acid to yield H2BO3+ which reacts with the substrate in a fast step are suggested as rate-determining. In diphenyl sulphide H2BO3+ is proposed as the oxidising species.