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1.
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. 相似文献
2.
Catalytic hydrogenation of linoleic acid was studied on Ir/Al 2O 3. A detailed analysis of geometrical and positional isomers of octadecenoic acid (18:1) in the products was performed by capillary
gas-liquid chromatography with a new capillary column coated with isocyanopropyl trisilphenylene siloxane (TC-70). Well-resolved
peaks of 10 species of 18:1 were observed in the product. In addition to monoenoic acid isomers, four species of trans-dienoic isomers and conjugated dienoic isomers were found. From the distribution of 18:1 isomers, it was found that the double
bond closer to the methyl end (Δ12) showed higher reactivity than that closer to the carboxyl end (Δ9) for hydrogenation.
Because cis-8 18:1 and trans-8 18:1 were not observed but cis-10 18:1 and trans-10 18:1 were observed in the products, the double-bond Δ9 did not migrate to the carboxyl end but migrated to the methyl
end. On the other hand, the Δ12 bond migrated to both methyl and carboxyl ends. From the distribution of 18:1 isomers in the
reaction pathway, the hydrogenation of linoleic acid proceeds via half-hydrogenation states. Cis-18:1 isomers were produced predominantly in the initial stage of the reaction, while trans-18:1 isomers were produced during progress of the reaction. The cis/trans and positional isomerization took place by readsorption of 18:1 produced by the partial hydrogenation of linoleic acid. 相似文献
3.
The catalytic activity and selectivity for hydrogenation of linoleic acid were studied on Ni, Cu, and Pd catalysts. A detailed
analysis of the reaction product was performed by a gas-liquid chromatograph, equipped with a capillary column, and Fourier
transform-infrared spectroscopy. Geometrical and positional isomerization of linoleic acid occurred during hydrogenation,
and many kinds of linoleic acid isomers ( trans-9,trans-12; trans-8,cis-12 or cis-9,trans-13; cis-9,trans-12; trans-9,cis-12 and cis-9,cis-12 18∶2) were contained in the reaction products. The monoenoic acids in the partial hydrogenation products contained eight
kinds of isomers and showed different isomer distributions on Ni, Cu, and Pd catalysts, respectively. The positional isomers
of monoenoic acid were produced by double-bond migration during hydrogenation. On Ni and Pd catalysts, the yield of cis-12 and trans-12 monoenoic acids was larger than that of cis-9 and trans-9 monoenoic acids. On the contrary, the yield of cis-9 and trans-9 monoenoic acids was larger than that of cis-12 and trans-12 monoenoic acids on Cu catalyst. From these results, it is concluded that the double bond closer to the methyl group (Δ12)
and that to the carboxyl group (Δ9) show different reactivity for hydrogenation on Ni, Cu, and Pd catalysts. Monoenoic acid
formation was more selective on Cu catalyst than on Ni and Pd catalysts. 相似文献
4.
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 the cis and trans 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 both cis and trans 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% of trans monoenes (in which the 10- and 11-monoenes constitute 32% each) were formed. The IV then fell only slowly, and up to 38%
of cis monoene (mostly 9- and 12-isomers) was formed. Addition of fresh catalyst caused a major shift of cis monoenes to trans 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. 相似文献
5.
The products formed by hydrogenation of methyl cis-9, trans-12- and trans-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 the trans 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 predominately trans 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. 相似文献
6.
Catalytic activity and selectivity for hydrogenation of linoleic acid ( cis-9, cis-12 18:2) were studied on Pt, Pd, Ru, and Ir supported on Al 2O 3. Stearic acid (18:0) and 10 different octadecenoic isomers (18:1) in the products could be separated completely by using a new capillary column coated by isocyanopropyl trisilphenylene siloxane for gas-liquid chromatography. The monoenoic acid isomers and dienoic acid isomers in the products on the various catalysts showed different distributions. The catalysts exhibited nearly equal selectivity for stearic acid formation. The 12-position double bond in linoleic acid has higher reactivity than the 9-position double bond in catalytic hydrogenation on platinum-group metal catalysts. In addition to hydrogenation products of linoleic acid, geometrical and positional dienoic acid isomers ( trans-9, trans-12; trans-8, cis-12; cis-9, trans-13; trans-9, cis-13; cis-9, trans-12 18:2), due to isomerization of linoleic acid during hydrogenation, were contained in the reaction products. Ru/Al 2O 3 exhibited the highest activity for isomerization of linoleic acid with the noble metal catalysts. Conjugated octadecadienoic acid isomers have been observed in products of the reaction on Pt/Al 2O 3, Ru/Al 2O 3, and Ir/Al 2O 3. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd. 相似文献
7.
