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

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The oxidation of hydrogen peroxide by AgIII 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 [AgIII], [HO2-], 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[AgIII]/Δ[HO2-] = 1 at high [HO2-] to 2 at excess [AgIII] leads to the conclusion that a bivalent silver intermediate is produced.

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Journal of the Chemical Society, Dalton Transactions