Hydrolysis of imines: kinetics and mechanism of spontaneous acid-, base-, and metal ion-induced hydrolysis of N-salicylidene-2-aminothiazole

Abstract

The kinetics of hydrolysis of N-salicylidene-2-aminothiazole (HL) have been investigated in aqueous 5% MeOH (I= 0.1 mol dm^–3) in the presence and absence of Co^II, Ni^II, Cu^II, and Zn^II. The solvent deuterium isotope effect on the rate of spontaneous and hydroxide-catalysed hydrolysis of the Schiff-base anion (L^–) is consistent with intramolecular catalysis by the phenoxide anion. Of all the metal ions, only copper(II) retards the rate of hydrolysis of the imine significantly. This is due to the formation of less reactive [CuL]⁺ species. Such a species, however, undergoes both spontaneous and acid-catalysed hydrolysis of the imine linkage in the pH range 4.22–5.2. The mixed-ligand complex [Zn(im)₂L]⁺(im = imidazole) is also found to be an effective catalyst. The imine linkage in [Zn(im)₂L]⁺ is hydrolysed about three times faster than that in [CuL]⁺ and L^– in the pH-independent path.