Mechanism of the permanganate oxidation of unsaturated compounds. Part II. Stopped-flow kinetic study of the oxidation of acetylenedicarboxylic acid

Abstract

The kinetics of oxidation of acetylenedicarboxylic acid by permanganate have been studied by the stopped-flow technique in aqueous solution between pH 0·25 and 5·3. The reaction is of the first order with respect to both permanganate and the substrate. The apparent second-order rate constant increases with decreasing pH, indicating the reactivity order: undissociated acid > monoanion > dianion. The individual rate constants are in the above order: k₁= 1420; k₂= 632; k₃= 40 I mol^–1 s^–1. The temperature-dependence of k₃ studied in the 13·7–30·3 °C interval yields the activation parameters ΔH‡= 25·5 kJ mol^–1 and ΔS‡=–135 J K^–1 mol^–1. The kinetic behaviour is consistent with the rate-determining formation of a short-lived cyclic intermediate containing manganese(V).