2-Aminobenzimidazole [934-32-7-A] C7H7N3
2-Aminobenzimidazole is an important building block in synthetic chemistry, for example in the production of pesticides. It can be obtained by ring closure of 1,2-phenylenediamine with bromocyan. As an alternative to the hazardous bromocyan, the more accessible cyanamide is used in the following procedure.
Procedure: In a 250-ml three-neck round-bottom flask, place 54.1 g (0.50 mol) of 1,2-phenylenediamine and 15 ml of concentrated hydrochloric acid. Equip the flask with a Dimroth condenser, dropping funnel, and thermometer (0 to 200 °C). Heat the mixture in an oil bath to boiling. Then, add 23.1 g (0.55 mol) of a 50% aqueous cyanamide solution dropwise from the dropping funnel within 20 minutes. Subsequently, heat for one hour in the oil bath at 100 °C. After this time, remove the dropping funnel and replace it with an adapter NS 14/23 to hose connection. Attach a PE hose that leads into the fume hood. Then add 14 ml of concentrated sodium hydroxide solution to the reaction mixture and heat until ammonia evolution ceases. The residue of 2-aminobenzimidazole is filtered off and washed with water until chloride-free. After drying in a drying oven at 100 °C, 61.3 g of 2-aminobenzimidazole is obtained as light brown crystalline flakes. The yield corresponds to 91% of the theoretical amount. The melting point of the product is 228-229 °C.
Source: S. Weiss, H. Michaud, H. Prietzel, H. Krommer, Angew. Chem., 85 (19), 1973, p. 866-867
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Last updated: 29/09/2006
Other names: 2-Amino-benzimidazole; 2-AB; 2-Amino-1H-benzimidazole; 2-Aminobenzimidazole; 1H-Benzimidazol-2-amine; 2-Benzimidazolamine; 1H-Benzimidazol-2-ylamine; 2-Benzimidazolylamine; 2-Iminobenzimidazoline; NSC 27793; NSC 7628