Methyl oleate, oxidation

The oxidation of nonsaturated esters with double bonds far away from the ester group occurs like the oxidation of olefins (see Chapter 2). Esters like methyl oleate have weak bonds near the double bond. The peroxyl radical attacks these bonds, and the oxidation reaction occurs far from the ester group. The ester group influences the oxidation rate through its solvent properties. 

Recently an analogous mechanism for cyclic chain termination has been established for quinones [47], Quinones, which can act as acceptors of alkyl radicals, do not practically retard the oxidation of hydrocarbons at concentrations of up to 5 x 10 3 mol L 1, because the alkyl radicals react very rapidly with dioxygen. However, the ternary system, /V-phenylquinonc imine (Q) + H202 + acid (HA), efficiently retards the initiated oxidation of methyl oleate and ethylbenzene [47]. This is indicated by the following results obtained for the oxidation of ethylbenzene (343 K, p02 = 98 kPa, Vi = 5.21 x 10-7 mol L 1 s 1). 

In 1977, Kellogg and Fridovich [28] showed that superoxide produced by the XO-acetaldehyde system initiated the oxidation of liposomes and hemolysis of erythrocytes. Lipid peroxidation was inhibited by SOD and catalase but not the hydroxyl radical scavenger mannitol. Gutteridge et al. [29] showed that the superoxide-generating system (aldehyde-XO) oxidized lipid micelles and decomposed deoxyribose. Superoxide and iron ions are apparently involved in the NADPH-dependent lipid peroxidation in human placental mitochondria [30], Ohyashiki and Nunomura [31] have found that the ferric ion-dependent lipid peroxidation of phospholipid liposomes was enhanced under acidic conditions (from pH 7.4 to 5.5). This reaction was inhibited by SOD, catalase, and hydroxyl radical scavengers. Ohyashiki and Nunomura suggested that superoxide, hydrogen peroxide, and hydroxyl radicals participate in the initiation of liposome oxidation. It has also been shown [32] that SOD inhibited the chain oxidation of methyl linoleate (but not methyl oleate) in phosphate buffer. 

While the extracts of SPMDs are generally less difficult to purify than are extracts of tissue or sediment, certain interferences can be problematic for some types of analyses. The most important of these potential interferences are codialyzed polyethylene oligomers (i.e., the so-called polyethylene waxes), oleic acid, and methyl oleate. The latter two interferences are residual from the synthesis of the triolein. Also, oxidation products of triolein may be present in dialysates of SPMDs that have been exposed (especially in the presence of light) to air for periods exceeding 30 d. For a standard 1-mL triolein SPMD, the mass of all these interferences in dialysates is generally <30 mg or about 6 mg g of SPMD (Huckins et al., 1996). Another potential interference is elemental sulfur, which is often present in sediment pore water and is concentrated by SPMDs. However, both polyethylene waxes and elemental sulfur are readily removed using the previously described SEC procedure. 

Inactivated alkenes are oxidatively cleaved by the hydrotrioxide to give ketones. For example, methyl oleate 73 reacts with the hydrotrioxide to produce two aldehydes, followed by LiAlFLj reduction to give 1-nonanol and nonane-1,9- diol in 64 and 74% yields (equation 81). 

The latter observations with methyl oleate, together with thermodynamic considerations and EPR evidence for free radical intermediates, suggest an alternative explanation for the dramatic increase in oxidation rates once hydroperoxides accumulate, namely that bimolecular decomposition may be specific to allylic hydroperoxides and proceed via LOO radical-induced decomposition rather than by dissociation of hydrogen-bonded dimers (280). Reaction sequence 63 is analogous to Reactions 49 and 50a, where one slowly reacting radical reacts with a... 

Similar oxidants are used for epoxidation of esters of unsaturated carboxylic acids. Methyl oleate is oxidized with peroxybenzoic acid [295] or peroxylauric acid [174] to methyl 9,10-epoxystearate acid in respective yields of 67 and 76%. Alkaline 50% hydrogen peroxide in methanolic solution transforms diethyl ethylidenemalonate at pH 8.5-9.0 and at 35-40 C over a period of 1 h into ethyl 2-ethoxycarbonyl-2,3-epoxybutyrate in 82% yield [145], A somewhat exotic oxidizing agent, dimethyldioxirane, converts ethyl tra/u-cinnamate into ethyl 2,3-epoxyhydrocinnamate in 63% isolated yield [210]. 

On oxidation with O2, methyl oleate (methyl 9-c/5-octadecenoate) was found to yield a mixture of hydroperoxides of formula CigH3404. In these, the —OOH group was found attached not only to C-8 and C-11 but also to C-9 and C-10. What is the probable structure of these last two hydroperoxides How did they arise Show all steps in a likely mechanism for the reaction. 

Azelaic acid can be prepared by the oxidation of castor oil with nitric acid by the oxidation of ricinoleic acid with nitric acid and with alkaline permanganate by the oxidation of methyl oleate with alkaline permanganate by the ozonization of oleic acid and decomposition of the ozonide by the ozonization of methyl ricinoleate and decomposition of the ozonide by the action of carbon dioxide upon 1,7-heptamethylene magnesium bromide by the hydrolysis of i,7-di(yanoheptane. ... 

The methylene groups 1 and 11 of the IR monomer unit have different reactivities because of the methyl substituent on the double bond. The question as to which methylene group Is more susceptible to oxidation has been controversial. Bolland (30) predicted that methylene 11 Is more reactive from structural analysis of the products In the oxidation of 1-methylcyclohexene at 55°C and methyl oleate at 75 C. 

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