Catalytic hydrogenation of linoleic acid on nickel,copper, and palladium

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 orcis-9,trans-13; cis-9,trans-12; trans-9,cis-12 andcis-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 ofcis-12 andtrans-12 monoenoic acids was larger than that ofcis-9 andtrans-9 monoenoic acids. On the contrary, the yield ofcis-9 andtrans-9 monoenoic acids was larger than that ofcis-12 andtrans-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.     

Gas-liquid chromatographic analysis of geometrical and positional octadecenoic and octadecadienoic acid isomers produced by catalytic hydrogenation of linoleic acid on Ir/Al2O3

Catalytic hydrogenation of linoleic acid was studied on Ir/Al₂O₃. 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.     

Positional and geometrical isomers of linoleic acid in partially hydrogenated oils

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 werecis-9,trans-12;trans-9,cis-12 andcis-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 weretrans-9,trans-12;trans-8,cis-12;trans-8,cis-13;cis-8,cis-13;trans-9,cis-15;trans-10,cis-15 andcis-9,cis-13. The proportions of the various isomers are given for some margarines in the Canadian retail market. The amounts oftrans-9,trans-12 isomer in Canadian margarines were generally below 0.5% of the total fatty acids.     

Polymer-supported catalysts—selective hydrogenation of acid chlorides over palladium/polyamide

The catalytic behaviour of palladium supported on aromatic polyamides was studied in the liquid phase hydrogenation of benzoyl chloride at 1 atm total pressure and between 348 and 408 K. The specific activity of the catalysts as a function of palladium concentration was found to increase with metal loading. It is suggested that palladium in a metallic state is the active site for the acid chloride hydrogenation. A decrease in the reaction rate has been observed at the highest temperatures indicating that under these conditions the availability of hydrogen becomes the rate determining step. Results on the liquid phase hydrogenation of acyl- and aroyl-chlorides are reported. No strong influence of the nature of the substituents was observed on reaction parameters.     

Comparison of two palladium catalysts on different supports during hydrogenation

Soybean oil was hydrogenated using two different palladium-based catalysts, 5% palladium on carbon (Pd/C) and 10% palladium on alumina (Pd/A), at various ratios in a 4-L reactor under constant conditions (165°C, 2 bar H₂, and 500 rpm stirring rate). Reaction rate, trans isomer formation, selectivity ratios, and melting behaviors of the samples were monitored. Activity of Pd/C was about 10 times higher than that of Pd/A, and the reaction rate showed a strong dependency on the support material. Increases in the concentrations of both Pd catalysts did not have considerable effect on trans formation, which is slightly dependent on support material. Oleate selectivity (S ₂₁) for all runs varied between 2.48 and 30.34, and type of support material did not have an effect on selectivity. Melting behaviors of the samples were mainly dependent on reaction rates.     

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. II. Hydrogenation selectivity studies

Soybean oil has been hydrogenated electrochemically in a solid polymer electrolyte (SPE) reactor at 60°C and 1 atm pressure. These experiments focused on identifying cathode designs and reactor operation conditions that improved fatty acid hydrogenation selectivities. Increasing oil mass transfer into and out of the Pd-black cathode catalyst layer (by increasing the porosity of the cathode carbon paper/cloth backing material, increasing the oil feed flow rate, and inserting a turbulence promoter into the oil feed flow channel) decreased the concentrations of stearic acid and linolenic acid in oil products [for example, an iodine value (IV) 98 oil contained 12.2% C_18:0 and 2.3% C_18:3]. When a second metal (Ni, Cd, Zn, Pb, Cr, Fe, Ag, Cu, or Co) was electrodeposited on a Pd-black powder cathode, substantial increases in the linolenate, linoleate, and oleate selectivities were observed. For example, a Pd/Co cathode was used to synthesize an IV 113 soybean oil with 5.3% stearic acid and 2.3% linolenic acid. The trans isomer content of soybean oil products was in the range of 6–9.5% (corresponding to specific isomerization indices of 0.15–0.40, depending on the product IV) and did not increase significantly for high fatty acid hydrogenation selectivity conditions.     

