Isomerization of unsaturated fatty esters by iron pentacarbonyl. Preparation of iron tricarbonyl complexes of polyunsaturated fats

Iron pentacarbonyl is a powerful isomerization agent of unsaturated fatty esters. Highly conjugated fats are obtained when polyunsaturated fatty esters are treated with an excess Fe(CO)₅ to form complexes followed by decomposition of the complexes with FeCl₃. Iron tricarbonyl complexes were prepared in 80 to 95% yields from methyl linoleate, linolenate and polyunsaturated fatty esters of soybean, linseed and safflower oils by heating at 180–185C with 2 moles Fe(CO)₅ per mole ester under nitrogen pressure. Decomposition of these complexes with FeCl₃ resulted in 90 to 97% conjugation of the polyunsaturated fatty esters mainly in the alltrans configuration. Isolatedtrans unsaturation reached levels of 18 to 30%. Methyl oleate yielded 74%trans unsaturation but no complex of iron carbonyl was obtained. Presented in part at AOCS meeting in Houston, 1965. No. Utiliz. Res. Dev. Div., ARS, USDA.     

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.     

Oxidation of lipids: III. Oxidation of methyl linoleate in solution

The effects of oxygen pressure, substrate concentration and solvent on the rate and products of oxidation of methyl linoleate were studied at 50 C with azobisisobutyronitrile as a radical initiator. The absolute and quantitative numbers for oxygen uptake, substrate disappearance, and formation of conjugated diene and hydroperoxides were measured. Under the present conditions, 4 conjugated diene hydroperoxides, 13-hydroperoxy-9-cis, 11-trans-(2a), 13-hydroperoxy-9-trans, 11-trans-(3a), 9-hydroperoxy-10-trans, 12-cis-(4a), and 9-hydroperoxy-10-trans, 12-trans-(5a) octadecadienoic acid methyl esters, were formed almost quantitatively. The rate of oxidation decreased with decreasing oxygen pressure. However, the ratio ofcis,trans totrans,trans hydroperoxides, (2a+4a)/(3a+5a), was independent of oxygen pressure, and this ratio increased with increasing methyl linoleate concentration, as found recently by Porter. Further, the rate of oxidation and the ratio ofcis,trans/trans,trans hydroperoxides were dependent on solvent and increased with an increase in dielectric constant of solvent. A mechanism of methyl linoleate oxidation consistent with these results is discussed. Presented at the 15th Symposium on Oxidation Reactions, Nagoya, October 1981.     

Quantitative separations of higher fatty acid methyl esters by adsorption chromatography on silica impregnated with silver nitrate

A chromatographic adsorbent has been developed for the separation of geometric isomers of fatty acid methyl esters. The adsorbent consists of silicic acid impregnated with silver nitrate. Quantitative separations of saturated,cis-, andtrans-monoenoic and polyenoic methyl esters in 30 to 100 mg quantities are reported.     

Cyclic fatty esters: Synthesis and characterization of methyl ω-(6-alkyl-3-cyclohexenyl) alkenoates

Diunsaturated C₁₈ cyclic fatty acid methyl esters of known structure and configuration were synthesized as model derivatives of cyclic fatty acids formed in heat-abused vegetable oils for characterization and further biological evaluation. The Wittig reaction was used to prepare 5 pure methyl esters: (a) 12-(3-cyclohexenyl)-11-dodecenoate, (b) 11-(6-methyl-3-cyclohexenyl)-10-undecenoate, (c) 10-(6-ethyl-3-cyclohexenyl)-9-decenoate, (d) 9-(6-propyl-3-cyclohexenyl)-8-nonenoate and (e) 8-(6-butyl-3-cyclohexenyl)-7-octenoate. Diels-Alder cycloaddition reactions between 1,3-butadiene and appropriate (E)-2-alkenals produced 3-cyclohexenal intermediates. The appropriate methyl ω-bromoesters and their triphenylphosphonium bromides were made and converted to their respective ylids with NaOCH₃ in DMF. The appropriate 3-cyclohexenals and phospho-ylids were reacted, and the desired cyclic ester products were isolated in crude yields of 30–83% as liquids and fractionally distilled. The crude cyclic esters were purified either by preparative TLC or by saponification-esterification. Double bonds in purified cyclic esters weretrans-isomerized and hydrogenated. Each derivative was characterized by IR,¹H-NMR,¹³C-NMR, capillary GLC and GC-MS. On the basis of these analyses, no positional isomers were detected, Z-unsaturated isomers were produced in better than 90% purity, and the alkyl and ester ring substituents were predominantlytrans to each other. Presented in part at the AOCS meeting, New Orleans, LA, May 1981.     

