4-Nitrophthalimide (1.4 g, 9.1 mmol) was suspended in an aqueous solution (30 mL) of cyanogen bromide (0.97 g, 9.2 mmol) and heated to reflux for 7 hr. Upon completion of the reaction, the reaction mixture was cooled and neutralized with 25% NH4OH solution to pH 10-11. Subsequently, the precipitate formed was collected by filtration, washed with water, dried over air, and finally recrystallized from hot water to give 2-amino-6-nitrobenzimidazole as orange-yellow shiny crystals. Yield: 1.28 g (91.4%); Melting point: 245-247 °C. 1H NMR (400 MHz, DMSO-d6, δ ppm): 8.10 (d, 1H, J = 2.2 Hz, ArH), 7.90 (dd, 1H, J = 8.70, 2.2 Hz, ArH), 7.20 (d, 1H, J = 8.7 Hz, ArH). 6.90 (s, 2H, NH2). 13C NMR (400 MHz, DMSO-d6, δ ppm): 158.91, 139.92, 136.67, 116.50, 111.16, 106.16. IR (KBr, cm-1): 3514, 3457 (NH stretching vibration), 3092 (aromatic CH stretching vibration), 1658 (C=NH stretching vibration), 1658 (C=NH stretching vibration). ), 1658 (C=N ring stretching vibration), 1587, 1507 (skeletal vibrational bands), 1421 (asymmetric N=O stretching vibration), 1471 (NH shear vibration), 1336 (symmetric N=O stretching vibration), 876 (NH wobble vibration).MS (+ESI-QTOF): m/z calculated value C7H6N4O2 [M+H]+ 179.14, measured value 179.1 (100%).
