THE REACTION OF NITROUS ACID WITH 4-SUBSTITUTED-THIOSEMICARBAZIDES

The reaction of nitrous acid with 4-alkyl- or 4-aryl-thiosemicarbazides, as well as the reaction of alkyl- or aryl-isothiocyanates with hydrazoic acid, leads to the identical 5-(substituted)amino-1,2,3,4-thiatriazole. This has been established by infrared absorption and chemical degradation studies. The reaction of the 5-(substituted)amino-1,2,3,4-thiatriazoles with aqueous bases leads to two competitive reactions: (1) degradation to an isothiocyanate and azide ion, and (2) isomerization to a 1-substituted-tetrazole-5-thiol, the extent of path (1) or (2) depending on the nature of the substituent. Path (1) predominates when the substituent is alkyl, whereas when the substituent is aryl both paths (1) and (2) occur, the relative proportion depending on the electrical nature of the aromatic group, path (2) increasing as the electronegativity increases. The 1-aryl-tetrazole-5-thiols were found to be thermally unstable at their melting points, degrading more or less violently to one mole proportion of pure nitrogen with the formation of sulphur and organic products of lower melting point as yet unidentified. Theories to account for these observations are presented and discussed.