Reactivity of ferrate(V) with aminopolycarboxylates in alkaline medium: A premix pulse radiolysis

A premix pulse radiolysis technique was used to study the reaction between Fe(V) and APCs. Fe(V) reactions with glycine, IDA, NTA, EDTA and DTPA were measured at pH 12.5. Spectral results showed that Fe(V) is reduced to Fe(III); therefore, the reaction of Fe(V) with APCs proceeds via a concerted two-electron oxidation, which converts Fe(V) to Fe(III). The rate law for the oxidation of these APCs by Fe(V) is first-order with respect to each reactant at this pH. Fe(V) reactivity with APCs at pH 12.5 was found to increase in the order of tertiary < secondary < primary and vary from 1.6 × 102 M−1 s−1 to 1.4 × 104 M−1 s−1. Both EDTA and DTPA reacted faster than NTA with Fe(V) and Fe(VI). The order of reactivity of amines with Fe(V) suggests that FeO 4 3 - attacks at the nitrogen atom sites of the APCs, which leads to large differences in the rate constants. In addition, Fe(V) is approximately three- to five-orders of magnitude more reactive than Fe(VI). The reaction of Fe(V) with EDTA was studied as a function of pH (9.0–12.5). The rate constants increased as the pH decreased. The speciation of EDTA and Fe(V) were used to fit the data.