The decisions to limit (Europe) or declare (USA) the trans isomer content of certain fatty foodstuffs have caused a demand for hardstocks with a reduced trans isomer content. One way to produce such hardstocks is by interesterifying high‐melting components such as palm stearin or fully hydrogenated vegetable oils with lauric or liquid oils. Another way is to modify the hydrogenation process. Possible modifications are reviewed. A moderate reduction in trans isomer content results from operating the hydrogenation process at much reduced temperature, but this also leads to an increase in saturates. Larger reductions in trans isomers may well be made possible by the recent development of new catalysts. One development involves the use of zeolites that allow the rather straight trans isomer to enter the pores while keeping the more curved cis isomers outside. The other development involves a precious metal catalyst that may have been modified in such a way that it has a reduced affinity for monounsaturated fatty acid moieties. 相似文献
8.
Fractionation of products obtained from partial catalytic hydrogenation of methyl cis-9, cis-12-octadecadienoate (9c,12c-18:2) with tris(triphenylphosphine) chlororhodium [RhCl(Ph 3P) 3] provided a facile method for preparation of a nearly equal molar mixture of methyl cis-9- and cis-12-octadecenoate (9c-18∶1 and 12c-18∶1). Isolation of products was achieved by silver resin and C18 reverse phase liquid
chromatography. Catalytic deuteration of 9c,12c-18∶2 yields a mixture of 9c-18∶1-12,13-d 2 and 12c-18∶1-9,10-d 2 with an isotopic purity of 85%. Final isolated yield of the mixture of 9c- and 12c-18∶1 products was 30%. Isolation of products
from partial hydrogenation of conjugated octadecadienoates (9c,11t-18∶2 or 10t,12c-18∶2) provided a convenient method for
synthesis of an almost equal molar mixture of methyl trans-10 and trans-11-octadecenoate (10t-18∶1 and 11t-18∶1). Characterization of the reaction products from hydrogenation of 9c,12c-28∶2 indicates
that the 9c- and 12c-18∶1 products are formed by the expected 1,2-hydride addition. The presence of small amounts of 10t-
and 11t-18∶1 and conjugated octadecadienoates was evidence for a secondary isomerization-1,4-hydride addition pathway. Isolation
and characterization of products from RhCl(Ph 3P) 3-catalyzed hydrogenation of 9c,11t-18∶2 and 10t,12c-18∶2 indicate that both 1,2- and 1,4-hydride addition to the conjugated
diene isomers occurs at about equal rates, but only the cis bond is reduced by the 1,2-hydride addition pathway and the 1,4-hydride addition pathway yields only a trans-18∶1. Because of this unusual selectivity for a cis bond conjugated with a trans bond, hydrogenation of both 9c,11t-18∶2 and 10t,12c-18∶2 yields the same mixture of t-18∶1 isomers. 相似文献
9.
Directed isomerisation of safflower oil under very low hydrogen partial pressure of 7 psi over a novel bifunctional highly structured rhodium‐based catalyst (Rh/SBA‐15), having narrow pore size distribution ranging from 4 to 8 nm, and BET‐specific surface of ≈1,000 m 2 g ?1, was investigated as a new chemocatalytic approach for vegetable oil hardening and simultaneously producing health‐beneficial conjugated linoleic acids (CLA). Time course profiles of ( cis‐9, trans‐11)‐; ( cis‐10, trans‐12)‐; ( trans‐10, cis‐12)‐; ( cis,cis)‐ and ( trans, trans)‐octadecadienoic isomers (CLAs) as well as the other fatty acids traditionally encountered during the hydrogenation of vegetable oils are presented and discussed under selected process conditions. Preliminary results show that it is possible to tailor characteristics of the hydrogenation catalyst in such way to confer its bi‐functional activity: hydrogenation and conjugation isomerisation. © 2011 Canadian Society for Chemical Engineering 相似文献
10.
