Nucleophilic addition of hydrogen sulfide to methyl oleate,methyl linoleate,and soybean oil

Hydrogen sulfide was added to methyl oleate, methyl linoleate, and soybean oil at −70 and 25 C in the presence of boron trifluoride. Major reaction compounds were identified by gas liquid chromatography and mass spectrometry. At −70 C with a 200 molar ratio of hydrogen sulfide to ester, the reactions were complete in 4 hr. Primary reaction product from methyl oleate was methyl 9(10)-mercaptostearate. Methyl linoleate gave ca. equal amounts of methyl 9-(2-pentyl-1-thiolan-5-yl) nonanoate and methyl 8-(2-hexyl-1-thiolan-5-yl) octanoate. At 25 C, the reaction of methyl oleate and linoleate with hydrogen sulfide was less complete, and more side reactions were noted. When equimolar amounts of methyl oleate and methyl 9(10)-mercaptostearate were reacted in the presence of boron trifluoride at 25 C, a new compound was formed, bis(methyl n-octadecanoate 9[10]-yl) sulfide. The addition of liquid hydrogen sulfide to soybean oil at −70 C in the presence of boron trifluoride yields a product which, upon saponification, acidification, and methylation analyzes by gas liquid chromatography as ca. 52% thiolan, 27% mercaptostearate, 10% palmitate, 6% stearate, and 5% unidentified compounds.     

Polymerization of drying oils. III. Some observations on reaction of maleic anhydride with methyl oleate and methyl linoleate

Summary Adducts of maleic anhydride with methyl oleate, methyl linoleate, and monomeric distillate have been prepared. Reaction of the adducts with ethylene diamine gave a linear, soluble polyamide in the case of the oleate adduct, but gelation occurred at a low degree of reaction with other adducts. The linoleate adduct was separated into monomeric and polymeric components. It is suggested that this polymeric component is responsible for the rapid gelation of polyamides from the adducts of methyl linoleate and monomeric distillate. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Products formed by photosensitized oxidation of unsaturated fatty acid esters

Photosensitized oxidation of unsaturated fatty acid methyl ester was carried out using methylene blue as a sensitizer. Oxidation products, monohydro-peroxides, were identified as trimethylsilyl derivatives. Methyl oleate gave the 9- and 10-isomers; methyl linoleate, the 9-, 10-, 12-, and 13-isomers; and methyl linolenate, the 9-, 10-, 12-, 13-, 15-, and 16-isomers, respectively. The double bond to which the hydroperoxide group attached was shifted to the adjacent position in each isomer. Thus, both conjugated and nonconjugated isomers were present in methyl linoleate monohydroperoxides and methyl linolenate monohydroperoxides. By the inhibition experiment, it was ascertained that the above reaction proceeded via singlet oxygen. The relative rates of methyl oleate, methyl linoleate, and methyl linolenate were 1.0∶1.7∶2.3, respectively. These results obtained from the methyl esters were applied to the photosensitized oxidation of triglycerides purified from vegetable oils, and the reaction mechanism on triglycerides was proposed.     

Hydrogen sulfide adducts of methyl oleate and linoleate

Sulfur compounds derived from photochemical addition of hydrogen sulfide to methyl oleate and linoleate were separated by preparative gas chromatography. The major compounds were investigated by NMR, mass and IR spectroscopy and by elemental analysis. The primary product of the methyl oleate reaction was methyl 9(10)-mercaptostearate. Gas chromatograms of the product from methyl linoleate showed four principal peaks. From mass spectra and NMR data, we identified methyl 9-(2-pentyl-1-thiolan-5-yl)nonanoate, methyl 8-(2-hexyl-1-thiolan-5-yl)octanoate and methyl 9-(3-hexyl-1,2-dithiolan-5-yl)nonanoate. Evidence for the formation of methyl mercapto-octadecenoates and methyl dimercaptostearates was also obtained. ARS, USDA.     

