General procedure for the synthesis of 4-bromo-3-nitrobenzonitrile from 4-bromobenzonitrile: To a concentrated solution of 4-bromobenzonitrile (4.0 g, 22 mmol) was added concentrated sulfuric acid (10 mL) and nitric acid (6 mL) slowly and dropwise at 0 °C. The reaction mixture was kept stirred at 0 °C for 30 min, then warmed up to room temperature and continued stirring for 2.5 h. The reaction was carried out at room temperature. Upon completion of the reaction, the mixture was slowly poured into ice water. The resulting white precipitate was collected by filtration and washed with water until the washings were neutral. The resulting solid was recrystallized twice by ethanol/water solvent mixture (1:1, 20 mL) to finally obtain 4-bromo-3-nitrobenzonitrile as a white crystalline solid (2.8 g, 56% yield). The product was identified by 1H NMR (300 MHz, DMSO-d6): δ8.54 (s, 1H), 8.06 (d, J = 8.4 Hz, 1H), 7.99 (d, J = 8.4 Hz, 1H); 13C NMR (75 MHz, DMSO-d6) δ150.4,137.4,136.6,129.6,119.6, 117.0,112.6; HPLC retention time 1.96 min (10-100% CH3CN, gradient 5 min); ESI-MS m/z 227.1 ([MH]+).