The geometrical and positional isomers of linoleic acid of a partially hydrogenated canola oil-based spread were isolated
and identified. Through partial hydrazine reduction and mass spectral studies, cis-9, trans-13 octadecadienoic acid was identified as the major isomer. Other quantitatively important isomers characterized were cis-9, trans-12; trans-9, cis-12 and cis-9, cis-15. These four were also the major isomers in margarine based on common vegetable oils. A number of minor isomers were detected
and some structures identified were trans-9, trans-12; trans-8, cis-12; trans-8, cis-13; cis-8, cis-13; trans-9, cis-15; trans-10, cis-15 and cis-9, cis-13. The proportions of the various isomers are given for some margarines in the Canadian retail market. The amounts of trans-9, trans-12 isomer in Canadian margarines were generally below 0.5% of the total fatty acids. 相似文献
11.
Conjugated linoleic acid (CLA) is commercially produced by alkali isomerization of linoleic acid (LNA). However, this method constitutes a relatively high content of undesirable CLA isomers. In present study, microwave-assisted and ultrasound-assisted alkali isomerization techniques were applied for production of CLA as an alternative to traditional alkali isomerization. This study was aimed to evaluate the isomerization degree of LNA, by using various process conditions such as microwave power, ultrasound amplitude, and their reaction times. The best conditions for LNA isomerization were a microwave power of 700 W and a reaction time of 6 h for microwave-assisted alkali isomerization and an ultrasound amplitude of 100% and a reaction time of 6 h for ultrasound-assisted alkali isomerization. Under determined conditions, microwave-assisted alkali isomerization (97.21%) resulted in a higher isomerization degree compared to ultrasound-assisted alkali isomerization (76.98%) while the content of undesirable CLA isomers in ultrasound-assisted alkali isomerization (0.62%) was lower than that of microwave-assisted alkali isomerization (1.87%). This study showed that application of the both techniques resulted in equal amounts of desirable CLA isomers. The content of desirable CLA isomers was 47.09% cis-9, trans-11 and 48.25% trans-10, cis-12 for microwave-assisted alkali isomerization and 36.34% cis-9, trans-11 and 40.02% trans-10, cis-12 for ultrasound-assisted alkali isomerization. 相似文献
12.
The kinetics of trans‐β‐carotene and trans‐lutein degradation were individually investigated in palm olein and Vegetaline®, at four temperatures ranging from 120 to 180 °C. HPLC‐DAD analysis was carried out to monitor trans and cis carotenoid variations over the heating time at each temperature. In both oils, initial trans‐β‐carotene and trans‐lutein degradation rates increased with temperature. Trans‐lutein was found to degrade at a slower rate than trans‐β‐carotene, suggesting a higher thermal resistance. The isomers identified were 13‐ cis‐ and 9‐ cis‐β‐carotene, and 13‐ cis‐, 9‐ cis‐, 13'‐ cis‐, and 9'‐ cis‐lutein. In spite of the higher number of lutein cis isomers, their total amount was lower than that of β‐carotene cis isomers. Trans and cis carotenoids were involved in degradation reactions at rates that increased with temperature. All degradation rates were generally found to be lower in Vegetaline® than in palm olein. These results were explained by the initial composition of the two oils and especially their peroxide and vitamin E contents. 相似文献
13.
A gas chromatographic method has been developed for quantitative determination of the cis and trans percentages in octadecenoate and octadecodienoate esters. To separate cis- and trans-monoene and diene isomers on a packed GC column, the fatty esters were stereospecifically epoxipized with peracetic acid.
