Influence of Boric Acid on the Hydrolysis Rate of a Hydroxy Schiff Base

Abstract

Abstract Effects of boric acid on the rate of hydrolysis of a Schiff base derived from α-hydroxyisobutyrophenone and 2-methoxyethylamine were examined in the pH range 4.2–10.4 at 30 °C. The rate increased above pH 7 but decreased below pH 7 with increasing borate concentration following a saturation curve. This is consistent with a reaction sequence involving a preequilibrium formation of a borate–substrate complex followed by its rate-determining decay to the hydrolysis products. The formation constant of the complex showed a bellshaped change with pH but the rate constant for the complex decay was constant above pH 7, a small change being observed at lower pH. A mechanism involving an intramolecular transfer of the boron-coordinated hydroxide ion to the imine carbon within the complex is presented. Hydrazone formation from the hydroxy ketone was also examined in the presence of boric acid.