Alkali isomerization of linoleate isomers: Characterization of products

Geometrical isomers of methyl linoleate were reacted with alakli, and the resulting conjugated isomers were separated intotrans,trans;cis,trans; andcis,cis fractions. The position of double bonds in the various fractions was determined by reductive ozonolysis.trans-9,trans-12-Isomer of linoleate formedtrans,trans- andcis,trans-conjugated dienes, whereascis-9,trans-12- andtrans-9,cis-12-isomers in addition formedcis,cis-conjugated dienes. The formation of the products is in accordance with the theoretical predictions. During conjugationtrans double bonds shifted to form atrans bond preferentially. During conjugation ofcis-9,trans-12- andtrans-9,cis-12-linoleate isomers, thecis double bond shifted preferentially over thetrans double bond. A small amount of diene not conjugated was probably a geometrical and positional isomer of the starting material.     

Selective hydrogenation with copper catalysts: I. Isolation and identification of isomers formed during hydrogenation of linolenate

Methyl linolenate was hydrogenated with 10% copper chromite catalyst at 150 C and atmospheric hydrogen pressure. The product was separated into monoene, diene and triene fractions by countercurrent distribution. These fractions were further separated into various geometrical isomers. The double bond location in the various fractions was determined by reductive ozonolysis. Double bonds in bothcis andtrans monoene fractions, as well as incis,trans andtrans,trans conjugated dienes, were extensively isomerized. A monoene containing vinylic unsaturation was one of the major products. The nonconjugated dienes were mostly dienes whose double bonds were widely separated. Results are explained on the basis of conjugation of the double bonds in linolenate followed by hydrogen addition. 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 of linolenate. VII. Separation and identification of isomeric dienes and monoenes

Isomeric dienes and monoenes produced by partial hydrogenation of linolenic acid have been separated by the combined use of low-temp crystallization and countercurrent distribution.Cis, trans dienes have been separated fromcis, cis dienes.Cis, cis conjugatable dienes have been partially separated fromcis,cis nonconjugatable dienes. Dienes with onetrans double bond were separated by gas chromatography into two groups:cis, trans andtrans, cis. Individual positional isomers could not be separated. Cis-9 monoene was separated fromcis-12,cis-15, andtrans monoenes by low-temp crystallization. Countercurrent distribution at 3,000 transfers only partially separated this mixture ofcis-12,cis-15, andtrans monoenes. The double bond in bothcis andtrans monoenes was found in all carbon positions, 7 through 16, showing for the first time that the 15, 16 bond of linolenic acid had moved away from the carboxyl. The majorcis bonds remained at carbons 9, 12, and 15. Combination of countercurrent distribution fractions has produced samples containing 95%cis, cis dienes; 90%cis, trans ortrans, cis dienes; 95%cis monoenes; and 90%trans monoenes. Presented at the AOCS meeting at Chicago, Ill., 1961. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

Deuteration of methyl linoleate with nickel,palladium, platinum and copper-chromite catalysts

Samples taken during deuteration of methyl linoleate with the title catalysts were separated into saturate, monoene and diene fractions. Monoenes were further separated intocis andtrans fractions. A comparison of the double bond distribution in monoenes with those from hydrogenation of alkaliconjugated linoleate indicated that up to 59% of the linoleate was reduced through a conjugated intermediate with nickel catalyst. The respective percentages for palladium and platinum catalysts were 51 and 23. Copper catalysts have previously been shown to reduce linoleate solely through conjugated intermediates. Copper-chromite catalyst showed infinite selectivity for the reduction of linoleate, because stearate did not form. The decreasing order of various catalysts for the selective reduction was copper-chromite>>>Ni at 195 C>Pd>Ni at 100 C>Pt. Computer simulation of platinum reduction indicated that ca. 20% of the linoleate was directly reduced to stearate through a shunt. Geometrical isomers of linoleate were formed during reduction with all catalysts except copper-chromite. Nickel catalyst formed bothtrans,trans- andcis,trans-isomers, as well as nonconjugatable dienes. These isomers were favored at the higher temperature and deuterium was incorporated into them. Palladium and platinum did not isomerize linoleate to nonconjugatable dienes. Because conjugated dienes are more reactive than linoleate, they were not found in appreciable amounts during reduction. Conjugated dienes were the only isomers formed with copper-chromite catalyst. Deuterium was found in these conjugated dienes, which were also extensively isomerized. As a result of isomerization and exchange during reduction of linoleate-as well as further exchange between deuterium and monoenes-a wide distribution of isotopic isomers in monoenes was found with nickel, palladium and platinum catalysts. Since isomerization of monoenes with copper-chromite is negligible, the isotopic distribution of monoenes must be due to exchange of intermediate conjugated dienes followed by addition. Presented at the AOCS Meeting, Ottawa, September 1972. ARS, USDA.     

