2-Bromo-6-chloro-4-methylaniline (30 mmol) was used as a starting material, which was dissolved in a mixed solution of acetic acid (60 mL), water (25 mL), and concentrated hydrochloric acid (7 mL), and the reaction system was subsequently cooled to 5 °C. A solution of sodium nitrite (48 mmol, 3.31 g) in water (12 mL) was added slowly and dropwise while keeping the temperature below 5 °C. After the dropwise addition, the reaction mixture was continued to be stirred at 5-10 °C for 2 hours. Subsequently, the reaction solution was poured into a 50% hypophosphite solution pre-cooled to 0 °C and stirred for 48 h at room temperature. Upon completion of the reaction, extraction was carried out with dichloromethane (3 x 120 mL). The organic phases were combined, washed with saturated saline (100 mL), dried over anhydrous sodium sulfate, and concentrated under reduced pressure to remove the solvent. Finally, the residue was purified by fast column chromatography to obtain the target product 3-bromo-5-chlorotoluene.
