Kinetics of the Reduction of the Tetrahydroxoargentate(III) Ion by Arsenite
Date of Original Version
The reaction of [formula-omitted] with arsenite ion to give Ag(I) and arsenate in strong base was studied by stopped-flow spectrophotometry. The reaction was found to fit a second-order rate law in which all three arsenite species present, [formula-omitted], [formula-omitted], and [formula-omitted], participate. Second-order rate constants for the three paths at 25 °C and μ- 1.2 M are respectively K1, = (6.2 ± 1.0) × 103 M-1 s-1, k2 = (3.7 ± 0.3) X 104 M-1 s-1 and k3 = (1.8 ± 0.5) × 104 M-1 s-1. In order to evaluate the activation parameters, the temperature dependence of the deprotonation of arsenite by [OH-] was studied. The equilibrium parameters are ΔH2(for [formula-omitted]) = 5 ± 1 kcal/mol and Δh3(for [formula-omitted]) = -2 ± 7 kcal/mol (μ = 1 M). The redox reaction appears to proceed by a one-step oxygen atom transfer. Two kinetically indistinguishable mechanisms are discussed: one involving initial attack of an As(III) oxygen at an axial silver(III) site and the other involving initial interaction between the arsenic and a bound hydroxyl. Differences in activation parameters are indicative of a larger barrier to redox for [formula-omitted] compared to those for the other two arsenite species. The dependence of the reaction rate on ionic strength supports the formulation of the Ag(III) species as the mononegatively charged ion [formula-omitted]. © 1983, American Chemical Society. All rights reserved.
Publication Title, e.g., Journal
Kirschenbaum, Louis J., and James D. Rush. "Kinetics of the Reduction of the Tetrahydroxoargentate(III) Ion by Arsenite." Inorganic Chemistry 22, 22 (1983). doi: 10.1021/ic00164a025.