Kinetics and mechanism of hydrogen peroxide oxidation by silver(III) in aqueous alkaline media

Abstract

The oxidation of hydrogen peroxide by Ag^III in strongly alkaline media has been studied by stopped-flow spectrophotometry in the temperature range 6–45 °C at a total ionic strength of 1.2 mol dm^–3(NaClO₄). The reaction is first order in [Ag^III], [HO^2–], and [OH^–] with a third-order rate constant of (4.2 ± 0.6)× 10⁵ dm⁶ mol^–2 s^–1 at 25 °C. The form of the rate law and the activation parameters (ΔH^‡= 25 ± 5kJ mol^–1, ΔS^‡=–113 ± 5 J K^–1 mol^–1) suggest the formation of a five-co-ordinate intermediate of the form [Ag(OH)₄O₂]^3–. Although kinetic results do not distinguish between a oneor two-electron transfer, a change in stoicheiometry from Δ[Ag^III]/Δ[HO₂^–]= 1 at high [HO₂^–] to 2 at excess [Ag^III] leads to the conclusion that a bivalent silver intermediate is produced.