Kinetics and mechanism of the electron transfer in [N,N′-bis(salicylidene)-1,2-ethanediamine]chromium(III) complex by N-bromosuccinimide: evidence for the catalytic effect of iron(II) ions

Abstract

Kinetics of oxidation of [N,N′-bis(salicylidene)-1,2-ethanediamine]chromium(III) complex, [Cr(L)(H2O)2]3+ (L = N,N′-bis(salicylidene)-1,2-ethanediamine, by N-bromosuccinimide (NBS) has been studied over 20–40 °C range, pH 3.0–4.2, and ionic strength 0.10–0.50 mol dm−3 for a range of [NBS] and complex concentrations. The rate of reaction was first-order dependence on both, [NBS] and [Cr(III)], and increased with pH over the range studied. It was proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of N-bromosuccinimide to chromium(III) in a step preceding the rate determining steps. The catalytic effect of iron(II) and copper(II) ions on the reaction rate have been studied over 0–5.0 × 10−4 mol dm−3. The reaction was catalyzed by iron(II) ions and the catalysis is believed to be due to the oxidation of iron(II) to iron(III) ions, which act as the oxidizing agent. Copper(II) ions have no effect on the reaction rate over the range studied.