General procedure for the synthesis of 3,5-pyrazoledicarboxylic acid and 5-methyl-1H-pyrazole-3-carboxylic acid from 3,5-dimethylpyrazole: 3,5-dimethyl-1H-pyrazole (78.5 g, 0.818 mol) was dissolved in 700 mL of water heated to 70 °C, potassium permanganate (517 g, 3.271 mol) was added slowly, and the temperature was kept no higher than 90 °C. After completion of the reaction, the mixture was cooled to room temperature, filtered to remove the resulting MnO2 precipitate, and washed with distilled water. The filtrate was acidified to pH 2 with dilute aqueous hydrochloric acid and allowed to stand overnight. The precipitate was collected by filtration and washed with distilled water to afford 3,5-pyrazoledicarboxylic acid (41.75 g, 33% yield) as white crystals with melting point 257-258 °C. 1H NMR (D2O, δ): 7.07 (s, 1H, 4-H). After isolation of 3,5-pyrazoledicarboxylic acid, the remaining aqueous phase filtrate was neutralized to pH 5-6, the precipitate was collected by filtration and washed with distilled water to afford 5-methyl-1H-pyrazole-3-carboxylic acid (18.1 g, 18% yield) as white crystals, melting point 210-211°C.1H NMR (D2O, δ): 2.25 (s, 3H, CH3), 6.42 (s, 1H, 4-H). 4-H).
