1, 2, 4-Triazoles. II. The Tautomerism of 3-α-Pyridyl-1, 2, 4-triazoline-5-thione and Its Methyl Derivatives

Abstract

Tautomerism of 3-α-pyridyl-1, 2, 4-triazoline-5-thione (I) and its methyl derivatives has been studied. The infrared spectra of these compounds indicated the presence of strong intermolecular hydrogen bonding in a solid state. Comparison of the ultraviolet (UV) spectrum of 5-methylthio-3-α-pyridyl-1, 2, 4-triazole (II) with those of the fixed compounds revealed that II exists as 2H-5-methylthio-3-α-pyridyl-1, 2, 4-triazole both in ethanol and in cyclohexane. In the same way, it was found 1-, 2-, and 4-methyl-3-α-pyridyl-1, 2, 4-triazoline-5-thiones (III, IV, and V), which are capable of existing in thione-thiol tautomerism, exist in thione form in ethanol. The parent compound I was also found by means of UV spectroscopy to exist in the thione form of 1H, 4H-3-α-pyridyl-1, 2, 4-triazoline-5-thione in ethanol.