N-Iodosuccinimide (NIS, 2.25 g, 10.0 mmol) was added batchwise to a solution of 2,6-difluorobenzoic acid (1.58 g, 10.0 mmol) in concentrated sulfuric acid (25 mL) at 0 °C. The reaction mixture was stirred continuously at 0°C for 3.5 hours. Subsequently, the mixture was slowly poured into crushed ice (10 g) and 3% sodium sulfite solution (10 mL) was added to quench the reaction. The resulting slurry was continued to be stirred at 0 °C for 1 h, after which the product was separated by filtration. The product was washed with water and dried to afford the target compound 2,6-difluoro-3-iodobenzoic acid (Compound 3) as a white solid (2.05 g, 72% yield). The structure of the product was confirmed by 1H NMR (CDCl3) δ 6.78-6.82 (t, 1H, J=8.4 Hz, ArH), 7.78-7.83 (m, 1H, ArH) and GC-MS (m/z: 240 [M-44]+).
