Kinetics and mechanism of catalytic carboxyester hydrolysis using Zn(II) complexes of l,3,5-tri-(N-alpha-pyridylmethylenic aminomethylenic) benzene

摘要

Zn(II) complex with a novel tripod ligand has been examined as a catalyst for the hydrolysis of 4-nitrophenyl acetate (NA).The kinetics of hydrolysis has been investigated by observing the rate of release of p-nitrophenolate ion in the buffers at 278 K and at different pH.The new ligands form a l:3(ligand:zinc) zinc complex in the pH range 7.5approx9.4.The kinetic studies have been performed using the zinc complexes in 10% (v/v) CH_3CN at 278K,I=0.10 mol·dm~(-3) KNO_3 and pH 7.5approx9.4.The results show that Zn(II) complex serves as a good nucleophile that effectively catalyzes NA hydrolysis.The hydrolysis rate follows the law v=(kappa_(obs)~(com)[complex]+kappa_(OH)[OH-]+kappa_0)[NA].The second order hydrolysis rate constant using Zn_3LH_(-1) is 0.371mol~(-1) dm~3s~(-1),which obviously is larger than the corresponding value using other Zn(II) complexes of multidentate ligands.