Tautomerism and Reactions of 1H-1,2,4-Triazole-5-thiones with Hydrazonoyl Halides
作者:Mosselhi A. N. Mosselhi、Magda A. Abdallah、Sayed M. Riyadh、Abdelhamid E. Harhash、Ahmad S. Shawali
DOI:10.1002/prac.19983400209
日期:——
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 tautomeric form namely the thione form. Reactions of 1 with hydrazonoyl chlorides 2 gave the thiohydrazides 5. Similar reaction of 3-phenyl-1H(4H)-1,2,4-triazole-5-thione 1g with 2a gave the thiohydrazide 5h which was converted into 1,3,5-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 discussed.