In a 1 liter three-necked flask, 300 g of a 30% hydrochloric acid solution was added under nitrogen protection. The reaction system was heated to 80-95°C. 200 g of the intermediate 1-(2,2,2-trichloroethyl)-3,4-dimethylbenzene was slowly added dropwise. After the dropwise addition was completed, the reaction was kept at temperature for 10 hours. After completion of the reaction, the system was quenched by cooling to room temperature. After filtration, washing and drying, 190 g of crude product was obtained. The crude product was recrystallized using 200 g of toluene, resulting in 101.1 g of pure 3,4-dimethylphenylacetic acid with a melting point of 87-89°C and an HPLC purity greater than 99 wt%.
