Under nitrogen protection, 2642.3 g of a 48% aqueous solution of hydrogen bromide was added to the reactor. The temperature of the system was adjusted to 30 °C, followed by the slow dropwise addition of 1760.0 g of a mixed solution of water and 880.0 g of acetic acid while stirring. Next, 880.0 g of 2-methyl-5-aminobenzotrifluoride (isomer content 0.037%, determined by gas phase area normalization) was added. After the dropwise addition, the reaction temperature was raised to 95 °C with continuous stirring for 30 min to obtain the corresponding hydrogen bromide salt solution. The reaction solution was cooled to 0 °C, at which temperature 1213.3 g of a 30% aqueous sodium nitrite solution was slowly added dropwise. After completion of the dropwise addition, the reaction was continued for 1.0 hour to ensure complete reaction. The prepared diazonium salt solution was slowly added dropwise at 65 °C to a pre-prepared mixture containing 360.4 g of copper bromide and 4997.0 g of 48% aqueous hydrogen bromide. A large amount of nitrogen release was observed during the reaction. After dropwise addition, stirring was continued for 1 hour to obtain a solution of 4-bromo-1-methyl-2-(trifluoromethyl)benzene. At the end of the reaction, the reaction solution was cooled to 20 °C, stirred for 1.0 h and left to stratify. 1046.0 g of the organic layer was separated and 3661.0 g of water was added and the pH was adjusted with 5.0% alkali metal hydroxide solution to 7. Subsequent steam distillation afforded 1032.0 g of a pale yellow 4-bromo-1-methyl-2-(trifluoromethyl)benzene product in 85.9% yield and 99.2% gas phase purity. Gas chromatographic analysis showed that the isomer content in the product was less than 0.1%.
