General procedure for the synthesis of 2-nitroimidazole from 2-aminoimidazole sulfate: 2-aminoimidazole sulfate (1.57 g, 6.01 mmol) was dissolved in water (10 mL) and 50% w/v fluoroboric acid (7 mL). The reaction solution was cooled to -20 °C in an acetone/dry ice bath and a solution of sodium nitrite (4.14 g, 59.6 mmol) in water (10 mL) was added slowly and dropwise. The reaction temperature was maintained at -10 °C and stirred for 30 min. Subsequently, the reaction solution was poured into a solution of copper sulfate (20.0 g, 119 mmol) in water (200 mL). Sodium nitrite (4.14 g, 59.6 mmol) was then added and the reaction mixture was stirred for 2 hours at room temperature. After completion of the reaction, the extract was carried out for 6 hours using a continuous extractor with ethyl acetate (200 mL) as the extractant. The organic phases were combined, concentrated under reduced pressure and the residue was recrystallized from ethanol to give the target compound 2-nitroimidazole as yellow needle-like crystals (870 mg, 65% yield).
