Transmission of polar effects. Part 17. Ionisation and esterification with diazodiphenylmethane of 5-substituted triptycene-7-carboxylic acids and the alkaline hydrolysis of their methyl esters

Abstract

The pK_a values of a series of 5-substituted triptycene-7-carboxylic acids have been measured in 80%(w/w) 2-methoxyethanol-water at 25 °C. The rate coefficients for their esterification with diazodiphenylmethane in 2-methoxyethanol have been measured at 30 °C. The rate coefficients for the alkaline hydrolysis of the corresponding methyl esters have also been determined in 70%(v/v) dioxane–water at both 30.4 and 56.3 °C. In the ionisation reaction reversed substituent polar effects were found and Kirkwood–Westheimer calculations were carried out which confirm that they arise from a field effect. The results for the esterification reaction show similar, but reduced, substituent effects. In the alkaline hydrolysis of the esters a microscopic solvent effect was noted in addition to the dipolar substituent effects.