C[O:2][C:3](=[O:22])[C:4]1[CH:9]=[C:8]([CH2:10][C:11]2[CH:16]=[CH:15][CH:14]=[C:13]([Cl:17])[C:12]=2[F:18])[C:7]([O:19][CH3:20])=[CH:6][C:5]=1[F:21].[OH-].[Na+].O.Cl>CN1CCCC1=O>[Cl:17][C:13]1[C:12]([F:18])=[C:11]([CH:16]=[CH:15][CH:14]=1)[CH2:10][C:8]1[C:7]([O:19][CH3:20])=[CH:6][C:5]([F:21])=[C:4]([CH:9]=1)[C:3]([OH:22])=[O:2]
5-(3-Chloro-2-fluorobenzyl)-2-fluoro-4-methoxybenzoic acid methyl ester (100 g) obtained in Example 2, Step III was dissolved in 1-methyl-2-pyrrolidinone (500 ml), and 2.5% V/W aqueous alkali solution prepared from 8N-aqueous sodium hydroxide solution (54.7 ml) and water (192.6 ml) was added dropwise with stirring at room temperature. After the dropwise addition, the mixture was stirred for 3.5 hr, and acidified by dropwise addition of 2N-hydrochloric acid (240 ml) with stirring at room temperature. The precipitated crystals were stirred for 2 hr and collected by filtration. The filtrate was washed with 50% methanol aqueous solution (100 ml) and dried at an outer temperature of 70° C. to give 5-(3-chloro-2-fluorobenzyl)-2-fluoro-4-methoxybenzoic acid (89.4 g, yield 93.4%).
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