Bleaching of vegetable oils. II. Conversions of methyl oleate and linoleate

Methyl oleate and linoleate were treated with 10% acid activated clay at 90–100 C for 1–50 hr with and without admission of air. Positional and geometric isomers of fatty acid esters were found. Polar compounds were detected having one or more functional groups with respect to the starting esters. Preparative thin layer chromatography and gas liquid chromatography were used in isolating the compounds, while IR, NMR, mass spectroscopy, and gas liquid chromatography analysis were employed for identification. The unsaturation of the isolated isomers was present at carbon atoms 5–11. The polar compounds were, among others, 9- and 10-keto octadecanoic methyl esters, isomeric keto octadecenoic methyl esters, isomeric epoxy octadecanoic methyl esters, 9- and 10-hydroxy octadecanoic methyl esters, and some mono methyl ester dicarbonic acids. It may be concluded that geometric, as well as positional, isomerization occurs and that small amounts of compounds with one or more functional groups are formed when unsaturated fatty acids were treated with acid-activated clay.     

Singlet oxygen oxidation of methyl linoleate: Isolation and characterization of the NaBH4-reduced products

The mixture of diene hydroperoxides from methylene blue-sensitized oxidation of methyl linoleate was reduced with NaBH₄ and the resulting alcohols were separated by high pressure liquid chromatography (HPLC). Four diene alcohols were isolated in approximately equal yields from adsorption and reversed phase HPLC; the isomers were identified as methyl esters of 9-hydroxy-10,12-, 10-hydroxy-8,12-, 12-hydroxy-9,13- and 13-hydroxy-9,11-octadecadienoate. Formation of equal yields of both conjugated and nonconjugated diene alcohols from methyl linoleate is characteristic of singlet oxygen oxidations. The detection of the easily separated nonconjugated isomer methyl 10-hydroxy-trans-8,cis-12-octadecadienoate from methyl linoleate is proposed as a test to probe the involvement of singlet oxygen in biological oxidations. A preliminary report of these results was presented at the 177th meeting of the American Chemical Society, Honolulu, HI, April 1–6, 1979; see abstracts of papers, paper No. ORGN-375.     

Chemical synthesis and spectroscopic characteristics of C18 1,2-disubstituted cyclopentyl fatty acid methyl esters

The chemical synthesis of methyl 9-(2′-n-butylcyclopentyl)nonanoate and methyl 10-(2′-n-propylcyclopentyl)-decanoate was performed using a Wittig reaction between 2-alkylcyclopentanones and the corresponding ω-carbomethoxyalkyl triphenylphosphonium bromides. The intermediate alkylcyclopentylidene alkanoate esters were isolated from the reaction mixture, characterized by spectrometric methods, and then catalytically hydrogenated to the desired cyclopentyl esters. Gas chromatographymass spectrometry (GC-MS) showed that the final products contained a mixture oftrans- andcis-ring isomers with small amounts of other cyclic by-products. The GC-retention features, the mass fragmentation pattern, and the spectroscopic characteristics of both the final and the unsaturated intermediate products are discussed.     

Ethylene adduct of conjugated octadecadienoic acids: III. Aromatization of C20 cyclohexene methyl esters

A procedure is described for the catalytic aromatization of the ethylene adduct of conjugated isomers of methyl octadecadieonate. When the C₂₀ cyclohexene fatty methyl esters were heated at 290–300 C with palladium and 1-octadecene as hydrogen acceptor, C₂₀ aromatic cyclic esters were obtained in 90–95% yield.     

Preparation of malvalic and sterculic acid methyl esters from Bombax munguba and Sterculia foetida seed oils

A method has been developed for the preparation of highly pure malvalic (cis-8,9-methyleneheptadec-8-enoic) and sterculic (cis-9,10-methyleneoctadec-9-enoic) acid methyl esters starting from Bombax munguba and Sterculia foetida seed oils. The methyl esters of these oils were prepared by sodium methylate-catalyzed transmethylation followed by cooling (6°C) the hexane solution of crude methyl esters and separation of insoluble fatty acid methyl esters by centrifugation in the case of B. munguba and by column chromatography in the case of S. foetida. Subsequently, the saturated straight-chain fatty acid methyl esters were almost quantitatively removed by urea adduct formation. Finally, methyl malvalate and methyl sterculate were separated from the remaining unsaturated fatty acid methyl esters, in particular methyl oleate and methyl linoleate, by preparative high-performance liquid chromatography on C₁₈ reversed-phase using acetonitrile isocratically. Methyl malvalate and methyl sterculate were obtained with purities of 95–97 and 95–98%, respectively.     

