Isomerization during hydrogenation of soap. I. Potassium oleate

Potassium oleate in slightly alkaline solution was hydrogenated for up to 7 hr with Rufert nickel catalyst at 150C and 20 kg/sq cm pressure. With 1% catalyst, the iodine value dropped by 12 units in the first hour, and only slightly thereafter. With 2% catalyst there was a drop of 24 units in iodine value in the first hour, a steady state for the next 3 hr, and a second sharp drop of 30 units prior to the seventh hour. Samples of fat hydrogenated over 1% catalyst for 3 hr and 7 hr respectively were analyzed by gas-liquid chromatography, thecis andtrans monoenes were separated by argentation thin-layer chromatography, and the positional isomers in each were determined by oxidation of the total fraction to dicarboxylic acids, which were then estimated by GLC. Apart from double-bond saturation during the first 3 hr of hydrogenation, extensive double-bond migration yielded 23.5% oftrans 8- to 13-monoene, accompanied by small amounts only of positionalcis monoenes other than the starting material. After 7 hr of hydrogenation, extensivecis tocis isomerization occurs, accompanied by lesscis totrans shift; thecis:trans ratio for each monoene consequently tended toward 1:1. The results are explained on the sorption mechanism of hydrogenation and suggest that soap hydrogenation, involving catalyst poisoning, may represent a magnified version of normal fat hydrogenation.     

Industrial hydrogenation of cottonseed oil: A compositional study

Intermediate samples during a typical plant hydrogenation of cottonseed oil for vanaspati (shortening) manufacture have been examined for their fatty acid composition by gas-liquid chromatography andtrans isomers content by infrared spectrophotometry. In the initial stages, hydrogenation of linoleate proceeds almost exclusively in preference to that of oleate. During this period,trans isomers are also formed at a rapid rate. It has been proposed that this high selectivity and hightrans isomer formation are linked to the formation of conjugated diene from linoleate as a first step in the hydrogenation. It has been found that a linear relationship exists between the linoleate content and thetrans isomers content or the^k10.38 μ values of the glycerides. The practical utility of this plot is that it can be employed as a guide to arrest the process at any desired linoleate level.     

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.     

Empirical modeling of soybean oil hydrogenation

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 determiningtrans-isomer content, which in turn influences the melting characteristics of the hydrogenated oil. Pressures above 30 psig were found to have little effect ontrans-isomer content, although pressure was very important in determining reaction rate. Reaction temperature was observed as the most important factor in determining thetrans-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.     

Selectivity and isomerization during partial hydrogenation of cottonseed oil and methyl oleate: Effect of operating variables

Results are now available for hydrogenation of cottonseed oil and methyl oleate in which sufficient agitation was provided to eliminate mass transfer resistances from the catalyst surface. The ratio of thetrans-to-cis isomers of oleic acid groups approaches 2.0 even at high pressures and high degrees of agitation. The rates of hydrogenation for bothcis andtrans isomers and for positional isomers are all essentially identical. A reaction scheme has been devised that is consistent with extensive experimental data, and the method of evaluating the relative reaction rate constants for each step is outlined. Using these rates constants, selectivity can be quantitatively evaluated.     

Electrochemical hydrogenation of canola oil using a hydrogen transfer agent

A novel low-temperature process for the electrochemical hydrogenation of canola oil is described. An emulsion of oil and water containing formic acid and a nickel hydrogenation catalyst, placed in the cathode compartment of an electrolysis cell and subjected to an electrical current, underwent hydrogenation at temperatures as low as 45°C. At these low temperatures of hydrogenation, the trans FA content of the hydrogenated canola oil was very low as compared with that of the edible oils hydrogenated by commercial processes using high temperature and high partial pressure of hydrogen gas. Because of its adverse health effects, a high trans FA content in edbile oils is viewed as undesirable. In addition to the commercially available nickel supported on silica, amorphous nickelphosphorus alloys supported on a variety of substrates were also used. Amorphous alloys are generally very corrosion resistant because of the absence of grain boundaries. A mechanism for hydrogenation using the hydrogen transfer agent of formic acid and its continuous regeneration at the cathode was evoked to explain the experimental data.     

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.     

Effects ofbis homoallylic and homoallylic hydroxyl substitution on the olefinic13C resonance shifts in fatty acid methyl esters

Substitution of a hydroxyl group at thebis homoallylic position (OH group located three carbons away from the olefinic carbon) in C₁₈ unsaturated fatty acid esters (FAE) induces a 0.73±0.05 ppm upfield and a 0.73±0.06 ppm downfield shift on the δ and ε olefinic¹³C resonances relative to the unsubstituted FAE, respectively. If the hydroxyl group is located on the carboxyl side of the double bond of thebis homoallylic hydroxy fatty acid esters (BHAHFA), the olefinic resonances are uniformly shifted apart by [|1.46+|Δδdb_u‖] where Δδdb_u represents the absolute value of the double bond resonance separation in the unsubstituted FAE and 1.46 ppm is the sum of the absolute values of the δ and ε shift parameters. With hydroxyl substitution on the terminal methyl side of the double bond, the olefinic shift separation is equal to [|1.46−|Δδdb_u‖]. In homoallylic (OH group located two carbons away from the olefinic carbon) substituted FAE the γ and δ induced hydroxyl shifts for thecis double bond resonances are +3.08 and −4.63 ppm, respectively while thetrans double bond parameters are +4.06 and −4.18 ppm, respectively. The double bond resonance separation in homoallylic hydroxy fatty acid esters (HAHFA) can be calculated from the formula [|7.71−|Δδdb_u‖] forcis and [|8.24−|Δδdb_u‖] for thetrans case when the OH substitution is on the carboxyl side of the double bond. Conversely, when the OH resides on the terminal methyl side, the double bond shift separations forcis andtrans isomers are [|7.71+|Δδdb_u‖] and [|8.24+|Δδdb_u‖], respectively. The derived shift parameters can verify the positions of both the double bond and hydroxyl substitution from the olefinic resonance separation in long-chain fatty acid derivatives, obviating the need for destructive analytical methods. Reference to brand or firm name does not constitute endorsement by the United States Department of Agriculture over others of a similar nature not mentioned.     

