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[CrIII(H2O) 5(OH)] T2+[IDA]/(1+Kosc[IDA]).While the kinetics of oxidation of CrIII(IDA)2(H2O)2]− by N-bromosuccinimide (NBS) in aqueous solution to chromium(VI) were carried out and obey the following equation:d[CrVI]/dt=(k4K2+k5K3K1/[H+])[CrIII(IDA) 2(H2O) 2] -[NBS].d[CrVI]/dt=(k4K2+k5K3K1/[H+])[CrIII(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).