HOMOGENEOUS CATALYTIC HYDROGENATION OF UNSATURATED FATS - GROUP VIB METAL CARBONYL COMPLEXES

Carbonyl complexes of Cr, Mo and W have been studied as soluble catalysts for the hydrogenation of methyl sorbate and of methyl esters from soybean oil. With methyl sorbate, relative catalytic activity decreased in the approximate order: mesitylene-Mo(CO)3, cycloheptatriene-Mo(CO)3, cycloheptatriene-Cr(CO)3, bicyclo (2,2,1) hepta-2,5-diene-Mo(CO)4, chlorobenzene-Cr(CO)3, methyl benzoate-Cr(CO)3, mesitylene-W(CO)3, benzene-Cr(CO)3, toluene-Cr(CO)3, mesitylene-Cr(CO)3, and hexamethylbenzene-Cr(CO)3. Order of catalytic activity was related to thermal stability of the complexes during hydrogenation. With mesitylene-M(CO)3 complexes, selectivity varied in the order Cr>Mo>W. Under certain conditions the mesitylene complexes of W, Cr and Mo reduced methyl sorbate respectively to methyl 2-, 3-, and 4-hexenoates as main products. The more active and thermally stable Cr(CO)3 complexes catalyzed effectively the hydrogenation of linoleate and linolenate in soybean oil esters with little or no stearate formation. The hydrogenated products formed with the benzoate complex at 165-175 C contained 50-67% monoene, 18-30% diene, 2-7% conjugated diene, and only 3-7%trans unsaturation. Linolenate-linoleate selectivity values varied from 3 to 5 and linoleate-oleate selectivity from 7 to 80. Monoene fractions had 40-50% of the double bond in the C-9 position; the rest of the unsaturation was distributed mainly between the C-10 and C-12 positions. Conjugation is apparently an intermediate step in the hydrogenation of linoleate and linolenate. The Cr(CO)3 complexes are unique in catalyzing the hydrogenation of polyunsaturated fatty esters to monounsaturated fatty esters of low trans content. © 1969 AOCS Press.