Electrochemical fluorination of aromatic compounds in liquid R4NF•mHF.: Part VI.: The fluorination of toluene, monofluoromethylbenzene and difluoromethylbenzene

Electrochemical fluorinations of toluene (la), monofluoromethylbenzene (Ib) and difluoromethylbenzene (Ic) in neat Et4NF . mHF (Et = C2H5, m = 3.5 or 4.0) were carried out on a platinum anode at 1.9-2.7 V vs Ag/Ag+ (0.01 mol dm(-3)). The anodic fluorination of la produced-exclusively wb as the primary product. The fluorination of Ib occurred competitively both on the side-chain (formation of Ic) and on the benzene-ring (formation of 1 -monofluoromethyl-2-fluorobenzene (2b) and 1 -monofluoromethyl-4-fuo ro benzene (4b)). However, the fluorination of Ic occurred only oil the benzene-ring, and three kinds of difluoromethylfluorobenzenes (I-difluoromethyl 2-fluorobenzene (2c), I-diflucromethyl-3-fluorobenzene (3c) and I-difluoromethyl-4-fluorobenzene (4c)), were obtained as the primary products. 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 la, Ib and Ic. A cyclic voltammogram of la (0.01 M) showed the characteristic three anodic current peaks which correspond to the oxidation of la (E(p)1 = 1.80 V), 1b (E(p)2 = 2.04) and 1c (E(p)3 = 2.24). Therefore, the profile of the fluorination products during the fluorination of la varied with the applied potentials. (C) 1998 Elsevier Science Ltd.