Heat treatment of vegetable oils III. GC-MS characterization of cyclic fatty acid monomers in heated sunflower and linseed oils after total hydrogenation

Fractions of cyclic fatty acid monomers (CFAM) were isolated from linseed oil heated at 275°C for 12 hr under nitrogen, at 240°C for 10 hr under nitrogen and at 240°C for 10 hr under air. Cyclic fatty acid monomers fractions were also isolated from a sunflower oil heated at 275°C for 12 hr under nitrogen and at 200°C for 48 hr in a commercial fryer. The CFAM fractions were hydrogenated and their composition studied by gas liquid chromatography coupled with mass spectrometry (GC-MS). The CFAM in the fraction isolated from heated linseed oil samples were a mixture (1:1) ofcis andtrans cyclopentyl and cyclohexyl isomers, while the CFAM in the fractions isolated from heated sunflower oils were mostly cyclopentyl isomers. The major cyclopentyl isomers weretrans andcis methyl 7-(2′-hexylcyclopentyl) -heptanoate, methyl 9-(2′-butyl-cyclopentyl)-nonanoate and methyl 10-(2′-propylcyclo-pentyl)-decanoate. The major cyclohexyl isomers were thetrans andcis methyl 9-(2′-propylcyclohexyl)-nonanoate which represented about 50% of the CFAM isomers isolated from heated linseed oil samples. For part II in this series see Ref. 1.     

Reaction of α-tocopherol with alkyl and alkylperoxyl radicals of methyl linoleate

α-Tocopherol was reacted with alkyl and alkylperoxyl radicals at 37°C in bulk phase. The lipid-free radicals were generated by the reaction of methyl linoleate with the free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN) under air-insufficient conditions. The products were isolated by high-performance liquid chromatography. Their structures were identified as 2-(α-tocopheroxy)-2,4-dimethylvaleronitrile (1), a mixture of methyl 9-(8a-peroxy-α-tocopherone)-10(E),12(Z)-octadecadienoate and methyl 13-(8a-peroxy-α-tocopherone)-9(Z),11(E)-octadecadienoate (2), methyl 9-(α-tocopheroxy)-10(E),12(Z)-octadecadienoate (3a), methyl 13-(α-tocopheroxy)-9(Z),11(E)-octadecadienoate (3b), α-tocopherol spirodiene dimer (4) and α-tocopherol trimer (5). When methyl linoleate containing α-tocopherol was oxidized with AMVN under airsufficient conditions, the main products were 8a-alkyl-peroxy-α-tocopherones (2). In addition to these compounds, 6-O-alkyl-α-tocopherols (1, 3a and 3b) were formed when the reaction was carried out under air-insufficient conditions. The results indicate that α-tocopherol can react with both alkyl and alkylperoxyl radicals during the autoxidation of polyunsaturated lipids.     

Reaction products of α-tocopherol with methyl linoleate-peroxyl radicals

α-Tocopherol was reacted with methyl linoleateperoxyl radicals at 37°C. The peroxyl radicals were generated by the reaction of methyl linoleate with a free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile). The primary products of α-tocopherol with methyl linoleate-peroxyl radicals were isolated by reversephase and normal-phase high performance liquid chromatography (HPLC), and their structures were characterized by ultraviolet (UV), infrared (IR),¹H and¹³C nuclear magnetic resonance (NMR) and mass spectrometry (MS). There were four stereoisomers of methyl 13-(8a-peroxy-α-tocopherone)-9(Z),11(E)-octadecadienoate and four stereoisomers of methyl9-(8a-peroxy-α-tocopherone)-10(E),12(Z)-octadecadienoate.     

