Kinetics and mechanism of the oxidation of methanol by aquomanganese(III) ions in aqueous perchlorate media

Abstract

The rate of oxidation of methanol by Mn^III ions in aqueous perchlorate media is first order in both [Mn^III]_Total and [CH₃OH]_Total, and the observed second-order rate constant varies with both [HClO₄] and [Mn²⁺]. As Mn^III–methanol complexes have been detected spectrophotometrically, it is suggested that the oxidation is an inner-sphere reaction with [Mn³⁺CH₃OH_aq] and [Mn³⁺CH₃O^–aq][Mn³⁺_aq] and [MnOH²⁺_aq]. Various mechanisms to account for the retarding influence of Mn²⁺ ions and the effect of H⁺ ions are tested experimentally, and it is concluded that the Mn²⁺ ion, the ·CH₂OH radical and H⁺_aq ion are formed initially in a solvent cage with the rate of the back reaction increased by additional Mn²⁺ ions present in the wall of the solvent cage.