General procedure for the synthesis of 2,4-difluoro-5-nitrobenzonitrile from 2,4-difluorobenzonitrile: Potassium nitrate (16.4 g, 147.4 mmol) was slowly added to concentrated sulfuric acid (85 ml, 1582 mmol) at 0 °C, followed by 2,4-difluorobenzonitrile (11.0 g, 79.1 mmol) dropwise. The reaction mixture was stirred at this temperature for 4 hours. Upon completion of the reaction, the mixture was quenched by pouring into ice/water (800 mL). The precipitated solid product was collected by filtration and dried to give 2,4-difluoro-5-nitrobenzonitrile (13.8 g, 95% yield) as a white solid. The product was confirmed by NMR hydrogen spectrum (400 MHz, CDCl3): δ 8.48 (m, 1H), 7.24 (m, 1H).
