Structure of hydroperoxides obtained from autoxidized methyl linoleate

Abstract

SummaryA 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.

Oxygen Absorption at the Process of the Degradation of Linoleic Acid Hydroperoxides

“…8). The pathways, A, B, C and D, have already been ascertained or suggested (7,(30)(31)(32), and the pathway E is proposed from the present experiments. The pathways F, G and H could be suggested by these overall considerations.…”

Some of the most significant changes in the Fourier transform infrared spectra of edible oils under oxidative conditions

“…Fig 1 (0 days) shows as an example the infrared spectrum of a non‐oxidised sample of rapeseed oil. Some of the most significant bands1, 22, 29 are the following: the band at 3468 cm −1 assigned to the overtone of the glyceride ester carbonyl absorption; the band near 3006 cm −1 due to the cis double‐bond stretching vibration; bands at 2924 and 2854 cm −1 due to the asymmetric and symmetric stretching vibration of the aliphatic CH 2 functional group; the band at 1746 cm −1 due to the ester carbonyl functional group of the triglycerides; the weak band near 1654 cm −1 associated with the stretching vibration of the carbon–carbon double bonds of cis ‐olefins; the band near 1464 cm −1 due to the bending vibrations of the CH 2 and CH 3 aliphatic groups; the band near 1417 cm −1 tentatively assigned to rocking vibrations of CH bonds of cis ‐disubstituted olefins; the band near 1377 cm −1 due to bending vibrations of CH 2 groups; bands near 1238 and 1163 cm −1 both associated with the stretching vibration of the CO ester groups and with the bending vibration of the CH 2 group and both related to the proportion of saturated acyl groups; bands near 1119 and 1099 cm −1 associated with the stretching vibration of the CO ester groups, the first being related in an inverse way to the proportion of saturated acyl groups; the very weak band near 983 cm −1 associated with CH conjugated olefinic groups, with bending vibrations of either CH trans,trans ‐conjugated olefinic groups or cis,trans ‐conjugated olefinic groups or of both;30–32 the weak band near 967 cm −1 associated with bending vibrations of CH functional groups of isolated trans ‐olefins; the band near 914 cm −1 , absent in olive oil, and difficult to assign; and finally the band near 723 cm −1 due to the overlapping of the CH 2 rocking vibration and to the out‐of‐plane vibration of cis ‐disubstituted olefins.…”

A kinetic study on the autoxidation of sunflowerseed oil

“…Other pioneers in this field and their major contributions include Privett and coworkers at the Hormel Institute (8,9) who described the autoxidation mechanism and kinetics of unsaturated fatty acids.…”