Metal Ion Chelates of Lipophilic Alkyl Diazinyl Ketoximes as Hydrolytic Catalysts

Abstract

A series of lipophilic dodecyl hetaryl ketoximes (hetaryl = pyridin-2-yl, pyridazin-3-yl, pyrimidin-2-yl, pyrimidin-4-yl, pyrazin-2-yl as well as their methyl hetaryl homologues was synthesized and hydrolytic activity of their chelates with Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ in a micellar matrix of hexadecyltrimethylammonium bromide or in homogeneous aqueous solutions was investigated using 4-nitrophenyl acetate, 4-nitrophenyl hexanoate and 4-nitrophenyl diphenyl phosphate as model substrates. While Co 2+ and Cu 2+ chelates are almost inactive, those of Ni 2+ and Zn 2+ exhibit considerable activity. None of the studied chelates promotes hydrolysis of the used phosphate. The effective species are chelates of the metal : ligand stoichiometry 1 : 3 and 1 : 1 with Ni 2+ and Zn 2+ , respectively, when the ester cleavage proceeds in the micellar matrix. The 1 : 2 stoichiometry was found in aqueous solutions of Ni 2+ and Zn 2+ chelates of methyl ketoximes.