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.