Reactions in strongly basic media. Part V. The kinetics and mechanism of the alkaline hydrolysis of substituted 2-alkoxytropones

Abstract

The rate coefficients for the alkaline hydrolysis of a series of substituted 2-alkoxytropones in 40% v/v aqueous dioxan and 40% v/v aqueous dimethyl sulphoxide have been measured at 30·0°. The effect of variation of the composition of the medium and the temperature has been investigated for the hydrolysis of selected substrates. Kinetic solvent isotope and salt effects have also been studied. These measurements have also been carried out on two model systems, 3- and 4-substituted methyl benzoates and 4-substituted 1-methoxy-2-nitrobenzenes. The effects of substitution in these three systems have been assessed by linear free energy relations. The alkaline hydrolysis of the 2-alkoxytropones appears to proceed by an addition–elimination mechanism, involving a rate-determining direct attack by hydroxide anion at the 2-position.