[O:1]([C:8]1[CH:13]=[CH:12][C:11]([CH2:14][C:15]([OH:17])=[O:16])=[CH:10][CH:9]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[C:18]1(C)C=CC(S(O)(=O)=O)=C[CH:19]=1>C(O)C>[O:1]([C:8]1[CH:9]=[CH:10][C:11]([CH2:14][C:15]([O:17][CH2:18][CH3:19])=[O:16])=[CH:12][CH:13]=1)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a suspension of (4′-phenoxyphenyl)acetic acid (0.456 g) in 4 ml of ethanol is added para-toluensulfonic acid (0.076 g) and the resulting mixture is refluxed for 2 hours. The solvent is evaporated off, the residue is dissolved in diethyl ether and the organic phase is washed with saturated aqueous solution of sodium hydrogencarbonate and then with brine. The organic phase is dried over sodium sulfate and concentrated to dryness to give 0.458 g of the product as a brown oil.
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