4-ACYLAMINO-4H-1,2,4-TRIAZOLES AND RELATED STRUCTURES - NEW INVESTIGATIONS OF THEIR CHEMICAL AND PHYSICOCHEMICAL PROPERTIES ASSOCIATED WITHTHEIR PARTICULAR EXOCYCLIC AMIDE FUNCTION

The acido-basic behavior of 4-acylamino-4H-1,2,4-triazoles and of the related structures, 4-acylamino-4H-1,2,4-triazolium salts, 4-acylamino -1,2,4-triazoline-3-thiones, and 4-acylamino-1,2,4-triazolin-3-ones, h as been compared. Among the triazolium salts examined, the 1-carboxyme thyl-4-phenylacetylamino derivative has been selected as a particular triazolium salt bearing two acidic centres, a carboxylic acid group an d an exocyclic amide group. This compound has been isolated in three d ifferent ionic forms corresponding to different protonation and deprot onation states of the molecule. For these compounds, IR, NMR, and X-ra y data were compared and the preferential localization site of the lab ile proton on the betainic intermediate structure has been discussed. Taking into account that deprotonation of the amide function of 4-acyl amino-4H-1,2,4-triazolium salts may introduce a negative pole in the p roximity of the strong electrophilic carbon atom in the 2-position of the ring, reactivity of different triazolium salts toward the nucleoph ilic addition of the hydride ion has been compared. In particular, 4-a cylamino-4H-1,2,4-triazolium salts free of alkyl substituent on the am ide nitrogen failed to give the corresponding 4-acylamino-DELTA2-1,2,4 -triazolines after reaction with the hydride ion, while, under the sam e conditions, the 4-N-methyl derivatives were transformed into this un usual ring system in good yields. In this case, no decrease of reactiv ity toward the nucleophilic agent was observed since, as a result of t he N-alkylation, no deprotonation of the amide group can occur in thes e alkaline experimental conditions.