372-18-9

327-92-4

The embodiment was the same as Example 1, with the difference that the molar ratio of concentrated nitric acid to 1,3-difluorobenzene was 6:1, i.e., the dosage of concentrated nitric acid was 265mL, and the rest of the steps were the same as Example 1. The reaction yield was 95.7% and the product purity was 98.2%. The specific operation was as follows: under magnetic stirring, 220 mL of 98% concentrated sulfuric acid was added to a 1000 mL three-necked flask, cooled to a suitable temperature in an ice-water bath, and then 220 mL (5.0 mol) of 95% fuming nitric acid was added slowly and dropwise to ensure that the volume ratio of the concentrated sulfuric acid to the nitration agent, nitric acid, was 1:1. When the fuming nitric acid was completely dissolved in the sulfuric acid, the system was continued to be stirred in an ice-bath condition for for 15 minutes. Subsequently, 114 g (1.0 mol) of 1,3-difluorobenzene was added slowly by dropwise acceleration so that the temperature of the system did not exceed 10°C. After the dropwise acceleration, the system was maintained in ice water. After the dropwise addition, the ice-water bath condition was maintained and stirring was continued for 3 hours. After that, the reaction system was gradually warmed up to room temperature with continuous stirring. The reaction progress was monitored by thin-layer chromatography (TLC) using ethyl acetate:petroleum ether=1:20 as eluent, and the reaction was judged to be complete when the raw material point (Rf=0.6) disappeared after 20 h. The reaction was then carried out at the same time. The reaction solution was slowly poured into stirred ice water and a large amount of pale yellow solid was precipitated. When the precipitation was complete, filtration was carried out and the filter cake was washed sequentially with hexane and distilled water until neutral. The filter cake was collected and dried in air to give 193.95 g of 1,5-difluoro-2,4-dinitrobenzene as a beige solid with 95.1% yield and 98.2% purity.