The oxidation of iodide by the tetrahydroxoargentate(III) ion in aqueous alkaline media

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Iodide is rapidly oxidized by [Ag(OH)4]- in strongly alkaline media to give hypoiodite and AgI according to the stoicheiometric equation (i). Stoicheiometry measurements are consistent with [Ag(OH)4]- + I- → AgI + 2OH- + IO- + H2O (i) complementary two-electron redox both at excess of AgIII and excess of I-. The kinetics of the reaction are first order in the silver(III) and iodide concentrations. The second-order rate constant is 76 ± 1 dm3 mol-1 s-1(25°C, I = 1.2 mol dm-3) and the enthalpy and entropy of activation are 32.5 ± 0.6 kJ mol-1 and -100 ± 2 J K-1, respectively. While precipitation of AgI interferes with spectral measurements at lower (excess) iodide concentrations, the product formation has no effect on the kinetics of the system. The mechanism proposed involves a simultaneous two-electron transfer within an intermediate of composition [Ag(OH)4I]2-. The values of the activation parameters are similar to those of other silver(III) reactions.

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Journal of the Chemical Society, Dalton Transactions