General procedure for the synthesis of 3,4-dichlorobenzyl bromide from 3,4-dichlorotoluene: In a reaction flask equipped with a stirrer, a reflux condenser, a thermometer, and an off-gas absorption device, 3,4-dichlorotoluene (6.4 g, 40 mmol), sodium bromate (2.5 g, 16.7 mmol), sodium bromide (3.5 g, 33.6 mmol), and 1,2-dichloroethane ( 30 mL). After heating to reflux, 1/3 of the total volume of the initiator solution (0.05 g AIBN and 0.05 g BPO dissolved in 10 mL of 1,2-dichloroethane) was added rapidly. Subsequently, sulfuric acid was added slowly and dropwise (2.5 g of concentrated sulfuric acid diluted with 2.5 mL of water, equivalent to 25.2 mmol). After the dropwise addition was completed, the remaining initiator solution was used for gas chromatographic analysis. After the reaction was completed, the reaction mixture was cooled to room temperature. Saturated sodium bisulfite solution (10 mL) was added, stirred until the red color faded, and left to stratify. The organic phase was separated and the aqueous phase was extracted twice with 1,2-dichloroethane (10 mL x 2). The organic phases were combined, washed with saturated sodium chloride solution, dried and concentrated. The crude product was purified by column chromatography (eluent was petroleum ether) to give 7.7 g of 3,4-dichlorobenzyl bromide in 81% yield. The product was a colorless liquid.
