The anodic oxidation of aqueous solutions of acetate ions at smooth platinum electrodes: Part II. The non-steady state of the kolbe synthesis of ethane

Abstract

The kinetics of the Kolbe electrosynthesis of ethane from acetate ions at smooth platinum electrodes in aqueous solutions has been examined by a new repetitive potential pulse technique. The integral yields of the products of electrolysis have been measured as a function of oxidation time. At short times acetate ions are oxidised completely to carbon dioxide. With increasing time this process is inhibited and the alternative oxidation to ethane increases to the steady state value at 10 −3 sec. The yields of these and the minor products are related to the catalytic activity of the platinum substrate. From the form of the variation of the yield of ethane with time and its dependence on potential the discharge-bi-radical mechanism has been assigned to the Kolbe reaction, the discharge step being rate determining. Limiting values are given, for the heterogeneous rate constants of the discharge and bi-radical steps. The effect of a number of complicating factors (the ratio of the real to apparent area, time dependence of surface oxide formation, the influence of more than one adsorbed intermediate, deviations from “Langmuir” conditions) are briefly considered.