Kinetics of reduction of gold(III) by platinum(II) and iron(III) in aqueous chloride solutions

Abstract

Rate constants for the gold(III)–platinum(II) and the gold (III)–iron(II) redox reactions in aqueous chloride solutions have been measured under various conditions using spectrophotometric and amperometric methods respectively. There is no evidence for the formation of gold metal at short times (1–2 h) after mixing of dilute solutions of the reactants. The data for the reduction of Au^III by Pt^II are consistent with a mechanism requiring a complementary two-electron transfer, whereas the data for reduction by Fe^II indicate that the reaction proceeds via the formation of an intermediate containing Au^II. For the gold(III)–iron(II) reaction the data for the dependence of the rate on chloride concentration have been interpreted in terms of a mechanism consisting of parallel paths involving Fe²⁺ and [FeCl]⁺. A value for the dissociation constant of HAuCl₄ has been computed from the data for the hydrogen-ion dependence of the rate of this reaction.