Studies on the nuclear magnetic resonance spectra of olefinic protons of conjugated fatty acid methyl esters

The NMR spectra of olefinic protons in the four representative conjugated fatty acid methyl esters, methylcis-9,trans-11-octadecadienoate, methyltrans-9,trans-11-octadecadienoate, methyl α eleostearate, and methyl β eleostearate, were studied. The chemical shift of each olefinic proton in these compounds was determined by considering their intramolecular environment. Coupling constants were also obtained as the results of spectral analysis.     

Highly selective asymmetric synthesis of 2-hydroxy fatty acid methyl esters through chiral oxazolidinone carboximides

Highly selective asymmetric synthesis of 2-hydroxy fatty acid methyl esters has been accomplioshed through chiral imide enolates. Five chiral oleic acid imides were prepared by reaction of oleioc acid with pivaloyl chloride followed by reaction with five different lithiated chiral oxazolidinones including (R)-(+)-4-benzyl-2-, (S)-(-)-4-benzyl-2-, (4R,5S)-(+)-4-methyl-5-phenyl-2-, (4S,5R)-(-)-4-methyl-5-phenyl-2-, and (R)-(+)-4-isopropyl-2-oxazolidinones in 88–92% yileds. The chiral imides were reacted with NaN(Me₃Si)₂ at −78°C to give enolates, which subsequently reacted with 2-(phenylsulfonyl)-3-phenyloxaziridine to give hydroxylated products in 78–83% yields. Methanolysis of the hydroxylated products with magnesium methoxide gave methyl 2-hydroxyoleate. Enantiomeric excesses (ee) of the products were determined to be very high (98–99% ee) by ¹H nuclear magnetic resonance study after esterification of the hydroxy group with (S)-(+)-O-acetylmandelic acid. Enantioselective hydroxylation of other fatty acids including elaidic, petroselinic, vaccenic, and linoleic was evaluated under the similar conditions using (4R, 5S)-(+)-4-methyl-5-phenyl-2-oxazolidinone as a chiral auxiliary to give 98% ee values for all cases.     

Preparation of deuterium-labelled methyl linoleate and its geometric isomers from natural seed oils

Multi-gram quantities of deuterium-labelled methyl linoleate (methyl cis-9,cis-12-octadecadienoate) and its geometric isomers are readily synthesized fromCrépis alpina (70–80% cis-9-octadecen-12-ynoic acid) andVernonia galamensis (70–80% 12,13-epoxy-cis-9-octadecenoic acid) seed oils. Methylcis- 9,cis- 12- andtrans- 9,cis- – octadecadienoate-12,13-d₂ were prepared by the Lindlar-catalyzed reduction (with D₂ gas) of methylcis- 9- and trans-9-octadecen-12-ynoates, respectively. Methyltrans- 9- octadecen-12-ynoate was synthesized by thep-toluene-sulfinic acid-catalyzed isomerization of the corresponding cis isomer. Methylcis- 9fiis- 12., trans- 9fiis- 12;cis- 9,trans- 12- andtrans- 9, frans-12-octadecadienoate-d₂, d₄ and d₆ were prepared by the Wittig coupling (with stereochemical control) of the appropriate d₂-, d₄- or de-alkyltriphenyl-phosphonium salt with methyl 12-oxo-cis-9- ortrans- 9- dodecenoate (prepared by the para-periodic acid cleavage of methyl 12,13-dihydroxy-cis-9- or trans-9-octadecenoate). Thecis dihydroxy ester was synthesized fromVernonia galamensis seed oil by acetolysis, saponification and then esterification. Thecis dihydroxy ester was isomerized by nitric acid/sodium nitrite to thetrans form and purified by silver resin chromatography. Isotopic purities ranged from 88% (for the d₆ isomers) to 99% (for the d₂ isomers). The mention of firm names or trade products does not imply that they are endorsed or recommended over other firms or similar products not mentioned.     

