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.     

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.     

Selective hydrogenation of soybean oil: IV. Fatty acid isomers formed with copper catalysts

Two samples of soybean oil hydrogenated with copper-containing catalysts at 170 and 200 C were analyzed for their natural and isomeric fatty acids. Methyl esters of the hydrogenated oils were separated into saturates, monoenes, dienes and trienes by countercurrent distribution between acetonitrile and pentane-hexane. Monoenes were further separated intocis- andtrans-isomers on a silver-saturated resin column. Double bond location in these fractions was determined by a microozonolysis-pyrolysis technique. The diene fraction was separated with an argentation countercurrent distribution method, and linoleate was identified by infrared, ozonolysis and alkaliisomerization data. The double bonds in thecis-monoenes were located in the 9-position almost exclusively. However, the double bonds in thetrans-monoene were quite scattered with 10- and 11-isomers predominating. About 86% to 92% of the dienes consisted of linoleate as measured by alkali isomerization. Other isomers identified as minor components includecis,trans andtrans, trans conjugated dienes and dienes whose double bonds are separated by more than one methylene group. 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.     

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     

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.     

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.     

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.     

Hydrogenation of linolenate. II. Hydrazine reduction

Observations by Aylward and Rao that hydrazine is a reducing agent for a number of unsaturated fatty acids were extended. The hydrazine reaction on linolenic acid was followed by periodic sampling until methyl esters prepared from the reduced acids had an iodine value of 162. These esters were shown by countercurrent distribution to consist of 26% triene, 43% diene, 26% monoene, and 5% stearate and by infrared analysis to contain notrans bonds. Oxidation of the separated monoene and diene fractions by permanganate-periodate mixtures and gas chromatography of the dibasic acids showed that the double bonds were in the original 9, 12, and 15 positions and that the double bonds farthest from the carboxyl were reduced at a slightly faster rate. Gas chromatography of the monoene fraction indicated three components that were identified in the order of elution from the column as 9, 12, and 15 monoenes; in the diene fraction three components were identified in the order of elution as 9,12; 9,15; and 12,15 dienes. After alkali isomerization of this diene fraction, the conjugated material was reacted with maleic anhydride; the unreacted 9,15 diene isomer was separated by distillation. Presented at fall meeting, American Oil Chemists’ Society, New York, October 17–19, 1960. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.     

Selective homogeneous hydrogenation of triunsaturated fats catalyzed by tricarbonyl chromium complexes

The need for a selective catalyst to hydrogenate linolenate in soybean oil has prompted our continuing study of various model triunsaturated fats. Hydrogenation of methylβ-eleostearate (methyltrans,trans,trans-9,11,13-octadecatrienoate) with Cr(CO)₃ complexes yielded diene products expected from 1,4-addition (trans-9,cis-12- andcis-10,trans-13-octadecadienoates). Withα-eleostearate (cis,trans,trans-9,11,13-octadecatrienoate), stereoselective 1,4-reduction of thetrans,trans-diene portion yielded linoleate (cis,cis-9,12-octadecadienoate). However,cis,trans-1,4-dienes were also formed from the apparent isomerization ofα- toβ-eleostearate. Hydrogenation of methyl linolenate (methylcis,cis,cis-9,12,15-octadecatrienoate) produced a mixture of isomeric dienes and monoenes attributed to conjugation occurring as an intermediate step. The hydrogenation ofα-eleostearin in tung oil was more stereoselective in forming thecis,cis-diene than the corresponding methyl ester. Hydrogenation of linseed oil yielded a mixture of dienes and monoenes containing 7%trans unsaturation. We have suggested how the mechanism of stereoselective hydrogenation with Cr(CO)₃ catalysts can be applied to the problem of selective hydrogenation of linolenate in soybean oil. No. Market. Nutr. Res. Div., 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.     

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.     

