STRUCTURES OF DIMERS PRODUCED FROM METHYL LINOLEATE DURING INITIAL-STAGE OF AUTOXIDATION

A structural investigation on the main fraction of dimers formed during the induction period of autoxidation in methyl linoleate (ML) was carried out. The dimeric fraction (A2), which was isolated from the autoxidized ML by various chromatographic techniques and gave a single spot on TLC, was further seperated into 4 major components (components 1-4) by high performance liquid chromatography (HPLC). The mean MW of these components were 643-655 and component 4 gave the parent peak 652 on an FD-mass spectrum which corresponded to 2 x ML + 40. The reduced products of each component with stannous chloride were identified in common as methyl 9- or 13-hydroxy octadecadienoate and methyl 9,13-dihydroxy octadecenoate by GC-MS [gas chromatography-mass spectrometry]. Evidently, all of these dimers contained a peroxide bridge linking between a pair of ML across C-9 or C-13 on one of the ML and C-9 or C-13 on the other, with a hydroperoxy group.