A simple and quantitative epoxidation procedure allows the cis- and trans-epoxyoctadecanoates to be analyzed without prior isolation from the reaction mixture. No positional or geometric isomerization
of the double bond occurred during epoxidation. Synthetic mixtures containing cis- and trans-6,-9 and-12 octadecenoate isomers were completely separated into cis and trans fractions trans-15-Octadecenoate was the only isomer investigated that partially interfered in the analysis. Diene mixtures containing rans,trans-, cis,trans- and cis,-cis-9,12-octadecadienoates were also successfully analyzed by gas liquid chromatography (GLC) after epoxidation with peracetic
acid. Each diene isomer formed two pairs of diepoxy diastereomers, some of which could be separated. One cis,cis-diepoxyoctadecanoate diastereomer peak overlapped the cis,trans-diepoxyoctadecanoate peaks. The total cis,-cis-diepoxyoctadecanoate percentages were calculated by using the ratio of the two cis,cis-diepoxyoctadecanoate diastereomers. Other positional octadecadienoate isomers were also epoxidized and analyzed by GLC. The
large number of possible octadecadienoate isomers requires that some preeiminary fractionation be made before GC analysis
is practical for diene isomers.
Presented at the AOCS Meeting, Atlantic, City, October 1971
N. Market. Nutr. Res. Div., ARS, USDA. 相似文献
14.
Empirical hydrogenation models were generated from statistically designed laboratory experiments. These models, consisting
of a set of polynomial equations, relate the operating variables of soybean oil hydrogenation to properties of the reaction
and of the fat produced. These properties include reaction rate, trans-isomer content and melting point. Operating variables included in the models were temperature, hydrogen pressure, catalyst
concentration, agitation rate and iodine value.
The effects of catalyst concentration and agitation rate were found to be significant in determining trans-isomer content, which in turn influences the melting characteristics of the hydrogenated oil. Pressures above 30 psig were
found to have little effect on trans-isomer content, although pressure was very important in determining reaction rate. Reaction temperature was observed as the
most important factor in determining the trans-isomer content for a given iodine value. Generally, 50 to 60% trans isomer content is predicted by the model for the iodine value range and operating conditions used in this study. Thus, these
predictive models can assist in scaling up hydrogenation processes and in determining the optimum operating parameters for
running commercial hydrogenation.
Presented at the AOCS Meeting, Chicago, May 1983. 相似文献
15.
The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence
of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolated trans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation
products. The hydrogenation by trans-1,2-cyclohexanediol catalyzed by RuH 2(PPh 3) 4 also showed rather high selectivity to cis-monoenes. In the reaction catalyzed by RuH 2(PPh 3) 4, also showed rather high selectivity to cis-monoenes. In the reaction catalyzed by RuH 2(PPh 3) 4, the presence of these hydroxy compounds increased the isomerization of methyl elaidate to cis-monoenes. 相似文献
16.
A new supported bimetallic catalyst, rhenium-tin, is able to reduce oleic acid to 9-octadecen-1-ol ( cis and trans isomers) with appreciable yield under mild hydrogenation conditions. This paper reports investigations on the effects of
catalyst preparation methods, types of support, catalyst raw materials, mole ratio of the metals, activation and reaction
conditions on the activity and selectivity of the catalyst. Catalyst derived from the combination of ammonium perrhenate and
stannic chloride on alumina gave the best performance, and the presence of tin in the catalyst is essential for the preservation
of the olefinic bond of the oleic acid during hydrogenation. 相似文献
17.
Selective hydrogenation of citral to unsaturated alcohol [geraniol ( trans) + nerol ( cis)] was carried out in supercritical carbon dioxide (scCO 2) using an MCM‐41 supported plantinum catalyst (∼1 wt% Pt). A remarkable rate of isomerization of the unsaturated alcohol [nerol ( cis) to geraniol ( trans)] during the hydrogenation of citral was achieved simply by tuning the density of CO 2. Optimum reaction conditions were developed to obtain only geraniol ( trans) with a selectivity of 98.8% and citral conversion of 99.8%. A significant change in the cis: trans ratio of the product (1:82.3) from the substrate (1:1.3) was observed depending on the various reaction parameters like carbon dioxide and hydrogen pressure, reactant concentration, reaction time and, particularly, the total selectivity for unsaturated alcohol [geraniol ( trans) +nerol ( cis)]. It has been observed that the presence of hydrogen is necessary for isomerization. Our results were explained in terms of a density‐dependent, two‐step model. The kinetic behaviour shows that the rate of isomerization was higher in scCO 2 compared to other organic solvents and the pure form of geraniol ( trans) was obtained exclusively. A probable reaction pathway was proposed in order to explain the isomerization during hydrogenation of citral in scCO 2 medium. 相似文献
18.
