The Ketonization Reaction of Mixed Fatty Acids on Metal Oxides

Abstract

The selectivity for the ketonization reaction from the mixture of fatty acid, CH3COOH and C2H3COOH, on metal oxide catalysts (ZnO, CoO, SrO, r-Al2O3, Bi2O3, Nd2O3, La2O3, Fe2O3) and a possible reaction mechanism have kineticallybeen investigated.
That the catalytic selectivity for the formation of ethyl methyl ketone as asymmetric ketone on metal oxides shows a volcano-type correlation with respect to the heats of formation (-ΔH0 kcal/acetate-ion) of the corresponding metal acetates as is shown in Fig.4. The ratedetermining step of ketonization reaction is the decarbonylation process of an acid-anhydride intermediate produced from fatty acid ion and acyl cation.
In order to examine this step in further detail, the isotope effect for ketonization reaction has been studied by using CD3COOD and CH3COOD. The primary isotope effect was observed in the cases of Fe2O3, Bi2O3, and Al2O3 except for ZnO, CoO, SrO, Nd2O3, and La2O3. However, no isotope effect was observed when CH3COOD was used as a reactant.
It was also found by the use of deuterium isotope that the rate-determining stepof ketonization on Fe2O3, Bi2O3, and Al2O3 is the C-H bond cleavage process of an acid-anhydride intermediate.