C[O:2][C:3](=[O:19])[CH:4]([C:6]1[CH:11]=[CH:10][C:9]([N:12]2[CH:16]=[C:15]([Cl:17])[CH:14]=[N:13]2)=[C:8]([Cl:18])[CH:7]=1)[CH3:5].[OH-].[K+].O>C(O)C>[Cl:18][C:8]1[CH:7]=[C:6]([CH:4]([CH3:5])[C:3]([OH:19])=[O:2])[CH:11]=[CH:10][C:9]=1[N:12]1[CH:16]=[C:15]([Cl:17])[CH:14]=[N:13]13.0 g (10 mmoles) of 2-[3-chloro-4-(4-chloropyrazol-1-yl)phenyl]propionic acid methyl ester, 1.4 g of potassium hydroxide, 1.5 ml of water and 20 ml of ethanol are heated to the boil for 2 hours, the alcohol is distilled off, water is added and extraction with benzene is effected. This is followed by clarification of the aqueous phase with activated charcoal and acification with 2 N hydrochloric acid to produce 2.7 g (95% of theory) of 2-[3-chloro-4-(4-chloropyrazol-1-yl)-phenyl]propionic acid (m.p. 102° to 103° C.).
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