Fifty grams (0.2591 mol) of 4'-methyl-2-cyanobiphenyl, 500 g of ethylene dichloride, and 4.0 g (0.0130 mol) of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) were placed in a reaction vessel, and the internal temperature was controlled to 40°±2° C. Thereafter, 41.4 g (0.2591 mol) of Br 2 was added dropwise at the same temperature over a period of 2 hours, and then the reaction mixture was kept at that temperature for one hour. At this point of reaction, samples were taken out from the reaction mixture, and they were subjected to LC analysis. As a result, it was found that the mixture contained 2.5% of the starting material, 92.0% of the monobromo-product, and 5.0% of the dibromo-product. Accordingly, the selectivity of the monobromo-product over the dibromo-product was 94.8%. Thereafter, the reaction mixture was washed with 250 g of water, and then the mixture was separated to two layers. The organic layer was condensed by removing the solvent. The obtained solid was recrystallized from ethylene dichloride (150 ml)-n-heptane (600 ml), to give 63.1 g of 4'-bromomethyl-2-cyanobiphenyl with an LC purity of 99.0%. The yield was 89.4%, based on the starting material.
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