Mechanism of tetrachloroplatinate(ii) oxidation by hydrogen peroxide in hydrochloric acid solution

Abstract

Oxidation of tetrachloroplatinate(ii) by hydrogen peroxide in hydrochloric acid was studied by UV-Vis spectrophotometry. Oxidation takes place via two parallel reactions with hypochlorous acid and hydrogen peroxide, respectively, according to the overall rate law d[Pt(iv)]/dt = (k0 + k H2O2[Pt(ii)])[H2O2]. For oxidation of [PtCl4]2- at relatively low concentrations, [PtCl4]2- ≪ 0.5 mM, hypochlorous acid formation is fast relative to the oxidation of [PtCl4]2- by hydrogen peroxide, as a result of the rate determining reaction H2O 2 + H+ + Cl- → HOCl + H2O, resulting in a rate law d[Pt(iv)]/dt = k0[H2O2] with a value k0 = (8 ± 2) × 10-7 s -1 at 35 °C. For concentrations of [PtCl4] 2- > 0.5 mM, oxidation by hydrogen peroxide becomes dominant, resulting in the pseudo-first order rate law d[Pt(iv)]/dt = kH2 O2[Pt(ii)][H2O2] with the value kH2O2 = (1.5 ± 0.1) × 10 -2 M-1 s-1 at 35°C. The final oxidation product is a mixture of [PtCl5(H2O)]- and [PtCl6]2-, with [PtCl6]2- formed as a result of [PtCl4]2- assisted chloride anation reactions. This journal is © the Partner Organisations 2014.