The general procedure for the synthesis of 3-chloro-5-fluorophenol from 1-chloro-3-fluoro-5-methoxybenzene was as follows: 3-chloro-5-fluoroanisole (10 g, 62 mmol) was dissolved in dichloromethane (50 mL) under argon protection and the solution was cooled to -70 °C. Boron tribromide (11.8 mL, 124 mmol) was slowly added dropwise at -70 °C under vigorous stirring, and the dropwise process was controlled to be completed within 15 minutes. Upon completion of the reaction, the mixture was gradually warmed to room temperature and the pH was adjusted with saturated sodium bicarbonate solution to 6. Subsequently, the organic and aqueous layers were separated, and the aqueous layer was extracted with dichloromethane (2 x 50 mL). All organic layers were combined, washed with saturated brine, dried over anhydrous sodium sulfate, and finally the solvent was evaporated under vacuum to afford the target product 3-chloro-5-fluorophenol (8 g, 88% yield, 54.6 mmol) as a yellow oil. The product was characterized by 1H NMR (DMSO-d6): δ 10.36 (s, 1H, OH), 6.73-6.79 (m, 1H, Ar-H), 6.64-6.68 (m, 1H, Ar-H), 6.53-6.59 (m, 1H, Ar-H).
