Kinetics and mechanism of the reaction between 4-t-butylphenolate anion and tetrahydroxoargentate(III) in aqueous alkaline media

Abstract

The reaction of [Ag(OH)₄]^– with 4-t-butylphenolate (L^–) follows a biphasic absorbance change, each phase exhibiting pseudo-first-order kinetics under limiting conditions of the silver(III). A subsequent, slow, and very small absorbance increase (t_0.5 > 1 h) is accompanied by the precipitation of metallic silver. In the [L^–] range 0.5 × 10^–3– 10 × 10^–3 and [OH^–] range 0.12–1.2 mol dm^–3 at 25 °C and in aqueous medium, the pseudo-first-order rate constant for the initial, faster phase, K_f(in s^–1), corresponds to the first one-electron transfer from L^– to the initial silver(III) species and obeys the relation (i). The pseudo-first-order rate constant for the second, k_f=(0.330 ± 0.09)+(1.26 ± 0.09)× 10³[L^–]+(2.64 ± 0.28)× 10²[L^–]/[OH^–](i), slower phase, K_s(in s^–1), represents the second one-electron transfer from L^– to an intermediate silver(II) species produced as a result of the first one-electron transfer and satisfies an [OH^–]-independent expression (ii). The k_f and k_s values are not influenced by the ionic strength (0.3–1.2, k_s=(1.46 ± 0.02)× 10²[L^–]/{1 +(56.0 ± 3.5)[L^–]}(ii) mol dm^–3) of the medium nor by the presence of added pyrophosphate or silver(I) ions. Kinetic and spectral results are interpreted as suggesting that each of the processes mentioned most probably proceeds by a substitution-controlled mechanism at the silver centre.