A MECHANISTIC STUDY OF OLEATE AUTOXIDATION - COMPETING PEROXYL H-ATOM ABSTRACTION AND REARRANGEMENT

The mechanism of methyl oleate autoxidation was investigated. HPLC techniques were developed to analyze the products of autoxidation (hydroperoxides and the corresponding alcohols). The alcohols could be completely resolved by normal-phase chromatography, six products being characterized having oxygen substitution and double position as follows: 11-OOH-trans-Delta(9-10), 11-OOH-cis-Delta(9-10), 10-OOH-trans-Delta(8-9), 9-OOH-trans-Delta(10-11), 8-OOH-trans-Delta(9-10), 8-OOH-cis-Delta(9-10) As the hydrogen atom donor concentration of the medium of autoxidation is increased, increased 11-cis, 8-cis, 9-trans, and 10-trans hydroperoxides and decreased 11-trans and 8-trans hydroperoxides were obtained, consistent with a mechanism in which peroxyl H-atom abstraction and [2,3] allylperoxyl rearrangement are in competition. An iterative computer kinetic analysis was developed which modeled the oleate autoxidation mechanism, and rearrangement rate constants were determined. Allylperoxyl radicals undergo rearrangement with different rates depending on the geometry of the allylperoxyl.