[CH3:1][O:2][C:3](=[O:15])[C:4]1[CH:13]=[C:12]([F:14])[CH:11]=[C:6]([C:7]([O:9]C)=[O:8])[CH:5]=1.[OH-].[Na+]>CO>[CH3:1][O:2][C:3](=[O:15])[C:4]1[CH:13]=[C:12]([F:14])[CH:11]=[C:6]([C:7]([OH:9])=[O:8])[CH:5]=1A suspension of 5-fluoro-isophthalic acid dimethyl ester (1.7 g, 8.0 mmol) in methanol (41 ml) was treated with 1.0 N sodium hydroxide (7.2 ml, 7.2 mmol). The reaction was left stirring overnight at room temperature. After the solution was concentrated, the residue was dissolved in water and transferred to a separatory funnel. The aqueous layer was washed with dichloromethane (3 times) and then acidified with 1.0 N HCl to pH 2. Ethyl acetate was used to extract the precipitate, which was then washed with brine and dried over anhydrous sodium sulphate. After removal of solvent in vacuo, a total of 1.3 g (83%) of 5-fluoro-isophthalic acid monomethyl ester was isolated as a white solid. 1H NMR (DMSO), δ (ppm): 8.31 (t, 1H), 7.96 (m, 2H), 3.91 (s, 3H).
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