Kinetic comparison of the relative susceptibility to steric hindrance of an intra- and an inter-molecular cleavage of the ester bond in a series of 2- and 4-carbamoylphenyl esters of 2,4,6-trialkylated benzoic acids

Abstract

The rates of intramolecular nucelophilic attack by the amide group and of intermolecular nucleophilic attack by hydroxide ion on the ester carbonyl group of a series of carbamoylphenyl esters of 2,4,6-trialkylated benzoic acids have been determined. Both the intra- and inter-molecular processes showed a closely similar response to progressive increase of steric hindrance about the ester carbonyl group. An excellent correlation of rates along both reaction series with the steric substituent constant (E_s) derived by Taft from hydrolyses of esters of aliphatic acids indicated that progressive decoupling of the aromatic ring and the ester group with increasing 2,6-substitution was negligible (except when the substituent is hydrogen).