A round bottom flask was charged with 3-chloro-4-fluorobenzoic acid (2.50 g, 14.32 mmol) and sulfuric acid (10 ml), and nitric acid (0.91 mL, 21.48 mmol) was added slowly. The reaction mixture was stirred at rt for 30 min and then heated to 100 °C and stirred at that temperature for 2h. After cooling to room temperature, the reaction mixture was poured into ice cold water and the precipitated solids were collected by filtration and washed with water and dried to afford 3-Chloro-4-fluoro-5-nitro-benzoic acid (2.44 g, 78%).
