Synthesis of 3,4-difluorobenzonitrile and monofluorobenzonitriles by means of halogen-exchange fluorination

Abstract

3,4-Difluorobenzonitrile has been prepared by a halogen- exchange reaction between 3,4-dichlorobenzonitrile and spray- dried potassium fluoride in the presence of tetraphenylphosphonium bromide in refluxing 1,3-dimethylimidazolidine-2- one. In the fluorination reaction, 4-chloro-3-fluorobenzonitrile seems to be a key intermediate. 3,4-Difluorobenzonitrile, 2-, 3-, and 4-fluorobenzonitriles have also been produced from the corresponding chlorobenzonitrile derivatives by halogen-exchange at 290 °C in DMI in a pressure reactor.