Kinetics and mechanism of oxidation of pyruvate by permanganate ion in aqueous perchlorate solution

Abstract

The kinetics and mechanism of permanganate oxidation of pyruvic acid in aqueous perchlorate at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The pseudo-first-order plots showed two distinct phases for the reaction, characterized as induction and auto-acceleration periods. The induction phase is relatively slow at the early stages of reaction and is followed by a faster process. The rate law for the oxidation was described by the sum of two exponential terms. The oxidation showed overall second-order kinetics with respect to the reactants in the initial slow phase. However, second-order kinetics was not maintained throughout the faster second stage. The effects of added salts lead to the conclusion that Mn(III) and/or Mn(IV) play the main role in the reaction kinetics of the second stage. A reaction mechanism consistent with the kinetic results is suggested and discussed.