General procedure for the synthesis of 2-fluoro-5-nitrobenzoic acid from o-fluorobenzoic acid: Nitric acid (60% solution, 5.0 mL) was slowly added dropwise to pre-cooled concentrated sulfuric acid (5.0 mL), and the reaction temperature was controlled to not exceed 10 °C. Subsequently, o-fluorobenzoic acid (2.1 g, 15.0 mmol) was added in batches and the reaction temperature was maintained between 15 and 25 °C. The reaction mixture was stirred at room temperature for 2 hours. After completion of the reaction, the reaction was quenched by addition of ice water and the precipitate was collected by filtration. The product was dried at room temperature to give the intermediate 2-fluoro-5-nitrobenzoic acid as a white powder. Yield: 93%; Melting point: 135-137 °C; 1H NMR (300 MHz, DMSO-d6): δ=7.32 (t, 1H, H3, 3JH3_H4=JH3-F=9.2 Hz), 8.43 (dt, 1H, H4, 3JH4_H3=9.2 Hz, 4JH4_F=4JH4_H6=3.5 Hz), 8.89 (dd, 1H, H6, 4JH6_F=5.8 Hz, 4JH6_H4=3.0 Hz); 13C NMR (75 MHz, DMSO-d6): δ=118.7 (d, C1, 2JC-F=10.9 Hz), 118.7 (d, C3, 2JC-F=25.0 Hz), 128.9 (d, C6, 3JC -F=2.2 Hz), 130.6 (d, C4, 3JC-F=10.9 Hz), 143.9 (C5), 165.7 (d, C2, 1JC-F=272.0 Hz), 166.7 (d, COOH, 3JC-F=3.8 Hz).
