Reactions of carbonyl compounds in basic solutions. Part I. The alkaline ring fission of coumarins

Abstract

Rate coefficients have been measured for the alkaline ring fission of substituted coumarins in 70 % v/v dioxan–water at several temperatures by a conductimetric method. The enthalpies and entropies of activation have been evaluated. The proton nuclear magnetic resonance spectra of the coumarins and the reaction products have been investigated. The mechanism of the reaction has been further elucidated. Substituent effects have been correlated by means of a modified Hammett equation. This indicates transmissive contributions via the ethylenic and oxygen links, similar to those observed for the hydrolysis of substituted cinnamates and phenyl esters, respectively.