Abstract The reaction of benzoyl isothiocyanates and methoxycarbonyl isothiocyanate with 4- amino-4, 5-dihydro-3-(methylthio)-1, 2, 4-triazin-5-ones in acetonitrile gave several substituted 4H-1, 3, 4-thiadiazolo [2, 3-c]-1, 2, 4-triazin-4-ones VIa-h instead of the expected thioureas. In addition, benzoyl isothiocyanate reacted with 4-amino-3-(methylthio)-5- (trifluoromethyl)-4H-1, 2, 4-triazole to give the benzoyl thiourea IX and with 4-amino-3- ...