[C:1]1(=[O:11])[O:6][C:4](=[O:5])[C:3]2=[CH:7][CH:8]=[CH:9][CH:10]=[C:2]12.[F:12][C:13]1[CH:18]=[CH:17][CH:16]=[C:15]([F:19])[CH:14]=1.[Al+3].[Cl-].[Cl-].[Cl-]>ClCC(Cl)(Cl)Cl>[F:12][C:13]1[CH:14]=[C:15]([F:19])[CH:16]=[CH:17][C:18]=1[C:4]([C:3]1[CH:7]=[CH:8][CH:9]=[CH:10][C:2]=1[C:1]([OH:6])=[O:11])=[O:5]To a mixture of phthalic anhydride (64.8 g, 438 mmol), tetrachloroethane (600 mL) and 1,3-difluorobenzene (100 g, 877 mmol) was added anhydrous AlCl3 (141 g, 964 mmol) over 20 minutes while maintaining the reaction temperature below 40° C. The temperature was increased to 90° C. for 2 hours, the reaction mixture was cooled and poured into ice/6N HCl. The mixture was extracted with ether (2×1.2 L) and the combined ether extracts were dried over Na2SO4. The solvent was removed in vacuo and the residue was recrystallized from hot ethyl acetate to afford 86.5 g (75%) of 2-(2,4-difluorobenzoyl)benzoic acid, m.p. 129°-131° C.
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