P-Toluic Acid → 3,5-Dichloro-4-methylbenzoic acid

Reaction equation

[CH3:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]([OH:10])=[O:9])=[CH:6][CH:7]=1.[Cl-:11].[Al+3].[Cl-:13].[Cl-].ClCl>C(Cl)Cl>[Cl:11][C:3]1[CH:4]=[C:5]([CH:6]=[C:7]([Cl:13])[C:2]=1[CH3:1])[C:8]([OH:10])=[O:9]

Participants

Procedure

To a solution of p-toluic acid (95.0 g, 0.698 mole) in methylene chloride (1 liter), was added aluminum chloride (260.0 g, 1.948 mole) portionwise keeping the reaction temperature below 10° C. (ice-water bath). When the addition was completed (approx. 30 minutes) chlorine gas was bubbled in at such a rate as to keep the temperature below 10° C. The reaction was followed by gas-liquid chromatography. After about 4 hours, most of the starting material had been converted to the expected compound. The resulting mixture was poured into ice and concentrated hydrochloric acid and then extracted with ethyl acetate several times. The combined organic layers were then washed with water and dried over anhydrous sodium sulfate. Removing the solvent in a rotavap yielded the crude product as a white solid. Recrystallization from acetone/water or ethyl acetate/hexane yielded 3,5-dichloro-4-methylbenzoic acid with minor impurities 115.4 g (81% yield of product).