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

Abstract

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°C and I = 0.1 mol/L (KNO₃). The kinetics of 4-nitrophenyl acetate (NA) hydrolysis catalyzed by the complex was determined spectrophotometrically at 25 ± 0.1°C and I = 0.1 mol/L (KNO₃) in CH₃CN (10 % 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 value of 8.5 × 10⁻² mol⁻¹ · L · s⁻¹ at pH 9.04.

Acknowledgments