General procedure for the synthesis of 2-bromo-3-chloro-5-(trifluoromethyl)pyridine from 3-chloro-2-hydroxy-5-(trifluoromethyl)pyridine: 3-chloro-5-(trifluoromethyl)-2-hydroxypyridine (17.1 g, 0.087 mol) was added to 150 mL of tribromophosphorus oxide and heated to 150 °C for 6 hours. After the reaction was completed, it was cooled to room temperature. The reaction mixture was slowly and carefully added to ice water at -5 to 0 °C and stirred vigorously at 200 rpm for 1 hour. The resulting mixture was extracted three times with dichloromethane. The organic phases were combined, dried with anhydrous sodium sulfate, filtered and concentrated to give the crude product. The crude product was purified by silica gel column chromatography using dichloromethane-methanol (100:1 to 20:1, v/v) as eluent to give 13.1 g of 2-bromo-3-chloro-5-(trifluoromethyl)pyridine (0.05 mol) in 58% yield.
