REACTIVITY OF FERRATE(V) WITH CARBOXYLIC-ACIDS - A PRE-MIX PULSE-RADIOLYSIS STUDY

Rates of reduction of ferrate(VI) to ferrate(V) by a number of organic acid and ester radicals (monocarboxylic acids, dicarboxylic acids, am ino acids, malonic acid esters), generated by the pulse radiolysis tec hnique, vary from 10(7)-10(9) dm3 mol-1 s-1. The rate at which these r adicals reduce ferrate(VI) depends upon the nature of the substituents at the alpha-carbon atom and decrease in the order alpha-C-NH2 > alph a-C-OH > alpha-C-H. A similar dependence upon the alpha-C-group(s) has been observed for the oxidation of the parent organic acid by ferrate (V), for which the rate constants vary from 10(1)-10(6) dm3 mol-1 s-1. An oxidation mechanism is being proposed in which ferrate(V) oxidizes the carboxylic acid by a two-electron process. The rate of the oxidat ion process is dependent on the protonation of ferrate(V). For example , in the oxidation of gluconic acid with H2FeVO4-/HFeVO42-; k10(H2FeVO 4- + gluconate) = 1.1 x 10(6) dm3 mol-1 s-1 and k11(HFeVO42- + glucona te) = 2.0 x 10(5) dm3 mol-1 s-1. The oxidation mechanisms for malate a nd aspartate by OH radicals and ferrate(V) are compared.