OXIDATION OF NICKEL(II) ETHYLENEDIAMINETETRAACETATE BY CARBONATE RADICAL

Reactions of the carbonate radical (CO3.-), generated by photolysis or by radiolysis of a carbonate solution, with nickel(II) ethylenediaminetetraacetate [Ni(II)(edta)]2- were studied at pH 11.4 and ionic strength (I) = 0.2 mol dm-3. Time-resolved spectroscopy and kinetics for the transients were studied using flash photolysis whereas the stable products arising from ligand degradation of the complex were ascertained by steady-state radiolysis experiments. From the kinetic data it is suggested that CO3.- reacts initially with [Ni(II)(edta)]2- to form a five-co-ordinated Ni(III) species [k = (4.5 +/- 0.4) x 10(7) dm3 mol-1 s-1] which undergoes aquation with a first-order rate constant of (1.1 +/- 0.3) x 10(3) s-1 to give [Ni(III)(edta)(H2O)]-. The latter reacts with iodide with a rate constant of (5.5 +/- 0.4) x 10(5) dm3 mol-1 s-1. At the alkaline pH used [Ni(III)(edta)(H2O)]- undergoes transformation to give a radical intermediate which reacts with [Ni(II)(edta)]2- to give ligand degradation products of which glyoxylic acid and formaldehyde were detected.