General procedure for the synthesis of 2,5-difluoro-4-nitrotoluene from 2,5-difluorotoluene: To a stirred solution of 2,5-difluorotoluene (0.544 g, 4.25 mmol, Aldrich, for direct use) in concentrated sulfuric acid (5.0 mL) was added a single addition of potassium nitrate (KNO3, 0.430 g, 4.25 mmol) at 0 °C. The reaction mixture was gradually warmed to 28 °C and stirred at this temperature overnight. Upon completion of the reaction, the mixture was quenched by pouring into ice (25 g) and extracted with ethyl acetate (40 mL). The organic layers were combined, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure to give 2,5-difluoro-4-nitrotoluene (0.555 g, 91% yield) as a light red oil. The product was characterized by 1H NMR (CDCl3): δ 2.369 (d, 3H, J = 1.8 Hz), 7.127 (dd, 1H, J1 = 8.1 Hz, J2 = 6.0 Hz), 7.734 (dd, 1H, J1 = 8.4 Hz, J2 = 6.3 Hz).
