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 pKa 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 ΔpKa 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.