TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The reaction is carried out at 40-260 degrees C for 2-6 hours. The distillation is carried out continuously. Preferred Process: The fluoride source is sodium fluoride, potassium fluoride, triethylamine hydrofluoride, diazabicyclo(4.3.0)non-5-ene.2,6 hydrofluoride and/or potassium bifluoride. The catalyst comprises tetramethylammonium chloride, tetramethylammonium bromide, tetraethylammonium chloride, tetraethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, octyltriethylammonium chloride, octyltriethylammonium bromide, tetraphenylphosphonium chloride, triethylbenzylamonium chloride, tetraphenylphosphonium bromide, hexamethylguanidinium chloride, hexamethylguanidinium bromide, (N,N-dimethylimidazolidino)-tetramethylguanidinium chloride, 1-ethyl-3-methylimidazolium-trifluoromethane sulfonate and/or 1-ethyl-3-methylimidazolium-tetrafluoroborate. The solvent is the organic solvent comprising sulfoxide, sulfone and/or amide. The amount of the catalyst and fluoride source is 0.001-0.5 mole and 0.8-2 equivalents, respectively, relative to 1 mole of chlorine to be replaced by fluorine that is bound to 3,4,5-trichlorobenzotrifluoride. The amount of 3-chloro-4,5-difluorobenzotrifluoride is taken from the reaction mixture by distillation is equivalent to the amount of 3,4,5-trichlorobenzotrifluoride added to the reaction mixture. EXAMPLE - Tetramethylene sulfone (1066 ml) and potassium fluoride (6.395 mole) were added in a reaction vessel and distilled under vacuum. Then tetraphenylphosphonium bromide (0.078 mole) was added under nitrogen atmosphere and the reaction mixture was heated at 180 degrees C under stirring. Then 3,4,5-trichlorobenzotrifluoride (1.606 mole) was added dropwise within 4 hours. The target product was continuously removed by distillation under normal pressure from the reaction mixture. After fine distillation of the product under normal pressure, 3-chloro-4,5-difluorobenzotrifluoride ((74% theory), 193 g) was obtained as a colorless liquid.