Isomerization during hydrogenation of soap: II. Potassium elaidate and potassium linoleate

Potassium elaidate in slightly alkaline solution was hydrogenated for up to 7 hr with 1.5% of Rufert nickel catalyst at 150 C and 20 kg/sq cm pressure. Potassium linoleate was similarly hydrogenated with 1.0% catalyst for 7 hr, and the hydrogenation continued for another 7 hr after addition of 0.5% fresh catalyst. Periodic samples from each were analyzed for component acids. The positional isomers in thecis andtrans monoenes, isolated by preparative argentation thin layer (TLC) or column chromatography, were estimated after oxidation to dicarboxylic acids. Some diene fractions were isolated for further examination. In potassium elaidate hydrogenation,cis monoenes were initially produced in considerable amounts, but to a lesser extent thereafter. Positional isomers were similarly distributed in bothcis andtrans monoenes after prolonged hydrogenation. In the hydrogenation of potassium linoleate, a drop in iodine value (IV) of 60 units occurred in the first hour, and 38% oftrans monoenes (in which the 10- and 11-monoenes constitute 32% each) were formed. The IV then fell only slowly, and up to 38% ofcis monoene (mostly 9- and 12-isomers) was formed. Addition of fresh catalyst caused a major shift ofcis monoenes totrans forms. The diene fraction was mostly nonconjugated material with the first double bond at the 9, 8 and 10-positions. Minor amounts of conjugated dienes were present as well as a dimeric product.     

Deuteration of methylcis-9,cis-15-octadecadienoate with nickel catalyst

Methylcis-9,cis-15-octadecadienoate was partially deuterated with nickel catalyst, and the product was separated into saturate, monoene and diene fractions. Monoenes were separated intotrans andcis fractions, and dienes intotrans,trans, cis,trans andcis,cis fractions. Monoene isomers with double bonds at the 9 and 15 positions predominated in bothcis- andtrans-monoene fractions. Considerable amounts of isomers with double bonds situated on either side of the original 9 and 15 positions were found in thetrans-monoene fraction. Diene was extensively isomerized to positional and geometrical isomers, and deuterium was incorporated into these isomers. Double bond migration was greatest intrans,trans-dienes and smallest incis,cis-dienes. The amount of deuterium in the dienes was proportional to the extent of isomerization experienced by the dienes. ARS, USDA.     

Nonmetallic palladium-on-resin: A very active and selective catalyst for the hydrogenation of diunsaturated fatty acid esters I

Methylcis-9,cis-12-octadecadienoate (methyl linoleate;c9,c12) and the correspondingcis,trans andtrans.trans geometric isomers (c9,t12 andt9,t12) were hydrogenated at 40 C and atmospheric hydrogen pressure in acetone as solvent, with nonmetallic palladium-on-resin catalyst. These catalysts were prepared by impregnation of cationic exchange resins with an aqueous solution of palladium dichloride. The methyleneinterrupted dienes were hydrogenated to the monoene stage with almost infinite selectivity, especially withc9,c12, whereast9,t12 was hydrogenated somewhat less selectively. The latter isomer was reduced considerably more slowly than the first, whereasc9,t12 occupied an intermediate position. The hydrogenation proceeded for an important part via a straightforward reduction of one of the double bonds, though conjugation prior to hydrogenation also occurred. The methylene-interrupted dienes isomerized to a high degree geometrically during hydrogenation, but they scarcely isomerized positionally, resulting in small amounts of inactive ethylene-interrupted dienes.     

The chemistry of polymerized oils. V. The autoxidation of methyl linoleate

1. The geometrical forms obtained during autoxidation of methyl linoleate at ordinary temperatures are largely conjugatedcis-trans andtrans-trans as shown by previous workers; there is a possibility that conjugatedcis-cis forms are also produced. 2. Thetrans-trans molecules arise partly, at least, by thermal rearrangement of already formedcis-trans peroxide. 3. Some proportion, at least, of thecis-trans molecules have theirtrans double bonds nearest to the hydroperoxide group. 4. A partial separation of the geometrical forms can be accomplished by reversed phase partition chromatography both on methyl linoleate hydroperoxides and on the corresponding mixed hydroxy compounds; isolation of thetrans-trans forms can be accomplished in the latter case by urea complex fractionation. 5. No position isomers except the known 9- and 13-isomers have been positively identified; there is a possibility that very minor amounts of the 2-isomer are formed; the 9- and 13-isomers are present in about equal amounts; the 11-isomer was not detected by the methods applied. 6. Various ways in which the linoleate autoxidation problem might be advanced further are suggested.     

