1. Cyanogen bromide solution (5.0 mL, 5 M in acetonitrile, 25 mmol) was slowly added to a suspension in water (50 mL) containing methyl 3,4-diaminobenzoate (3.0 g, 18 mmol).
2. The reaction mixture was stirred overnight at room temperature.
3. Upon completion of the reaction, ammonia (20 mL) and ethyl acetate (100 mL) were added to the mixture and mixed thoroughly to separate the organic and aqueous layers.
4. The organic layer was dried with anhydrous sodium sulfate, filtered to remove the desiccant, and the organic phase was subsequently concentrated under reduced pressure.
5. 2 N aqueous hydrochloric acid (18 mL, 36.0 mmol) was added to the concentrated crude product and the mixture was heated to reflux and the reaction continued overnight.
6. At the end of the reaction, the reaction mixture was concentrated under reduced pressure to afford 2-amino-1H-benzo[d]imidazole-5-carboxylic acid (2.90 g, 97% yield).
7. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 2H), 7.84 (s, 1H), 7.77 (dd, J = 1.2, 8.4 Hz, 1H), 7.38 (d, J = 8.4 Hz, 1H).
