solution of dibutylmagnesium in heptane (0.9 M, 10 mmol/L, 11 mL) was added dropwise to a solution of 1,3-bis(trifluoromethylbenzene) (2.14 g, 10 mmol) in diethyl ether (10 mL) under vacuum and at room temperature. The resulting solution was cooled to 0°C and a solution of n-butyllithium in hexane (2.5 M, 10 mmol/L, 4 mL) was added. The reaction mixture was kept at 20°C for 4 hours, then poured onto solid carbon dioxide in fine powder form and kept under vigorous stirring. The mixture was then placed at room temperature and acidified to pH 1-2 with 0.1 M HCl. The resulting reaction mixture was extracted with dichloromethane and the phase was separated. The organic phase was extracted with a 10% NaOH aqueous solution, the alkaline aqueous extract was acidified to pH 1.2 with HCl, and then the aqueous extract was extracted with dichloromethane. The resulting organic extract was washed with water and dried over sodium sulfate. After evaporation of the solvent under vacuum, 2,4-bis(trifluoromethyl)benzoic acid (1.8 g) was obtained, bp 107-109°C. ¹H-NMR (CDCl₃) δ (ppm): 7.95 (m, ¹H), 8.06 (m, ¹H), 8.12 (m, ¹H), 11.8 (broad, ¹H).
