The general procedure for the synthesis of 3-cyano-5-fluorobenzoic acid from methyl 3-chloro-5-cyanobenzoate was as follows: the crude methyl 3-chloro-5-cyanobenzoate was dissolved in 350 mL of methanol at room temperature, 45 mL of 4N sodium hydroxide solution (180 mmol) was added, and the reaction was carried out for 4 hours. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure. The residue was dissolved in ethyl acetate and the organic phase was washed with 5% aqueous hydrochloric acid and saturated saline in turn. Finally, it was purified by silica gel column chromatography to afford 7.0 g (54% yield) of the target product 3-cyano-5-fluorobenzoic acid.