On the kinetics of the autoxidation of fats. II. Monounsaturated substrates

The autoxidation of methyl oleate and oleic acid shows some differences as compared to the autoxidation of linoleate,e.g., the formation of water at an early stage. Linearization of experimental data on the autoxidation to high oxidation degrees of methyl oleate and other monounsaturated substrates shows that the rate equations previously derived for methyl linoleate in the range of 1–25% oxidation are valid, provided the correct expression for the remaining unreacted substrate is used. With monounsaturated substrates, part of the oxygen is consumed by a secondary oxidation reaction almost from the beginning, and only a certain constant fraction α of the total O₂ consumption is consumed in hydroperoxide formation. The fraction α is different for methyl oleate, oleyl alcohol, oleic acid andcis 9-octadecene, but the rate constant for the hydroperoxide formation is the same for all of them when experimental conditions are the same. The main difference between oleate and linoleate autoxidation is the much faster decomposition of the oleate hydroperoxides relative to their slow formation.     

Analysis of oleate and linoleate hydroperoxides in oxidized ester mixtures

The hydroperoxides in oxidized mixtures of methyl oleate and linoleate were reduced to the corresponding hydroxyesters, which were separated from unoxidized esters by thin layer chromatography on silica gel. The hydroxyesters from oleate and linoleate were converted to trimethylsilyl ethers and separated by gas chromatography on OV 225. The results suggest that methyl linoleate oxidizes about ten times faster than methyl oleate, but oleate hydroperoxides are formed in appreciable amounts, even in mixtures containing 87% methyl linoleate. Journal Paper No. J-8658 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 2143.     

Comparison of methods for determining fatty acid oxidation produced by ultraviolet irradiation

Summary The thiobarbituric acid (TBA) reaction for fatty acid oxidation has been compared with Lundberg and Chipault's method for peroxides, the Kreis test for aldehydes, and with the degree of conjugation, using fatty acid esters exposed to ultraviolet light for various periods. The TBA test paralleled the other methods for methyl linolenate and methyl linoleate but was essentially negative for methyl oleate oxidation. The sensitivity of the TBA test for linolenate was 30–80 times that for linoleate at the same peroxide values. The TBA test appears to be a reliable method of estimating the oxidation products of linolenic and linoleic acids in tissues and other biological material. Supported by a grant from the Atomic Energy Commission.     

Methods of analysis of mixtures of oleic,linoleic and saturated esters and their application to highly purified methyl oleate and methyl linoleate

Summary Iodine numbers by the Hanus and Wijs methods and thiocyanogen numbers using various absorption periods, were determined on methyl oleate and methyl linoleate and on mixtures of these esters. It is concluded that iodine numbers by the Wijs method and three-hour thiocyanogen numbers are more satisfactory for methyl linoleate and for mixtures containing large amounts of this ester. Small amounts of higher saturated acids were determined with a precision of about 0.1 unit-percent by means of the Bertram procedure. A purified specimen of methyl oleate was found to contain about 0.2 percent of saturated ester by this method. Food Research Division Contribution No. 428.     

Thermal Decomposition of Some Acetoxyoctadecenoates and Acetoxyoctadecadienoates

The rates of the thermal decomposition (dehydroacetoxylation) and the activation energies of the following three samples have been determined: A) acetylated methyl ricinoleate; B) methyl ester mixture of vicinally unsaturated acetoxyoctadecenoates prepared by reacting methyl oleate and mercuric acetate in acetic acid; C) methyl ester mixture of vicinally unsaturated acetoxyoctadecadienoates prepared by reacting methyl linoleate and mercuric acetate in acetic acid. The thermal decomposition is shown to be a first-order reaction.     

Free radical addition of hydrogen sulfide to conjugated and nonconjugated methyl esters and to vegetable oils

The rate of addition of hydrogen sulfide to high purity methyl oleate, methyl linoleate, methyl linolenate, methyl 9,11-trans,trans-octade-cadienoate and methyl β-eleostearate was investigated at 25 C with UV irradiation. A similar study was carried out with soybean, linseed and tung oils in the absence and presence of 2,2′-azo-bis(isobutyronitrile) with UV photolysis. Initially the reaction of hydrogen sulfide with methyl esters appears to follow pseudo-zero-order kinetics although as the reaction proceeds the kinetics of the polyunsaturated ester reactions become more complex. For nonconjugated systems the overall rate is determined by the initiation step, whereas the overall rate of addition to conjugated systems is a function of the stability of the resonance-stabilized addition radical in the chain transfer step. For methyl esters the following order of reactivity appears to hold: Methyl oleate ≅ methyl linoleate ≅ methyl linolenate >> methyl 9,11-trans,trans-octadecadienoate > methyl β-eleostearate. Using 2,2′-azo-bis(isobutyronitrile) with UV photolysis markedly increases the rate of addition of hydrogen sulfide to nonconjugated vegetable oils. Presented at the AOCS Meeting, New York, October 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Gas chromatography ofCis-Trans fatty acid isomers on nitrile silicone capillary columns

