Double bond location in polyenoic fatty esters through partial oxymercuration

A rapid micro-procedure has been developed to locate double bonds in fatty acid methyl esters containing from one to four double bonds. Reaction of the ester with an equal molar amount of mercuric acetate in methanol and reduction with sodium borohydride, followed by hydrogenation, produce a mixture of monomethoxy alkanoates. The mass spectrum of this mixture is simpler and more definitive than that from the completely methoxylated polyenoate. Only one methoxyl group is present per molecule, and the mass spectrum of the mixture is indicative of all olefinic positions. Four intense ions are observed for all double bonds examined, except Δ3, where the double bond is represented, by only two ions. Hydrogenation in a gas chromatograph reduces total analysis time to 1 hr. Presented at the AOCS Meeting, Cincinnati, September 28–October 1, 1975.     

Homogeneous catalytic hydrogenation of unsaturated fats: Cobalt carbonyl

Homogeneous hydrogenation of unsaturated fats by cobalt carbonyl has been compared with the previously reported catalysis by iron carbonyl. Soybean methyl esters, methyl linoleate and linolenate have been hydrogenated at 75–180C, 250–3,000 psi H₂ and 0.02 molar concn of catalyst. The cobalt carbonyl catalyst is more active at lower temp than iron carbonyl. The partially reduced products are similar to those observed with iron carbonyl, but the reaction differs in showing much less accumulation of conjugated dienes, no selectivity toward linolenate, almost complete absence of monoene hydrogenation to saturates, less double bond migration and moretrans isomerization. No evidence was found for a stable complex between cobalt carbonyl and unsaturated fats as previously observed with iron carbonyl. The rates of hydrogenation/double bond were the same for linoleate and linolenate on one hand, and for alkali-conjugated linoleate and nonconjugated linoleate on the other. Presented at AOCS Meeting in Minneapolis, 1963. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, USDA.     

Platinum‐Catalysed Hydrosilylation of Unsaturated Fatty Acid Esters

Different Pt(IV), Pt(II) and Pt(0) catalysts were screened for the hydrosilylation of fatty acid esters containing terminal as well as internal double bonds. The reaction of terminally unsaturated fatty acid esters proceeded smoothly with short reaction times for nearly all examined catalysts, whereas Pt(IV) species and Pt(II) or Pt(0) species with labile ligands were sufficiently active in the reaction of internally unsaturated compounds. For methyl linoleate, a conjugation of the two internal double bonds before the hydrosilylation was observed. The reaction was carried out in substance as well as in solvent systems permitting a catalyst recycling and reuse. In these systems, however, hydrogenation and double bond isomerisation were found as side reactions.     

Homogeneous catalytic hydrogenation of unsaturated fats: Metal acetylacetonates

Hydrogenation of linseed and soybean methyl esters was achieved at 100–180C, 100–1000 psi H₂ and 0.05–0.25 moles catalyst per mole of ester. The relative activity of metal acetylacetonates in decreasing order was: nickel (III), cobalt (III), copper (II) and iron (III). Reduction occurred readily in methanol solution but only slowly in dimethylformamide and acetic acid. No reduction occurred in the absence of solvents. Soybean oil was also hydrogenated rapidly with nickel (III) acetylacetonate in methanol, but in this system the triglycerides were converted to methyl esters. Nickel (III) acetylacetonate was the most selective catalyst toward linolenate hydrogenation. Methyl linoleate and linolenate hydrogenated with nickel(III) acetylacetonate were fractionated into monoenes, dienes and trienes. Thecis monoenes separated in 62 to 68% yield had double bonds in the original position. The remainingtrans monoenes had extensively scattered unsaturation. The dienes and trienes showed no conjugation, but some of the double bonds in the dienes were not conjugatable with alkali. Little stearate was formed. Presented at AOCS meeting in Chicago, 1964 No. Util. Res. and Dev. Div. ARS, USDA     

Selektivhydrierung von Fettstoffen mit metallorganischen Mischkatalysatoren nach Ziegler-Sloan-Lapporte I: Selektive Hydrierung von Linolsäuremethylester und Modelldienen mit isolierten Doppelbindungen

Selective Hydrogenation of Fats and Derivatives Using Ziegler-Type Organometallic Catalysts I: Selective Hydrogenation of Methyllinoleat and Other Dienic Compounds with Isolated Double Bonds Homogeneous catalysts of Ziegler-Sloan-Lapporte-type, containing nickel, cobalt or palladium, were used to hydrogenate methyllinoleate under very mild conditions selectively to monounsaturated products. The question, wether this selectivity is caused by the 1,4-position of the olefinic double bonds, led to hydrogenation experiments with non-conjugated α,ω-dienes of different chain length. A significant selectivity was only observed for the reduction of 1,4-pentadiene to pentene, dienes with greater distance between the double bonds than in linoleic acid were hydrogenated with less selectivity. To explain these facts, a kinetic model, including catalyst-substrate-complexes of different stabilities, is proposed.     

