Linoleic acids, esters

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.

FIGURE 10.1 Schematic of the mechanisms of lipid peroxidation using a linoleic acid ester as a substrate. 

In recent years some work has been done to link oleochemicals with petrochemicals via oligomerization. One possibility is the Dids-Alder reaction of linoleic acid esters with dienophiles, for instance with quinones or ,/Tun saturated aldehydes and ketones [80]. Using scandium or copper triflates as catalysts the reaction can be carried out at very mild temperature conditions (25-40°C) with good yields (< 94%). For the first time in oleochemistry it was possible to carry out Diels-Alder cycloadditions with low catalyst concentrations instead of stoichiometric amounts of Lewis acids. The most successful way to recycle the catalyst was the successive extraction of the triflates with water. After removing the water and drying in vacuum the catalyst was used three times without any loss of yield. 

FIGURE 10.5 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. 

Larock et cd. [28] investigated the isomerization of double bonds in methyl linoleate in the presence of a phosphine-modified Rh(I) catalyst and a Lewis acid (SnCl2 2H20) in absolute ethanol at 60 "C (24h) (Scheme 6.85). Evidence was provided that a hydrido-rhodium species formed as an intermediary was able to convert rapidly two isolated conjugated double bonds. With the ester of natural linoleic acid, conjugated linoleic acid esters (CLAs) were formed. Among all possible product isomers, (9Z,11 )- and (10 ,12Z)-CLA were dominant in the range 76.2-93.4%. 

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). 

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. 

A soap-based powder can be produced in combination with ester sulfonates. Thirty-five percent of a sodium soap mixture (5% lauric acid, 5% myristic acid, 52% palmitic acid, 21% stearic acid, 12% oleic acid, and 5% linoleic acid) is mixed with 15% sodium a-sulfo palm oil fatty acid methyl ester, 3% lauric acid ethoxylate, 5% sodium silicate, 17% sodium carbonate, 20% Na2S04- 10H2O, and 5% water [79]. 

Oleic acid, linolic acid, ricinolic acid, and 2-bromostearic acid methyl ester as well are reacting with diethyl phosphite in the presence of benzoyl peroxide to the corresponding phosphono fatty acid esters [156-158]. 

Marcuse, R. (1962). The effect of some amino acids on the oxidation of linoleic acid and its methyl ester. Journal of the American Oil Chemists Society, Vol. 39, No.2 (February 1962) pp. 97-103, ISSN 0003-021X. 

The photobleaching of P-carotene by fluorescent light in fatty acid ester solutions showed an autoxidation kinetic profile with the rate of degradation of P-carotene in the order laurate > oleate > linoleate (Carnevale et al. 1979). The presence of a radical scavenger retarded the autoxidation, thus leading to the view that protection against autoxidation is built into the system by the unsaturation in the fatty acid. 

Linoleic acid is a polyunsaturated fatty acid (compound containing two or more double bonds) occurs as an ester in polyunsaturated fats. 

Acetic acid, butyl ester Acetic acid, pentyl ester Acetic acid, decyl ester Acetic acid, benzyl ester Acetic acid, benzyl ester Acetic acid, 1-cyclohexenyl ester Acetic acid, 3-cyclohexenyl ester Butyric acid, benzyl ester Phenylacetic acid, propyl ester Oleic acid, methyl ester Linoleic acid, methyl ester Linolenic acid, methyl ester Adipic acid, methyl ester Adipic acid, ethyl ester Adipic acid, diethyl ester Adipic acid, dipropyl ester Adipic acid, (methylethyl)ester Adipic acid,... 

Belkner et al. [32] demonstrated that 15-LOX oxidized preferably LDL cholesterol esters. Even in the presence of free linoleic acid, cholesteryl linoleate continued to be a major LOX substrate. It was also found that the depletion of LDL from a-tocopherol has not prevented the LDL oxidation. This is of a special interest in connection with the role of a-tocopherol in LDL oxidation. As the majority of cholesteryl esters is normally buried in the core of a lipoprotein particle and cannot be directly oxidized by LOX, it has been suggested that LDL oxidation might be initiated by a-tocopheryl radical formed during the oxidation of a-tocopherol [33,34]. Correspondingly, it was concluded that the oxidation of LDL by soybean and recombinant human 15-LOXs may occur by two pathways (a) LDL-free fatty acids are oxidized enzymatically with the formation of a-tocopheryl radical, and (b) the a-tocopheryl-mediated oxidation of cholesteryl esters occurs via a nonenzymatic way. Pro and con proofs related to the prooxidant role of a-tocopherol were considered in Chapter 25 in connection with the study of nonenzymatic lipid oxidation and in Chapter 29 dedicated to antioxidants. It should be stressed that comparison of the possible effects of a-tocopherol and nitric oxide on LDL oxidation does not support importance of a-tocopherol prooxidant activity. It should be mentioned that the above data describing the activity of cholesteryl esters in LDL oxidation are in contradiction with some earlier results. Thus in 1988, Sparrow et al. [35] suggested that the 15-LOX-catalyzed oxidation of LDL is accelerated in the presence of phospholipase A2, i.e., the hydrolysis of cholesterol esters is an important step in LDL oxidation. 

Soybean oil is a statistical mixture of glycerol esters of palmitic acid (10%), stearic acid (3%), oleic acid (23%), linoleic acid (55%), and linolenic acid (9%). 

These processes are shown for the CoA ester of linoleic acid, the most common of the polyunsaturated acids. 

E,Z, Z,E- or Z,Z-) can be assigned with the help of retention time considerations and DA-UVD . Examples of the analytical process reqnired for the peroxides derived from linoleic acid are shown in Scheme 20, Section VUI.E and for cholesteryl esters (191) in Section VIII.C.3. 

A GC trace of methanolysed almond oil is shown in Figure 11.9. It can be seen that the methyl esters stearic, oleic and linoleic acid are incompletely resolved on a BPX-5 column. The esters of the minor C-20 and C-22 acids are also incompletely... 

Linalool, cis, oxide 0 , 1 S172 Linalool, trans, oxide 1 3172 Linalool Pi , Resin , Lf 0 ° Linoleic acid methyl ester 1 73172 Linoleic acid 1 73172 gjCSl34 Linolenic acid methyl ester 0 Linolenic acid 1 3172 gjCSl34 Longifolene, (+) 1 3068 Longifolene 1 3172 qCS156 Inflorescence... 

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