Competitive fluorination on methyl-group and benzene-ring during the anodic fluorination of fluorotoluenes in Et4NF · mHF

Article abstract of DOI:10.1016/S0022-1139(97)00141-3

Electrochemical fluorinations of 2-fluorotoluene (2a), 3-fluorotoluene (3a) and 4-fluorotoluene (4a) in neat Et₄NF · mHF (Et = C₂H₅, m = 3.5 or 4.0) were carried out on a platinum anode. The fluorination of 2a, 3a and 4a occurred competitively both on the side-chain (formation of monofluoromethylfluorobenzenes) and on the benzene-ring (formation of methyltrifluoro-1,4-cyclohexadienes). These results are explained by the facility of proton elimination from the methyl groups of the radical cations which have been formed by the anodic one-electron transfer reactions of 2a, 3a and 4a. A cyclic voltammogram of 4a showed three anodic current peaks which correspond to the oxidation of 4a, 1-fluoromethyl-4-fluorobenzene (4b) and 1-difluoromethyl-4-fluorolbenzene (4c). On the other hand, voltammograms of 2a and 3a showed two anodic current peaks and no difluoromethylfluorobenzenes was obtained during the fluorination of 2a and 3a.