Further studies on artificial geometrical isomers of α-linolenic acid in edible linolenic acid-containing oils

Fifteen samples of commercial edible soybean and rapeseed oils (and mixtures of these) from Belgium, Great Britain and Germany have been analyzed for theirtrans-polyunsaturated fatty acid content. Only one sample out of the 13 refined samples, and the two cold-pressed samples, contained trace amounts oftrans isomers. Others contained between 1 and 3.3% of their total fatty acids as geometrical isomers of linoleic and linolenic acids. The degree of isomerization (DI) of linolenic acid varied between 10.5 and 26.9%. Combining results obtained in this study together with corresponding data for French oils (totalling 21 samples) indicates that the relative percentages of individual linolenic acid geometrical isomers depend on linolenic acid DI. Relationships linking these parameters could be approximated by straight lines, at least for DIs lying between 9 and 30%. Extrapolation to DI=0 suggests that the relative probabilities of isomerization of double bonds in positions 9, 12, and 15 are 41.7, 6.1 and 52.1%, respectively, at the very beginning of the isomerization reaction. At that time, the probability of a simultaneous isomerization of double bonds in positions 9 and 15 is close to zero. Thet,c,t isomer is apparently formedvia thec,c,t and thet,c,c isomers, the former being somewhat more prone to a second geometrical isomerization than the latter. The relative proportion of thec,t,c isomer is practically independent from the DI, at least between 9 and 30%, which would suggest that this isomer is an “end-product” of thecis-trans isomerization reaction.     

Catalytic hydrogenation of carbon monoxide over silica-supported Ir-Mo-Rh catalyst

We present here some results on Ir-Mo-Rh metallic catalysts for the synthesis of C₂-C₄ alcohols from syngas. It was found that Ir-Mo-Rh supported on silica containing small amounts of Rh exhibited much higher activity for CO hydrogenation than Ir-Mo bimetallic catalyst. The selectivity to various alcohols did not change very much upon the addition of Rh. The activity was greatly affected by the impregnation procedure of the metals in the catalyst preparation.     

The composition of hydrogenated fats by high-resolution13C nuclear magnetic resonance spectroscopy

The high-resolution¹³C nuclear magnetic resonance spectra of twelve hydrogenated fats have been examined. Each spectrum contains 50–100 signals and reveals much about the nature of the acyl chains of both double-bond position and configuration. The signals for the ω1, ω2 and ω3 carbon atoms give information on thecis andtrans isomers of the Δ15, Δ14, Δ13 and Δ12 18:1 esters, respectively. Allylic signals distinguish betweencis andtrans esters, and the proportion of totalcis to totaltrans isomers can be obtained from these. Olefinic signals are the most informative, and most of these have been assigned. This leads to a semi-quantitative estimate of the various 18:1 isomers present. Assignments are based mainly on information already in the literature, but some were confirmed after urea fractionation of the acids from a hydrogenated oil in whichcis andtrans monoene acids were separately concentrated.     

Analysis of the monoenoic fatty acid distribution in hydrogenated vegetable oils by silver-ion high-performance liquid chromatography

A silver-ion high-performance liquid chromatography column (hexane/acetonitrile as solvent, ultraviolet detection) was used to analyze the fatty acid distribution (as fatty acid methyl esters) of a representative sample of hydrogenated oil. Fractions containingcis- andtrans-18:1 isomers were readily separated. The positional fatty acid isomers were separated by rechromatographing these fractions. The elution order and percent compositions were compared with results obtained by gas chromatography. Of the Δ8 to Δ14trans-18:1 isomers, only the Δ8 and Δ9 pair could not be separated. The Δ8 and Δ9cis-18:1 pair also could not be separated, and the Δ10 isomer was poorly separated from this pair. Area percents were comparable to results obtained by gas chromatography.     

