Transmission of polar effects. Part 15. Ionisation and esterification with diazodiphenylmethane of [2.2]paracyclophane-4-carboxylic acid and its pseudo-bromo-substituted derivatives, and the alkaline hydrolysis of their methyl esters

Abstract

The pK_a values of [2.2]paracyclophane-4-carboxylic acid and its four pseudo-bromo-substituted derivatives have been determined in 80%(w/w) 2-methoxyethanol–water at 25°C. The rate coefficients for the esterification of these acids with diazodiphenylmethane have been measured in 2-methoxyethanol at 30°C. The rate coefficients for the alkaline hydrolysis of the corresponding methyl esters have been determined in 70%(v/v) dimethyl sulphoxide–water at both 56.3 and 76.3°C. In the ionisation and esterification reactions both normal and reversed substituent polar effects were detected. Kirkwood–Westheimer calculations were carried out for the ionisation reaction and account for ΔpK_a values both qualitatively and (for the pseudo-ortho-, -meta-, and -para-isomers) quantitatively. In the alkaline hydrolysis of the esters, significant steric retardation was observed for the pseudo-gem-isomer.