A NEW MECHANISM FOR PERSULPHATE OXIDATIONS

Abstract

A new mechanism for oxidations by persulphate is presented, wherein it is postulated that the persulphate ion dissociates reversibly, by means of a heterolytic cleavage, into a sulphate ion and a molecule of sulphur tetroxide. Sulphur tetroxide is considered to be the active oxidizing species, combining reversibly with the substrate to form a complex whose subsequent decomposition gives the principal reaction products. The very small equilibrium concentration of sulphur tetroxide becomes the limiting factor in the rate of oxidation when a readily oxidizable substrate is present in relatively high concentration. The mechanism is applied to the data of Eager and Winkler for the oxidation of mercaptans, in which a limiting rate was attained above a certain mercaptan concentration. An empirical equation relating the rate constant to the mercaptan concentration is developed to fit the experimental data. Rate equations showing the rate dependence on mercaptan concentration are derived from the proposed mechanism and are found to be of the same form as the empirical equation. The mechanism is applied also to the persulphate oxidation of water.