Three nitrile silicone polymers have been evaluated as liquid phases for gas chromatographic separation of the geometric isomers of methyl oleate, methyl linoleate, and methyl linolenate on capillary columns. A polymer of β-cyanoethylmethylsiloxane proved the most effective. This liquid phase separated oleate from elaidate, resolved the four geometric isomers of linoleate into three peaks, and divided the eight geometric isomers of linolenate into six peaks. Two other copolymers of dimethylsiloxane and β-cyanoethylmethylsiloxane gave poorer resolution ofcis-trans isomers, but showed different elution patterns for the geometric isomers of linoleate and linolenate. Presented at the AOCS meeting, Atlanta, Ga., 1963.     

High-pressure liquid chromatography of autoxidized lipids: I. Methyl oleate and linoleate

Autoxidized methyl oleate and linoleate were reduced with NaBH₄ and fractionated with a preparative high-pressure liquid chromatography (HPLC) reverse phase column. Products characterized from reduced-oxidized oleate included monohydroxy- and dihydroxyotadecenoates, dihydroxy- and epoxyoctadecanoates. Products characterized from reduced-oxidized linoleate included hydroxy-cis,trans- andtrans,trans-octadecadienoates, monohydroxy-, dihydroxy-, trihydroxy-, epoxyhydroxy-, and epoxyoctadecenoates. Quantitation of oxidation products by HPLC was in agreement with gas chromatography of trimethylsilyl ether derivative. Epoxyoctadecanoate in oleate and epoxy- and epoxyhydroxyoctadecenoates in linoleate were the most abundant secondary oxidation products. Some mechanisms are discussed to explain formation of these secondary products.     

异构化反应改善小桐梓油生物柴油的低温流动性

以小桐梓油生物柴油为原料,在固定床连续反应器中,以Hβ型分子筛为催化剂,采用异构化反应改善生物柴油的低温流动性。考察了反应温度、质量空速、助剂(水)加入量等不同条件对生物柴油低温流动性的影响。实验结果表明,催化剂选用硅铝比为25的Hβ分子筛的情况下,反应温度为250℃、质量空速为1.0 h-1、助剂加入量为1.2%为最佳反应条件,小桐梓油生物柴油在最佳反应条件下进行异构化反应,凝点从1℃降低到-5℃,降幅为6℃。对生物柴油和异构化产物进行了色谱、质谱、核磁共振等表征,结果发现,低温流动性改善的原因是生物柴油的主要成分油酸甲酯、亚油酸甲酯发生了异构化反应,产生了带支链的异构体。     

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

To clarify the sources of undesirable flavors, pure hydroperoxides from autoxidized and photosensitized oxidized fatty esters were thermally decomposed in the injector port of a gas chromatograph-mass spectrometer system. Major volatile products were identified from the hydroperoxides of methyl oleate, linoleate and linolenate. Although the hydroperoxides from autoxidized esters are isomerically different in position and concentration than those from photosensitized oxidized esters, the same major volatile products were formed but in different relative amounts. Distinguishing volatiles were, however, produced from each type of hydroperoxide. The 9- and 10-hydroperoxides of photosensitized oxidized methyl oleate were thermally isomerized in the injector port into a mixture of 8-, 9-, 10- and 11-hydroperoxides similar to that of autoxidized methyl oleate. Under the same conditions, the hydroperoxides from autoxidized linoleate and linolenate did not undergo significant interconversion with those from the corresponding photosensitized oxidized esters. The compositions of the major volatile decomposition products are explained by the classical scheme involving carboncarbon scission on either side of alkoxy radical intermediates. Secondary reactions of hydroperoxides are also postulated, and the hydroperoxy cyclic peroxides from methyl linoleate (photosensitized oxidized) and methyl linolenate (both autoxidized and photosensitized oxidized) are suggested as important precursors of volatiles.     

