Mechanisms of peroxide reactions: kinetics of reduction of peroxo-monosulphuric and peroxomonophosphoric acids by iodide ion

Abstract

The kinetics of iodide-ion oxidation by H₂SO₅ and H₂PO₅ have been investigated. The rate of the first reaction is given by equation (i) where k= 1.73 × 10³ dm³ mol^–1 s^–1 in aqueous solution at 25 °C and I= 0.2 mol dm^–3. Rate =k[HSO₅^–][I^–](i) The rate equation for rhe second reaction is given by the three-term expression (ii) with k₁= 1.57 × 10³. k₂= 57.5, and k₃= 0.418 dm³ mol^–1 s^–1 under the same conditions. Rate =(k₁[H₃PO₅]+k₂[H₂PO₅^–]+k₃[HPO₅^2–])[I^–](ii) The effect of electrolyte addition has been investigated. An inverse linear dependence of the logarithms of the rate constants on the basiclty of the leaving group has been found. The mechanism is consistent with nucleophilic attack by I^– on the external peroxidic oxygen leading to breaking of the oxygen–oxygen bond.