General procedure for the synthesis of 1-methyl-4-nitropyrazole from 1-methylpyrazole: In a 100 mL four-necked flask equipped with a mechanical stirrer, a thermometer, and a constant-pressure dropping funnel, 8 mL of 98% concentrated sulfuric acid was added. 1 g (0.012 mol) of 1-methylpyrazole was added dropwise to the concentrated sulfuric acid through a constant pressure dropping funnel at 20 °C. After the dropwise addition, the reaction system was warmed up to 35 °C and 2.7 g (0.024 mol) of N-nitropyrazole was added in 10 portions of 0.0024 mol. The reaction was kept at a constant temperature for 6 h. Upon completion of the reaction, the reaction mixture was poured into a beaker with ice and stirred, and a white fine crystalline solid was precipitated. After the ice melted, the white solid I was collected by suction filtration. the filtrate was extracted with ether, the organic phases were combined, and the solvent was removed by spin distillation under reduced pressure to obtain white solid II. white solid I and white solid II were combined, and recrystallized with ethanol to obtain the target product 1-methyl-4-nitropyrazole. The structural characterization of the target product in Example 1 was as expected. The product obtained in Example 3 was confirmed to be 1-methyl-4-nitropyrazole with a purity of 99.2%, a melting point of 90-91 °C and a yield of 74.01%.
