2-Methyl-4-nitro-2H-pyrazole-3-carboxylic acid

16034-46-1

92534-69-5

The general procedure for the synthesis of 1-methyl-4-nitro-pyrazole-5-carboxylic acid from 1-methyl-1H-pyrazole-5-carboxylic acid was as follows: fuming sulfuric acid (1977 mmol) was slowly added dropwise to fuming nitric acid (777 mmol) under strictly controlled temperature conditions. Subsequently, 1-methyl-1H-pyrazole-5-carboxylic acid (277 mmol) was added in batches to ensure that the reaction temperature was maintained below 60 °C. The reaction was carried out at the same temperature. After the addition was completed, the reaction mixture was stirred continuously at the same temperature for 1 hour. Upon completion of the reaction, the mixture was quenched by careful pouring into crushed ice and extracted with ethyl acetate (300 mL x 3). The organic phases were combined, washed sequentially with water (250 mL x 2) and dried with anhydrous sodium sulfate. Finally, the solvent was removed by distillation under reduced pressure to afford 1-methyl-4-nitro-pyrazole-5-carboxylic acid as a light yellow solid in a yield of 23.6 g in 50% yield. [00251] 1H NMR (400 MHz, DMSO-d6) δ: 8.29 (1H, s); 3.95 (3H, s).