Thermal reactions of methyl linoleate. III. Characterization of C18 cyclic esters

This third paper presents the isolation and characterization of nonaromatic cyclic monomers formed from the heated linoleate. The esters were isolated by a series of column chromatographic separations, followed by repeated gas chromatography to obtain fractions containing C₁₈ cyclic esters. Characterization of the esters was achieved by use of infrared, NMR, mass spectroscopy, and standard chemical analyses. Also characterized were the isomers found in a complex mixture of cyclic monomers which had been partially separated by column chromatography. Use of both physical and chemical methods of analyses permitted characterization of the mixture of isomers without their having been separated from each other.     

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.     

The total synthesis and metabolism of 4-decenoate,dodeca-3,6-dienoate,tetradeca-5,8-dienoate and hexadeca-7,10-dienoate in the fat-deficient rat

Methyl 4-decenoate (10∶1ω6), methyl dodeca-3,6-dienoate (12∶2ω6), methyl tetradeca-5,8-dienoate (14∶2ω6) and methyl hexadeca-7,10-dienoate (16∶2ω6) were prepared by total synthesis. Rats raised on a fat-deficient diet for 2 1/2 months received 100 mg per day of one of the experimental acids or methyl linoleate for a period of 16 days. The liver lipids were extracted, converted to methyl esters and analyzed by gas-liquid chromatography. Neither 10∶1ω6 nor 12∶2ω6 served as biosynthetic precursors for linoleate. Small amounts of 14∶2ω6 were convered to linoleate while 16∶2ω6 served as an efficient precursor for linoleate and longer chain ω6 acids. None of the short chain ω6 acids were incorporated directly into liver lipids.     

Dimer acid structures. The dehydro-dimer from methyl stearate and di-tertiary-butyl peroxide

Previous work by Sutton, and by Harrison, McCaleb and Wheeler has shown that methyl stearate is converted to dimers plus higher polymers by the action of di-t-butyl peroxide. The latter suggested that in the dimer, there was considerable linkage at carbon 2, the carbon α- to the COOCH₃ group, since the dimer ester was incompletely saponified by the usual procedures. Further proof of α-linkage is now presented. A fraction which is predominantly α-,α′-linked dimer was isolated as the nonpolymeric cyclic anhydride (α-,α′-dicetyl succinic anhydride) by molecular distillation from the linear polymeric non-α-linked polyanhydride. The isolated cyclic anhydride appeared identical with a synthetic α-,α′-dicetyl succinic anhydride, whose synthesis is described. The original dimer ester, the α-,α′-cyclic anhydride fraction, and the dimethyl ester derived from it, were examined by mass spectrometry. The expected mol wt were confirmed by the parent ion peaks. Fragmentation patterns indicated appreciable α-linkage in the original dimer ester, and almost exclusive α-linkage in the ester from the isolated cyclic anhydride. Aside from preference for the α-position, joining appears to be randomly distributed. Presented at AOCS Meeting, New Orleans, 1964. Journal Series No. 363.     

Analysis of the dark-colored impurities in sulfonated fatty acid methyl ester

A fractionally distilled C₁₄−C₁₆ fatty acid methyl ester, derived from palm oil, was sulfonated with gaseous SO₃ in a falling film reactor to form an α-sulfo fatty acid methyl ester (α-SF; unbleached and unneutralized form). The included dark-colored impurities were then separated from α-SF as a diethyl ether-insoluble matter. After purification by thin-layer chromatography, the colored species were analyzed by ion-exchange chromatography, gel-permeation chromatography, and nuclear magnetic resonance spectrometry. These data suggested that the colored species were polysulfonated compounds with conjugated double bonds. Minor components in the raw fatty acid methyl ester, found by gas chromatography/mass spectrometry, were spiked into the purified methyl palmitate and then sulfonated. The unsaturated methyl ester and hydroxy ester showed the worst color results. The methyl oleate and methyl 12-hydroxystearate were then sulfonated and analyzed. Deep black products were obtained, which showed the same properties as the colored species in α-SF. It was concluded that low levels of unsaturated fatty acid methyl esters and hydroxy esters in the fatty acid methyl ester are the main causes of the coloring.     

