Methyl linoleate autoxidation

Styrene autoxidation in chlorobenzene, 3QUC. Reference QO. b Methyl linoleate autoxidation in t-butanol, 37°C. Reference 92. c Ethylbenzene autoxidation in o-dichlorobenzene. 25°C. 

PEDRIELLI p, PEDULLi G F and SKIBSTED L H (2001a) Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-braining reaction of quercetin and epicatechin in autoxidation of methyl linoleate, JAgric Food Chem, 49, 3034-40. 

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

Chan, H.W.S. and Levett, G. (1977). Autoxidation of methyl linoleate. Separation and analysis of isomeric mixtures of methyl linoleate hydroperoxides and methyl hydrox-ylinoleates. Lipids 12, 99. 

Tphe major objective of this work was to understand better the effect - of heavy metals in autoxidation reactions in view of the importance of trace metals in oils, fats, rubber, plastics, and other materials. Because of our interest in the stability of polyolefins such as polyethylene and polypropylene the major model substance used was 2,6,10,14-tetramethyl-pentadecane. With its four tertiary C—H bonds it is a suitable model for either polypropylene or branched polyethylene. Hexadec-l-ene was also used since its mono-olefinic character could be typical of some residual unsaturation in polyethylene. N-alkylamides served as model substances for polyamides, and a few experiments were also carried out with methyl linoleate. While studying the causes of initiation of the autoxidation of these substances we observed that certain compounds were catalysts at low concentrations but became inhibitors at higher concentrations. The phenomenon was called catalyst-inhibitor conversion. ... 

Many authors128, 142-146 have proposed reaction (112), or a variant of it, in an attempt to explain kinetic data. For example, Uri145 proposed the following mechanism for the initiation of cobaltous stearate-catalyzed autoxidation of methyl linoleate in benzene ... 

Metal phthalocyanine complexes are also frequently used as autoxidation catalysts (see Section II.B.2). They have generally been found to be more active than the corresponding stearates or acetylacetonates. Thus, Uri145 compared the catalytic activity of a series of transition metal stearates with the corresponding metal phthalocyanines in the autoxidation of methyl linoleate. The phthalocyanine complexes afforded faster rates of oxidation. In addition, the phthalocyanine ligand is stable and is not easily destroyed under autoxidizing conditions. Interest in metal phthalocyanine catalysts has also been stimulated by their resemblance to the metal-porphyrin structures contained in many oxidative enzymes (see Sections II.B.2 and V). 

Ha, K.-H. and Igarashi, O. 1990. The Oxidation Products from Two Kinds of Tocopherols Co-Existing in Autoxidation System of Methyl Linoleate. J. Nutr. Sci. Vitaminol. 36 411—421. 

During the inhibited self-initiated autoxidation of methyl linoleate by a-Toc in solution, Niki and coworkers made the interesting observation that a-Toc acts as an antioxidant at low concentrations, but high concentrations (up to 18.3 mM) actually increased hydroperoxide formation due to a pro-oxidant effect. The pro-oxidant effect of a-Toc was observed earlier by Cillard and coworkers in aqueous micellar systems and they found that the presence of co-antioxidants such as cysteine, BHT, hydroquinone or ascor-byl palmitate inverted the reaction into antioxidant activity, apparently by reduction of a-To" to a-Toc . Liu and coworkers ° found that a mixture of linoleic acid and linoleate hydroperoxides and a-Toc in SDS micelles exhibited oxygen uptake after the addition of a-Toc. The typical ESR spectrum of the a-To" radical was observed from the mixture. They attributed the rapid oxidation to decomposition of linoleate hydroperoxides, resulting in the formation of linoleate oxy radicals which initiated reactions on the lipid in the high concentration of the micellar micro-environment. Niki and coworkers reported pro-oxidant activity of a-Toc when it was added with metal ions, Fe3+25i Qj. jjj (jjg oxidation of phosphatidyl choline liposomes. a-Toc was found... 

It is formed in a very small amount (but as a predominant odor compound) during autoxidation of linoleic acid (Cis 2) and methyl linoleate (Ullrich and Grosch, 1987). 

