ELECTROCHEMICAL FLUORINATION OF AROMATIC-COMPOUNDS IN LIQUID R4NF-CENTER-DOT-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-exclusi vely wb as the primary product. The fluorination of Ib occurred compet itively both on the side-chain (formation of Ic) and on the benzene-ri ng (formation of 1 -monofluoromethyl-2-fluorobenzene (2b) and 1 -monof luoromethyl-4-fuo ro benzene (4b)). However, the fluorination of Ic oc curred only oil the benzene-ring, and three kinds of difluoromethylflu orobenzenes (I-difluoromethyl 2-fluorobenzene (2c), I-diflucromethyl-3 -fluorobenzene (3c) and I-difluoromethyl-4-fluorobenzene (4c)), were o btained as the primary products. These results are explained by the fa cility of proton elimination from the methyl groups of the radical cat ions which have been formed by the anodic one-electron transfer reacti ons of la, Ib and Ic. A cyclic voltammogram of la (0.01 M) showed the characteristic three anodic current peaks which correspond to the oxid ation 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 fluori nation of la varied with the applied potentials. (C) 1998 Elsevier Sci ence Ltd.