A mixture of 2-fluoro4-nitrotoluene (31.1 g, 0.2 mol), tetrabutylammonium bromide (3.2 g,0.01 mol), 1.0 L of 1N NaOH, and KMnO4 (20.0 g) was stirred at room temperature. After 10 min, the resulting mixture was heated to 95 °Cwith stirring. Additional 30.0 g portions of KMnO 4 were added after 2 h and 3 h. After stirring at 95 °C for an additional 10 h, the reaction mixture was cooled to room temperature and filtered through Celite to remove MnO2. The filtrate was acidified to pH 2 by adding concentrated hydrochloric acid. An off-white precipitate formed that was collected by vacuum filtration. The crude solid was dissolved in 300 mL of 1N aqueous NaOH, acidified to pH 2 using concentrated hydrochloric acid, and the mixture extracted with CH 2 Cl 2 (3 × 200 mL). The combined CH2 Cl 2extracts were washed with 0.1 N aqueous HCl (2 × 100 mL), dried over anhydrous Na2SO4, and concentrated in vacuo to afford 27.3 g (73.7%)of 2-fluoro-4-nitrobenzoic acid as a white crystalline solid, m.p. 174.5–176.0 °C (lit 7. m.p. 176–177 °C)[1].
[1] Defeng Xu, Zhiling Zhu, Xing Xu. “A Convenient Synthesis of 4-amino-2-fluoro-N-methyl-benzamide.” Journal of Chemical Research-s 17 1 (2013): 615–616.
