Propionic Acid → Benzoic acid, 4-chloro-3-fluoro-, ethyl ester

A 50-mL round-bottom flask was equipped with a magnetic stir bar, reflux condenser, thermometer, nitrogen inlet, and heating mantle attached to a temperature controller. The flask was charged with ethyl 2,4-dichloro-5-fluorobenzoate (5.09 g, 21.4 mmol) and copper powder (2.72 g, 42.8 mmol). Propionic acid (10 mL) was added, and the resulting mixture was heated to 135° C. The reaction was monitored by GC analysis and was judged to be complete when the starting material was no longer detectable (5 hours). Toluene (25 mL) was added as the reaction was cooled to room temperature. The resulting mixture was filtered, and the solids were washed with toluene. The filtrates were blue-green. The filtrates were combined and washed with 1M hydrochloric acid solution until the blue-green color disappeared. The resulting yellow organic layer was washed with water and dried over sodium sulfate. The solvent was removed by evaporation under reduced pressure. The residue was dried under vacuum to give 2.97 g of ethyl 4-chloro-3-fluorobenzoate as a pale yellow oil.