Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products.

Unsaturated fatty acid monolayers on silica gel have been autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies have been studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60 C. The rates of autoxidation of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates are considerably faster than that in bulk phase, and the rates conform to apparent first order kinetics. Autoxidation of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amount of diene conjugation, and the major products formed were identified as 9,10-epoxy and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidation is stereospecific, with cis and trans olefins giving cis and trans epoxides, respectively. Oleic acid was autoxidized to only a small extent during 27 hr and produced no detectable amount of epoxide.