Isomerization during hydrogenation of soap. I. Potassium oleate

Potassium oleate in slightly alkaline solution was hydrogenated for up to 7 hr with Rufert nickel catalyst at 150C and 20 kg/sq cm pressure. With 1% catalyst, the iodine value dropped by 12 units in the first hour, and only slightly thereafter. With 2% catalyst there was a drop of 24 units in iodine value in the first hour, a steady state for the next 3 hr, and a second sharp drop of 30 units prior to the seventh hour. Samples of fat hydrogenated over 1% catalyst for 3 hr and 7 hr respectively were analyzed by gas‐liquid chromatography, thecis andtrans monoenes were separated by argentation thin‐layer chromatography, and the positional isomers in each were determined by oxidation of the total fraction to dicarboxylic acids, which were then estimated by GLC. Apart from double‐bond saturation during the first 3 hr of hydrogenation, extensive double‐bond migration yielded 23.5% oftrans 8‐ to 13‐monoene, accompanied by small amounts only of positionalcis monoenes other than the starting material. After 7 hr of hydrogenation, extensivecis tocis isomerization occurs, accompanied by lesscis totrans shift; thecis:trans ratio for each monoene consequently tended toward 1:1. The results are explained on the sorption mechanism of hydrogenation and suggest that soap hydrogenation, involving catalyst poisoning, may represent a magnified version of normal fat hydrogenation.