Reactions of carbonyl compounds in basic solutions. Part 13. The mechanism of the alkaline hydrolysis of 3-(3-substituted phenoxy)phthalides, -3-methyl-phthalides, -3-phenylphthalides, naphthalides, -3-phenylnaphthalides, and phenanthralides, and of 3-substituted 3-methoxyphthalides

Abstract

Rate coefficients have been measured for the alkaline hydrolysis of 3-(3-substituted phenoxy)phthalides, -3-methylphthalides, -3-phenylphthalides, naphthalides, -3-phenylnaphthalides, and phenanthralides at 30.0 and 50.0 °C and for a series of methyl pseudo-2-acylbenzoates at several temperatures in 70%(v/v) dioxane–water. The enthalpies and entropies of activation have been evaluated. The effects of substitution on the phenoxy esters have been assessed by means of, the Hammett equation. The results for the methyl esters are related to the steric effect of substituents using the Taft equation. All the pseudo-esters are hydrolysed with rate-determining attack by hydroxide anion at the carbonyl group, followed by rapid ring fission to form the carboxylate anion of the corresponding acid as the product. Reactivity–selectivity is not shown over the whole range of the six series of the phenyl pseudo-esters. These results are discussed in terms of the structure of the transition state and the steric, stereochemical and polar factors influencing reactivity.