THE OXIDATION OF MERCAPTANS BY POTASSIUM PERSULPHATE IN HOMOGENEOUS SOLUTION

Abstract

In the homogeneous oxidation of mercaptans by potassium persulphate in concentrated acetic acid, the rate of disappearance of potassium persulphate during an experiment is first order with respect to the measured persulphate concentration. The rate constant is independent of the kind of mercaptan used, and is independent of mercaptan concentration over a wide range of mercaptan concentrations. The rate constant falls off, however, at low mercaptan concentrations, this falling-off being less pronounced if the rate is reduced by the addition of salts. The mercaptan concentration at which the rate constant, calculated from persulphate disappearance, becomes independent of mercaptan concentration increases as the temperature is increased. A salt effect prevails, the rate constant being decreased with increased potassium ion concentration. The equivalent conductance of solutions of potassium persulphate in the solvent used shows a behavior on dilution which indicates that potassium persulphate is incompletely ionized in the solvent. A mechanism is proposed for the reaction, in which it is assumed that dissociation of persulphate ions into sulphate free radicals is rate-controlling, with an activation energy of the order 26,000 cal. per mole.