Formation of dimers during the initial stage of autoxidation in methyl linoleate.

The formation of dimers in the initial stage of methyl linoleate (ML)autoxidation was demonstrated.The oxidation profile of freshly prepared ML was followed by TLC during autoxidation by aeration at 30°C for 192 hr.After 24hr of autoxidation, the peroxide value of ML was still 0.6, and two unknownpolar spots appeared besides intact MLand methyl linoleate hydroperoxides (MLHPO).These two spots were identified as dimers by successive gel and high performance liquid chromatographic separations and by molecular weight determination.The ratio of dimers/MLHPO reached a maximum(0.74)after 96 hr of autoxidation.This result indicates that the formation of dimers in the initial stage of autoxidation was slightly less than that of MLHPO.The dimers were linked through -C-O-O-C-bonds and contained hydroperoxy and/or carbonyl groups and conjugated dienes.Many papers have been published on the autoxidation of unsaturated oils and it is generally accepted that autoxidation of oils involves a free radical mechanism.1~6)It is also well knownthat in the course of autoxidation of lipids, the primary stable oxidation products are monomeric hydroperoxides and many secondary products, including such as