33641-15-5

88398-78-1

33641-15-5

The general procedure for the synthesis of 1-methyl-5-hydroxypyrazole-4-carboxylic acid from ethyl 1-methyl-5-hydroxypyrazole-4-carboxylate is as follows: 22 g of sodium hydroxide was dissolved in 300 mL of water, 42.5 g of intermediate (ethyl 1-methyl-5-hydroxypyrazole-4-carboxylate) was added, and the reaction was stirred for 3 hr at 40 °C, then cooled to room temperature. 55 mL of concentrated hydrochloric acid was added dropwise, followed by heating and refluxing for 3 hours. After completion of the reaction, the solvent was removed by distillation under reduced pressure, 200 mL of anhydrous ethanol was added to the residue, and the precipitate was collected by filtration after thorough stirring. The filtrate was concentrated under reduced pressure to give 24 g of white solid product (1-methyl-5-hydroxypyrazole) in 98.0% yield and 96.50% HPLC purity.