The electrochemical fluorination of benzenes containing one or two trifluoromethyl groups has been carried out. They afforded perfluorocyclohexane derivatives with the trifluoromethyl group in good yields. Chlorobenzenes containing a trifluoromethyl group yielded chlorinecontaining perfluorocyclohexane derivatives carrying the trifluoromethyl group. Trifluoromethylbenzonitriles gave perfluoro(dimethylcyclohexane)s