Über die Reduktion ungesättigter Fettsäuren und deren Ester zu ungesättigten Fettalkoholen durch selektive katalytische Hochdruckhydrierung III: Metallische und metallisch-oxidische Kupfer-Cadmium-Kontakte

Reduction of Unsaturated Fatty Acids and Their Esters to Unsaturated Fatty Alcohols by Selective Catalytic High Pressure Hydrogenation III: Metallic and Metal Oxide Copper-Chromium Catalysts Influence of catalyst composition and reaction conditions on the high pressure reduction of unsaturated fatty acids and their esters is described for metallic and mixed metal oxide copper-chromium catalysts. From these investigations and from a comparison with the efficacy of other metals in hydrogenation a hypothesis on the mechanism of the catalytic reaction in the reduction of carboxyl group and saturation of C? C double bonds is developed. The optimum reaction data of oleic acid and methyl oleate, which were used as test substances, are given.     

Hydrogenation of unsaturated fatty esters during isobutane chemical ionization mass spectrometry

Hydrogenation of double bonds was observed to occur during the isobutane chemical ionization mass spectrometry (MS) of unsaturated fatty esters. Chemical ionization (CI) spectra of a series of methyl esters in the C16–C20 carbon range containing 0–4 double bonds showed a variety of ionization characteristics in the molecular ion cluster, including hydride abstraction, charge exchange, protonation and, for the unsaturated fatty acids (FA), hydrogenation of the double bond followed by protonation. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Hydrogenation of unsaturated fatty esters with copper-chromite catalyst: Kinetics,mechanism and isomerization

Hydrogenation of linolenate with copper chromite produced a large amount of conjugated diene and minor amounts of nonconjugatable dienes. The double bonds in conjugated dienes and monoenes were scrambled all along the chain. This product distribution can be explained if it is assumed that conjugation of the double bonds is followed by hydrogenation. In competitive hydrogenation, fatty esters with conjugated double bonds were reduced preferentially over fatty esters with methylene-interrupted double bonds. Isomerization of conjugated double bonds (geometric and positional) occurred more rapidly than reduction. Reduction of conjugated double bonds in the presence of deuterium resulted in a majority of the products containing no deuterium. Most of the added deuterium was incorporated into the unreacted material. Mechanisms are proposed to account for the products formed during the hydrogenation of linolenate, linoleate and their isomers. One of 10 papers to be published from the Symposium “Hydrogenation,” presented at the AOCS Meeting, New Orleans, April 1970. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Selective hydrogenation with copper catalysts: V. Kinetics and mechanism at high pressure

The mechanism of hydrogenation at 900~950 psi with copper-chromite catalyst was investigated with pure methyl esters as well as their mixtures. A comparison of double bond distribution intrans-monoenes formed during hydrogenation of linoleate and alkali-conjugated linoleate revealed that 85~95% of the double bonds in linoleate conjugated prior to hydrogenation. The mode of hydrogen addition to conjugated triene and diene at high pressure is similar to that at low pressure but positional and geometric isomerizations of unreduced conjugated esters were less at high pressure. Geometric isomerization of methyl linoleate and linolenate was considerable at high pressure whereas it was negligible at low pressure. The absence of conjugated products during hydrogenation of polyunsaturated fatty acid esters resulted from their high reactivity. Conjugated dienes are 12 times more reactive than the triene, methyl linolenate, and 31 times more reactive than the diene, methyl linoleate. The products of methyl linolenate hydrogenation were the same as those predicted by the conjugation mechanism. Presented at the 70th Annual Meeting of the American Oil Chemists' Society, San Francisco, April 29~May 3, 1979.     

Competitive hydrogenation rates of isomeric methyl octadecadienoates

Determination of the relative reaction rates of isomeric methyl octadecadienoates is possible by competitive reduction of a mixture containing an inactive diene and a radioactively labeled isomer. The hydrogenation rate of methylcis-9,cis-12-octadecadienoate with platinum and nickel catalysts is compared to the hydrogenation rate of each of several isomers of methyl octadecadienoate, and the relative rate of the competitive hydrogenations is calculated by a digital computer. Methylcis-9,cis-12 linoleate is reduced the most rapidly of all the dienes studied. The relative rates of the positional isomers tend to decrease with the increasing number of methylene groups between the double bonds, except when one of the double bonds is in the more reactive 15 position. Comparison of the geometric isomers shows thattrans,trans diene is hydrogenated at a slower rate thancis,cis linoleate.

