Reactivity of ferrate(V) with carboxylic acids: A pre-mix pulse radiolysis study

Abstract

Rates of reduction of ferrate(VI) to ferrate(V) by a number of organic acid and ester radicals (monocarboxylic acids, dicarboxylic acids, amino acids, malonic acid esters), generated by the pulse radiolysis technique, vary from 10 7–10 9 dm 3 mol -1 s -1. The rate at which these radicals reduce ferrate(VI) depends upon the nature of the substituents at the α-carbon atom and decrease in the order α- C-NH 2>α-C-OH>α-C-H.A similar dependence upon the α-C-groups(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 dm 3 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 oxidation process is dependent on the protonation of ferrate(V). For example, in the oxidation of gluconic acid with H 2Fe VO 4 -/HF e VO 4 2-; k 10(H 2Fe VO 4 - + gluconate) = 1.1 × 10 6 dm 3 mol -1 s -1 and k 11(HFe VO 4 2- + gluconate) = 2.0 × 10 5dm 3 mol -1 s -1. The oxidation mechanisms for malate and asparate by OH radicals and ferrate(V) are compared.