1-Amino-2-hydrazinobenzimidazole and its reactions with some carbonyl compounds

1-Amino-2-hydrazinobenzimidazole was obtained for the first time by treating 1-aminobenzimidazole-2-sulfonic acid with hydrazine hydrate. This compound readily condensed with aromatic aldehydes involving both amino groups. The condensation with 2,4-pentanedione affords 1-amino-2-(3,5-dimethylpyrazol-1-yl)benzimidazole, and with α-ketoacids in glacial acetic acid yields mixtures of 10-acetylamino-3-R-1,2,4-triazino4,3-a]benzimidazol-4(10H)-ones and 4-amino-2-R-1,2,4-triazino2,3-a]benzimidazol-3(4H)-ones.