Mechanism of the permanganate oxidation of unsaturated compounds. Part III. Intermediates in the oxidation of maleic and fumaric acids

The intermediates in the permanganate oxidation of maleic and fumaric acids have been studied in acidic solutions. The accumulation and decay of manganese(III) has been demonstrated by the stopped-flow technique. The concomitant four-electron oxidation of the substrates leads to the formation of formyl(hydroxy)acetic acid. The subsequent reactions reveal a complex pattern in which hydroxymalonic, glyoxylic, and oxalic acid are further intermediates. The product distribution has been determined as a function of the pH and the mole ratio of the reactants. A reaction scheme is suggested which rationalises the observed behaviour.