Modification of vegetable oils. XI. The formation of trans isomers during the hydrogenation of methyl oleate and triolein

Summary 1. During the hydrogenation of methyl oleate, trans isomers are formed at a very rapid rate. As much as 38% of trans isomers formed while the first 10% of methyl stearte was formed. 2. The rate of formation of trans isomers in methyl oleate undergoing hydrogenation is increased by increasing the temperature, increasing the catalyst concentration, and decreasing the degree of dispersion of the hydrogen. 3. The hydrogenation of methyl oleate always resulted in the establishment of an equilibrium between cis and trans isomers, and irrespective of the conditions employed the concentration of trans isomers was always 67%, calculated on the basis of total unsaturated constituents. 4. It is concluded that all of the iso-oleic acids formed during the hydrogenation of methyl oleate adsorb hydrogen at the same rate as oleic acid and are adsorbed and desorbed from the nickel catalyst with equal ease. 5. Trans isomers are formed at a slightly lower rate during the hydrogenation of triolein than in the case of methyl oleate. 6. Partial hydrogenation of triolein also results in the establishment of an equilibrium between cis and trans isomers of oleic acid but at values of less than 67% of trans constituents (based on the total unsaturated constituents) observed with methyl oleate. The equilibrium concentration was found to vary with the conditions of hydrogenation and was found to be 62% at 200°C. and 57% at 175°C. Report of study made under the Research and Marketing Act of 1946. Presented at the 24th Fall Meeting of the American Oil Chemists’ Society, San Francisco, Calif., Sept. 26–28, 1950. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.