Kinetics and mechanisms of the oxidation by permanganate of L-alanine

Abstract

The oxidation of L-alanine by permanganate ion in aqueous phosphate buffers is autocatalysed by the inorganic reaction product, a solube form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ion on its surface. The rate of the non-catalytic reaction pathway is first-order in both the oxidizing and reducing agent, is not affected by potassium chloride addition to the solution, and increases with the pH of the medium, its associated activation energy being 74.0 kJ mol^–1. The rate of the catalytic reaction pathway is first order in both the oxidizing and autocatalytic agent, follows the Freundlich adsorption isotherm as far as the reducing agent concentration is concerned, is not affected by potassium chloride addition to the solution, and increases with the pH of the medium, its associated activation energy being 67.2 kJ mol^–1. Mechanisms consistent with the experimental data are proposed.