General procedure for the synthesis of 4-bromo-4'-chloro-1,1'-biphenyl from 4-chlorobiphenyl: Bromine (1.1 mL, 20.7 mmol) was slowly added to a solution of 4-chlorobiphenyl (3.0 g, 15.9 mmol) in acetic acid (50 mL) at room temperature. The reaction mixture was heated to reflux and held for 4 hours. Upon completion of the reaction, it was cooled to room temperature and excess propylene was added until the mixture became clear. Subsequently, the solution was concentrated to a thick slurry, diluted with dichloromethane (50 mL) and washed sequentially with water and 2N sodium hydroxide solution. The organic layer was dried with anhydrous magnesium sulfate, filtered and concentrated. Purification by recrystallization from ethyl acetate afforded the target product 4-bromo-4'-chloro-1,1'-biphenyl (3.57 g, 84% yield) as a white crystalline solid.1H NMR (CDCl3) δ 7.57 (m, 2H), 7.48 (m, 2H), 7.41 (m, 4H).
