Kinetics and mechanism of the reaction of manganese(III) octaethylporphine with hydrogen peroxide

Abstract

A spectroscopic and kinetic study of the oxidation of (chloro)(octaethylporphinato)manganese(III) (Cl)MnOEP with hydrogen peroxide in an aqueous-organic medium at 288–308 K was made. The nature and composition of the reaction products differ depending on the reaction conditions (H2O2 concentration). Based on the data on reaction rates, thermodynamic parameters of activation, and form of the rate equations of the (C1)MnOEP oxidation, a multistep reaction mechanism is suggested and substantiated, in which the decisive role is played by the limiting step, two-electron oxidation of the metal porphyrin with the coordinated peroxide or partial reduction of the oxidized form of the manganese porphyrin with the second peroxide molecule (in the form of HO 2 − ), and by acid-base equilibria of the peroxide.