Manganese(III) Oxidation of L-Methionine in Aqueous Acetic Acid Medium: A Kinetic and Mechanistic Study

Abstract

A solution of manganese(III) acetate in aqueous acetic acid medium has been prepared by a standard electrochemical method. The nature of the oxidizing species present in manganese(III) solution has been characterized by spectrophotometric and redox potential measurements. Kinetics of oxidation of L-methionine (Met) by manganese(III) in aqueous acetic acid (60%v/v) at 323 K has been studied. The experimental rate law obtained is: rate = [Mn(III)]x [Met]y [OAc−]z /[H+]n, where x, y, z and n represent fractional orders. Effects of varying ionic strength, solvent composition, and added ions such as fluoride, chloride, and perchlorate have been investigated. Activation parameters have been evaluated using Arrhenius and Eyring plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. A rate law has been derived based on the mechanism.