Kinetics of the reduction of platinum(IV) by tin(II) and copper(I) in aqueous chloride solutions

Abstract

Rate constants for the Pt^IV+ Sn^II and the Pt^IV+ Cu^I redox reactions have been measured under various conditions using spectrophotometric and amperometric methods respectively. Rate equations (i) and (ii) describe the data for –d[Pt^IV]/dt=k_obs.[Pt^IV][Sn^II](i), –d[Cu^I]//_dt=2k₁k₂[Pt^IV][Cu^I]²//_{k–1[Cu^II]+K2[Cu^I]}(ii) the two reactions. The rate of reduction of Pt^IV by Sn^II is much faster than the rate of formation of the 1 : 1 complex between Pt^II and Sn^II. The rate of reduction by Sn^II varies linearlywith increasing chloride concentration in nitrate and sulphate solutions. A possible explanation is offered for the higher rates in perchlorate solutions. The data for the Pt^IV+ Cu^I system indicate that the reaction proceeds via an intermediate containing Pt^III, but there is no evidence for the formation of Pt^III in the reduction of Pt^IV by Sn^II. The mechanisms for both reactions are discussed in terms of complementary and non-complementary processes.