Oleuropein appears to interfere with some biological processes such as lipoprotein oxidation, platelet aggregation, platelet and leukocyte eicosanoid production and cardiovascular control too. As previously described, oleuropein and hydroxy-tyrosol are characterised by a catechol moiety that appears to be needed for their scavenger and antioxidant activities. In fact, it was demonstrated that these compounds prevent thermally initiated autoxidation of methyl linoleate in homogenous solutions [56], protect LDL from oxidation [57] and inhibit production of... 

The hypothesis of a bimolecular initiation reaction for liquid phase autoxida-tions was extended beyond cyclohexanone as a reaction partner. Also other substances featuring abstractable H-atoms are able to assist in this radical formation process. The initiation barrier was found to be linearly dependent on the C-H bond strength, ranging from 30 kcal/mol for cyclohexane to 5 kcal/mol for methyl linoleate [14, 15]. Substrates that yield autoxidation products that lack weaker C-H bonds than the substrate (e.g., ethylbenzene) do not show an exponential rate increase as the chain initiation rate is not product enhanced [16]. 

Kraybill (1956) observed that 10-30 % of the tocopherols in dairy products were destroyed when irradiated with 80,000 roentgens per hour. Rose et al. (1961) irradiated solutions of DL-alpha-tocopherol with a Co source and observed extensive destruction of this vitamin and a rise in products similar to those obtained by autoxidation. Irradiation in saturated solvents destroyed more tocopherol than did irradiation in unsaturated solvents (such as methyl linoleate). 

HPODE (methyl ester) was isolated from an autoxidation reaction of methyl linoleate conducted using a higher than usual amount of a-tocopherol [31]. a-Tocopherol was included in order to drive the reaction toward formation of the aUyUc 8- and 14-hydroperoxides, as had been described to occur earlier [33]. While these products were not found, the bis-sA y ic ll(9Z,12Z)-HPODE was obtained as one of the major... 

Brash, A. R. 2000. Autoxidation of methyl linoleate Identification of the his-aUyhc 11-hydroperoxide. 35 947-952. 

Autoxidation and photo-oxygenation are two aspects of the non-enzymic reaction between oxygen and unsaturated fatty acids. The enzymic reactions are discussed in Section 10.3. Oxidation of lipids during storage and handling, involving complex substrates and ill-defined reaction conditions, proved difficult to understand. This difficulty is enhanced by the fact that the primary oxidation products are labile and readily converted to secondary oxidation products of several kinds. Understanding of these processes has come from studies of simpler substrates such as methyl oleate or methyl linoleate under clearly defined reaction conditions. 

In contrast, methyl linoleate gives only two autoxidation products in equivalent amount. These are the 9- and 13-hydroperoxides and there is no evidence of any other hydroperoxide. These individual compounds, however, can change from Cyt to tyt dienes with exchange of the hydroperoxide group from C9 to C13 or vice versa (see following section). 

Chan HWS and Levett G Autoxidation of methyl linoleate separation and analysis of isoneric mixtures of methyl linoleate hydroperoxides and methyl hydrojQ linoleates. LipldUi 12 99-104, 1977. 

The autoxidation of trilinolein was more complicated than that of the simple fatty esters and did not follow the same rate equation. The order of the reaction was about 0.84 compared to 1.0 for the simple fatty esters. The efficiency of the initiators used, DMVN, was increased to 100% in the trilinolein compared to about 75% in the simple fatty esters. The difference in kinetic behavior between trilinolein and methyl linoleate was attributed to the tendency of the triacylglycerol to form aggregates. The kinetic induction period approach used to measure oxidizability may be subject to errors because of the changes in efficiency of some of the artificial initiators used according to the system and the lipid substrate. Phenolic antioxidants such as a-tocopherol are also affected by the colloidal properties of the lipids used in the oxidation test system employed (Chapter 9). 

Table 2.2. Hydroperoxides from autoxidation of methyl linoleate (as % of total) ...

Erankel, E.N., Neff, W.E., Rohwedder, W.K., Khambay, B.P.S., Garwood, R.F. and Weedon, B.C.L. Analysis of autoxidized fats by gas chromatography-mass spectrometry II. Methyl linoleate. Lipids 12, 908-913 (1977b). 

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