Direct liquid-phase fluorination of aromatic compounds. New advances in electrophilic fluorination

Elemental fluorine is rarely used in fluorination reactions of aromatic substrates because of the uncontrollable course of reaction. The interest in a practical application of this method excited a lot of research on this matter, in order to find experimental conditions able to allow the reaction control. At present available experimental data confirm that a reaction control is possible by using operational conditions able to favour an ionic mechanism, but they also show as mono–fluorinated products are obtained in low yields. Our research was devoted to study how operational conditions influence the reaction course; a particular interest was paid to solvent and to additives able to lead to compounds having a fluorine atom bonded to an oxygen atom (ipofluorites). Fluorination by elemental fluorine of benzene, toluene, phenol, benzoic acid, 2-naphthol and pyridine was so studied in different solvents (CHCl3, CCI3F, CF3COOH, CF3CH2OH). The use of water and methanol, rarely used in these reactions, resulted particularly interesting: experimental data show very high yield of mono–fluorinated products and suggest interesting practical applications of the proposed method. Important remarks can also be made with regard to reaction mechanism.