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

Pieter Murray,Rudi Van Eldik,Klaus R Koch

doi:10.1039/c3dt53057d

Pieter Murray, Rudi Van Eldik + Show 1 more

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https://doi.org/10.1039/c3dt53057d

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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 = (k(0) + 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 H2O2 + H(+) + Cl(-) → HOCl + H2O, resulting in a rate law d[Pt(IV)]/dt = k(0)[H2O2] with a value k(0) = (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 = k(H2O2)[Pt(II)][H2O2] with the value k(H2O2) = (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.

Highlights

Oxidation of Pt(II) square-planar complexes by hydrogen peroxide has been exploited in many areas of research, as a strategy towards the design of new complexes.[1]
Hydrogen peroxide is not used in the refining industry, as part of ongoing work in this context, we examined in detail the oxidation of [PtCl4]2− by hydrogen peroxide in hydrochloric acid as a benchmark system
For oxidation of [PtCl4]2− at relatively low concentrations, [PtCl4]2− ≪ 0.5 mM, hypochlorous acid formation is faster relative to oxidation of [PtCl4]2− by hydrogen peroxide, as a result of the rate determining reaction H2O2 + H+ + Cl− → HOCl + H2O, such that the rate law d[Pt(IV)]/dt = k0[H2O2] gives the value k1 = (8 ± 2) × 10−7 s−1 at 35 °C

Summary

Introduction

Oxidation of Pt(II) square-planar complexes by hydrogen peroxide has been exploited in many areas of research, as a strategy towards the design of new complexes.[1] Many of these studies rely on the formation of hydroxido complexes by the oxidation with hydrogen peroxide, which provides more stability and control. The square-planar configuration of the original Pt(II) complex is retained furnishing a Pt(IV) product with new ligands coordinated trans to each other. Oxidation of [PtCl4]2− by hydrogen peroxide in water yields trans-[PtCl4(OH)2]2− quantitatively according to eqn (1).. Oxidation of [PtCl4]2− by hydrogen peroxide in acidic medium yields trans-[PtCl4(H2O)2], while relatively fast Pt(II) assisted ligand scrambling reactions cause a

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Conclusion