Comparison of silver-ion high-performance liquid chromatographic quantification of free and methylated conjugated linoleic acids

Silver-ion high-performance liquid chromatography was used to fractionate a mixture of conjugated linoleic acid (CLA) isomers (as the free fatty acids, CLAFFA) in commercial CLA mixtures and biological samples. Due to the unchanged retention mechanism, it was assumed that the elution order of the isomers remained the same as that of methyl esters separated on the same column. The most abundant isomers, cis/trans 10,12-18:2 and cis/trans 9,11-18:2, were separated better as free acids on a single column than in the methyl ester form. Quantification of the CLA standard was used as the reference profile to evaluate different methylation methods commonly used to prepare CLA methyl esters for quantitation. Acid- and vuigi base-catalyzed derivatization methods resulted in CLA intraisomerization and losses in total conjugated dienes content. Acid (HCl and BF₃) methylations significantly elevated the level of trans,trans isomers and significantly reduced the cis/trans isomers. Base methylation, tetramethylguanidine/methanol, resulted in loss of trans,trans isomers, and a substantial loss of total underivatized conjugated dienes. Other catalysts such as the trimethylsilyldiazomethane produced additional peaks of unidentified artifacts. The analysis of CLAFFA appears to provide more accurate quantification of CLA isomers in commercial and biological samples.     

GC-MS characterization (Chemical lonization and electron impact modes) of the methyl esters and oxazoline derivatives of cyclopropenoid fatty acids 1

The CI-(CH₄) mass spectra of the methyl esters and the EI mass spectra of the oxazoline derivatives of three cyclopropenoid fatty acids (malvalic, sterculic and α- hydroxy-sterculic acid) from the seed oil ofPachira aquatica were found to be useful for structure elucidation of such compounds. Furthermore, some hitherto unknown minor fatty acids were identified and the nuclear magnetic resonance data of the oil and α-hydroxysterculic acid methyl ester are presented.     

Reactions of conjugated fatty acids. V. Preparation and properties of diels-alder adducts and their esters fromtrans,trans-conjugated fatty acids derived from soybean oil

Summary Soybean fatty acids were conjugated with alkali, and the contained, conjugated dienoic acids were isomerized with iodine to thetrans,trans configuration. Adducts were prepared from thesetrans,trans-conjugated acids by condensation with maleic anhydride and acrylic acid. The adducts were isolated, purified, and converted to esters by using a variety of alcohols, including methyl, ethyl,n-propyl,n-butyl, and allyl alcohols. Esters made from saturated alcohols were converted into the corresponding epoxy derivatives. All of the esters (except allyl) and all of the epoxy esters were compatible with an equal weight of polyvinyl chloride and appeared to be primary plasticizers for this plastic. The epoxy esters were effective in inhibiting heat deterioration of polyvinyl chloride. Presented at fall meeting. American Oil Chemists' Society, September 23–26, 1956, Chicago, Ill.     

