First, 8 mL of 30% fuming sulfuric acid was cooled to 5 °C, and then 1.45 g of 65% nitric acid (equivalent to 15 mmol of nitric acid) was slowly added dropwise. After the dropwise addition, the reaction system was warmed up to room temperature with continuous stirring for 5 min. Subsequently, 2.71 g (10 mmol) of 1,2-dibromo-4,5-difluorobenzene was added to the reaction system. The temperature of the reaction mixture was raised to 35 °C and stirred at this temperature for 1.5 hours. After completion of the reaction, the mixture was cooled to room temperature. The reaction mixture was slowly poured into ice water and the organic phase was extracted with ethyl acetate. The combined organic phases were sequentially washed twice with water, once with saturated aqueous sodium bicarbonate, once with saturated brine and finally dried with anhydrous magnesium sulfate. The dried organic phase was filtered to remove the magnesium sulfate, and the yield of 2,3-dibromo-5,6-difluoronitrobenzene was determined to be 94% by quantitative analysis with high performance liquid chromatography (HPLC).
