Hydrogen bonding abilities and self-association of some potentially bifunctional catalysts. Part 2. Mercaptoazole derivatives

Abstract

Hydrogen bonding abilities of 2-mercaptoazoles (1)–(3) towards dimethyl sulphoxide (K_A) or 4-chlorophenol (K_B) have been studied quantitatively in CCl₄ by i.r. spectroscopy at 25 °C. The N–H proton of mercaptoazoles exhibits a high tendency to hydrogen bonding (40 < K_A < 3 000 l mol^–1) which is correlated with the basicity of the 2-alkylazole analogues. The CS sulphur atom shows good hydrogen bonding ability (20 < K_B < 250 l mol^–1) which roughly parallels its nucleophilic reactivity towards methyl iodide. Knowledge of the K_A and K_B constants allows a better understanding of the factors which affect the self-association constants of mercaptoazoles (100 < K_D < 4 700 l mol^–1).