Kinetics and mechanism of electron-transfer reactions of bismuth(V) in aqueous acidic perchlorate–fluoride media. Part 1. Oxidation of hypophosphorous acid

Abstract

Solutions of bismuth(V) from NaBiO₃ have been obtained in 1.0 mol dm^–3 HClO₄ and 1.5 mol dm^–3 HF with a view to studying the redox system involving Bi^V and H₃PO₂. The reaction is first order in the concentration of each of Bi^V, H₃PO₂, and H⁺. It is catalysed by Bi^III through complex formation with the reactive species HBiF₆. The rate law (i) holds where K_p is the protonation –d[Bi^V]//_dt=(K_pk′+K_pKk[Bi^III])//_{1 +K[Bi^III])}[Bi^V][H₃PO₂][H⁺](i) constant of [BiF₆]^– and K the complex formation constant between Bi^V and Bi^III. The values of K_pk and K were found to be 0.125 ± 0.015 dm⁶ mol^–2 s^–1 and 45 ± 6 dm³ mol^–1 respectively at 35° C and I= 2.0 mol dm^–3; k′ and k are the second-order rate constants for the reaction between HBiF₆ and H₃PO₂, and the complex and H₂PO₂ respectively. Bismuth(V) does not absorb in the u.v. region but Bi ^III does, the wavelength depending on the source of Bi^III and the medium.