ethyl 3-(4-chloro-2-fluorophenyl)-3-oxopropanoate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 428.4 g of ethyl 3-(4-chloro-2-fluorophenyl)-3-oxopropionate were initially charged in 1400 ml of ethanol. Over a period of 15 min, 92 g of hydrazine hydrate were added dropwise, the mixture was stirred at room temperature overnight, the precipitated solid was filtered off and the filtrate was concentrated to ⅓ of its original volume. The mixture was stirred for another two nights, the resulting solid was filtered off with suction and the filtrate was again concentrated to ⅓ of its original volume. This gave a total of 289.1 g (77.7%) of 3-(4-chloro-2-fluorophenyl)-5-hydroxy-1H-pyrazole as a colorless solid. M.p.: 194° C. the precipitated solid was filtered off the filtrate was concentrated The mixture was stirred for another two nights the resulting solid was filtered off with suction the filtrate was again concentrated