Conjugation of polyunsaturated acids

Abstract

The isomerization reaction of methyl linoleate and methyl linolenate with potassium t-butoxide has been investigated. The compositions of the reaction products formed at three temperatures have been determined and the relationships between these analyses and observed differences in absorptivities by UV spectrometry are discussed. Conclusions concerning the reaction mechanisms are based on compositional analysis and results of experiments using radioactive or stable isotope labeled reagent. Double bonds in molecules which are not conjugated during the reaction retain the original cis configuration. The double bond in the A12 position is the most susceptible to positional isomerization to form the conjugated system. With the diene, this selectivity is small, while with the triene, the shifting of the A 12 bond is the preponderant initial reaction. Isotopic experiments yielded direct evidence for the postulated carbanion mechanism of reaction. An activated methylene group is generally required for the formation of the carbanion. While the UV spectra of the reaction products formed from methyl linolenate at 140 C showed no peak in the diene region, 34% conjugated diene-triene was present. The intact conjugated systems can migrate when the reaction is sufficiently energentic to produce conjugated trienes with double bonds other than the 10, 12, 14 system. The conjugation of triene is a stepwise reaction through the conjugated dienetriene.

Screening analysis of unknown seed oils

“…By a treatment with hydrochloric acid the original fatty acids can be recovered quantitatively without stereochemical changes. Unfortunately, the method cannot be applied to conjugated fatty acids as the recovery is uncomplete as decomposition occurs [140]. The reaction is also irreversible for acetylenic compounds.…”

Conjugated linoleic acid (CLA) isomers: formation, analysis, amounts in foods, and dietary intake

“…In contrast to dairy products and meats from ruminants, which contain primarily rumenic acid, synthetically prepared CLA mixtures have been shown to contain a mixture of two or four major positional CLA isomers [18,23]. Synthetic CLA mixtures are produced by alkali isomerization of linoleic acid or oils rich in this fatty acid, such as sunflower oil.…”

Conjugated linoleic acid and octadecenoic acids: Extraction and isolation of lipids

“…On the other hand, synthetic preparations of CLA, produced by alkali isomerization of linoleic acid, or oils rich in this fatty acid such as sunflower or safflower oils, were believed to yield two CLA isomers in about equal proportion, i.e., 9c,11t-C18:2 and 10t,12c-C18:2 [7]. However, earlier work had shown that significant amounts of two additional isomers could also be formed by more extensive alkali isomerization of linoleic acid [12]. These isomers were identified as 8,10-C18:2 and 11,13-C18:2 [12], and their geometric configuration was determined as 8t,10c-C18:2 and 11c,13t-C18:2 [10,13].…”

“…However, earlier work had shown that significant amounts of two additional isomers could also be formed by more extensive alkali isomerization of linoleic acid [12]. These isomers were identified as 8,10-C18:2 and 11,13-C18:2 [12], and their geometric configuration was determined as 8t,10c-C18:2 and 11c,13t-C18:2 [10,13].…”