生物柴油脂肪酸甲酯的成分及含量分析

采用GC/MS技术分析了由精棉籽油和棕榈油为原料通过酯交换反应得到的脂肪酸甲酯。结果表明,精棉籽油脂肪酸甲酯主要为棕榈酸甲酯、亚油酸甲酯和油酸甲酯,含量分别为22.23%,53.18%和18.09%。棕榈油脂肪酸甲酯主要为棕榈酸甲酯、油酸甲酯和硬脂酸甲酯,含量分别为40.3%,50.07%和7.02%。     

Differences in Oxidation Kinetics Between Conjugated and Non-Conjugated Methyl Linoleate

The oxidation kinetics of conjugated methyl linoleate was compared with that of non-conjugated methyl linoleate under mild oxidation conditions (30 °C in the dark). Samples of methyl 9-cis,11-trans-linoleate, methyl 10-trans,12-cis linoleate and methyl 9-cis,12-cis linoleate were assayed separately and in mixtures. For comparative purposes, methyl α-linolenate and methyl oleate were also used. Two complementary analytical approaches were selected to monitor the progress of oxidation, (1) the traditional follow-up of residual substrate by gas liquid chromatography, and (2) an analytical procedure by high-performance size-exclusion chromatography (HPSEC) for direct measurement of the oxidation compounds formed. The HPSEC method enabled us to quantitate oxidized monomers, dimers and polymers concomitantly in a rapid and direct analysis. Results showed that conjugated methyl linoleate samples oxidized later than their non-conjugated counterparts, and showed a very different oxidation pattern. Thus, formation of oxidized monomers was negligible and the first and major compounds formed were polymerization products. Also, under the conditions used, non-conjugated and conjugated methyl linoleate samples in 1:1 mixtures led to decreased oxidation rate of non-conjugated methyl linoleate and increased oxidation rate of conjugated methyl linoleate. This study supports the view that oxidation kinetics of conjugated dienes differ substantially from that of methylene-interrupted dienes.     

The purification of fatty acid methyl esters by high pressure liquid chromatography

Procedures are described for the rapid purification of gram quantities of methyl oleate, methyl linoleate, methyl α- and γ-linolenates and methyl ricinoleate from appropriate natural oils by high pressure liquid chromatography (HPLC).     

Oxygen absorption of methyl esters of fat acids,and the effect of antioxidants

Summary The oxygen absorption of methyl linolenate, methyl linoleate, methyl oleate, methyl stearate, the distilled methyl esters of lard, and various mixtures of the four individual methyl esters were measured at 100° C. in the Barcroft-Warburg apparatus. Mixtures of methyl esters absorbed oxygen at a rate which could be approximately predicted from the rate of oxygen absorption of each component and the percentage of each present. The antioxidants nordihydroguaiaretic acid (NDGA), propyl gallate, benzylhydroquinone, α-tocopherol, and their synergistic combinations with citric acid, d-isoascorbyl palmitate, and lecithin were tested with the substrates methyl linoleate, methyl oleate, methyl stearate, and the distilled methyl esters of lard. Citric acid showed marked synergism with each antioxidant. The two most effective were the combinations of citric acid with nordihydroguaiaretic acid and with propyl gallate. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.     

Transesterification of cholesteryl esters

The transesterification of cholesteryl stearate, oleate, linoleate, linolenate and arachidonate to the fatty acid methyl ester and free cholesterol under mild conditions is described. In adaptation of a published procedure the transesterification was carried out for two hr at room temperature in 1N NaOH in methanol:benzene (60:40, v/v). After addition of saturated sodium chloride solution the reaction mixture was extracted with ethyl acetate. The product mixture was checked for cholesterol oxides by HPLC fractionation followed by measurement of the oxides by direct on-column capillary GC. Although transesterification of cholesteryl stearate and oleate was complete (>99%) in 30 min, a uniform reaction period of two hr, required by the polyunsaturated esters, was used for all cholesteryl esters. 7-Ketocholesterol, a principal oxidation product, was unaffected by the reaction conditions. Presented in part at the AOCS meeting in New Orleans, LA, in May 1987.     

Solubilities of six cottonseed oil fatty acid methyl esters in methanol

Solubilities of six cottonseed oil fatty acid methyl esters in metha-nol have been determined. The esters were: methyl oleate, methyl linoleate, methyl malvalate, methyl dihydromalvalate, methyl sterculate and methyl dihydrosterculate. The solubility/temperature data are presented in graphical and tabular form.