The kinetics of the oxidation of molecular bromine by aquocobalt(III) ions in perchlorate media

Abstract

The slow rate of oxidation of molecular bromine by cobalt(III) ions is first order in both [Co^III] and [Br₂], and the bimolecular rate constant is inversely proportional to [H⁺]². This is interpreted as the reaction of a hydrolysed dimer of Co^III with Br₂, and the latter is converted into the bromate condition. At high acidity this slow reaction is followed by a very rapid oxidation initiated by the reaction of the hydroxyl radical with bromine. Evidence exists for the formation of a complex between Co^III and Br₂: the variation of optical density with [Co^III], [Br₂], and [HClO₄] suggests a 1 : 1 complex between unhydrolysed dimer and molecular bromine.