Kinetics and mechanism of the silver(I)-catalyzed oxidations of arsenic(III) and antimony(III) with peroxodiphosphate in acetate buffers

Abstract

A kinetic study of the silver(I)-catalyzed oxidations of As^III and Sb^III with peroxodiphosphate (pdp) was performed by estimating As^III and Sb^III with permanganate. The oxidation of As^III was found to conform to the rate law (i) in the range pH 2.10—4.52, where K₂ and K₃ are the acid-dissociation –d[As^III]/dt=[pdp][As^III][Ag^I](k₁K₂^–1[H⁺]²+k₂[H⁺])/([H⁺]+K₃)(i), constants of H₃P₂O₈^– and H₂P₂O₈^2–; k₁/K₂ and K₂ were found to be (5.0 ± 0.2)× 10⁴ dm⁹ mol^–3 s^–1 and 38 ± 3 dm⁶ mol^–2 s^–1 at 50 °C. The oxidation of Sb^III was first order in [Sb^III], [pdp], and [Ag^I], and independent of pH, [acetate], and [tartrate]; the third-order rate was found to be 18 ± 1 dm⁶ mol^–2 s^–1 at 50 °C in the range pH 3.00—4.61. The silver(I) catalysis operates through complex formation of pdp and Ag^I rather than Ag^I/Ag^III redox cycling.