C[O:2][C:3]1[C:15]([C:16]([OH:18])=[O:17])=[CH:14][C:6]2[O:7][C:8]3[CH:13]=[CH:12][CH:11]=[CH:10][C:9]=3[C:5]=2[CH:4]=1.Br.BrC>C(O)(=O)C>[OH:2][C:3]1[C:15]([C:16]([OH:18])=[O:17])=[CH:14][C:6]2[O:7][C:8]3[CH:13]=[CH:12][CH:11]=[CH:10][C:9]=3[C:5]=2[CH:4]=1A mixture of 2-methoxydibenzofuran-3-carboxylic acid 21.62 g, (prepared by the method disclosed in Cl. Routier, Ng. Ph. Buu-Hoi, and R. Royer, J. Chem. Soc., 4276 [1956] which is incorporated herein by reference), 48% hydrobromic acid (250 ml) and acetic acid (175 ml) was boiled under reflux, allowing bromomethane to escape, for 2 hrs, removed from the heat source, diluted with 400 ml of water with stirring, and cooled in ice to 30° C. The crystalline product was filtered, washed with water, and dried, to give 19.9 g (98%) of 2-hydroxy-dibenzofuran-3-carboxylic acid, m.p. 301°-2° dec. An analytical sample was prepared by twice recrystallizing a portion from 2-ethoxyethanol, m.p. 301°-303° dec.
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