Direct Isomerization of Linoleic Acid to Conjugated Linoleic Acids (CLA) using Gold Catalysts

Supported gold catalysts, e.g., Au on Al₂O₃, Fe₂O₃, CeO₂, MnO₂, TiO₂, ZrO₂, activated carbon, titanium silicalite TS‐1, were prepared and used for the isomerization of linoleic acid (cis‐9,cis‐12‐octadecadienoic acid) to conjugated linoleic acids (CLA) in the presence of hydrogen at 165 °C in a batch reactor. The best results were obtained using a catalyst with 2 wt % Au on TS‐1, which exhibits a high selectivity (78 %) towards CLA. The two biologically active target CLA isomers, i.e., cis‐9,trans‐11‐CLA and trans‐10,cis‐12‐CLA, were the main products. During the isomerization of linoleic acid to CLA, consecutive reactions also took place. These were the hydrogenation of linoleic acid and CLA to monounsaturated octadecenoic acids and the further hydrogenation of monounsaturated acids to stearic acid. Thus, gold catalysts are capable of isomerizing linoleic acid to CLA and hydrogenating their double bonds to an extent that depends on the Au catalyst used.