Carboxylato bound chromium (V ) oxidation of potassium hexachloroiridate(lll) & potassium tetrachloroplatinate(ll)

Abstract

Carboxylato bound chromium(V) oxidises hexachloroiridate(IlI) in acetate-acetic acid buffer at <i>p</i>H 4.1 and 30 ± 0.2°C. The reaction proceeds via the formation of a highly absorbing species whose formation and decay have been studied. Under the same conditions, the reaction between potassium tetrachloroplatinate( ill) and oxochromate(V) exhibits total second order kinetics-first order with respect to each reactant. As Ir(Ill) forms a complex with the unbound ligand, the rate of reduction of Cr(V) increases with increase in [unbound carboxylic acid] and in contrast, the added carboxylic acid has little effect on Cr(V)-Pt(II) reaction. As 1 mol of Cr(V) needs 2 mol of Ir(III), the precursor complex formed between Cr(V) and Ir(Ill) through a chloro bridge, possibly undergoes 1 electron transfer in the slow step. The chromium(IV) complex in the second stage induces electron transfer in mandelatopentaamminecobalt(lll) complex, yielding cobalt(ll). Although 1mol of Cr(V) oxidises 1mol of Pt(II), in the presence of mandelatopentaamminecobalt (III) complex, 1 mol of Cr(V) oxidises about 0.70 mol of Pt{II) yielding about 40% of cobalt(II), indicating the formation of intermediate chromium(IV) in this reaction also.