Linoleic acid reactions

The fate of other fatty acids and minor components during processing has not been investigated. The conditions used to conjugate linoleic acid have little or no effect on either monounsaturated or saturated fatty acids, however, any polyunsaturated fatty acids may be conjugated. The products of the reaction of alkali catalysts on these fatty acids are more complex than that discussed for linoleic acid (Reaction 4) and will not be discussed except to note that these reactions may produce undesirable products. 

Recently St. Angelo et al. (38 ) presented data reaffirming their previous observation that hexanal is an enzymically produced volatile product of the peanut lipoxygenase-linoleic acid reaction. They also confirmed the observations of Pattee and co-workers (33) that pentane is present in the headspace volatiles from the reaction. St. Angelo et al. (38) further showed that care must be excerised to prevent pentane artifacts from arising from the known thermal degradation of hydroperoxide products (39) present in the aqueous solution. 

The isolation of the geometrical isomers of hydroperoxy-octadecadienolc acid from the peanut lipoxygenase-linoleic acid reaction (, ) raised the question as to which were enzymically produced and which were autoxidatlvely produced. Earlier,... 

In the area of moleculady designed hot-melt adhesives, the most widely used resins are the polyamides (qv), formed upon reaction of a diamine and a dimer acid. Dimer acids (qv) are obtained from the Diels-Alder reaction of unsaturated fatty acids. Linoleic acid is an example. Judicious selection of diamine and diacid leads to a wide range of adhesive properties. Typical shear characteristics are in the range of thousands of kilopascals and are dependent upon temperature. Although hot-melt adhesives normally become quite brittle below the glass-transition temperature, these materials can often attain physical properties that approach those of a stmctural adhesive. These properties severely degrade as the material becomes Hquid above the melt temperature. 

Refluxing linoleic acid and a primary or secondary alkyl amine with -toluenesulfonic acid in toluene for 8—18 h also yields the substituted amides (32—34). The reaction of methyl esters with primary or secondary amines to make substituted amides is catalyzed with sodium methoxide. Reactions are rapid at 30°C under anhydrous conditions (35). Acid chlorides can also be used. Ai,A/-dibutyloleamide [5831-80-17 has been prepared from oleoyl chloride and dibutyl amine (36). 

Liquid Ghromatography/Mass Spectrometry. Increased use of Hquid chromatography/mass spectrometry (Ic/ms) for stmctural identification and trace analysis has become apparent. Thermospray Ic/ms has been used to identify by-products in phenyl isocyanate precolumn derivatization reactions (74). Five compounds resulting from the reaction of phenyUsocyanate and the reaction medium were identified two from a reaction between phenyl isocyanate and methanol, two from the reaction between phenyl isocyanate and water, and one from the polymerisation of phenyl isocyanate. There were also two reports of derivatisation to enhance either the response or stmctural information from thermospray Ic/ms for linoleic acid hpoxygenase metabohtes (75) and for cortisol (76). 

Conjugation as well as geometric and positional isomerization occur when an alkadienoic acid such as linoleic acid is treated with a strong base at an elevated temperature. CycHc fatty acids result from isomerization of linolenic acid ia strong base at about 250°C (58). Conjugated fatty acids undergo the Diels-Alder reaction with many dienophiles including ethylene, propylene, acryUc acid, and maleic anhydride. 

C-21 dicarboxyhc acids are produced by Westvaco Corporation in Charleston, South Carolina in multimillion kg quantities. The process involves reaction of tall oil fatty acids (TOFA) (containing about 50% oleic acid and 50% hnoleic acid) with acryhc acid [79-10-7] and iodine at 220—250°C for about 2 hours (90). A yield of C-21 as high as 42% was reported. The function of the iodine is apparendy to conjugate the double bond in linoleic acid, after which the acryhc acid adds via a Diels-Alder type reaction to form the cycHc reaction product. Other catalysts have been described and include clay (91), palladium, and sulfur dioxide (92). After the reaction is complete, the unreacted oleic acid is removed by distillation, and the cmde C-21 diacid can be further purified by thin film distillation or molecular distillation. 

Structure and Mechanism of Formation. Thermal dimerization of unsaturated fatty acids has been explaiaed both by a Diels-Alder mechanism and by a free-radical route involving hydrogen transfer. The Diels-Alder reaction appears to apply to starting materials high ia linoleic acid content satisfactorily, but oleic acid oligomerization seems better rationalized by a free-radical reaction (8—10). 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

By depolymerizing PET waste with a polyol and subsequently condensing the oligomeric product with a polycarboxylic acid or anhydride, polyester resins are produced which have wide industrial applications. Depending on the polyol and polycarboxylic acid or anhydride used, saturated resins, alkyd resins, or unsaturated resins are obtained. PET wastes have been used for the production of alkyd resins in water thinnable paints. The materials obtained from the reaction of PET with a mixture of fatty acids high in linoleic acid content and trimethylolethane have been used in the preparation of water-dispersible coatings. Products of the depolymerization of PET with trimethylolpropane and pentaerythritol are used in the manufacture of high-solids paints. In the first step, PET is depolymerized with trimethylopropane and pentaerythritol at temperatures of 230-240°C. The final paint compositions contain 30-50% of PET depolymerization products.12... 

