II.[Mg].Br[C:5]1[CH:10]=[CH:9][C:8]([C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=2)=[C:7]([Cl:17])[CH:6]=1.[C:18](=[O:20])=[O:19].Cl>O1CCCC1>[Cl:17][C:7]1[CH:6]=[C:5]([C:18]([OH:20])=[O:19])[CH:10]=[CH:9][C:8]=1[C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1Few crystals of iodine are added to tetrahydrofuran (200 mL) containing magnesium turnings (2.8 g, 0.117 mol). The mixture is heated at 60-70° C. A solution of 4-bromo-2-chlorobiphenyl (26 g, 0.097 mol) in tetrahydrofuran (50 mL) is added dropwise to the reaction mixture and refluxed for 1 hr. Reaction mixture is brought to room temperature and then cooled to −20° C. Carbon dioxide gas is passed through the reaction mixture for 45 minutes. The reaction mixture is treated with 3N HCl (125 mL) and extracted with ethyl acetate (2×200 mL). Combined organic layer is dried over sodium sulphate. Removal of solvent under reduced pressure gives a solid which is washed with diethyl ether (2×100 mL) and then dried to furnish 2-chlorobiphenyl-4-carboxylic acid.
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