Autoxidation of methyl linoleate. Separation and analysis of isomeric mixtures of methyl linoleate hydroperoxides and methyl hydroxylinoleates

The mixture of conjugated diene hydroperoxide isomers obtained from autoxidation of methyl linoleate was separated by high performance liquid chromatography (HPLC). Four major isomers were obtained from adsorption chromatography and identified as the 9 and 13 positional isomers having thetrans-trans andcis-trans configurations. The latter geometrical isomers have thetrans double bond adjacent to the hydroperoxide group. The hydroxy compounds (methyl hydroxylinoleates) obtained from the hydroperoxides by NaBH₄ reduction were similarly separated but with improved resolution. This is the first instance of the complete separation of these compounds and provides a rapid method for their analysis. Unlike adsorption chromatography, reversed-phase chromatography separates the mixtures only according to the geometrical isomerism of the double bonds and not according to the position of the hydroxy or hydroperoxide function.     

Partial reduction of α-Eleostearic acid with hydrazine

The following products are formed during partial reduction of α-eleostearic acid with hydrazine:cis,trans-9,11-octadecadienoic andtrans,trans-11,13-octadecadienoic acids;cis-9-,trans-11- andtrans-13-octadecenoic acids; and stearic acid. The double bonds are reduced individually in the conjugated triene and also in the conjugated dienes that are formed. However, the reduction is selective since thetrans-11 double bonds in the conjugated triene is reduced only slightly to yield the isolated 9,13-diene. Thetrans double bond of thecis,trans conjugated diene reduces at a faster rate than thecis bond. No differences were observed in the rate of reduction of thecis-9 andtrans-13 bonds in the triene or of the bonds in thetrans,trans conjugated diene. No. Utiliz. Res. & Dev. Div., ARS, USDA.     

Hydrogenation of linolenate. I. Fractionation and characterization studies

Methyl linolenate hydrogenated at 140°C, with 0.5% Ni catalyst and 1.1 mole of hydrogen at atmospheric pressure was separated into octadecenoate, octadecadienoate, and octadecatrienoate fractions by countercurrent distribution. Gas chromatography on a 200-ft. capillary Apiezon L column revealed one component in the triene fraction, four in the diene fraction, and nine in the monoene fraction. These components were partially fractionated by low-temperature crystallization, and their solubilities were correlated with alkali conjugation results, with infrared data forcis andtrans configuration of bonds and with dibasic acids isolated from the fractions after oxidative cleavage. Approximately 45% oftrans acids were present in both the monoene and diene fractions. Considerable migration of double bonds from the original 9, 12, and 15 positions occurred.Cis,cis dienes which could not be conjugated by alkali were formed. Little alteration of the residual methyl linolenate was observed. The results demonstrate the applicability and utility of new techniques of fractionation and analysis to the study of the hydrogenation mechanism. Presented at 51st annual meeting, American Oil Chemists' Society, Dallas, Tex., April 4–6, 1960. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

The effect of trans-isomers on the physical properties of hydrogenated oils

Data have been presented which indicate a positive relationship between thetrans-isomer content of a hydrogenated oil and the congeal point, Wiley melting-point, and solids index. It has also been shown that cottonseed oil and soybean oil undergo substantially the same type of reaction under identical hydrogenating conditions. This conclusion is based on the relationship oftrans-isomer formation to total reduction in unsaturation up to the point that equilibrium is reached and saturation of thetrans-isomers occurs. This equilibrium was noted at between 60–70 iodine value. The relationship oftrans-isomer formation to the total reduction in double bonds can be expressed as the hydrogenation index. This is a reliable indication of the type of reaction taking place up to the point where appreciable hydrogenation of thetrans-isomers occur.     

Studies on monoene fatty acid isomers in hydrogenated fish oils

An analytical study of the geometrical and positional isomerisation of the monoenoic acids of partially hydrogenated fish oil is presented. The results showed that the monoene fatty acids of chain lengths 16, 18, 20 and 22 consisted of 75% in thetrans-form and 25% in thecis-form. The double bonds were distributed symmetrically over the chain length, with well defined maxima in position Δ-9 for the fatty acids of chain length 16 and 18, and in position Δ-11 for the fatty acids of chain length 20 and 22.Trans- andcis-isomers showed the same positional distribution. Geometric as well as positional isomerization seemed to have reached an equilibrium state in the sample investigated. Presented at the ISF-AOCS World Congress, Chicago, October 1970.     

