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

The present study investigates the conditions of trifluoromethylation of va rious aromatic compounds via the Kolbe oxidation of trifluoroacetic acid. T he preparative electrolyse conditions were first optimized on the laborator y scale using the trifluoromethylation of benzonitrile in acetonitrile solu tions as a model case. Sodium or pyridinium trifluoroacetates were tried as a source of trifluoromethyl radicals, the partial neutralization of triflu oroacetic acid by pyridine provided the best yield of trifluoromethylbenzon itrile (46%). The trifluoromethylation of the other aromatic compounds such as acetophenone, benzaldehyde and nitrobenzene led to yields slightly lowe r than those observed in the case of benzonitrile. The trifluoromethylation of benzonitrile was then studied in a commercially available how cell. Yie lds were consistent with those obtained on the laboratory scale.