Identification of nine acetylenic fatty acids, 9-hydroxystearic acid and 9,10-epoxystearic acid in the seed oil ofJodina rhombifolia hook et arn. (Santalaceae)

In addition to some usual fatty acids, the seed oil ofJodina rhombifolia (Santalaceae) contains nine acetylenic fatty acids [9-octadecynoic acid (stearolic acid) (1.1%),trans-10-heptadecen-8-ynoic acid (pyrulic acid) (20.1%), 7-hydroxy-trans-10-heptadecen-8-ynoic acid (2.3%),trans-10,16-heptadecadien-8-ynoic acid (0.7%), 7-hydroxy-trans-10,16-heptadecadien-8-ynoic acid (0.1%),trans-11-octadecen-9-ynoic acid (ximenynic acid) (20.3%), 8-hydroxy-trans-11-octadecen-9-ynoic acid (12.2%),trans-11,17-octadecadien-9-ynoic acid (1.5%), 8-hydroxy-trans-11,17-octadecadien-9-ynoic acid (1.3%), 9-hydroxystearic acid (<0.1%) and 9,10-epoxystearic acid (0.7%)]. The fatty acids have been analyzed by gas chromatography/mass spectrometry of their methyl ester and 4,4-dimethyloxazoline derivatives. The hydroxy fatty acid methyl esters have been examined also as trimethyl-silyl ethers. Furthermore, the fatty acid methyl esters (FAME) have been fractionated according to their polarity (FAME-A: nonhydroxy; FAME-B: hydroxy fatty acids) and to their degree of unsaturation (FAME-A1/A2; FAME-B1/B2) by preparative thin-layer chromatography and argentation chromatography, respectively. All of these fractions have been analyzed by ultraviolet and infrared spectroscopy, and the fractions FAME-A and FAME-B have been analyzed further by nuclear magnetic resonance (¹H,¹³C, 2D H/C, attached proton test) spectroscopy and gas chromatography/mass spectrometry. This work is dedicated to the 65th birthday of Prof. Dr. K. Pfeilsticker, Institut of Food Science, University Bonn (Germany).     

Large-scale synthesis of methyl cis-9, trans-11-octadecadienoate from methyl ricinoleate

The conjugated linoleic acid methyl cis-9,trans-11-octadecadienoate has been prepared on a large scale from methyl ricinoleate. Methyl ricinoleate was purified from castor esters by a partition method. It was converted to the mesylate, which was reacted with a base (1,8-diazabicyclo[5,4,0]-undec-7-ene) to give a product that contained 66% of the desired ester. Two urea crystallizations produced a product containing 83% methyl cis-9,trans-11-octadecadienoate, the identity of which was confirmed by gas chromatography linked to mass spectrometry and by Fourier transform infrared spectroscopy. The remaining impurities were methyl cis-9,cis-11- and cis-9-,trans-12-octadecadienoate.     

Enzymatic synthesis of monosaccharide fatty acid esters and their comparison with conventional products

5-O-Acyl-1,2-O-isopropylidene-D-xylofuranose and 6-O-acyl1,2∶3,4-di-O-isopropylidene-D-galactopyranose were enzymatically prepared from the corresponding monosaccharide acetals and commercial (crude) fatty acid mixtures. Subsequent acid-catalyzed hydrolysis of the isopropylidene group(s) gave monosaccharide esters with overall yields of 59–88%, where the monoester content was at least 80% (galactose oleate) and typically 90% for the other preparations. In contrast to sugar fatty acid esters prepared by conventional, high-temperature (trans)esterification, the enzymatically obtained monosaccharide esters contained no appreciable quantities of undersirable side products, and the only contaminants were monosaccharides and fatty acids.     

The geometric isomers of conjugated octadecadienoates from dehydrated methyl ricinoleate

The dehydration of methyl ricinoleate by heatingin vacuo in the presence of KHSO₄ resulted in the formation of the following conjugated octadecadienoates expressed as a percentage of the final product:cis, trans (trans, cis), 14.3;cis, cis, 11.2;trans, trans, 7.3. The isomers contained the double bonds predominantly in the 9,11 position but the possible presence of traces of 8,10 and other conjugated isomers is not excluded. Using urea “inclusion” fractionation and low temp crystallization from acetone methyl,cis-9,cis-11-octadecadienoate was isolated. The methyl esters of commercially dehydrated castor oil fatty acids on the other hand, contained the following percentages of conjugated octadecadienoate isomers:cis, trans (trans, cis), 20.3;cis, cis, 8.0;trans, trans, 5.4. From these mixtures conc ofcis, trans (trans, cis)- andtrans, trans-octadecadienoates were prepared by fractional distillation and low temp crystallization. It was found that the conjugated octadecadienoates consisted of mixtures of positional isomers with double bonds mainly in the 8,10 and 9,11 positions with lesser amounts in the 7,9 and 10,12 positions.     