Deodorization of vegetable oils. Part I: Modelling the geometrical isomerization of polyunsaturated fatty acids

Laboratory-scale treatments of canola oils similar to deodorization were carried out by applying the following conditions: reduced pressure with nitrogen or steam stripping at different temperatures ranging from 210 to 270°C for 2–65 h. The formation of the group of trans linolenic acid isomers follows a first-order reaction and the kinetic constant varies according to the Arrhenius’ law. Similar results were observed for the trans isomerization of linoleic acid. Based on these experiments, a mathematical model was developed to describe the isomerization reaction steps occurring in linoleic and linolenic acids during deodorization. The calculated degrees of isomerization are independent of the composition of the oil but related to both time and temperature of deodorization. The degree of isomerization of linolenic acid is unaffected by the decrease of this acid content observed during the deodorization. Deodorization at about 220–230°C appears to be a critical limit beyond which the linolenic isomerization increases very strongly. The newly established model can be a tool for manufacturers to reduce the total trans isomer content of refined oils, and was applied to produce a special selectively isomerized oil for a European Nutritional Project.     

Deodorization of vegetable oils: Prediction of trans polyunsaturated fatty acid content

Kinetics of the formation of trans linoleic acid and trans linolenic acid were compared. Pilot plant-scale tests on canola oils were carried out to validate the laboratory-scale kinetic model of geometrical isomerization of polyunsaturated fatty acids described in our earlier publication. The reliability of the model was confirmed by statistical calculations. Formation of the individual trans linoleic and linolenic acids was studied, as well as the effect of the degree of isomerization on the distribution of the trans fatty acid isomers. Oil samples were deodorized at temperatures from 204 to 230°C from 2 to 86 h. Results showed an increase in the relative percentage of isomerized linolenic and linoleic acid with an increase in either the deodorization time or the temperature. The percentage of trans linoleic acid (compared to the total) after deodorization ranged from <1 to nearly 6%, whereas the percentage of trans linolenic acid ranged from <1 to >65%. Applying this model, the researchers determined the conditions required to produce a specially isomerized oil for a nutritional study. The practical applications of these trials are as follows: (i) the trans fatty acid level of refined oils can be predicted for given deodorization conditions, (ii) the conditions to meet increasingly strict consumer demands concerning the trans isomer content can be calculated, and (iii) the deodorizer design can be characterized by the deviation from the theoretical trans fatty acid content of the deodorized oil.     

Characterization of monomers produced from thermal high-pressure conversion of meadowfoam and oleic acids into estolides

The monomers produced from thermal high-pressure conversion of meadowfoam or oleic acids into estolides were characterized as a complex mixture of fatty acids. Mild reaction conditions produced little change in the starting acids. However, vigorous reaction conditions,e.g. ≥3 h at 250°C with stirring, significantly altered the starting fatty acids.Cis/trans isomerization occurred readily, with the proportion oftrans isomers reaching 57%. In addition, the double bonds migrated throughout all positions of the hydrocarbon chain with concentrations diminishing outward from the starting double bond position. Branching was also observed to a small extent under these conditions and was even more pronounced in the absence of water. Lactones were also identified in the reaction mixture, with contents near 16% in the meadowfoam series. All products can be explainedvia carbocation rearrangement mechanisms that result from protonation of the starting olefins.     

The Diversity of Health Effects of Individual <Emphasis Type="Italic">trans</Emphasis> Fatty Acid Isomers

There are multiple adverse effects of trans fatty acids (TFA) that are produced by partial hydrogenation (i.e., manufactured TFA), on CVD, blood lipids, inflammation, oxidative stress, endothelial health, body weight, insulin sensitivity, and cancer. It is not yet clear how specific TFA isomers vary in their biological activity and mechanisms of action. There is evidence of health benefits on some of the endpoints that have been studied for some animal TFA isomers, such as conjugated linoleic acid; however, these are not a major TFA source in the diet. Future research will bring clarity to our understanding of the biological effects of the individual TFA isomers. At this point, it is not possible to plan diets that emphasize individual TFA from animal sources at levels that would be expected to have significant health effects. Due to the multiple adverse effects of manufactured TFA, numerous agencies and governing bodies recommend limiting TFA in the diet and reducing TFA in the food supply. These initiatives and regulations, along with potential TFA alternatives, are presented herein.     

