Isomerization of unsaturated fatty esters by iron pentacarbonyl. Preparation of iron tricarbonyl complexes of polyunsaturated fats

Iron pentacarbonyl is a powerful isomerization agent of unsaturated fatty esters. Highly conjugated fats are obtained when polyunsaturated fatty esters are treated with an excess Fe(CO)5 to form complexes followed by decomposition of the complexes with FeCl3. Iron tricarbonyl complexes were prepared in 80 to 95% yields from methyl linoleate, linolenate and polyunsaturated fatty esters of soybean, linseed and safflower oils by heating at 180舑185C with 2 moles Fe(CO)5 per mole ester under nitrogen pressure. Decomposition of these complexes with FeCl3 resulted in 90 to 97% conjugation of the polyunsaturated fatty esters mainly in the alltrans configuration. Isolatedtrans unsaturation reached levels of 18 to 30%. Methyl oleate yielded 74%trans unsaturation but no complex of iron carbonyl was obtained.