328-69-8

Step 2: To an aqueous suspension of 3-amino-5-trifluoromethylbenzoic acid (4.36 g, 21.3 mmol) was slowly added concentrated sulfuric acid (10.6 mL, 191 mmol) at 0 °C. The reaction mixture was stirred continuously until the solid was completely dissolved. Subsequently, an aqueous solution (40 mL) of sodium nitrite (1.47 g, 21.3 mmol) was added dropwise. The reaction mixture was continued to be stirred at 0 °C for 15 min, and then warmed up to reflux state maintained for 15 min. Upon completion of the reaction, the mixture was cooled to room temperature and extracted three times with ether. All organic layers were combined, washed with saturated brine and dried over anhydrous magnesium sulfate. The desiccant was removed by filtration and the filtrate was concentrated under reduced pressure to give 3-hydroxy-5-(trifluoromethyl)benzoic acid (25-2, 4.06 g) as a yellow solid.

[1] Patent: WO2007/64045, 2007, A1. Location in patent: Page/Page column 341-342
[2] Patent: US2018/312523, 2018, A1. Location in patent: Paragraph 1842; 1844