[C:1]([OH:9])(=O)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.FC(F)(F)S(O)(=O)=O.[CH3:18][C:19]1[CH:20]=[CH:21][C:22]([CH3:25])=[CH:23][CH:24]=1>>[CH3:18][C:19]1[CH:20]=[CH:21][C:22]([CH3:25])=[CH:23][C:24]=1[C:1]([C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1)=[O:9]Benzoic acid (20 g, 0.16 mole), p-xylene (100 mL), and trifluoromethanesulfonic acid (5 mL) were heated at reflux in a 300 mL flask equipped with a Dean-Stark trap. After 16 hours, the mixture was extracted with 100 mL of 6% aqueous sodium hydroxide, washed with water, dried over magnesium sulfate and evaporated to give 15.4 g (0.073 mole) of 2,5-dimethylbenzophenone. The aqueous sodium hydroxide extract was acidified to give 8.1 g (0.066 mole) of unreacted benzoic acid.
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