Kinetics and mechanism of oxidations by peroxodiphosphate ions. Part I. Oxidation of arsenic(III) in aqueous perchloric acid

Abstract

Peroxodiphosphate, [P2O8]4–, oxidises arsenious acid in perchloric acid medium according to equation (i). H4P2O8+ H3AsO3+ H2O → 2H3PO4+ H3AsO4(i) The mechanism essentially involves hydrolysis of the species [H2P2O8]2–, [H3P2O8]–, and H4P2O8, and the rate of the redox reaction is independent of the arsenic (III) concentration. The rate law when 2.5 > [HClO4] > 0.1 mol dm–3 is as in (ii), and the values of k2 and k3 are (2.7 ± 0.2)× 10–4 and (8.65 ± 0.3)× 10–3 s–1 respectively at 45 °C. –d[P2O8]/dt=k2[H3P2O8–]+k3[H4P2O8](ii) The rate of reaction is independent of the ionic strength. Acrylamide, F–, Cu2+, Mn2+, Fe2+, and phosphate have no effect on the reaction, but Ag+ catalyzes the reaction.