Synthesis and structure of 1-methyl-2,3-dihydro-1,2,4-triazolium salts and their free bases

1-Methyl-2,3-dihydro-1,2,4-triazolium iodides can be obtained by reacting methylhydrazones with S-methylthioamide hydriodides, by condensing 2-methylamidrazone hydriodides with aldehydes and ketones, or by reacting methyl iodide with 1-alkylidene (or arylidene)benzamidrazones. In solutions these salts are capable of undergoing tautomerism to 1-alkylidene(or arylidene)-2-methylamidrazone hydriodides. The influence of the structural factors on the position of the tautomeric equilibrium has been studied. The free bases obtained by neutralization of the respective salts by an alkali metal hydroxide are heretofore undescribed 1-alkylidene(or arylidene)-2-methylhydrazidoimines or 4-triazolines, depending on their structure. Under the action of oxygen, these compounds are readily oxidized to substituted 1-methyl-1,2,4-triazoles with heating.Translated from Khimiya Geterotsiklicheskikh Soedineniii, No. 10, pp. 1415–1421, October, 1984.