Preparation of methyl 5,11,14,17-eicosatetraenoate-8,8,9,9-d 4

For studies of incorporation, elongation and desaturation of fats in humans and animals, methyl 5,11,14,17-eicosatetraenoate-8,8,9,9-d ₄ was prepared by Wittig coupling, in the presence of sodiumbis(trimethylsilyl) amide, of 6,9,12-pentadecatrienal-3,3,4,4-d ₄ and 4-carboxybutyltriphenylphosphonium bromide. The all-cis isomer was separated fromtrans isomers and other impurities by silver resin chromatography. Location and configuration of the double bonds and deuterium atoms were affirmed by nuclear magnetic resonance and mass spectrometry.     

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.     

Syntheses of tetra- and hexadeuterated octadecenoates

A study of the metabolism in man ofcis andtrans monoenoic acids required the synthesis of tetra- and hexadeutero-9-octadecenoates. Preparation of methyl 9-octadecenoate-8,8,11,11-d ₄ (90 mol % deuterium) by the Wittig reaction was accompanied by deuterium scattering with sodium methoxide as the base but not with alkyllithium. Scattering occurred in both the aldehyde and phosphorane moieties only when the aldehyde contained deuterium on the alpha carbon. Methyl 9-octadecenoate-8,8,13,13,14-14-d ₆ (98 mol % deuterium) was also prepared by the Wittig reaction. The deuterated octadecenoates were formed principally ascis isomers. Thetrans isomers were produced by nitrogen oxide isomerization and separation on a silver ion column. Presented at the AOCS Fall Meeting in Cincinnati, September 28–October 1, 1975.     

Diffusion of methyl esters of higher fatty acid in polypropylene

Diffusion coefficients of several methyl esters of linear higher fatty acid (C₁₀?C₁₈) into polypropylene (PP) were determined, over the temperature range of 50 to 110°C, using a mass uptake technique. The relations between an amount of mass uptake and t^1/2 were linear within 10 min, indicating Fickian diffusion. The diffusion coefficients were in the range of 4.6×10^?8 to 6.2×10^?12 cm² sec^?1, increased with temperature, and decreased with increasing n-alkyl chain length of fatty acid. The plots of In D vs. the molecular weight of methyl esters were approximately linear. The temperature dependence of diffusion followed an Arrhenius relationship, and the activation energies were in the range of 133 ? 147 KJ mol^?1 and increased with an increase in n-alkyl chain length of corresponding fatty acid. The diffusion coefficients were discussed with the interaction between methyl esters of higher fatty acid and PP. The diffusion coefficients of methyl esters, at the simultaneous diffusion process, were always higher than that derived from the single diffusion process, except for methyl decanoate with lower molecular weight. The difference in diffusion coefficients in single and simultaneous diffusion was discussed thermodynamically. © 1994 John Wiley & Sons, Inc.     

13C nuclear magnetic resonance spectral confirmation of Δ6-and Δ7-trans-18:1 fatty acid methyl ester positional isomers

Trans octadecenoic acid methyl ester isomers were obtained from a partially hydrognated soybean oil and isolated by silver-ion high-performance liquid chromatography. Recently, the double-bond positions for nine individual trans octadecenoic acid positional isomers (Δ8 through Δ16) were confirmed by gas chromatography-electron ionization mass spectrometry after derivatization to 2-alkenyl-4,4-dimethyloxazoline. In this communication, the presence of two additional trans-18:1 fatty acid methyl ester positional isomers (Δ6 and Δ7) in the same mixture is confirmed by ¹³C nuclear magnetic resonance spectroscopy. The identity of the Δ5-trans-18:1 fatty acid methyl ester positional isomer is inferred. Summer student researcher.