KINETICS AND MECHANISM OF LIGAND SUBSTITUTION IN TRIGLYCINATOVANADIUM(III) BY EDTA AND NTA IN AQUEOUS-SOLUTIONS

The kinetics of ligand substitution reactions in triglycinatovanadium( III) by EDTA and NTA as multidentate ligands were investigated at a co nstant ionic strength of 2.5 mol dm-3 spectrophotometrically. The subs titutions were second-order reactions, first order in both reactants. Their rate could be expressed in the form r = k [V(gly)3] [EDTA(NTA)] where k = 2.62 . 10(-2) and 6.96 . 10(-2) mol-1 dm3 s-1 at 25-degrees- C for EDTA and NTA, respectively. The results obtained at different pH indicated that [H-2edta]2- and [Hnta]2- ions were the most reactive s pecies in the substitution. Kinetic parameters have been evaluated and a tentative mechanism of the reaction has been proposed.