Investigation of Carboxyl Acid Ester Hydrolyses Catalyzed by Micellar Copper(II) Oximato Complexes

Abstract

In this paper, two oximato complexes, mononuclear [Cu(Hdmg)2] and binuclear [Cu2(Hdmg)2(H2dmg)]ClO4 · H2O (H2dmg: dimethylglyoxime), were synthesized and characterized. Hydrolyses of carboxyl acid esters, p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA), catalyzed by these two complexes were investigated in different micellar systems in the pH range from 6.58–8.65 at 25°C. The results obtained indicate that these two complexes exhibit good catalytic function. It also appears that both complexes accelerate the hydrolytic cleavage of PNPP and PNPA in cationic CTAB micellar solution faster than that in nonionic Brij35 micellar solution, which may be due to the different coordinating ability of substrates to complexes and electrostatic interaction between micelles and complexes. For binuclear Cu(II), the rate constant (k N) for the hydrolysis of PNPA is about two times larger than that for PNPP in CTAB micellar solution, while in Brij35 micellar solution, the k N values for PNPA and PNPP are roughly the same. This small difference may be ascribed to the configurations of intermediates formed during the reaction and electrostatic interaction between micelles and reactants.