of the condenser could be plugged by a stopper after the reaction was completed the reaction mixture was cooled to room temperature subsequently the reaction mixture was filtrated to obtain a filtered cake the filtered cake was washed by using ch 2 cl 2 and distilled under reduced pressure to obtain ch 2 cl 2 and 1 4 bis difluoromethyl tetrafluorobenzene dfmtfb since 1 4 bis difluoromethyl tetrafluorobenzene was capable of sublimation and condensed on the condenser the crude product was washed by using ch 2 cl 2 to collect 1 4 bis difluoromethyl tetrafluorobenzene after ch 2 cl 2 was removed 6 51 g of 1 4 bis difluoromethyl tetrafluorobenzene were obtained and its resultant yield was 27 2 the resultant product of the present example was verified to be 1 4 bis difluoromethyl tetrafluorobenzene through chemical analyses the data of the chemical analyses are listed as follows 5 00 g 0 063 mole of 1 4 bis dichloromethyl tetrafluorobenzene dcmtfb 0 50 g of tetraphenylphosphonium bromide ptc br 8 50 g of kf and 30 g of n n dimethylformamide dmf were added into the reacting flask the oil bath was heated to 120 u00b0 c and stirred by a stirrer to perform the reaction for 17 hours the product was analyzed by gas chromatography gc to obtain compounds 4f 2f dcmtfb 20 7 47 2 22 1 gc area the compound 4f as formula.