ELECTROCHEMICAL FLUORINATION OF AROMATIC-COMPOUNDS IN LIQUID R(4)NF-CENTER-DOT-MHF .2. FLUORINATION OF DI-FLUOROBENZENES AND TRI-FLUOROBENZENES

Di- and tri-fluorobenzenes were electrochemically fluorinated at a platinum anode at 2.5 V [vs. Ag/Ag+ (0.01 mol dm(-3))] in Et(4)NF.mHF (Et = C2H5, m = 4.0, 4.35). The fluorinated cyclohexadienes were obtained as the major final products in high yield, and neither deposition of a polymeric film on the anode surface nor a coloration of the electrolyte solution was observed. Some 1,2,4-trifluorobenzene (4) or 1,2,3,5-tetrafluorobenzene (6) was produced in the course of the fluorination of 1,3-difluorobenzene (2) or 1,3,5-trifluorobenzene (5), respectively These were produced chemically by the dehydrofluorination of 1,3,3,6-tetrafuoro-1,4-cyclohexadiene (2a) or 1,3,3,5,6-pentafluoro-1,4-cyclohexadiene (5a), which was produced by the anodic fluorination, and large portions of the resulting 4 and 6 were further fluorinated electrochemically to the corresponding fluorinated cyclohexadienes. The reaction paths to the major products were explained by the combination of electrochemical reactions, 1,4- or 1,2-addition of two fluoride anions to substrate compounds by an ECEC mechanism (which yielded the fluorinated cyclohexadienes) and a chemical reaction (the dehydrofluorination of some fluorinated cyclohexadienes) which yielded fluorobenzenes.