Synthesis
b) Methyl 5-hydroxy-1-methyl-1H-pyrazole-3-carboxylate (12.2 g, 65 mmol) was dissolved in xylene (65 mL) and p-toluenesulfonic acid (0.9 g, 4.7 mmol) was added. The reaction mixture was heated to reflux for 6 hours. Upon completion of the reaction, it was cooled to room temperature and stirred overnight. The precipitated solid was collected by filtration and dissolved in ethyl acetate. The organic phase was washed sequentially with sodium bicarbonate solution and saturated brine and dried over anhydrous sodium sulfate. After filtration, the organic phase was concentrated under reduced pressure to give methyl 1-methyl-5-hydroxypyrazole-3-carboxylate (7.49 g, 74% yield) as a light brown solid. The purity of the product was improved by diisopropyl ether milling. Mass spectrometry analysis showed: m/e = 157.2 [M + H]+.
