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22.7 g (0.1 mol) of the potassium salt of ethyl α-hydroxymethylene-phenylacetate and 18.2 g (0.1 mol) of 2-hydrazino-pyridine dihydrochloride in 200 ml of ethanol are stirred for 30 minutes at room temperature and then boiled under reflux for 5 hours. After the mixture has been cooled to room temperature, 19.1 g (1.7 mol) of potassium tert.-butylate are introduced in portions while nitrogen is simultaneously passed over the mixture. The mixture is stirred for 4 hours at room temperature and left to stand overnight. The precipitate formed is filtered off under suction and suspended in 100 ml of water, and the suspension is slightly acidified with acetic acid. The crystals are filtered off under suction, washed with water and dried in the air. 17.2 g (72.5% of theory) of 1 -pyrid-2-yl-4-phenyl-pyrazoline-5-one of melting point 132° to 133° C. (ethanol) are obtained.

1. temperatureunder reflux for 5 hours
2. waitleft
3. waitto stand overnight
4. customThe precipitate formed
5. filtrationis filtered off under suction
6. filtrationThe crystals are filtered off under suction
7. washwashed with water
8. customdried in the air