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     

Occurrence of octadecenoic fatty acid isomers from hydrogenated fats in human tissue lipid classes

The level oftrans-18∶1 isomers in several isolated lipid classes of human liver, heart, red blood cells and plasma was determined. Phospholipids contained substantially fewertrans-18∶1 isomers than triglycerides. The double bond distribution of thecis andtrans octadecenoate fraction of triglycerides and phosphatidylcholines from human liver and heart was determined. Whereas the double bond distribution of the triglycerides correlated closely with the pattern found in dietary hydrogenated vegetable oils, the phosphatidylcholine fraction showed evidence of selective incorporation or metabolism of specifictrans positional isomers. In general, isomers with double bonds near the methyl terminus were present at levels higher than expected from their relative abundance in the diet. Refinements in methodology needed to analyze octadecenoate double bond configuration and location in human tissues are presented.     

Hydrogenation of dienes with cationic rhodium complexes

Methylcis-9,cis-12-octadecadienoate (methyl linoleate;c9,c12), itst10,t12 andt10,c12 isomers and methylcis-9-octadecenoate (methyl oleate;c9) were hydrogenated with rhodium complexes, the active species of which consisted of [RhL₂]⁺ and [RhL₂H₂]⁺ with ligands L=P(C₂H₅)₂C₆H₅ (catalyst A) P(i-C₄H₉)₃ (catalyst B) and P(CH₃)₃ (catalyst C). Using these catalysts the influence of steric effects on the reaction mechanism of hydrogenation of dienes was studied. The reactions were carried out in 2-propanol at atmospheric hydrogen pressure and ambient temperature. During hydrogenation ofc9 on catalysts A and B, geometrical isomerization mainly occurred, whereas on catalyst C some positional isomerization also took place.C9,c12 was almost exclusively hydrogenated via conjugated intermediates on catalyst A. On catalyst C, one of the double bonds was hydrogenated directly, in most cases. In the absence of hydrogen, catalysts A and B conjugatedc9,c12 very fast. The conjugation activity of catalyst C was much lower. Catalyst C showed a high 1,5-shift activity for the conjugatedcis, trans andtrans, cis intermediates during hydrogenation, in contrast to catalysts A and B, which showed a poor activity in this respect.T10,t12 was hydrogenated almost exclusively via 1,4-addition of hydrogen to thecisoid conformation, whereas only a slight preference was found in this mechanism over 1,2-addition for the hydrogenation oft10,c12. On the sterically unhindered catalysts A and C thetrans double bond int10,c12 was preferentially hydrogenated whereas on catalyst B, with its bulky ligands, thecis double bond was reduced faster than thetrans double bond.     

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.     

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.

     

Separation ofcis andtrans-isomers of 1,2-benzylidene glyceryl esters

Separation of thecis- andtrans-isomers of 1,2-benzylidene glyceryl esters has not yet been achieved by column or gas liquid chromatography. However these isomers were separated by thin layer chromatography in the present study and the parent cyclic alcohols regenerated by alkaline hydrolysis.     

Quantitative analysis of long-chain trans-monoenes originating from hydrogenated marine oil

Gas chromatography (GC) is used for the analysis of trans-fatty acids in partially hydrogenated vegetable oils. Although trans-isomers of C₁₈ carbon length predominate in partially hydrogenated vegetable oils, trans-isomers of C₂₀ and C₂₂ carbon length occur in partially hydrogenated fish oil. We report a simple silver ion chromatographic combined with capillary GC technique for quantitative analysis of trans-monoenes derived from partially hydrogenated fish oil. Silver nitrate thinlayer chromatographic (TLC) plates are developed in toluene/hexane (50∶50, vol/vol). Fatty acid methyl esters are separated into saturates (R _f 0.79), trans-monoenes (R _f 0.49), cis-monoenes (R _f, 0.27), dienes (R _f, 0.10), and polyunsaturated fatty acids with three or more double bonds remaining at the origin. The isolated trans-monoenes are quantitatively analyzed by capillary GC. The technique of argentation TLC with GC analysis of isolated methyl esters is highly reproducible with 4.8% variation (i.e., coefficient of variation, CV%) in R _f values and 4.3 and 6.9% CV% in quantification within batch and between batch, respectively. Furthermore, the combined technique revealed that direct GC analysis underestimated the trans-content of margarines by at least 30%. In this study, C₂₀ and C₂₂ trans-monoenes were found in relatively large quantities; 13.9% (range 10.3–19.6%) and 7.5% (range 5.3–11.5%), respectively, in margarine purchased in 1995, but these C₂₀ and C₂₂ trans-monoenes were much reduced (0.1%) in a fresh selection of margarine purchased in 1998. Compositional data from labels underestimated the trans-content of margarines, especially those dervied from hydrogenated marine oil. Low levels of C₂₀ trans-monoenes (range 0.1–0.3%) and C₂₂ trans-monoenes (range 0.0–0.1%) were identified in adipose tissue obtained from healthy volunteers in 1995, presumably indicating consumption of partially hydrogenated fish oil.