Equilibria and kinetics for p H-dependent axial ligation of alkyl(aquo) cobaloximes with aromatic and aliphatic N-donor ligands

Equilibria and kinetics of the reaction of bromomethyl(aquo) cobaloxime with histamine, histidine, glycine and ethyl glycine ester and iodomethyl(aquo) cobaloxime with cyanide, imidazole and substituted imidazoles were studied as a function ofpH at 25°C, 10 M ionic strength (KCl) by spectrophotometry technique. The rate of substitution of H₂O varies with thepKa of the incoming ligand, thus establishing the existence of nucleophilic participation of the ligand in the transition state. Dissociation kinetic reactions were also studied as a function ofpH. Binding and kinetic data were interpreted based on the basicity, steric crowd of the entering ligand and HSAB principle. To compare the rate constants of the entering ligandspH independent second-order rate constants were calculated.