General procedure for the synthesis of 4-(2,2,2-trifluoroethoxy)benzoic acid from 4-(2,2,2-trifluoroethoxy)benzaldehyde: 4-(2,2,2-trifluoroethoxy)benzoaldehyde (0.6 g, 2.94 mmol) was dissolved in methanol (5 ml), 50% w/v aqueous potassium hydroxide (1.2 ml) was added, and stirred at 65 °C. Subsequently, 30 wt% aqueous hydrogen peroxide solution (2.4 ml) was added dropwise over a period of 20 minutes. After dropwise addition, the reaction mixture was continued to be heated at 65°C for 10 minutes. After completion of the reaction, it was cooled to room temperature, acidified with 1 M hydrochloric acid and then extracted with ether (3 x 30 ml). The organic phases were combined, washed with brine (20 ml) and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure to give 4-(2,2,2-trifluoroethoxy)benzoic acid (0.59 g, 91% yield) as a light yellow solid, which could be used for subsequent experiments without further purification.
