Bromine (2.15 mL, 42.2 mmol) was added slowly and dropwise to a mixed solution of 3-fluoro-4-nitroaniline (6.5 g, 42.2 mmol) in acetic acid (80 mL) and chloroform (25 mL) at 0 °C. The reaction mixture was stirred at room temperature for 2 hours and then poured into ice water. The pH of the mixture was adjusted to 8.0-9.0 with 10% aqueous sodium hydroxide solution under cooling in an ice bath, followed by extraction with ethyl acetate (50 mL × 3). The organic phases were combined, washed sequentially with water (80 mL × 2) and saturated saline (100 mL), dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford 2-bromo-5-fluoro-4-nitroaniline (9 g, 90% yield). The product was characterized by 1H-NMR (400 MHz, DMSO-d6): δ 8.26 (d, J=8.0 Hz, 1H), 7.07 (brs, 2H), 6.62 (d, J=9.6 Hz, 1H).
