Enhanced Hydrolysis of Carboxylic Acid Esters Catalyzed by Metallomicelles Made of Cu(II) and Zn(II) Complexes

摘要

Rate enhancement for hydrolysis of p-nitrophenyl picolinate (PNPP) and p-nitrophenyl acetate (PNPA) at 25 deg C in the pH range 6.5-8.5 have been measured kinetically in the presence of Cu(II) and Zn(II) complexes of substituted long alkyl pyridine ligand (L) under buffered co-micellar conditions with cationic surfactant CTAB. The results indicate that the activated ligand hydroxyl group can act as effective nucleophilic species in the reactions, and the complexes, especially that with Zn(II), effectively catalyze the hydrolysis of PNPP, which can be explained by the higher nucleophilicity of alkoxyl anion in Zn(II) complex than that in Cu(II) complex. A ternary complex kinetic model involving metal in, ligand, and substrate and a bimolecular micellar reaction model have been proposed for the catalytic hydrolysis of PNPP and PNPA, respectively. Relative kinetic and thermodynamic parameters have been obtained, and the results confirmed the reasonability of such kinetic models.