Conversion of linoleic acid to 10-hydroxy-12(Z)-octadecenoic acid byFlavobacterium sp. (NRRL B-14859)

A new microbial isolate,Flavobacterium sp. strain DS5, converts linoleic acid into 10-hydroxy-12(Z)-octadecenoic acid (10-HOA) with 55% yield. The product was characterized by gas chromatography (GC), GC/mass spectrometry, nuclear magnetic resonance and Fourier transform infrared spectroscopy. The specific optical rotation of 10-HOA is [α] _D ²⁴ =−5.58 (methanol). The optimum time, pH and temperature for the production of 10-HOA were 36h, 7.5 and 20–35°C, respectively. The enzyme(s) that converts linoleic acid to 10-HOA is soluble and located intracellulary in strain DS5. Two minor products, 10-methoxy-12-octade-cenoic acid and 10-keto-12-octadecenoic acid, were also identified. 10-HOA was further metabolized by strain DS5. Among the unsaturated fatty acids studied, the order of reactivity for the DS5 enzyme(s) is oleic>palmitoleic> linoleic>linolenic>γ-linolenic>myristoleic acid.     

Heat-induced geometrical isomerization of α-linolenic acid: Effect of temperature and heating time on the appearance of individual isomers

The formation of linolenic acid geometrical isomers (LAGIs) was studied in linseed oil that was heated under vacuum in sealed ampoules at different temperatures (190–260°C) for several durations (2–16 h). A temperature of about 190°C seems to be necessary to induce the formation of LAGIs. At higher temperatures, disappearance of linolenic acid follows a first-order kinetic. The formation of LAGIs increases with both heating time and temperature, degrees of isomerization of linolenic acid higher than 50–60% could easily be obtained by simply heating the oil under vacuum. Side reactions remain at a low level. The mean probabilities of isomerization of individual ethylenic bonds are similar to those determined in linolenic acid-containing oils marketed in European countries, 41.9, 4.7 and 53.3% for double bonds in positions 9, 12 and 15, respectively. The di-trans t,c,t (trans,cis,trans) isomer is formedvia the mono-trans c,c,t andt,c,c isomers by a two-step reaction. The proportions of thec,c,t andt,c,c isomers (relative to total LAGIs) decrease linearly with the heating time. The proportion of thec,t,c isomer is only slightly affected by this parameter; however, it increases with temperature. The proportion of thet,c,t isomer increases linearly with heating time at each tested temperature, at the expense of thec,c,t andt,c,c isomers. However, there is no simple relationship linking the disappearance of each of the mono-trans isomers and the formation of the di-trans isomer.     

Monooxygenase system of Bacillus megaterium ALA2: Studies on linoleic acid epoxidation products

Bacillus megaterium ALA2 produces many oxygenated FA from linoleic acid: 12,13-dihydroxy-9(Z)-octadecenoic acid; 12,13,17-trihydroxy-9(Z)-octadecenoic acid; 12,13,16-trihydroxy-9(Z)-octadecenoic acid; 12-hydroxy-13,16-epoxy-9 (Z)-octadecenoic acid; and 12,17;13,17-diepoxy-16-hydroxy-9 (Z)-octadecenoic acid. Recently, we studied the monooxygenase system of B. megaterium ALA2 by comparing its palmitic acid oxidation products with those of the well-studied catalytically self-sufficient P450 monooxygenase of B. megaterium ATCC 14581 (NRRL B-3712) and of B. subtilis strain 168 (NRRI B-4219). We found that their oxidation products are identical, indicating that their monooxygenase systems (hydroxylation) are similar. Now, we report that strain ALA2 epoxidizes linoleic acid to 12,13-epoxy-9(Z)-octadecenoic acid and 9,10-epoxy-12 (Z)-octadecenoic acid, the initial products in the linoleic acid oxidation. The epoxidation enzyme did not oxidize specific double bond of the linoleic acid. The epoxidation activity of strain ALA2 was compared with the above-mentioned two Bacillus strains. These two Bacillus strain also produced 12,13-expoxy-9 (Z)-octadecenoic acid and 9,10-epoxy-12(Z)-octadecenoic acid, indicating that their epoxidation enzyme systems might be similar. The ratios of epoxy FA production by these three strains (A1 A2, NRRI B-3712, and NRRI B-4219) were, respectively, 5.56∶0.66∶0.18 for 12,13-epoxy-9(Z)-octadecenoic acid and 2.43∶0.41∶0.57 for 9,10-epoxy-12(Z)-octadecenoic acid per 50 mL medium per 48 h.     

