Kinetics and Mechanism for Oxidation of Tetracyanoplatinate(II) by Chlorine and Hypochlorous Acid and for Hydrolysis of Chlorine in Aqueous Solution

Oxidation of Pt(CN)42- in aqueous solutions of chlorine has been followed by stopped-flow spectrophotometry. For pH less than ca. 7, the reaction takes place by two parallel paths with Cl2 and HOCl as oxidants. Rate law determined. In unbuffered solutions of chlorine in aqueous NaClO4, the slow HOCl path is predominant, whereas in weakly acidic solutions buffered with HCl, oxidation takes place via the five orders of magnitude faster Cl2 path. For certain conditions, the displacement of the hydrolysis equilibrium of chlorine becomes rate-determining for the oxidation of Pt(CN)42- by chlorine, which then appears to be zero order in complex. Equilibrium and rate constants determined. Oxidation by HOCl gives primarily trans-Pt(CN)4(OH)22-, which rapidly reacts with a second molecule of HOCl to form a stable hypochlorite complex. Oxidations with HOCl and ClO- are inner-sphere two-electron transfers with the oxygen of the hypochlorite as bridging atom.