Abstract: 4-Fluorobenzaldehyde is produced by a commercially feasible process. The process comprises heating a mixture of fluorobenzene and a strong Lewis acid with dissolved hydrogen halide in an atmosphere of carbon monoxide at about 45 to about 100° C. and at a total pressure of about 150 psig up to the maximum pressure rating of the reactor. Formed is a reaction mass containing a Lewis acid complex of 4-fluorobenzaldehyde and at least a halobis(fluorophenyl)methane by-product. The complex is broken by quenching the reaction mass with a Lewis acid-solvating liquid to liberate 4-fluorobenzaldehyde. By-product halobis(fluorophenyl)methane is converted to di(fluorophenyl)methanol to avoid potential corrosion problems and formation of light sensitive color bodies in the recovered 4-fluorobenzaldehyde.