TAUTOMERISM AND REACTIONS OF 1H-1,2,4-TRIAZOLE-5-THIONES WITH HYDRAZONOYL HALIDES

The acid dissociation constants (K-a) of a series of 3,4-diaryl-1H-1,2 ,4-triazole-5-thiones (1) were determined and were found to correlated Linearly with Hammett substituent constants; log K-a = 1.06 sigma(x) - 11.01. Such a result indicates that 1 exists essentially in one taut omeric form namely the thione form. Reactions of 1 with hydrazonoyl ch lorides 2 gave the thiohydrazides 5. Similar reaction of 3-phenyl-1H(4 H)-1,2,4-triazole-5-thione 1g with 2a gave the thiohydrazide 5h which was converted into 3,5-triphenyl-1,2,4-triazolo[3,4-c]-1,2,4-triazole (9). The latter was also prepared from 3-phenyl-5-methylthio-4H-1,2,4- triazole (6) and 2a. The mechanism of the reaction of 1 with 2 is disc ussed.