Syntheses of a linear pentadentate ligand and its zinc(II) complex and itspromoted hydrolysis of 4-nitrophenyl acetate

A linear pentadentate ligand, N-(2-hydroxyethyl)-N "-(2-hydroxy-benzyl)-die thylenetriamine (HL), and its zinc(II) complex were synthesized and charact erized by IR spectra, H-1 NMR spectra and elemental analyses. By pH potenti ometric titration, protonation constants of HL and stability constants of Z n(II) complexation with HL have been determined at 25 +/- 0.1 degreesC 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 degreesC and I = 0.1 mol/L (KNO3) in CH3CN (10 % nu/nu) at pH 7.0-9.04 ( 50 mmol/L buffers), and the second-order rate constants k(c) for NA hydroly sis were obtained. The experimental results indicate that Zn . . . -OR (R = alkyl) is a better nucleophile than Zn . . . -OAr (Ar = aryl). A good cata lysis was realized with a k(c) value of 8.5 x 10(-2) mol(-1) . L . s(-1) at pH 9.04.