3405-77-4

960225-75-6

The general procedure for the synthesis of 5-methyl-4-nitro-3-isoxazolecarboxylic acid from 5-methylisoxazole-3-carboxylic acid was as follows: 5-methylisoxazole-3-carboxylic acid (1.5 g, 12.04 mmol) was slowly added to a mixed solution containing potassium nitrate (1.83 g, 18.06 mmol) and concentrated sulfuric acid (5 mL) at room temperature. After the reactants were completely dissolved, the reaction system was warmed to 50 °C and stirred continuously at this temperature for 4 hours. Upon completion of the reaction, the mixture was cooled to 0 °C and the reaction was subsequently quenched by the addition of an appropriate amount of ice water. The reaction solution was neutralized with sodium bicarbonate solution to neutral. Next, the aqueous phase was extracted using ethyl acetate (3 x 30 mL), the organic phases were combined and dried over anhydrous sodium sulfate. After filtration to remove the desiccant, the organic phase was concentrated under reduced pressure to give 1.45 g of the white solid product 5-methyl-4-nitro-3-isoxazolecarboxylic acid (8.43 mmol, 70% yield). The product can be further purified by recrystallization from dichloromethane.