Structure of hydroperoxides obtained from autoxidized methyl linoleate

Abstract

Summary: A sample of debromination methyl linoleate has been autoxidized to a peroxide value of 671 m.e./kg. at approximately 0°C. in the dark. An essentially pure concentrate of methyl octadecadienoate monohy‐droperoxide was quantitatively separated; infrared and ultraviolet spectral studies were made on the peroxide concentrate and on the corresponding hydroxyl derivative obtained by reducing the peroxides with stannous chloride.The infrared data showed no conjugated peroxides having geometric configurations other than cis, trans; the same data also showed that the peroxide concentrate contained at least 90% conjugated cis,trans forms. Calculations based on ultraviolet spectrophotometric methods also indicated that the peroxides were at least 90% conjugated. The remaining 10% of the sample is most likely nonconjugated diene hydroperoxide. Since analogous cis, cis conjugated dienes have not been isolated and their infrared and ultraviolet properties are unknown, their presence here in small amounts is possible. Ultraviolet and infrared spectra of the reduced compounds conform closely to those of the peroxides except for reduction in the intensity of the OH bond at 2.88 μ.The infrared absorption spectra of the C−H structure and carbonyl groups of an essentially pure conjugated cis, trans methyl octadecadienoate monohydroperoxide were recorded, using a LiF prism.The infrared absorption spectra of the C−H strucfraction isolated from methyl linoleate autoxidized in the dark at 24°C. indicated that appreciable amounts of conjugated trans, trans hydroperoxides were present, in addition to those of the cis, trans type. It is possible that the conjugated cis, trans isomers were formed originally but were labile at the higher temperature and in the presence of catalysts (e.g., peroxides) were transformed to the thermodynamically more stable conjugated trans, trans isomer.