General procedure for the synthesis of 2-chloro-4-fluorobenzyl bromide from 2-chloro-4-fluorotoluene: A mixture of 77.6 g (0.54 mol) of 2-chloro-4-fluorotoluene, 95.6 g (0.54 mol) of N-bromosuccinimide, 1 g of benzoyl peroxide, and 1,000 mL of carbon tetrachloride was heated and refluxed for 3 hours. After completion of the reaction, the mixture was cooled to room temperature and filtered through a G3 glass sand core funnel. The precipitate was washed with 3 x 100 mL of carbon tetrachloride. The filtrates were combined and concentrated to dryness under reduced pressure. The residue was purified by fractional distillation and the fractions with boiling points of 97-99 °C/10 mmHg were collected to give pure 2-chloro-4-fluorobenzyl bromide in a yield of 106 g (88% yield). Elemental analysis (C7H5BrClF) Calculated values: C, 37.62; H, 2.26; measured values: C, 37.79; H, 2.34. 1H NMR (CDCl3) δ: 7.41 (dt, J = 8.4 Hz, 6.0 Hz, 1H, 6-H), 7.13 (dt, J = 8.4 Hz, 2.6 Hz, 1H, 3-H), and 6.97 (dt, J = 8.4 Hz, 2.6 Hz, 1H, 5-H), 4.55 (s, 2H, CH2).
