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 (NaClO 4). The reaction is first order in [Ag III ], [HO 2- ], and [OH - ] with a third-order rate constant of (4.2 ± 0.6) × 10 5 dm 6 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) 4 O 2 ] 3-. Although kinetic results do not distinguish between a oneor two-electron transfer, a change in stoicheiometry from Δ[Ag III ]/Δ[HO 2 - ] = 1 at high [HO 2 - ] to 2 at excess [Ag III ] leads to the conclusion that a bivalent silver intermediate is produced.