Participation of thecis-12 ethylenic bond tocis-trans isomerization of thecis-9 andcis-15 ethylenic bonds in heated α-linolenic acid

To understand thecis-trans isomerization reaction of ethylenic bonds in heated octadecatrienoic acids (occurring during industrial deodorization of oils), we have prepared a mixture ofcis-9,cis-12,cis-15, andcis-9,cis-15 18:2 acids by partial hydrazine reduction ofcis-9,cis-12,cis-15 18:3 acid present in linseed oil. This mixture (as fatty acid methyl esters) was heated under vacuum at 270°C for 2.25 h. The two methylene-interrupted acids isomerize at a similar rate under such conditions, but the nonmethylene-interruptedcis-9,cis-15 18:2 acid remains unchanged. This means that the mechanism of isomerization does not involve a direct interaction between the two external ethylenic bonds as previously hypothesized. The centralcis-12 ethylenic bond is apparently necessary for the isomerization of the two externalcis-9 andcis-15 ethylenic bonds. However, this bond is itself rather protected against isomerization in the originalcis-9,cis-12,cis-15 18:3 acid which is mainly isomerized totrans-9,cis-12,trans-15,cis-9,cis-12,trans-15, andtrans-9,cis-12,cis-15 18:3 acids. Thecis-9,trans-12,cis-15 18:3 isomer is less than 10% of totaltrans isomers of α-linolenic acid. As a general rule, only one of the two double bonds in a methylene-interrupted diethylenic system can undergocis-trans isomerization when submitted to heat treatment, at least for temperatures equal to or less than 270°C.     

Analysis of C18:1 cis and trans fatty acid isomers by the combination of gas-liquid chromatography of 4,4-dimethyloxazoline derivatives and methyl esters

Trans fatty acids in foods are usually analyzed by gas-liquid chromatography (GLC) of fatty acid methyl esters (FAME). However, this method may produce erroneously low values because of insufficient separation between cis and trans isomers. Separation can be optimized by preceding silver-ion thin-layer chromatography (Ag-TLC), but this is laborious. We have developed an efficient method for the separation of 18-carbon trans fatty acid isomers by combining GLC of FAME with GLC of fatty acid 4,4-dimethyloxazoline (DMOX) derivatives. We validated this method against conventional GLC of FAME, with and without preceding Ag-TLC. Fatty acid isomers were identified by comparison with standards, based on retention times and mass spectrometry. Analysis of DMOX derivatives allowed the 13t, 14t, and 15t isomers to be separated from the cis isomers. The combination of the GLC analyses of FAME and DMOX derivatives gave results comparable with those obtained by GLC of FAME after preceding Ag-TLC, while saving about 100 h of manpower per 25 samples. It allowed the identification and quantitation of 11 trans and 8 cis isomers and resulted in 25% higher values for total C_18:1 trans, compared with the analysis of FAME alone. The combination of DMOX and FAME analyses, as applied to the analysis of 14 foods that contained ruminant fat and partially hydrogenated vegetable and fish oils, indicated that the most common isomers were 11t in ruminant fats, 9t in partially hydrogenated fish fats, and either 9t or 10t in partially hydrogenated vegetable fats. The combination of GLC analyses of FAME and DMOX derivatives of fatty acids improves the quantitation of 18-carbon fatty acid isomers and may replace the laborious and time-consuming Ag-TLC.