[Cl:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[C:4]([CH3:11])[CH:3]=1.S(=O)(=O)(O)O.[N+:17]([O-])([OH:19])=[O:18]>>[Cl:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[C:4]([CH3:11])[C:3]=1[N+:17]([O-:19])=[O:18]A round bottom flask was charged with 4-chloro-2-methylbenzoic acid (200 mg, 0.001 mol) and sulfuric acid (1 mL, 0.02 mol). Fuming nitric acid (0.05 mL, 0.001 mol) was added at −20° C. and the reaction was stirred for 1 hour at 70° C. and poured into ice cold water, whereupon the mixture of 2- and 4-nitro compounds precipitated out. The precipitate was filtered and dissolved in ethyl acetate (30 mL) and washed with saturated aqueous sodium bicarbonate solution and brine, and dried over sodium sulfate. The solvent was reduced to ¼ volume whereby the undesired isomer precipitated out. The precipitate was filtered and the filtrate was dried to afford a 1:1 mixture of isomers as a white solid.
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