High-yield, radical-initiated oxidative functionalization of ethane by perfluorocarboxylic acid anhydrides. Role of metal ions in catalytic alkane oxidations in the presence of perfluorocarboxylic acid anhydrides

Hydrogen peroxide and a trace of either ethene or propene initiated the conversion of ethane to propionic acid and its mixed anhydride (CH3CH2CO2H + CH3CH2COOCOCF3) and trifluoromethyl ethyl ketone, CH3CH2COCF3, by trifluoroacetic anhydride at 80 degrees C. For a fixed amount of H2O2, the amount of products formed increased with increasing amount of trifluoroacetic anhydride employed and was always higher than the amount of H2O2 added. These products. were also obtained when H2O2 was replaced by other radical initiators: m-chloroperbenzoic acid, azobisisobutyronitrile, and PbEt(4). With PbEt(4), ethene or propene was not required for product formation and close to 500 equiv of products was formed for every equivalent of PbEt(4) employed! Longer chain perfluorocarboxylic acid anhydrides reacted analogously; however, as the RI group increased in length, a corresponding increase in mixed anhydride to ketone selectivity was observed. Methane gave very little product under the reaction conditions whereas propane underwent simple stoichiometric oxidation to 2-propanol and acetone by H2O2. The addition of (CF3CO2)(2)Pd to the ethane reaction resulted in simple oxidation to ethanol and acetaldehyde in amounts lower than that corresponding to the H2O2 present. In complete contrast to the ethane reaction, the yield of products from methane increased significantly (although less than the H2O2 added) upon the addition of (CF3CO2)(2)Pd, with methanol being the principal product.