Transmission of polar effects. Part 18. Ionisation and esterification with diazodiphenylmethane of a series of 3-(8-substituted-1-naphthyl)propiolic and (E)-3-(8-substituted-1-naphthyl)acrylic acids and the alkaline hydrolysis of the methyl esters of the former series

Abstract

The pK_a values of 3-(1-naphthyl)propiolic acid, together with the 8-bromo- and 8-chloro-substituted derivative, and of (E)-3-(1-naphthyl)acrylic acid, together with the 8-bromo- and 8-chloro-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 propiolates have been determined in 70%(v/v) dioxane–water at both 30.0 and 50.1 °C. In the ionisation and esterification reactions, reversed dipolar substituent effects were observed. The ΔpK_a values are quantitatively accounted for either by comparison with the results for simple model compounds or by Kirkwood–Westheimer calculations. The retardations observed for the effect of 8-halo substituents in the alkaline hydrolysis reaction are in agreement with a reversed dipolar effect and no steric ‘bulk’ effects are observed.