Method for the preparation of pyrazoles

The formation of byproducts in the production of pyrazoles by the reaction of ketones with alkyl formates or carbon monoxide and subsequent reaction with a hydrazine is reduced by separating the intermediate by filtration or centrifugation prior to the reaction with hydrazine. Production of pyrazole...

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Bibliographic Details
Main Authors RIEBER, NORBERT, ERHARDT, KLAUS, BARTH, THOMAS
Format Patent
LanguageEnglish
French
German
Published 01.10.2003
Edition7
Subjects
CHEMISTRY
HETEROCYCLIC COMPOUNDS
METALLURGY
ORGANIC CHEMISTRY
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Summary:The formation of byproducts in the production of pyrazoles by the reaction of ketones with alkyl formates or carbon monoxide and subsequent reaction with a hydrazine is reduced by separating the intermediate by filtration or centrifugation prior to the reaction with hydrazine. Production of pyrazoles (I) comprises: (a) reaction of a ketone (II) in the presence of a strong base with (i) an alkyl formate (III) at -20 to 70 degrees C under 1-50 bar pressure or (ii) carbon monoxide (IV) at 0-100 degrees C under 1.5-150 bar pressure; (b) separation of the resulting intermediate by filtration or centrifugation; and (c) reaction of the separated intermediate with a hydrazine (V) in the presence of an organic or inorganic acid at 0-90 degrees C under 1-10 bar pressure. R , R and R = 1-20C alkyl; 3-8C cycloalkyl; or aryl or 7-20C aralkyl optionally substituted with 1-4C alkyl, halo and/or NO2; or R and R = H; R = 1-8C alkyl.
Bibliography:Application Number: EP19990113419