Revue des sciences chimiques

Mechanistic Investigation for the Acidic Hydrolysis of p-Methyl Benzyl-2-Theno Hydroxamic Acid

Abstract

S Shekhawat, SK Rajput

The rates of hydrolysis of p-Methyl Benzyl-2-Theno Hydroxamic Acid have been studied over a wide range of acidities in hydrochloric, sulphuric, and perchloric acids in 20% (v/v) dioxane-water at 55ºC. Plots of the first order rate constant, Kobs against H+ show maxima, which are caused by protonation of the substrate. The kinetics of the hydrolysis has been analyzed by Bunnett, Bunnett Olsen and Cox-Yates excess acidity methods. The variation of reaction rate with acid concentration can be described by a two parameter equation. The mechanism of the reactions was found to be A-2, which involves two steps. A rapid protonation is followed by rate determining step in which nucleophilic attack of water at the carbonyl carbon takes place giving a tetrahedral intermediate, which rapidly changes to the hydrolytic products. Arrhenius activation parameters were also determined.