Non-participation of cobalt(III) in potassium bromate oxidation of malonic acid in cobalt(III)-malonato complex

Abstract

The kinetics of potassium bromate {Br(V)} oxidation of malonic acid/cobalt(III)-malonato complex in the presence of Cd(OAc)₂, used as a scavenger of Br, exhibits total second order kinetics-first order each in [oxidant] and [substrate]. This is an acid-catalysed reaction. As malonic acid, both cobalt(III) bound and unbound, gets oxidised at a comparable rate, possibly the electrostatic influence of cobalt(III) is not felt at the reaction centre. Absence of reduction at the cobalt(III) centre and absence of acrylonitrile polymerisation, rule out the possibility of the reaction occurring via a radical mechanism. The proposed mechanism involves bromate ester formation through enol form of malonic acid, which dissociates in a slow step, to yield ultimately mesooxalic acid. In the case of malonatocobalt(III) complex mesooxalatocobalt(III) complex is the product.