Halogen exchange reactions for fluorinating haloaromatic compounds using alkali metal fluorides have been extensively studied heretofore. Typically they involve the reaction of a chloroaromatic compound with potassium fluoride, rubidium fluoride or cesium fluoride by heating the reactants to extremely high temperatures (above about 400.degree. C.) in the absence of an ancillary diluent or solvent, or by conducting the reaction at temperatures of around 200.degree. to 230.degree. C. in an aprotic solvent such as sulfolane. It has also been reported that organic fluorine compounds such as pentafluorobenzonitrile, tetrafluorophthalonitriles and pentafluoropyridine can be formed by reacting a corresponding chlorobromo-substituted compound with alkai metal halide such as potassium fluoride in benzonitrile as solvent at 190.degree. C. to 400.degree. C. in a sealed autoclave under autogenous pressure.
Use of catalysts in some exchange reactions has also been studied. Such catalysts have included quaternary ammonium salts, metal carbonyls, crown ethers and cryptates.
In most cases, the halogen exchange reaction is sluggish and tends to form product mixtures in which yields of polyfluorinated aromatics are relatively low, especially if the haloaromatic compound used is a polyhaloaromatic compound free from activating functionality such as nitro or carbonyl. For example, with hexachlorobenzene and potassium fluoride, typical product mixtures contain a mixture of co-products including hexafluorobenzene together with various chlorofluorobenzenes.
A need presently exists for a commercially feasible process whereby the halogen exchange reaction as applied to a wide variety of haloaromatic compounds may be conducted in large scale rection equipment under relatively mild reaction conditions while providing commercially acceptable yields of the desired products. In addition, a particularly welcome contribution to the art would be the provision of a process whereby fluorinated perhaloaromatic compounds such as chloropentafluorobenzene, bromopentafluorobezene, and hexafluorbenene can be produced on a large scale in good yield under relatively mild reaction conditions, thereby making possible the more efficient, lower cost production of a variety of industrially important end products, especially polymerization catalysts, and intermediates for producing such catalysts.
This invention is deemed to fulfill these needs most expeditiously.