Isomerization during hydrogenation. III. Linoleic acid

Summary The isomerization that takes place during the catalytic hydrogenation of linoleic acid and methyl linoleate producescis andtrans 9, 10, 11, and 12 monoenes. The double bond at the 12 position appears to hydrogenate slightly faster than that in the 9 position. More octadecenoic acids with double bonds at the 10 or 11 positions are produced during a selective (high temperature, low pressure) hydrogenation than during a non‐selective process. Although the degree of selectivity of the hydrogenation is determined by the amount of isomerization of the original pentadiene system to a conjugated diene, only part of the methylene‐interrupted diene goes through this type of isomerization even during a highly selective hydrogenation. The half hydrogenation‐dehydrogenation reaction mechanism is applied to explain the simultaneous positional and geometrical isomerizations.