Hydrochloric Acid → 1-Methyl-3-(trifluoromethyl)-4,5-dihydro-1H-pyrazole-4-carboxylic acid

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Reaction Steps

1-Methyl-3-trifluoromethyl-4,5-dihydro-1H-pyrazole-4-carboxylic acid ethyl ester (20 g, 90 mmol) was dissolved in 400 ml of dioxan. 400 ml of a 1 N aqueous sodium hydroxide solution (0.4 mol) were added and the reaction mixture was stirred for 2 h at room temperature. Subsequently the mixture was acidified with concentrated hydrochloric acid (pH 2). The dioxan was removed in vacuo, the residue was extracted with ethyl acetate. The combined organic layer was washed with brine, dried over magnesium sulfate and evaporated, delivering 15 g of 1-methyl-3-trifluoromethyl-4,5-dihydro-1H-pyrazole-4-carboxylic acid, which could be directly used in the next step without further purification.

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