Syntheses and Ring Closure Reactions of 1-Aryl-4-acylsemicarbazides

Abstract

Benzoyl, phenylacetyl, 2-furoyl, 2-thenoyl, is ophthaloyl and terephthaloyl isocyanates reacted with phenylhydrazine, giving the corresponding 1-phenyl-4-acylsemicarbazides quantitatively. The treatment of the above semicarbazides with aqueous hydrochloric acid or aqueous potassium hydroxide afforded the corresponding 3-hydroxy-1, 2, 4-triazoles in good yields. On the other hand, the thermal ring closure of the semicarbazides gave quantitatively the corresponding 1H-2, 3-dihydro-1, 2, 4-triazol-3-ones.
In the thermal ring closure of 1-(p-substituted phenyl)-4benzoylsemicarbazides which were obtained fr the reaction-of benzoyl isocyanate with p-substituted phenylhydrazines, however, the corresponding 3-hydroxy-1, 2, 4-triazole or 1H2, 3-dihydro-1, 2, 4-triazol-3-one, or both were formed the relative amount of the triazoles depending on the nature of the substituent. The reaction course of the thermal ring closure was briefly discussed.