The Initial Reaction Products in the Autoxidation of Methyl Docosapolyenoate

Abstract

Methyl esters of cuttle-fish oil fatty acids were segregated by urea-complex procedure, then distilled in vacuum and chromatographed to obtain methyl docosapolyenoate. Methyl pentaenoate and hexaenoate were not strictly separated. Autoxidation of this sample was performed in the dark at 0 to 2°C. Initial reaction products in the autoxidation of methyl docosapolyenoate were separated by the countercurrent distribution method, and then their ultraviolet and infrared spectra were determined. One of them showed the peroxide value (m equiv./kg) at 1.13 × 104, which is the highest value for lipid. From this value and infrared spectra, etc., dihydroperoxide may exist. Unsaturated carbonyl groups are little from the result of the ultraviolet spectra. By investigating the conjugation of these peroxide concentrates, and the infrared absorptions of α-methylene group and-OOH group etc., it was concluded that the peroxide concentrates probably contain the-OOH group at their α-methylene position. In the most promoted autoxidation fraction, the amount of conjugated diene is at about less than 0.5 per molecule, and cis-trans and trans-trans conjugated dienes exist. There is little conjugated triene in it. In the less autoxidized fraction, the amount of conjugated diene is larger, but conjugated triene are not found. In both fraction, conjugated tetraene and higher are not found. There are considerably many double bonds left as cis nonconjugated form.