Copper(II)-catalysed oxidation of hypophosphite by peroxydisulphate in perchloric acid solution

Abstract

The copper(II)-catalysed oxidation of hypophosphite by peroxydisulphate in aqueous perchloric acid solution was measured in the presence of varying amounts of Cu^II(1 × 10^–4– 4 × 10^–3M) in the range of hydrogen-ion concentration of 0·01–0·8M and at temperatures of 28, 35, and 40 °C. The rate law is (i) where K_d is the dissociation –d[S₂O₈^2–]//_dt=kK[Cu^II][S₂O₈^2–][H₃PO₂]//_{[H⁺]+Kd+K[H3PO2]}(i) constant for hypophosphorous acid and k and K were found to be 54·8 ± 2·4 (average) l mol^–1 min^–1 and 3·6 respectively at 35 °C and µ= 0·2M. Complex formation between Cu⁺⁺ and H₃PO₂ is suggested. Mn^II decreases the rate of reaction and a limiting rate is obtained by increasing the concentration of Mn^II. Sulphate ion is without any effect, but hydrogen sulphate decreases the rate. The overall energy of activation was found to be 10·7 kcal mol^–1. A chain mechanism has been suggested. The rate constant at 35 °C and energy of activation for the chain-initiating step were found to be 2·80 l mol^–1 min^–1 and 13·4 kcal mol^–1 respectively.