In a 250 ml three-necked flask, add 100 g of m-(trifluoromethyl)benzyl chloride, 0.5 g of initiator azodiisoheptanenitrile, warm up to 70C, start to pass dry chlorine gas, control the temperature of chlorine pass to keep between 70-75C, wait until the specific gravity of the reaction liquid reaches 1.48-1.50 when the chlorine pass is over, drive off the residual chlorine, and then evaporate under a reduced-pressure 2 mm Hg column at 53-55C, (German Patent DE2548970 (1997) reported under reduced pressure 11mmHg column, bp87 ), the content of 96.9% of 1-(trichloromethyl)-3-(trifluoromethyl)benzene 127g, yield 91.8%. Then put 50g of prepared 1-(trichloromethyl)-3-(trifluoromethyl)benzene, 1600g of 2.5% aqueous NaOH solution in a 3000ml three-necked flask, heated and refluxed for 12 hours, neutralized the pH of the reaction solution with 10% hydrochloric acid to 4, white precipitate precipitation precipitated, pumped and filtered, a small amount of water washed, dried in vacuum at 60 for 10 hours to obtain the white powdery m-(trifluoromethyl)benzoic acid crude product 32.4g, content 97.3%, melting point 103-104C, reaction yield 88.6%. After the crude product was recrystallized by CCl4, the melting point was 105.2-105.5 C, and the melting point of 99% pure m-(trifluoromethyl)benzoic acid was 105-106 C.
