Detection of monohydroperoxides with unconjugated diene systems as minor products of the autoxidation of methyl linoleate

Methyl linoleate was autoxidized for 70 h at - 5 °C in the presence of tert-butoxy radicals, which originate from the decay of di-tert-butyl peroxyoxalate. The monohydroperoxides formed were isolated and, after reduction to the corresponding hydroxy compounds, separated on Silica Gel/AgNO₃ into a major and a minor fraction (approx 1% of the monohydroperoxides). Hydroxy derivatives of the well-known 9- and 13-hydroperoxides with conjugate diene systems were identified in the major fraction. Two hydroxy fatty acid methylesters with isolated double-bonds were separated by HPLC from the minor fraction. On the basis of both the mass spectra of the corresponding methyl hydroxystearates and the chromatographic properties of the hydroxydienes, the formation of methyl 8- and methyl 14-hydroperoxyoctadecadienoates with isolated cis double bonds during the autoxidation of methyl linoleate was established.