Sulfuric Acid → 1-(2,4-dichloro-phenyl)-4-methyl-5-(4-trifluoromethyl-phenyl)-1H-pyrazole-3-carboxylic acid

Beteiligte Stoffe

Reaktionsschritte

A solution of 10 g of Lithium 3-ethoxycarbonyl-2-methyl-3-oxo-1-(4-trifluoromethyl-phenyl)-propan-1-olate, 6.9 g of (2,4-Dichloro-phenyl)-hydrazine hydrochloride and 74 ml of sulfuric acid (50%) in 184 ml of ethanol was heated to reflux for 7 h. After cooling to room temperature the organic solvents were removed under reduced pressure and the residue was diluted with 100 ml of water and extracted with ethyl acetate. The combined organic layers were dried over MgSO4 and the solvent was removed under reduced pressure. The residue was dissolved in 100 ml THF and a solution of 1.4 g of LiOH in 20 ml water was added at room temperature. The reaction mixture was heated to 60° C. for 7 h. Then, after cooling to room temperature the mixture was acidified to pH 1 by addition of half-concentrated hydrochloric acid. The precipitating product was collected by filtration and washed with water. The residue was codistilled twice with dichloromethane and twice with toluene. The isolated crude product was used in the next reaction step. Yield: 13 g.

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