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3-Bromo-4-fluorobenzonitrile is mainly used as an intermediate in the synthesis of pesticides, medicines, and dyes in organic synthesis. It is obtained by adding cuprous bromide (CuBr) to 4-fluorobenzonitrile. In industrial applications, halogens can be introduced through specific chemical reactions to synthesize more complex organic compounds.

General procedure for the synthesis of 3-bromo-4-fluorobenzonitrile from 3-bromo-4-fluorobenzaldehyde: Tetrahydrofuran (100 mL) was added to a 250 mL reaction flask. Under stirring conditions, 3-bromo-4-fluorobenzaldehyde (10 g, 49.2 mmol) and ammonia (40 mL) were added sequentially. After cooling the reaction mixture to 5 °C, elemental iodine (25 g, 98.5 mmol) was added in batches. Subsequently, the reaction system was warmed to room temperature and stirred continuously for 2 to 3 hours to ensure complete reaction. Upon completion of the reaction, the reaction solution was poured into 10% aqueous sodium sulfite solution (200 g) and extracted twice with methyl tert-butyl ether (100 mL). The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. To the residue was added n-heptane (20 mL) and the mixture was cooled to 0-10 °C and maintained for 1 h to promote crystallization. The solid product was collected by filtration and dried under reduced pressure to give 3-bromo-4-fluorobenzonitrile (9.6 g, yield: 97.5%). The resulting compound was confirmed to be structurally consistent with the target product by NMR spectral analysis.

[1] Patent: CN108623496, 2018, A. Location in patent: Page/Page column 0043-0048