Methyl oleate oxidation products

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. 

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. 

Kimura and co-workers reported the first iron-catalyzed olefin epoxidation with H2O2 as oxidant and Fe(acac)3 as the catalyst (89). The oxidation of cis- and troras-stilbene afforded troras-epoxide as the major product with a product yield of 96%. Similar stereochemical features were observed in the epoxidation of other substrates, such as methyl oleate and cis- or trons-9-octadecen-l-ol (89). 

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. 

Oxidation of methyl oleate has been extensively studied and is considered to be typical of all monoene acids/esters. Photo-oxygenation produces only two products - the 9-hydroperoxide (AlOt) and the 10-hydroperoxide (A8t) - in equal amounts. Reaction is confined to the olefinic carbon atoms and is accompanied by double-bond migration and stereomutation. As shown in Scheme 10.5 autoxidation of methyl oleate forms eight monohydroperoxides of which two (9-OOH A 10c and lO-OOH A8c) are only minor products. This range of compounds arises from initial attack at either allylic carbon atom to give a delocalized radical with oxygen finally attached to any one of four carbon atoms. 

Starting from oleic acid, [52] 9,10-dihydroxy-8,8,ll,l W4 was obtained after oxidation to 9,10-dioxo derivative followed by hydrogen-deuterium exchange as shown in Figure 4 and reduction of he keto groups to hydroxy groups. The product obtained was converted to methyl oleate-8,8,11,11- 4 in turn, the latter was used, together with others deuterium-labelled compounds, such as oleic acid-9, IO-J2 and Z-methionine-methyl-Js, to elucidate the... 

The vapor-pheise photochemical reaction of chlorine dioxide with ethylene was observed by Furst (65) to give chloroacetic acid. Leopold and Mutton (137) discovered that the reaction between triolein and chlorine dioxide is accelerated by light cind gives a mixture of products, containing carbonyl, hydroj l, euid epoxide groups, as well as chlorine. CSilorine dioxide oxidations carried out by Lindgren and co-workers on cyclohexene (143) and methyl oleate (142) in the cib-sence of special illumination showed only a little... 

From Frankel etal. (1977,1984) oxidation with neat methyl oleate products analysed by C-NMR as cis- and traju-hydroxyoctadecenoates separated by AgNO, thin layer chromatogr hy followed by GC-MS of the hydroxyoctadecanoate derivatives. 

From Porter etal. (1994) oxidation of methyl oleate in hexane solution inititated with di-tert-butyl hyponitrite products analysed as the hydroxyoctadecenoates by normal phase HPLC. Co-oxidation of oleate with tert-butyl hydroperoxide produced only the W-cis, 9-trans,10-transand 8-cis in a ratio of 1 1.2 for ll-cis 9-trans and i-cis 0-trans products. 

As with oleate and linoleate, some volatile decomposition compounds are formed from linolenate hydroperoxides that cannot be explained by the classical A and B cleavage mechanisms, including acetaldehyde, butanal, 2-butyl furan, methyl heptanoate, 4,5-epoxyhepta-2-enal, methyl nonanoate, methyl 8-oxooctanoate, and methyl lO-oxo-8-decenoate. Some of these minor volatile oxidation products can be attributed to further oxidation of unsaturated aldehydes. Other factors contribute to the complexity of volatile products formed from hydroperoxides, including temperature of oxidation, metal catalysts, stability of volatile products and competing secondary reactions including dimerization, cyclization, epoxidation and dihydroperoxidation (Section E). 

Frankel, E.N., Neff, W.E. and Selke, E. Analysis of autoxidized fats by gas chromatography-mass spectrometry VII. Volatile thermal decomposition products of pure hydroperoxides from autoxidized and photosensitized oxidized methyl oleate, linoleate, and linolenate. Lipids 16, 279-285 (1981). 

The acetoxylation of higher alkenes with Pd(OAc>2 is synthetically less useful, since it is always accompanied by allylic acetoxylation and/or diacetoxylation.t ( For instance, the acetoxylation of methyl oleate gives various products as shown in Scheme 3,3-Dimethyl-4-pentenoates, in which the allylic position is blocked by two Me groups, react with AcOH in the presence of Pd(OAc>2 catalyst to give the corresponding vinyl acetate, selectively (Scheme The catalysis is exerted by the use of O2 alone as the co-oxidant. 

Very similar spectra obtained from squalene, ubiquinone, triolein, oleic acid, linolenic acid, linoleic acid, mentha-1,8-diene, erucic acid, lecithin irradication of 25 nitro compounds (aryl) with methyl oleate all gave nitroxides derived from oxidation of ene product . 

The only oxide that has been used for catalyzed olefin metathesis at 25°C is Re207/Al203 (in the middle of the 1960s by British Petroleum), but it suffered from a low number of active sites, side reactions caused by the acid support and deactivation of the catalyst. On die other hand, the silica-supported rhenium catalyst [(SiO)(Re(C-f-Bu)(=CH-f-Bu)(CH2-f-Bu)] catalyzes the metathesis of propene at 25°C with an initial rate of 0.25 mol/(mol Re x s). The formation of 3,3-dimethyl-butene and 4,4-dimethylpentene in a 3 1 ratio results from cross metathesis between propene and the neopentyl idene ligand, and die ratio of cross-metathesis products matches the relative stability of the metallacyclobutane intermediates. Cross metathesis of propene and isobutene and self-metathesis of methyl oleate can also... 

Methyl oleate 6 was among the first unsaturated esters to be examined by Bickford et The reaction was conducted at 220°C, under a carbon dioxide atmosphere for 2 h. A structure was speculated on, again, involving allylic hydrogen. An ozonolysis study of the reaction product gave no conclusive information. Ross et showed, based on oxidation of the products, that the reaction produces a succinic acid derivative by first attack at either the 9 or 10 position of methyl oleate 6 with consequent migration of the double bond to the adjacent 10,11 or 8,9 positions, respectively. 

---