Water → Ethyl 1-methyl-5-propyl-1H-pyrazole-3-carboxylate

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Reaction Steps

10.4 g of methylhydrazine were initially charged in 50 ml of ethanol and, with stirring and external cooling, admixed with a solution of 42.9 g of ethyl 2,4-diketoheptanecarboxylate in 50 ml of ethanol, during which the internal temperature was kept at 5 to 10° C. (time for the dropwise addition: 10 minutes). The solution was stirred at 5 to 10° C. for another 30 minutes, the solvent and the water which had been formed were distilled off and the residue was fractionated under reduced pressure. The desired ethyl 1-methyl-3-n-propyl-pyrazole-5-carboxylate passed over at 125 to 128° C. (13 mm). The yield was 78.3% of theory. By further distillation (166 to 168° C./13 mm), the undesired isomer (=ethyl 1-methyl-5-n-propyl-pyrazole-3-carboxylate) was obtained in a yield of 7.9% of theory. Thus, the isomer ratio was approximately 10:1 in favor of the desired isomer.

Provenance & Evidence