Thermal reactions of methyl linoleate. I. Heating conditions,isolation techniques,biological studies and chemical changes

Methyl linoleate, diluted with an equal weight of methyl laurate, was heated without exclusion of air at 200C for 200 hours. The reaction mixture was separated by means of molecular distillation, urea adduction, column chromatography, and gas chromatography. Cyclic and aromatic materials were detected in the nonurea adductable monomer fractions. The dimer was separated into polar and nonpolar fractions. Analytical data for the nonpolar dimer are consistent with a cyclic Diels-Alder product. Bioassays showed the nonadductable monomer, the polar dimer, and a fraction of intermediate boiling point to be toxic when administered to weanling male rats. Urea-adductable fractions, nonpolar dimer, and polymer were not toxic. The concentrations of the toxic components were so low that the heated linoleate, before fractionation but after removal of the laurate, was not toxic.     

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).     

Characterization of some dicarbonyls from autoxidized methyl linoleate

The 2, 4-dinitrophenylosazones of dicarbonyl compounds isolated from oxidized methyl linoleate were resolved by means of adsorption and partition chromatography. Individual components were characterized by means of ultraviolet absorption, thin layer chromatographic techniques for class determination and for separation of homologous series, column co-chromatography of authentics and the unknowns, IR spectroscopy and melting point analysis. Evidence was obtained for the presence of glyoxal, methyl glyoxal, but-2-en-1, 4-dial, α-keto hexanal, α-keto heptanal, α-keto octanal, and α-keto nonanal. Technical Paper No. 1864, Oregon Agricultural Experiment Station.     

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.     

Separation of bile acid methyl esters by high-performance liquid chromatography

Conjugated bile acids, namely glyco- and tauro-3α,6α-dihydroxy-5β-cholanoic acid (hyodeoxycholic acid), 3α,7α-dihydroxy-5β-cholanoic acid (chenodeoxycholic acid), 3α,6α,7α-trihydroxy-5β-cholanoic acid (hyocholic acid) and 3α-hydroxy-6-oxo-5β-cholanoic acid (6-keto-litocholic acid) were isolated from pig bile, and subsequently transformed into the corresponding methyl esters. Separation of the methyl esters of the isolated bile acids by high-performance liquid chromatography (HPLC) was accomplished on a ZORBAX-CN column (Dupont, Boston, MA) withn-hexane/2-propanol/methylene chloride (89∶6∶5, by vol) as the mobile phase containing traces (≈1%) of amyl alcohol and water as moderators. HPLC analysis of the methyl esters also showed the presence of methyl 3α-hydroxy-6-oxo-5α-cholanoate, which was probably produced in the course of alkaline hydrolysis of the conjugated bile acids.     

Physical properties of fatty acid methyl esters. II. Refractive index and molar refraction

The refractive indices of methyl oleate, linoleate, linolenate, erucate, and the saturated fatty acid methyl esters from acetate to nonadecanoate have been measured at 20C and 40C for the Na_d, H _α , H _β , H _γ lines. The values for the saturated series have been correlated with the Smittenberg relation. Molar refractions have been computed and checked for additivity. The limiting refractive indices obtained from the Smittenberg relation are compared to those obtained from the molar refraction.     

Derivatization of keto fatty acids: V. Synthesis and characterization of 1,3-dioxolanes

The synthesis of substituted 1,3-dioxolanes from oxo fatty acid esters using 1,2-propanediol is described. This reagent, besides forming dioxolanes, also converts the methyl ester to the 2′-hydroxy propyl ester. Methyl 10-oxoundecanoate gives 2′-hydroxy propyl 10-(2″-methyl ethylene dioxolane) undecanoate (Ia, 75%) as a major product. Methyl 9-oxooctadecanoate reacts similarly and yields 2′-hydroxy propyl 9-(2″-methyl ethylene dioxolane) octadecanoate (IIb, 60%), along with the minor products (IIa, IIc). Methyl 2-oxooctadecanoate, after prolonged refluxing, affords only 2′-hydroxy propyl 2-(2″-methyl ethylene dioxolane) octadecanoate (IIIa) in 70% yield. Structures of each reaction product were established on the basis of elemental analysis, IR, NMR and a study of mass spectrometry.