N-(Hydroxybenzyl)benzamide Derivatives: Aqueous pH-Dependent Kinetics and Mechanistic Implications for the Aqueous Reactivity of Carbinolamides.

Abstract

The rate constants for the aqueous reaction, between pH 0 and 14, have been determined for a series of amide substituted N-(hydroxybenzyl)benzamide derivatives, in H2O, at 25 °C, I = 1.0 M (KCl). The N-(hydroxybenzyl)benzamide derivatives were found to react via three distinct mechanisms with the kinetically dominant mechanism being dependent on the pH of the reaction solution. It has been shown that the carbinolamides react via a specific-base-catalyzed mechanism (E1cB-like) under basic and pH neutral conditions. At lower pH values, an acid-catalyzed mechanism was kinetically dominant and, last, a water reaction was postulated at pH values where neither the hydroxide-dependent nor the general-acid-catalyzed mechanism was dominant. Contrary to earlier studies with N-(hydroxymethyl)benzamide compounds, no evidence for mechanistic variation based upon the nature of the amidic substituent was observed for any of the N-(hydroxybenzyl)benzamide derivatives studied between pH values of 0-14. The rate for the acid-catalyzed reaction (kH, ρ = -1.17), the apparent second-order hydroxide rate constant (k1', ρ = 0.87), the hydroxide-independent rate (k1, ρ = 0.65), and the pKa's of the hydroxyl group of the carbinolamide (ρ = 0.23) are reported.