A process for the preparation of 3-chloro-4,5-difluorobenzonitrile comprising the steps of (a) reacting an alkali metal fluoride with 4-chloro-3,5-dinitrobenzonitrile to form a 4-fluoro-3,5-dinitrobenzonitrile product; (b) chlorodenitrating the 4-fluoro product of step (a) to form the corresponding 3,5-dichloro-4-fluorobenzonitrile compound; and (c) reacting the 3,5-dichloro-4-fluorobenzonitrile compound prepared in step (b) with an alkali metal fluoride to form 3-chloro-4,5-difluorobenzonitrile.

Fluorobenzonitriles and chlorofluorobenzonitriles are prepared in an advantageous manner from the corresponding chlorobenzonitriles and an alkali metal fluoride in a chlorine-fluorine exchange reaction, by catalyzing the reaction with a quaternary ammonium compound comprising at least one alkoxypolyoxyalkyl radical.

A process for making 2,6-difluorobenzonitrile, comprising reacting 2,6-dichlorobenzonitrile with a substantially anhydrous metal fluoride at a temperature between about 160.degree. C. and about 300.degree. C. and in the presence of a phase transfer catalyst, which is typically a polyether, tetra-substituted phosphonium salt, tetra-substituted ammonium salt, and cryptand, but in the absence of a solvent. After taking off the product the resulting mixture may be recycled into the reactor for the next reaction cycle. Upon build-up of tars in the reaction process, the invention includes the separation of catalyst from the tars and the recycle thereof.