     

Displacement of the double bonds during hydrogenation of unsaturated fatty acid methyl esters

Summary The displacement of the double bond of several unsaturated fatty acid methyl esters during hydrogenation with a nickel-kieselguhr catalyst at 180°C. was investigated. The analysis of the dicarboxylic acids (obtained by oxidation of the reaction products with KMnO₄ in acetic acid solution) by means of partition chromatography enabled a reliable semiquantitative determination of the position isomers formed. During hydrogenation of methyl esters of oleic, elaidic, petroselinic, and linoleic acid formation of large amounts of position isomers was proved to occur. Migration of the double bonds in both directions took place but was in all cases strongly pronounced in a direction opposite the ester group. The place and configuration (cis or trans) of the double bonds in the starting material apparently were of little importance in this respect. It follows that hydrogenation of fatty acid esters leads to products which are far more complicated, as is generally known. This is especially of importance with respect to the application of hydrogenated fatty oils in the food industries.     

Homogeneous catalytic hydrogenation of unsaturated fats: Iron Pentacarbonyl

Iron pentacarbonyl is an effective homogeneous catalyst for the reduction of polyunsaturated fats. Hydrogenation of soybean oil and its methyl esters has been achieved at 180C, hydrogen pressures of 100-1,000 psi, and 0.05–0.5 molar concentrations of catalyst. Analyses of partially reduced products show considerable isomerization of double bonds, reduction of linolenate and linoleate with little or no increase in stearate, and accumulation ofcis,trans- andtrans, trans-conjugated dienes, and isolatedtrans monoenes. The unreduced trienes include diene conjugated fatty esters. The nonconjugated dienes contain large amounts oftrans and nonalkali conjugatable unsaturation. Considerable scattering of double bonds is evident in different fractions between the C₄ and C₁₆ positions. Complex formation between iron carbonyl and unsaturated fats is also indicated. The course of the homogeneous hydrogenation catalyzed by iron pentacarbonyl appears similar to the heterogeneous catalytic reaction. Metal carbonyls are well known for their isomerizing effects and their ability to form stable complexes with olefins. These homogeneous complexes provide suitable model systems to study the mechanism of catalytic hydrogenation of fats.     

Hydrogenation of α,β-Unsaturated Carbonyl Compounds Using Recyclable Water-Soluble FeII/EDTA Complex Catalyst

Hydrogenation of unsaturated carbonyl compounds like cinnamaldehyde and citral was studied in a biphasic media using water-soluble Fe^II/EDTA as a catalyst. It was observed that olefinic bond was selectively hydrogenated over the carbonyl group. Different reaction parameters like temperature, pressure, catalyst concentration were optimized for better selectivity of hydrocinnamaldehyde/dihydrocitronellal. The catalyst was further extended to hydrogenation of several other α,β-unsaturated carbonyl compounds.     

Selective hydrogenation with copper catalysts: III. Hydrogen addition and isomerization

β-Eleostearate was found to be reduced by 1,6 addition of hydrogen. Because of the extensive isomerization of conjugated trienes during hydrogenation, the occurrence of 1,2 and 1,4 addition reactions could not be proven. Conjugated dienes were reduced by both 1,2 and 1,4 addition of hydrogen. The double bond distribution in the products formed from linoleate, linolenate and their isomers was consistent with the assumption that the double bonds in polyunsaturated fatty esters conjugate and then add hydrogen. Extensive isomerization (positional and geometric) of the conjugated double bond systems occurred during hydrogenation. Monoenes were not isomerized under similar conditions of hydrogenation. Since double bond distribution in monoenes formed from linoleate and alkali-isomerized linoleate was identical, indications are that conjugation precedes hydrogenation. Presented in part at the symposium “Hydrogenation Process,” Division of Industrial Engineering Chemistry, 157th American Chemical Society Meeting, Minneapolis, April 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Hydrogenation ofcis-9,cis-12-,cis-9,trans-12- andtrans-9,trans-12- Octadecadienoates

The products formed by hydrogenation of methylcis-9,trans-12- andtrans-9,trans-12-octadecadienoates with nickel and platinum catalysts have been compared with those from methyl esters of the naturally occurring all-cis linoleate. Hydrogen uptake is slower for thetrans isomers. Much of the monoene consisted of esters with double bonds at the 9 and 12 positions with their original geometric configurations. Monoenoic esters with double bonds at the 10 and 11 positions were predominatelytrans and apparently formed by conjugation before hydrogenation. Nickel produced more isomerization than platinum but less than previously reported for copper. With both catalysts hydrogenation proceeded both directly and through conjugated intermediates, in contrast to copper in which all hydrogenation is believed to follow conjugation. Presented at the AOCS Meeting, Los Angeles, April 1972. ARS, USDA.     

