Catalytic hydrogenation of linoleic acid on nickel, copper, and palladium

The catalytic activity and selectivity for hydrogenation of linoleic acid were studied on Ni, Cu, and Pd catalysts. A detailed analysis of the reaction product was performed by a gas-liquid chromatograph, equipped with a capillary column, and Fourier transform-infrared spectroscopy. Geometrical and positional isomerization of linoleic acid occurred during hydrogenation, and many kinds of linoleic acid isomers (trans-9,trans-12; trans-8,cis-12 or cis-9,trans-13; cis-9,trans-12; trans-9,cis-12 and cis-9,cis-12 18:2) were contained in the reaction products. The monoenoic acids in the partial hydrogenation products contained eight kinds of isomers and showed different isomer distributions on Ni, Cu, and Pd catalysts, respectively. The positional isomers of monoenoic acid were produced by double- bond migration during hydrogenation. On Ni and Pd catalysts, the yield of cis-12 and trans-12 monoenoic acids was larger than that of cis-9 and trans-9 monoenoic acids. On the contrary, the yield of cis-9 and trans-9 monoenoic acids was larger than that of cis-12 and trans-12 monoenoic acids on Cu catalyst. From these results, it is concluded that the double bond closer to the methyl group (Delta 12) and that to the carboxyl group (Delta 9) show different reactivity for hydrogenation on Ni, Cu, and Pd catalysts. Monoenoic acid formation was more selective on Cu catalyst than on Ni and Pd catalysts.