CLA is a generic term describing different isomers of linoleic acid with two conjugated double bonds. Various metabolic effects
have been demonstrated following administration of CLA, including a change in body composition in animals. However, the effects
of pure CLA isomers are not fully understood. In addition, conjugated octadecatrienoic acids such as calendic acid have not
been extensively investigated. In this study, male and female ICR mice were fed pure CLA isomers ( cis9, trans11 or trans10, cis12) or calendic acid ( trans8, trans10, cis12) as their ethyl esters for 6 wk. Body protein content was significantly increased after feeding CLA isomers, either as
pure isomers or as a mixture. Calendic acid significantly decreased body fat content in males. CLA (pure isomers or a mixture)
significantly decreased body fat in both males and females, with the trans10, cis12 isomer being the most effective. The effect of the cis9, trans11 isomer was more pronounced in females than in males. It was concluded that the trans10, cis12 CLA isomer was mainly responsible for the decrease in fat content in mice, without a significant modification of feed efficiency,
and that it was more effective than calendic acid. 相似文献
19.
The abilities of lipases produced by the fungus Geotrichum candidum to selectively fractionate mixtures of conjugated linoleic acid (CLA) isomers during esterification of mixed CLA free fatty
acids and during hydrolysis of mixed CLA methyl esters were examined. The enzymes were highly selective for cis-9, trans-11–18∶2. A commercial CLA methyl ester preparation, containing at least 12 species representing four positional CLA isomers,
was incubated in aqueous solution with either a commercial G. candidum lipase preparation (Amano GC-4) or lipase produced from a cloned high-selectivity G. candidum lipase B gene. In both instances selective hydrolysis of the cis-9, trans-11–18∶2 methyl ester occurred, with negligible hydrolysis of other CLA isomers. The content of cis-9, trans-11–18∶2 in the resulting free fatty acid fraction was between 94 (lipase B reaction) and 77% (GC-4 reaction). The commercial
CLA mixture contained only trace amounts of trans-9, cis-11–18∶2, and there was no evidence that this isomer was hydrolyzed by the enzyme. Analogous results were obtained with these
enzymes in the esterification in organic solvent of a commercial preparation of CLA free fatty acids containing at least 12
CLA isomers. In this case, G. candidum lipase B generated a methyl ester fraction that contained >98% cis-9, trans-11–18∶2. Geotrichum candidum lipases B and GC-4 also demonstrated high selectivity in the esterification of CLA with ethanol, generating ethyl ester fractions
containing 96 and 80%, respectively, of the cis-9, trans-11 isomer. In a second set of experiments, CLA synthesized from pure linoleic acid, composed essentially of two isomers,
cis-9, trans-11 and trans-10, cis-12, was utilized. This was subjected to esterification with octanol in an aqueous reaction system using Amano GC-4 lipase
as catalyst. The resulting ester fraction contained up to 97% of the cis-9, trans-11 isomer. After adjustment of the reaction conditions, a concentration of 85% trans-10, cis-12–18∶2 could be obtained in the unreacted free fatty acid fraction. These lipase-catalyzed reactions provide a means for
the preparative-scale production of high-purity cis-9, trans-11–18∶2, and a corresponding CLA fraction depleted of this isomer. 相似文献
20.
Concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were heated at 140–240 °C for 2–8 h under nitrogen. The trans isomers were analysed by gas chromatography‐mass spectrometry on a BPX‐70 cyanopropyl column. All geometrical isomers of EPA and DHA with one trans double bond were observed. The rate constants ( k) for the isomerisation of the all‐ cis isomers were calculated and found to be higher than previously reported for linoleic acid and α‐linolenic acid. Arrhenius plots showed a linear relationship between ln k and the reciprocal absolute temperature above 180 °C. The distribution patterns of isomers with one trans double bond are approximately constant up to a degree of isomerisation of 25%. The degree of isomerisation can therefore be estimated from selected trans peaks. 相似文献
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