Abstract
Application of hydrazine hydrate to 2-chloro-5-R-1, 3, 4-thiadiazoles (IV:R=H, CH3, C2H5, C3H7, and iso-C4H9) and 2-amino-5-R-1, 3, 4-thiadiazoles (VII:R=H, CH3, C2H5, C3H7, iso-C4H9, C6H5, and (p) NO2C6H4) resulted in the so-called “Triazole conversion” to form 4H-1, 2, 4-triazole-3-thiols.
1) Reaction of (IV) under drastic conditions afforded 4-amino-5-R-4H-1, 2, 4-triazole-3-thiols (VI), the amount formed decreasing with increasing number of carbon atoms in the alkyl chain at 5-position. Under mild conditions, (IV) formed 2-hydrazino-5-R-4H-1, 2, 4-triazoles, although 2-chloro-1, 3, 4-thiadiazole (IV:R=H) afforded 4-amino-4H-1, 2, 4-triazole-3-thiol even under this mild condition.
2) Compounds of (VII) series tended to be affected greatly by the nature of a substituent present in 5-position, and only the compounds (VII) with R as H, CH3, and C2H5 formed (VI), giving 4-amino-5-hydrazino-4H-1, 2, 4-triazole-3-thiol (VIII) as a by-product. In the case of (VII) with R as nitrophenyl, the nitro group was reduced during the reaction to form 2-amino-5-p-aminophenyl-1, 3, 4-thiadiazole. The starting materials were recovered in the case of (VII) with R as propyl, isobutyl, and phenyl.
3) In the case of 2-amino-5-chloro-1, 3, 4-thiadiazole and 1, 3, 4-thiadiazole-3-thiol, 4, 5-diamino-4H-1, 2, 4-triazole-3-thiol (VI:R=NH2) and (VIII) were produced, while (VIII) alone was formed from 2, 5-dichloro-1, 3, 4-thiadiazole and 1, 3, 4-thiadiazole-2, 5-dithiol.
