Synthese
General procedure for the synthesis of 3-cyano-4-fluorobenzoic acid from 2-fluoro-5-formylbenzonitrile: 15.0 g (97.6 mmol) of 2-fluoro-5-formylbenzonitrile (Aldrich) was dissolved in a solvent mixture of 150 mL of water and 630 mL of tert-butanol under stirring conditions. Subsequently, 40.8 g (361 mmol) of sodium chlorite and 35.9 g (230 mmol) of disodium hydrogen phosphate dihydrate were added to this solution. The reaction mixture was stirred overnight at room temperature and poured into dilute aqueous hydrochloric acid solution and the pH was adjusted to 3.5. The pH was adjusted again to 3.5 with aqueous hydrochloric acid solution. the reaction solution was extracted three times with dichloromethane/isopropanol (10:1, v/v). The organic phases were combined, dried over anhydrous sodium sulfate and concentrated. The residue was purified by extraction with sodium bicarbonate solution and dichloromethane, acidification of the aqueous phase and filtration to afford the solid crude product 3-cyano-4-fluorobenzoic acid in 90% yield (14.5 g, 87.8 mmol), which could be used in the next reaction without further purification.MS-ESI: m/z 166 [M+H] (77). Elemental analysis: calculated values: C 58.19%, H 2.44%, F 11.51%, N 8.48%; measured values: C 58.81%, H 2.42%, F 11.41%, N 8.47%.
