Trifluoromethylation of aromatic compounds via Kolbe electrolysis in pure organic solvent. Study on laboratory and pilot scale

Abstract

The present study investigates the conditions of trifluoromethylation of various aromatic compounds via the Kolbe oxidation of trifluoroacetic acid. The preparative electrolyse conditions were first optimized on the laboratory scale using the trifluoromethylation of benzonitrile in acetonitrile solutions as a model case. Sodium or pyridinium trifluoroacetates were tried as a source of trifluoromethyl radicals, the partial neutralization of trifluoroacetic acid by pyridine provided the best yield of trifluoromethylbenzonitrile (46%). The trifluoromethylation of the other aromatic compounds such as acetophenone, benzaldehyde and nitrobenzene led to yields slightly lower than those observed in the case of benzonitrile. The trifluoromethylation of benzonitrile was then studied in a commercially available flow cell. Yields were consistent with those obtained on the laboratory scale.