SYNTHESES OF A LINEAR PENTADENTATE LIGAND AND ITS ZINC(II) COMPLEX AND ITS PROMOTED HYDROLYSIS OF 4-NITROPHENYL ACETATE

摘要

A linear pentadentate ligand, N-(2-hydroxyethyl)-N"-(2-hydroxybenzyl)-diethylenetriamine (HL), and its zinc(II) complex were synthesized and characterized by IR spectra, ~1H NMR spectra and elemental analyses. By pH potentiometric titration, protonation constants of HL and stability constants of Zn(II) complexation with HL have been determined at 25 +- 0.1 deg C and I = 0.1 mol/L (KNO_3). The kinetics of 4-nitrophenyl acetate (NA) hydrolysis catalyzed by the complex was determined spectrophotometrically at 25 +- 0.1 deg C and I = 0.1 mol/L (KNO_3) in CH_3CN (10 percent v/v) at pH 7.0-9.04 (50 mmol/L buffers), and the second-order rate constants k_c for NA hydrolysis were obtained. The experimental results indicate that Zn… ~-OR (R=alkyl) is a better nucleophile than Zn… ~-OAr (Ar=aryl). A good catalysis was realized with a k_c vale of 8.5 X 10~(-2) mol~(-1) centre dot L centre dot s~(-1) at pH 9.04.