Effect of solvent on the reaction of coordination complexes. Part 26. Kinetics of solvolysis of trans-(chloro)bis(ethylenediamine)(glycinato-O)cobalt(III) in methanol + water and propan-2-ol + water: delineation of preferential solvation

Abstract

The solvolysis of trans-(chloro)bis(ethylenediamine)(glycinato-O)cobalt(III) has been studied in methanol + water and propan-2-ol + water at 50.0 ± 0.1°C. The product, (glycinato-N,-O)bis(ethylenediamine)cobalt(III) species has resulted via the formation of trans-(aqua)(glycinato-O) bis (ethylenediamine)cobalt(III) intermediate. The rate constant for chloride release obeys first order kinetics and decreases with the increase of the mol fraction of the co-solvent (Xorg) ; the dependencies of log ks with 10²/DS (Ds is the bulk dielectric constant), Xorg and the solvent ionizing power (Y) have all been nonlinear and co-solvent specific. The variation of rate constant with Xorg can be interpreted satisfactorily on a preferential solvation model proposed earlier. The dependence of pK (the dissociation of the protonated amine function) on XPriOH also conforms to the results on the rate constants that hydrophobic interaction controls the rate and equilibria. However, there is no change in the intimate mechanism of the chloride substitution at cobalt(III) centre.