The kinetics and mechanism of the electrophilic substitution of heteroaromatic compounds. Part XXXVIII. Hydrogen exchange of isoxazoles and isothiazoles

Abstract

Acid-catalysed deuteriodeprotonation rates are recorded for isoxazole, isothiazole, and some methyl derivatives. The rates are extrapolated to give rate constants at 100° and pH 0 which are compared with those for other heteroaromatic ring systems to provide quantitative estimates of relative reactivity. Quantitative effects of methyl groups provide evidence for the relative degree of bond-fixation, and indicate that the aromaticity increases in the series isoxazole, pyrazole, isothiazole.