Carbon kinetic isotope effects in the oxidation of oxalate by permanganate in aqueous solutions of sulfuric acid

Fractionation of the carbon isotopes occurs during the oxidation of oxalate by permanganate in aqueous sulfuric acid. The isotope effect, expressed as k12/k13, rises from near unity in the very early stages of the reaction, to reach a value of 1.037 +-0.001 after completion of the induction period. Addition of fluoride prolongs the induction period, and reduces the isotope effect to values near 1.000. These observations are consistent with there being two essentially independent paths for formation of carbon dioxide. The first, operative in the early stages, involves rate-controlling electron transfers from Mn(VI) or Mn(IV) to the oxalate ion, while the second involves oxidative decomposition of an oxalate complex of Mn(III), for which the rate-controlling step is C-C bond rupture. (author)