Autoxidation of phenyl linoleate and phenyl oleate: HPLC analysis of the major and minor monohydroperoxides as phenyl hydroxystearates.

Phenyl linoleate was oxidized under different conditions. The monohydroperoxide products were isolated and subsequently hydrogenated. The isomers of phenyl hydroxysterate obtained were separated by high pressure liquid chromatography. On the basis of cochromatography with reference materials and mass spectroscopy, it was shown that the mixture was composed mainly (96%) of phenyl 9-hydroxy- and phenyl 13-hydroxysterates (9- and 13-HOPh) with 8-, 10-, 12- and 14-HOPh as minor compounds (4%). In the minor fraction, the 8- and 14-HOPh predominated in comparison to the 10- and 12-HOPh. The presence of α-tocopherol in the autoxidation experiment changed the proportion of the phenyl hydroxystearate isomers: the proportion of the 9- and 13-HOPh increased and those of the 8- and 14-HOPh decreased. After addition of 0.05% or higher concentrations of α-tocopherol, the minor fraction comprised approximately equal amounts of 8-, 10-, 12- and 14-HOPh. Autoxidation of phenyl oleate followed by hydrogenation of the monohydroperoxides resulted in the formation of a mixture of phenyl hydroxystearates containing approximately equal amounts of 8-, 9-, 10- and 11-HOPh.