REACTIVITY OF THE MN(III) AND MN(IV) INTERMEDIATES IN THE PERMANGANATE OXALIC-ACID SULFURIC-ACID REACTION - KINETIC DETERMINATION OF THE REDUCING SPECIES

UV/visible spectrophotometric analysis of the permanganate/oxalic acid reaction in sulfuric acid demonstrated the presence of two intermediates: bis(oxalato)manganate(III) and a soluble Mn(IV) compound. Their relative proportions were found to depend on the initial concentrations [H2C2O4](0) and [H2SO4](0). The proportion of bis(oxalato)manganate(III) was highest for a rise in [H2C2O4](0), while those of the soluble Mn(IV)(IV) compound increased for a simultaneous fall in [H2C2O4](0) and [H2SO4](0) A kinetic study together with a quantitative study of the effects of displacement of the equilibria of dissociation of the two diacids showed that, from a kinetic point of view, oxalate ion was the reducer of Mn(III) and molecular oxalic acid that of Mn(IV).