Identification of Unsaturated dinitrophenylhydrazones by partial hydrogenation

Small amounts of unsaturated carbonyl compounds, which originate from autoxidized fats, were converted into their corresponding 2,4-dinitrophenylhydrazones and subsequently partially hydrogenated. Neither hydrazine nor hydrogen gas and platinum oxide gave satisfactory results, but, using palladium on calcium carbonate as catalyst, the 2,4-dinitrophenylhydrazones could be hydrogenated partially. Only the double bonds of the aliphatic part of the molecule were reduced, whereas the carbon nitrogen double bond and the nitro groups were not attacked. After hydrogenation of 2,4-dinitrophenylhydrazones, the reaction mixture was analyzed by thin layer chromatography on a Kieselguhr plate impregnated with Carbowax. In this way, the chain length of the unsaturated carbonyl compound, as well as the number of double bonds, could be determined. Carbonyl conjugated double bonds appeared to be hydrogenated faster than isolated double bonds.     

A simple,rapid micromethod for the determination of the structure of unsaturated fatty acids via ozonolysis

A micromethod for the localization of double bonds in unsaturated fatty acids via ozonolysis employing pyrolytic cleavage of ozonides in the presence of a hydrogenation catalyst is described. Cleavage of the ozonides is carried out in a gasliquid chromatographie instrument in a small glass tube, containing the catalyst, inserted in the top of the column opposite the in input heaters at 225C. Ozonides of methyl esters of straight chain unsaturated fatty acids are cleaved through the action of the catalyst to aldehyde fragments which are swept simultaneously into the column for analysis. The double bond positions are deduced from the chain length of the fragments. The method is demonstrated on methyl oleate, linoleate, linolenate and arachidonate. Presented at the AOCS Meeting, Cincinnati, October, 1965.     

Biodiesel production from highly unsaturated feedstock via simultaneous transesterification and partial hydrogenation in supercritical methanol

In this study, a supercritical one-pot process combining transesterification and partial hydrogenation was proposed to test its technical feasibility. Simultaneous transesterification of soybean oil and partial hydrogenation of polyunsaturated compounds over Cu catalyst in supercritical methanol was performed at 320 °C and 20 MPa. Hydrogenation proceeded simultaneously during the transesterification of soybean oil in supercritical methanol, and hydrogenation occurred during the reaction despite the absence of hydrogen gas. The polyunsaturated methyl esters obtained in the biodiesel were mainly converted to monounsaturated methyl esters by partial hydrogenation. Key properties of the partially hydrogenated methyl esters were improved and complied with standard specifications for biodiesel.     

On-line hydrogenation in GC-MS analysis of cyclic fatty acid monomers isolated from heated linseed oil

A simple on-line hydrogenation method in GC-MS analysis of unsaturated fatty acid esters is described. Using hydrogen as carrier gas, hydrogenation takes place in a capillary reactor connected to the outlet of the analytical column in the oven of the gas chromatograph. The reactor is a fused silica tube (60 cm×0.32 mm i.d.) coated with palladium acetylacetonate. Selective hydrogenation of olefinic bonds is achieved after a normal chromatographic run. Structural information (carbon-skeleton, double bond equivalents) can thus be deduced, and structural correlations between the saturated and unsaturated components can be obtained. Structures of cyclic fatty acid esters isolated from heated linseed oil were elucidated using this simple method which was found very useful for structural investigations on unsaturated compounds by GC-MS. Presented in part at the AOCS meeting in May 1988, in Phoenix, AZ. INRA—Station de Recherches sur la Qualite des Aliments de l'Homme     

1H NMR Study of Methyl Linoleate Ozonation.

Unsaturated fatty acids are essential components of vegetable oils and cellular membranes and the involved aspect of unsaturated fatty acids ozonation have been widely studied by different authors. In this paper, in vitro ozonolysis of unsaturated fatty acids with addition of water or ethanol has been studied by Proton Nuclear Magnetic Resonance (¹H NMR) at 250?MHz in order to explore the possibility of this technique for the detection of Criegee ozonides in characterizing ozone reaction with these substrates. The ozonolysis of methyl linoleate showed that signal intensities from formed ozonides were increased with ozone concentration increments. However, the signal intensities with addition of water were higher than those in ethanol addition. Signal intensities from olefinic double bonds were found to decrease with the increment in ozonide signals. Thus, a correspondence of the behavior of these signals is observed with a proportional rate reaction between the number of double bonds in the substrate molecule. Signals from aldehyde formation were poorly detected at lower ozone concentration. It was concluded that the evaluation of ozonide and olefinic double bond signals from 250?MHz ¹H NMR can be a useful tool in assessing ozone reaction with biomolecules. The reaction mechanism for the ozone reaction with unsaturated fatty acids in the presence of water or ethanol is analyzed.