LIQUID-PHASE FLUORINATION OF AROMATIC-COMPOUNDS BY ELEMENTAL FLUORINE

The fluorination of aromatic compounds (benzene, toluene, phenol and b enzoic acid) by elemental fluorine diluted with nitrogen has been inve stigated in various solvents (Freon 11, chloroform, methanol, trifluor oacetic acid, 2,2,2-trifluoroethanol, water) in order to define the in fluence of the experimental conditions on the reaction. Experiments ha ve been carried out by varying the temperature, the substrate concentr ation in solution, the molar ratio of fluorine to substrate, and the c oncentration of fluorine in the fluorine/nitrogen mixture. In all case s, the effects on the yield of fluorinated products were studied. Mono fluorinated compounds were mainly found in the reaction mixture, the i somers formed being in accord with the mechanism for electrophilic sub stitution. The highest yield of monofluorinated products was obtained with polar solvents and the following order was found: CFCl3 < CHCl3 < CH3OH < CF3CH2OH < CF3COOH. Interesting results were also found using particular additives (for instance, KOH or C4F9SO3Na in methanol) or water as the solvent. A direct relationship was observed between the y ield of monofluorinated compounds and the molar ratio of fluorine to s ubstrate, which has to be less than one in order to obtain high yields . In contrast, low selectivity, expressed as the yield ratio of ortho to para (or metal isomers, was found.