At a bath temperature of -10°C, a solution (40 mL) of sodium nitrite (2.35 g, 34.13 mmol) was added dropwise to 170 mL of HBr containing 4-chloro-2-fluoroaniline (4.5 g, 31 mmol), and the mixture was stirred at a bath temperature of -10°C for 30 minutes. Simultaneously, copper sulfate (10.22 g, 24.29 mmol) and sodium bromide (3.79 g, 36.8 mmol) were mixed, and the reaction mixture was heated at 60°C for 30 minutes. Then, sodium sulfite (2.66 g, 21.2 mmol) was added to this copper sulfate reaction mixture, and the mixture was heated at 95°C for 30 minutes. The reaction mixture was cooled to room temperature and washed with water to give cuprous bromide as a white solid. The diazonium salt was added in a single addition to freshly prepared cuprous bromide in 40 mL of HBr at a bath temperature of -10 °C, and the reaction mixture was then allowed to return to room temperature. The reaction mixture was heated at 55 °C for 20 minutes, cooled, and then extracted three times with ethyl acetate. The combined organic layers were washed with water and saturated brine, dried over sodium sulfate, and concentrated. The crude substance was purified by column chromatography (5:95 ethyl acetate:petroleum ether) to give a solid product.
