Kinetics of reactions in heterocycles. Part X. Reactions of substituted N-methylpyridinium salts with hydroxide ions

Abstract

Kinetics of the reactions of halogeno-, methoxy-, methylthio-, and methylsulphonyl-substituted N-methylpyridinium salts with hydroxide ions have been determined. The salts with the leaving group in the 2-position were the most reactive: e.g. the k₂ values for 2-, 3-, and 4-methoxypyridine methiodides at 20° were 2·9 × 10^–2, 5·0 × 10^–9, and 7·6 × 10^–4 l mol^–1 s^–1, respectively. Quaternisation of 4-methylsulphonylpyridine by methylation increased its reactivity to hydroxide ions by 7·3 × 10⁸-fold at 20°, owing to a decrease in energy of activation of 7·1 kcal mol^–1, and an increase in log A 3·5 units. U.v. and ¹H n.m.r. spectra are recorded and discussed.