Mechanism of the formation of 1,2,4-thiadiazoles by condensation of aromatic thioamides and of N-substituted thioureas

The condensation reaction of thiobenzamide, (as well as thionicotinamide an d isothionicotinamide) in the presence of dimethyl sulfoxide and of an acid , affords 3,5-diphenyl-1,2,4-thiadiazole, Under the same experimental condi tions, N-substituted thioureas are also condensed to 1,2,4-thiadiazole deri vatives; their structure is ascertained by spectroscopic properties and by X-ray diffraction. Some information on the mechanism of thiadiazoles format ion from both starting classes of compounds, thiobenzamides and N-substitut ed thiourea, is collected and discussed.