150.7 g (0.560 mol) of 2,5-dichloro-4′-fluorobenzophenone, 114.4 g (1.68 mol) of imidazole, 100.6 g (0.728 mol) of potassium carbonate, and 840 mL of N,N-dimethyl acetamide were weighed in a 2 L three-necked flask equipped with a stirrer, thermometer, cooling pipe, and nitrogen inlet tube. The reaction solution was heated to 110° C. using an oil bath for 2 hours under a nitrogen atmosphere. After confirming the disappearance of raw materials by way of thin-layer chromatography, the reaction liquid was allowed to cool to room temperature. Thereafter, the reaction liquid was gradually added to 3 L of water, the product was solidified and filtered. The product obtained by filtering was dissolved in THF (1.2 L), toluene (4 L) was added, and the mixture was washed with a sodium chloride solution till the aqueous layer became neutral. The organic layer was dried using magnesium sulfate, and then the solvent was removed by an evaporator. The approximate yield amount was 180 g. The crude product was subjected to a recrystallization separating operation using a mixed solvent of 1 L toluene and 20 mL methanol heated at 80° C. to obtain 155 g of a white solid at a yield of 87%.
