Kinetics of Multidentate Ligand Substitution Reaction. III. Substitution Reactions of BT with Cobalt(II) and Nickel(II) Chelates of N-(2-Hydroxyethyl)-ethylenediamine-N,N′,N′-triacetic Acid and 2,2′-Ethylenedioxybis[ethyliminodi(acetic acid)]

BT can displace EDTA-OH and GEDTA from their cobalt(II) and nickel(II) chelate as in the case of the substitution reaction of BT with cobalt(II)-EDTA chelate or nickel(II)-EDTA chelate. In this paper, kinetics of the substitution reactions of BT with cobalt(II)- and nickel(II)-chelates of EDTA-OH and of GEDTA was studied spectrophotometrically. All substitution reactions were found to be first-order in BT and first-order in metal(II)-chelate of EDTA-OH or GEDTA, and to proceed through two simultaneous reaction paths analogous to those proposed for the substitution reaction of BT with cobalt(II)-EDTA chelate. Although EDTA-OH differs from EDTA by the presence of a hydroxyethyl group in place of one acetate group, its metal(II) chelate behaves in a nearly identical manner with EDTA chelate in the substitution reaction and the cleavage of the metal-nitrogen bond of the glycinate group is considered to be the probable rate-determining step. The substitution reactions of BT with GEDTA chelates are considered to be more favored thermodynamically over the reactions of EDTA-OH chelates, but were found to be less favored kinetically. This fact may suggest that the geometrical structure of metal(II)-GEDTA plays an important role in determining the rate of the substitution reaction of GEDTA.