Thionyl chloride (2.68 g, 0.023 mol) was slowly added dropwise to methanol (12 mL) via a syringe at -5 °C, ensuring that the reaction temperature did not exceed -4 °C. After the dropwise addition was completed, the reaction mixture was stirred continuously at -5 °C or lower for 1 hour. Subsequently, 4-amino-3-(trifluoromethoxy)benzoic acid (0.5 g, 0.003 mol) [Alfa Aesar] was added all at once. The reaction mixture was transferred to ambient temperature and stirred for 3 days. After completion of the reaction, the solvent was removed by vacuum concentration. Water (10 mL) was added to the residue and sodium bicarbonate (0.46 g, 5.4 mmol) was added all at once and stirred at ambient temperature for 30 min. The mixture was extracted several times using ethyl acetate. The organic phases were combined, dried with sodium sulfate, filtered and concentrated in vacuum to afford methyl 4-amino-3-(trifluoromethoxy)benzoate 1.02 g (96.2% yield), which was initially a reddish oily material, and gradually transformed to a brown solid after cooling. Mass Spectrometry (MS): m/z 236.1 (MH+). 1H NMR (500MHz, DMSO-d6) data: δ3.771 (s, 3H), 6.329 (s, 2H), 6.834 (d, 1H), 7.6181 (s, 1H), 7.655 (dd, 1H).