Selective hydrogenation of soybean oil: X. Ultra high pressure and low pressure1

Soybean oil was partially hydrogenated with copper-chromite catalyst at 170 C and up to 30,000 psig hydrogen pressure. Catalyst activity increased with increase in pressure up to 15,000 psig. The linolenate selectivity (S_Ln) of the reaction remained essentially unchanged over 50–1000 psig pressure range. A S_Ln of 5.5 to 5.6 was achieved at 15,000 to 30,000 psig pressure range. This value is somewhat lower than the selectivity at 50–1000 psig, but much higher than that obtained with nickel catalysts. Geometric isomerization increased as pressure increased up to 200 psig; above this pressure, the percenttrans remained the same up to 500 psig.trans Isomer content decreased when the pressure was increased to 30,000 psig. cis,trans Isomerization of linoleate was greater at 1000 psig and 15,000 psig than at 50 psig. At 15,000 psig, part of the linoleate in soybean oil was hydrogenated directly without prior conjugation, whereas at low pressures, all of the double bonds first conjugate prior to hydrogenation. This difference in mechanism might explain the lower selectivities obtained at high pressures. Conjugated diene isomers were found in the products up to 200 psig. Above this pressure conjugated diene was not measurable. No significant differences were found in the double bond distribution oftrans monoenes even though the amount oftrans monoene formed decreased as pressure was increased to 30,000 psig. 1 Presented at the AOCS meeting, San Francisco, May 1979.     

Hydrogenation of alkali-conjugated linoleate: Isomeric monoene profiles obtained with nickel,palladium and platinum catalysts

Alkali-conjugated linoleate (cis-9,trans-11- andtrans-10,cis-12-octadecadienoate) was hydrogenated with nickel, palladium and platinum catalysts. Thetrans andcis monoenes formed during reduction were isolated, and their double bond distribution was determined by reductive ozonolysis and gas liquid chromatography. About 44–69% of the monoenes were composed of δ¹⁰ and δ¹¹ trans monoene isomers, whereas the δ⁹ and δ¹² cis monoenes amounted to 20–26%. With nickel catalyst, composition of monoene isomers remained the same, even when the hydrogenation temperature was increased. The monoene isomer profiles between nickel and palladium catalysts were indistinguishable. Isomerization of monoenes with platinum catalyst was suppressed at 80 psi. The position of the double bonds in unreacted conjugated diene was always retained, except with nickel at both temperatures and with platinum at 150 C when a slight migration occurred. Geometrical isomerization totrans,trans-conjugated diene was observed in the unreacted diene with nickel (ca. 15% of diene) at both 100 C and 195 C, and with platinum (ca. 7% of diene) at 150 C. ARS, USDA.     

Chromatographic separation ofcis andtrans fatty esters by argentation with a macroreticular exchange resin

Methyl oleate and methyl elaidate, as well as other monoenecis andtrans isomers of fatty esters, can be separated quickly and conveniently by a preparative chromatographic procedure in which a silver-saturated ion-exchange resin is used. Separations are based on differences in stabilites of the silver-olefin complexes. Recoveries of better than 95% were made, and puretrans andcis monoene fractions were collected. This method can be used to separate saturates fromcis andtrans monoenes. Thecis,trans,cis,cis, andtrans,trans-9-12-octadecadienoates were separated. Whilecis,trans andtrans,trans dienes were cluted separately, thecis,cis diene isomer remained on the column. Presented at AOCS Meeting, in Minneapolis, 1963. A laboratory of the No. Utiliz. Res. and 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.     

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.     

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.     

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 and deuteration of conjugated isomers of linoleate and linolenate with palladium,platinum, nickel and lindlar catalysts

Conjugated isomers of methyl linoleate and linolenate were reduced with palladium, platinum, nickel and Lindlar catalysts at atmospheric hydrogen or deuterium pressure. After the products were separated, positions of their double bonds were determined by ozonolysis. Palladium and platinum catalysts reduced β-eleostearate directly to monoene. Nickel reduced β-eleostearate to dienes chiefly by 1,2-addition and to a lesser extent by 1,4- and 1,6-addition, whereas Lindlar catalyst reduced by 1,2-and 1,6-addition only. All catalysts reduced conjugated linoleate isomers by both 1,2- and 1,4-addition, with nickel being somewhat preferential for 1,2-addition. Selectivity for the catalytic reduction of dienes to monoenes decreased in the order: nickel, palladium and platinum. Lindlar catalyst did not isomerize or reduce monoenes that formed during reduction. Palladium and platinum did not isomerize conjugated dienes and trienes during their reduction, whereas nickel and Lindlar catalysts isomerized them slightly. Some deuterium was found in unreacted conjugated diene and triene with nickel and Lindlar catalysts, but none with palladium or platinum. Deuterated products contained a wide range of isotopic isomers with some products having up to 31 deuterium atoms. This wide deuterium distribution resulted from (a) exchange followed by addition, (b) addition followed by exchange and (c) exchange-addition-exchange reactions. Presented at the AOCS Meeting, Atlantic City, October 1971. ARS, USDA.