Kinetics of oxidation of manganese(II) by peroxomonosulfuric acid in aqueous acidic solution

Summary Oxidation of Mn_aq²⁺ by HSO₅^– in acetate buffer to manganese(IV) is autocatalytic, and obeys a rate expression of the general form -d[Mn^II]/dt = k₀[Mn^II] + k₁[Mn^II][MnO_x]. The first-order (k₀) and heterogenetic (k₁) rate constants show first-order dependences on [HSO₅^–] and on 1/[H⁺]. The reaction is catalyzed by the addition of the chelating ligand glycine; k₁ shows a first-order dependence on [glycine] at a fixed pH. This catalysis is ascribed to complexation, whereby the redox potential for Mn(gly)_n^(2–n)+ is lower than that for Mn_aq²⁺, facilitating oxidation. The stoichiometry of the reaction is Mn²⁺: HSO₅^– = 11, and the manganese(IV) oxide formed is of battery-active grade. Purity of the recovered product is not affected by the presence of high concentrations of natural sugars in the initial solution.