[Cl:1][C:2]1[CH:3]=[C:4]([CH:8]=[C:9]([Cl:12])[C:10]=1[CH3:11])[C:5]([OH:7])=[O:6].C(OOC(=O)C1C=CC=CC=1)(=O)C1C=CC=CC=1.[Br:31]N1C(=O)CCC1=O>C(Cl)(Cl)(Cl)Cl>[Br:31][CH2:11][C:10]1[C:2]([Cl:1])=[CH:3][C:4]([C:5]([OH:7])=[O:6])=[CH:8][C:9]=1[Cl:12]99 g (0.48 mole) of the previously prepared 3,5-dichloro-4-methylbenzoic acid and 0.5 g (0.002 mole) of benzoyl peroxide were dissolved in 800 ml of CCl4 and refluxed for 2 hours using a Dean Stark apparatus to remove moisture. The heating was continued at gentle reflux and 94 g (0.53 mole) of N-bromosuccinimide were added in 10×9.4 g portions at 10-15 min intervals with stirring. When addition was completed, the reaction mixture was refluxed for 30 minutes longer. At the end of this time analysis by gas chromatography showed 3% of starting material, 94% of the expected product and the rest dibromo derivatives and other impurities. The reaction mixture was cooled down to room temperature and filtered. The resulting organic solution was washed with concentrated sodium thiosulfate (2×250 ml), dried with anhydrous sodium sulfate and concentrated to give 47.2 g of an oily residue, which was mostly the expected compound. The solid was also the expected 4-bromomethyl-3,5-dichlorobenzoic acid contaminated with succinimide. The solid was slurried in 1 liter of water for 1 hour, filtered and then dried. This yielded another 89.0 g of 4-bromomethyl-3,5-dichlorobenzoic acid.
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