A method for the synthesis of TFPX (.alpha., .alpha., .alpha.', .alpha.'-tetrafluoro-p-xylene) is disclosed, which comprises the following steps: (a) providing a sulpholane solution comprising TCPX (.alpha., .alpha., .alpha.', .alpha.'-tetrachloro-p-xylene); (b) mixing the sulpholane solution with alkali metal fluoride, and phase transfer catalyst to form a mixture, wherein the phase transfer catalyst is quaternary phosphonium salt; and (c) heating the mixture.