Mechanism of the permanganate oxidation of unsaturated compounds. Part I. Short-lived intermediates of the oxidation of acetylenedicarboxylic acid

Abstract

Fast reaction techniques have been applied to the study of intermediates in the permanganate oxidation of acetylenedicarboxylic acid in acid. The accumulation and decay of Mn^III has been observed by stopped-flow spectrophotometry. The quenching of reacting solutions proves that oxalic acid is formed as an intermediate. The amount of oxalate found in the presence of pyrophosphate as scavenger for Mn^III provides evidence for a short-lived Mn^IV species. Oxygen-18 tracer experiments indicate complete oxygen transfer from permanganate to acetylenedicarboxylic acid. A number of mechanistic alternatives are systematically examined. It is suggested that the first step of oxidation is the formation of a cyclic intermediate containing manganese(V).