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9.2 g (0.2 mol) of methylhydrazine were added dropwise to a mixture of 34.4 g (0.2 mol) of pivaloylacetic acid ethyl ester, 10.8 g (0.2 mol) of sodium methylate and 100 ml of methanol at 20° C. After the exothermic reaction had subsided, the mixture was heated for two hours under reflux. The reaction mixture was then concentrated, the residue was taken up in 200 ml of water and this solution was acidified to pH 6 with concentrated hydrochloric acid. The resulting precipitate was filtered off, dried and recrystallized from isopropanol. 27 g (87% of theory) of 1-methyl-3-tert.-butyl-5-hydroxy-pyrazole were obtained in the form of colorless crystals with a melting point of 150° C.

1. customAfter the exothermic reaction
2. temperaturethe mixture was heated for two hours
3. temperatureunder reflux
4. concentrationThe reaction mixture was then concentrated
5. filtrationThe resulting precipitate was filtered off
6. customdried
7. customrecrystallized from isopropanol