A mixture of 34.5 g of 3-(4-t-butylphenyl)-1-(4-cyanophenyl)-4-ethoxycarbonyl-2-methyl-2H-pyrazol-5-one, 23.6 g of potassium carbonate, 621 ml of ethanol and 69 ml of water was refluxed under heating for 9 hours. The reaction solution was cooled to room temperature and adjusted to pH 1-2 with dilute hydrochloric acid. The resulting crystals were collected by filtration and dried under reduced pressure. The resulting crude crystals were recrystallized in methanol-ethyl acetate to give 12.2 g of the title compound as colorless crystals. The mother liquor was concentrated, and the resulting residue was crystallized in chloroform-diethyl ether to give 8.3 g of the title compound as pale yellow crystals.
