The general procedure for the synthesis of 5-hydroxy-1-methyl-1H-pyrazole-3-carboxylic acid from ethyl 1-methyl-5-hydroxypyrazole-3-carboxylate is as follows:
1. ester hydrolysis: ethyl 1-methyl-5-hydroxypyrazole-3-carboxylate (20.00 g, 0.11 mol) was dissolved in water (100 mL), and sodium hydroxide pellets were added slowly with stirring to adjust the pH of the reaction solution to about 13.
2. After the reaction was completed (stirring at room temperature for 5 hours), the pH of the reaction solution was adjusted to 1 with 2N hydrochloric acid, at which time a precipitate was generated, and the precipitate was collected by filtration.
3. The resulting solid was mixed with acetone and stirred, filtered and dried to give the off-white solid product 5-hydroxy-1-methyl-1H-pyrazole-3-carboxylic acid (9.20 g, 59% yield). Mass spectrometry analysis showed (M-H)- peak of 141.
