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

摘要

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 AuIII by PtII are consistent with a mechanism requiring a complementary two-electron transfer, whereas the data for reduction by FeII indicate that the reaction proceeds via the formation of an intermediate containing AuII. 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.