Hydrogen Bromide → 4-(Bromomethyl)phenylacetic acid

To a stirred solution of p-methylphenylacetic acid (0.175 mol, 27.8 g) in tetrachloromethane (250 mL) under a nitrogen atmosphere in a round bottom flask equipped with a reflux condenser and provision for trapping the released HBr was added bromine (0.175 mol, 27.8 g) dissolved in tetrachloromethane. The red/brown mixture was irradiated and brought to reflux with a 250 watt incandescent light source. Over the course of ten minutes, the color was discharged and a crystalline precipitate was formed. The mixture was allowed to cool to room temperature, and the solid was collected by vacuum filtration, and dried in a stream of nitrogen to give (4-bromomethyl-phenyl)-acetic acid as a white solid containing 6.3% by weight p-methylphenylacetic acid as an impurity. (25.1 g, 63%).