Phosphorus oxychloride → 5-Chloro-1-methyl-3-phenyl-1H-pyrazole

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Reaction Steps

To a solution of phosphorus oxychloride (2,015 g, 19 moles) is added solid 1-methyl-3-phenylpyrazolin-5-one (2,073 g, 11.9 moles) with stirring and warming. At 100° C. the mixture becomes homogeneous. The reflux temperature rises from 119° to 143° C. over a period of 30 hours. After cooling, the mixture is poured into ice and water (8 l) with stirring. After 4 hours the slurry is filtered and the filter cake added to 1 l of water containing 1.5 l of 10% sodium hydroxide solution with stirring. Removal of the solid by filtration followed by a recrystallization from hexane yields 1,523 g of product, having a melting point ranging from 61° to 62° C.

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