General procedure for the synthesis of 3-bromo-2,6-difluorobenzonitrile from 2,6-difluorobenzonitrile: 600mL of 60% sulfuric acid was added to a 2L four-necked flask, and 139.0g (1.0 mol) of 2,6-difluorobenzonitrile was added while stirring. Under the protection of nitrogen, the reaction temperature was controlled below 35°C. 250.5 g of potassium bromate (1.5 mol) was added in 10 portions. The progress of the reaction was monitored by thin layer chromatography (TLC) and the reaction continued for 5-6 days until the raw material spot disappeared. After completion of the reaction, 800 mL of 20% ice brine solution was prepared and the reaction mixture was slowly poured into the ice brine. After the product settled, it was quickly filtered and washed with carbon tetrachloride (CCl4) to obtain the crude product, which was orange in color. The crude product was washed sequentially with 5% sodium bisulfite (NaHSO3) solution and water until it was neutral by saturated sodium carbonate (Na2CO3) solution. After drying with anhydrous sodium sulfate, it was filtered and evaporated by rotary evaporation in a water bath at 60°C to obtain a light yellow liquid. The liquid was cooled to room temperature and allowed to stand, precipitating a light yellow solid. Reduced-pressure distillation was carried out, the condensed steam was heated and the temperature of the oil bath was raised to 90°C. The vapor fraction at 58-62°C was collected and cooled to give a white solid product with a yield of 71%.
