The mechanism of the chloride- and bromide-catalysed disproportionation of the µ-amido-µ-peroxo-bis{bis(ethylenediamine)cobalt(III)} complex in aqueous solutions

Abstract

Details of experiments relating to the mechanism of the chloride- and bromide-catalysed disproportionation of the peroxo-dicobalt complex (en)₂Co·µ(NH₂,O₂)·Co(en)₂³⁺ at temperatures in the range 10–25°, and in aqueous perchloric acid media, µ 3·0M(LiClO₄), are considered. In the chloride-catalysed reaction, with [Cl^–]= 0·02–2·0M the overall change is: [graphic omitted] where the amido-hydroxo-bridged complex which is formed is in equilibrium with the aquo-chloro-complex: [graphic omitted] Yields of the superoxo-complex are generally between 60 and 66%, in accordance with (i). In the bromide-catalysed reaction, with [Br^–]= 0·1–1·0M, similar reactions are effective but yields of the superoxo-complex are generally much smaller and in some cases less than 15%. Hypochlorous and hypobromous acids are believed to be formed as intermediates in the reactions. Low yields which are observed with bromide ions can be explained by considering the equilibrium: H⁺+ Br^–+ HOBr ⇌ H₂O + Br₂(aq)(K 1·7 × 10⁸ mole^–2|2). The reaction of hypobromous acid with the peroxo-complex may be slower than that of hypochlorous acid.