Kinetics and mechanism of the formation and oxidation of iminodiacetato–chromium(III) complex

The kinetics of formation of chromium(III)–iminodiacetic acid complex have been studied spectrophotometrically in the temperature range 35–55 ˚C. The reaction is first order with respect to chromium(III) and the rate of reaction increases with increasing of pH. The kinetics of formation obeys the rate law: Rate = kcKosc[Cr^III(H2O)5(OH)]^2+ T [IDA]/=(1 + Kosc[IDA]).While the kinetics of oxidation of Cr^III(IDA)2(H2O)2]^- by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) were carried out and obey the following equation: d[Cr^VI] dt= (k4K2 + k5K3K1/[H^+])[Cr^III(IDA)2(H2O)2]^-[NBS].Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of NBS to chromium(III).