Decomposition of dioxalatodiaquocobaltate(III) and trioxalatocobaltate(III) in aqueous solution

Abstract

The kinetics of the decompositions of Co(C₂O₄)₂(H₂O₂)₂^– and Co(C₂O₄)₃^3– in aqueous solutions to give Co^II and CO₂ have been studied. In each case the dependence of the concentration of the Co^III complex upon time t follows an equation of the form (i) where A, B, and C are constants independent of [Co^II] or [C₂O₄^2–]. These 2·3 log[Co^III]–A/[Co^III]=–Bt+C(i), results are not consistent with mechanisms involving the formation of free-radical intermediates. For both reactions a mechanism is suggested in which the single-ended dissociation of a chelate oxalate is followed by the reaction of the intermediate so formed with a second Co^III complex ion in a three-centre redox process.

The kinetic effects of several metal cations and of other Co^III complexes upon these decompositions have been studied and are interpreted in terms of the suggested mechanism.