Kinetics and mechanism of the reaction between chromium (III) and diethylenetriaminepentaacetic acid

Abstract

The kinetics and mechanism of complex formation between chromium (III) and diethylenetriaminepentaacetic acid (DTPA) were studied spectrophotometrically in an aqueous acid medium over the temperature range of 35-50C using large excess of the ligand. The reaction was found to be firstorder in chromium (III) concentration and zero-order in DTPA concentration. The rate of reaction showed inverse dependence on hydrogen ion concentration. Values of 104 kJ mol -1 and 14 JK -1 mol -1 were obtained for enthalpy and entropy of activations, respectively. I d mechanism has been proposed based upon the release of water molecule from the active species [Cr(H 2 O) 5 OH] 2+ in a rate-determining step. The rate law has been established to be: rate =