Abstract
Mechanism of the oxidation of [Cr-III(DPA)(OX)(H2O)] (-aEuro parts per thousand) (DPA = dipicolinate and OX = oxalate) by periodate in aqueous acidic medium has been studied spectrophotometrically over the pH range of 4.45-5.57 at different temperatures. The reaction is first order with respect to both and the complex concentration, and it obeys the following rate law:
d[Cr-VI]/dt = k(6)K(4)K(6)[IO4-][Cr-III](T)/{([H+] + K-4) + (K-5[H+] + K6K4)[IO4-]}.
The rate of the reaction increases with increasing pH due to the deprotonation equilibria of the complex. The experimental rate law is consistent with a mechanism in which the deprotonated form [Cr-III(DPA)(OX)(OH)](2 -aEuro parts per thousand) is more reactive than the conjugated acid. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of to chromium(III). Thermodynamic activation parameters were calculated using the transition state theory equation.