Sodium dodecyl sulfate and hydrogen dodecyl sulfate have been used as catalysts in the denitrosation iV-nitroso-iV-methyl-p-toluenesulfonamide [138]. The kinetics of condensation of benzidine and p-anisidine with p-dimethylamino-benzaldehyde was studied by spectrophotometry in the presence of micelles of sodium dodecyl sulfate, with the result that the surfactant increases the rate of reaction [188]. The kinetics of reversible complexation of Ni(II) and Fe(III) with oxalatopentaaminecobalt(III) has been investigated in aqueous micellar medium of sodium dodecyl sulfate. The reaction occurs exclusively on the micellar surface [189]. Vitamin E reacts rapidly with the peroxidized linoleic acid present in linoleic acid in micellar sodium dodecyl sulfate solutions, whereas no significant reaction occurs in ethanol solution [190]. 

Figure 22-4. Sequence of reactions in the oxidation of unsaturated fatty acids, eg, linoleic acid. A -c/s-fatty acids or fatty acids forming A -c/s-enoyl-CoA enter the pathway at the position shown. NADPH for the dienoyl-CoA reductase step is supplied by intramitochondrial sources such as glutamate dehydrogenase, isocitrate dehydrogenase,and NAD(P)H transhydrogenase.

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

De Groot, J.M.C., Garssen, G.J., Vliegenthart, J.F.G. and Boldingh, J. (1973). The detection of linoleic acid radicals in the anaerobic reaction of liproxygenase. Biochim. Biophys. Acta 326, 279-284. 

Sekiya, J. Aoshima, H., Kajiwara, T., Togo, T. and Hatanaka, A. (1977). Purification and some properties of potato tuber lipoxygenase and detection of linoleic acid radical in the enzyme reaction. Agric. Biol. Chem. 41, 827-832. 

We previously described [25] the function of soybean lipoxygenase-1 in a biphasic system (modified Lewis cell) composed of an aqueous phase (borate buffer) and octane. The substrate of the reaction is linoleic acid (LA) and the main product is hydro-peroxyoctadecadienoic acid (LIP). The system involves two phenomena LA transfer from the organic to the aqueous phase and lipoxygenase kinetics in the aqueous medium. 

Reaction yields depend on the nature of the substrate. Linseed oil contains two polyunsaturated fatty acids 50% linolenic acid and 18% linoleic acid. The corresponding hydroperoxides are obtained with low yields. 

Figure 10.7 Autoxidation of a linoleic acid ester. In step 1 the reaction is initiated by the attack of a radical on one of the hydrogen atoms of the -CH2-group between the two double bonds this hydrogen abstraction produces a radical that is a resonance hybrid. In step 2 this radical reacts with oxygen in the first of two chain-propagating steps to produce an oxygen-containing radical, which in step 3 can abstract a hydrogen from another molecule of the linoleic ester (Lin-H). The result of this second chain-propagating step is the formation of a hydroperoxide and a radical (Lin ) that can bring about a repetition of step 2.

Potato LOX has the potential to be used as an alternative model to the mammalian enzyme because of its great availability(Lopez-Nicolas and others 2000). To date, three isoenzymes of potato LOX have been isolated. Several works have reported linoleic acid as the optimum substrate for potato LOX-1, 9-hydroperoxide being the main product of the reaction. Another LOX substrate, linolenic acid, has been reported as the preferred substrate for both potato LOX-2 and -3, which produce 13-hydroperoxide as the main product. 

Hydroxy-10,12-octadecadienoic acid, which is formed by the reduction of 9-HPODE, was identified in the erythrocyte membrane phospholipid of diabetic patients [83]. It was suggested that this compound was formed as a result of glucose-induced oxidative stress in the reaction of hydroxyl radicals with linoleic acid. 

Although these are termed essential fatty acids, they are, in fact, precursors for the major polyunsaturated fatty acids that have essential roles in the body but are present only in small amounts in the diet. Linoleic acid is converted, via elongation and desaturation reactions, to dihomo-y-linolenic (20 3n-6) and then to arachidonic (20 4n-6) acid. a-Linolenic is converted to eicosapentaenoic (20 5n-3) and then docosahexae-noic (22 6n-3). The pathways for formation of these latter fatty acids, from their dietary precursors, are presented in Figures 11.11 and 11.12. Full details of one pathway are provided, as an example, in Appendix 11.4. For comparison of the two pathways, they are presented side by side in Figure 11.13. 

Figure 11.11 Outline of the pathway consisting of desaturation and elongation reactions that convert linoleic acid into arachidonic acid.

The question arises whether inhibition of the desaturase for this particular pathway can be overcome. The answer is yes. The product of the A desaturase when desaturating linoleic acid is y-linolenic acid. Supplementation of the diet with y-linolenic acid, which bypasses the A desaturase reaction, has been used to increase the formation of dihomo-y-linolenic acid and arachidonic acid (Figure... 

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