Kinetics of the axial ligation of aquocobaloximes in the presence of cetyltrimethylammonium acetate micelles

Abstract

The kinetics of the axial ligation of trans-Co(DH)₂(R)(H₂O), where R = NO₂, I, SO₃ or CH₃ and DH is dimethylglyoxime anion, by anionic (NCS^–, Br^–) or neutral (pyridine, benzimidazole) ligands was investigated in the presence of hexadecylammonium acetate micelles using the stoppedflow method or conventional spectrophotometry. Notable accelerations induced by micelles were observed in the reactions between NCS^– and the complexes trans-CO(DH)₂(I)(H₂O) and trans-CO(DH)₂(SO₃)(H₂O)^–. The competition between negatively charged reactants for positively charged micelle surface was manifested in the reaction kinetics in the latter case. In view of this effect, the theory of ionic reactions in micellar systems is discussed. The binding constants of reactants as well as the ratios of true rate constants in the micellar pseudo-phase (k^m₁) and in the aqueous solution (k^b₁) were estimated. Since k^m₁/k^b₁ 1 in all cases, it is concluded that the catalytic micellar effects are due to increasing concentrations of reactants in the micellar pseudo-phase.