The general procedure for the synthesis of 2-hydrazino-1H-1,3-benzimidazole was as follows: firstly, 2-bromobenzimidazole was prepared from 2-mercaptobenzimidazole according to the method reported in literature [13]. Subsequently, 2-bromobenzimidazole (1.97 g, 10 mmol) was dissolved in 20 mL of 80% hydrazine hydrate solution and reacted at reflux to obtain 2-hydrazinylbenzimidazole (1.35 g, 91% yield). Finally, diacetyl monoxime (1.01 g, 10 mmol) was added to a 20 mL methanol solution containing 2-hydrazinylbenzimidazole (1.48 g, 10 mmol) catalyzed by glacial acetic acid (3 drops). The reaction mixture was refluxed for 4 h. After cooling and filtration, the resulting white crystals were washed with cold methanol to afford the target product 2-hydrazino-1H-1,3-benzimidazole (1.6 g, 55% yield, melting point 240 °C).
