51986-17-5

60-34-4

40876-98-0

51986-17-5

The general procedure for the synthesis of ethyl 1-methyl-5-hydroxypyrazole-3-carboxylate from methylhydrazine and the sodium salt of diethyl oxaloacetate is as follows (Ref. Example 3): 3-ethoxycarbonyl-5-hydroxy-1-methylpyrazole synthesis. 50.0 g (0.24 mol) of diethyl oxaloacetate sodium salt was suspended in 500 ml of ethanol. To the suspension 25 ml of acetic acid was added. 15g (0.33 mol) of 97% methylhydrazine was slowly added dropwise over 0.5 h at room temperature and under stirring conditions. After the dropwise addition was completed, the reaction mixture was continued to be stirred at room temperature for 2 h. Subsequently, the temperature was raised to reflux temperature and stirring was continued for 5 h. After completion of the reaction, the mixture was cooled and ethanol was removed by distillation under reduced pressure. The residue was extracted by adding 200 ml of ethyl acetate and 100 ml of water to the residue. After separation of the organic phase, the extraction of the aqueous layer was repeated once more with 50 ml of ethyl acetate. The two combined ethyl acetate extracts were washed sequentially with 50 ml of water and 50 ml of saturated aqueous sodium chloride. The washed ethyl acetate layer was dried with anhydrous sodium sulfate and the solvent was subsequently removed by distillation under reduced pressure. Finally, 100 ml of water was added to the resulting crystals.