Hydrogenation of oleic acid to 9-octadecen-1-ol with rhenium-tin catalyst

A new supported bimetallic catalyst, rhenium-tin, is able to reduce oleic acid to 9-octadecen-1-ol (cis andtrans 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.     

Methyl Oct-cis-2-enoate. its synthesis,GLC behaviour and infrared spectra

Methyl oct-cis-2-enoate was synthesized by selective hydrogenation of methyl oct-2-ynoate at atmospheric pressure with quinoline poisoned palladium as catalyst. The resulting product contained only 7% of thetrans form, as determined by GLC. The structure was confirmed by infrared spectra. Analysis of the infrared spectra is given. The cis andtrans forms of methyl oct-2-enoate were separable by GLC in polar or non-polar columns. GLC runs in polar and non-polar phases showed that the α position of the double bond of methyl oct-2-enoate so affects its properties, that practically no interaction was observed between the double bond and the polar phase. Consequently volatility was the main factor determining the retention times of cis andtrans methyl oct-2-enoate in the polar and non-polar phases studied.     

Production of Low-trans Fatty Acids Edible Oil by Electrochemical Hydrogenation in a Diaphragm Reactor Under Controlled Conditions

Electrochemical hydrogenation is a novel, alternative process for selective hydrogenation of vegetable oils, because of its high extent of hydrogenation and low trans-isomer formation. Electrochemical hydrogenation of soybean oil in a diaphragm reactor with a formate ion concentration of 0.4 mol/l at pH 5.0 under moderate temperature conditions using a current density of 10 mA/cm² was investigated to identify the critical conditions affecting the selective hydrogenation reaction and the resulting fatty acid profile. The optimum composition was an oil-to-formate solution ratio of 0.3 (w/w), 2?C3 g EDDAB in 100 g soybean oil, and 0.8% Pd?CC catalyst loading. The electrochemical hydrogenation reaction of soybean oil was described by first-order kinetics, and the kinetic rate constants and reaction selectivity were determined accordingly. Re-use of the Pd?CC catalyst up to five times was found to be acceptable. A comprehensive evaluation revealed that the most significant conditions affecting the extent of hydrogenation and the trans fatty acids content of final products were operating temperature, pH of the formate solution, and catalyst loading.     

Asarones fromAcorus calamus L. Oil

Asarones (2, 4, 5-trimethoxypropenylbenzenes) isolated from the essential oil ofAcorus calamus L. rhizomes, are potent growth inhibitors and antifeedants to the variegated cutworm,Peridroma saucia Hubner.cis-Asarone added to artificial diet significantly inhibited growth and feeding by first-, third-, and fourth-instar larvae, whereas thetrans isomer produced an antifeedant effect alone. Gross dietary utilization (efficiency of conversion of ingested food, ECI) was decreased when the diet was supplemented withcis-asarone or when this compound was topically applied to fourth-instar larvae. Inhibition of growth occurred even at a moderate topical dose (5 μg/larva) primarily as a result of decreased efficiency of conversion of digested food (ECD), even though the approximate digestibility (AD) of the food was unchanged. Oral or topical treatment withtrans-asarone also significantly inhibited larval growth, but in this case the effect can be strictly attributed to decreased consumption, as dietary utilization (ECI) was not affected. Both isomers displayed a direct antifeedant effect based on leaf disk choice tests. Thecis isomer was 7.0 and 5.5 times more potent thant thetrans isomer against fourth- and fifth-instar larvae, respectively. Our data suggest that the two asarone isomers have different modes of action.cis-Asarone is toxic in addition to having strong antifeedant activity, whereas thetrans isomer acts only as an antifeedant with no appreciable toxicity.     

Catalytic hydrogenation of linoleic acid over platinum-group metals supported on alumina

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 Al₂O₃. 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/Al₂O₃ 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/Al₂O₃, Ru/Al₂O₃, and Ir/Al₂O₃. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd.     

Photo-activated metal carbonyl complexes as stereoselective catalysts for the homogeneous hydrogenation of dienes

Significantly increased activity of Cr(CO)₆ was achieved for the stereoselective homogeneous hydrogenation of methyl sorbate andtrans,trans-conjugated fatty esters at ambient temperature and pressure by exposing the catalyst to UV irradiation (3500 Å) in a solvent mixture of cyclohexane-acetonitrile (20:1). In this solvent mixture, methyl sorbate was converted quantitatively at ambient conditions into methylcis-3-hexenoate, and methyltrans-9,trans-11-octadecadienoate into methylcis-10-octadecenoate (99.9%). These products are expected by 1,4-addition of hydrogen. Under these conditions no hydrogenation of methyl linoleate occurred. Under the same conditions, cycloheptatriene-Cr(CO)₃ showed lower activity than Cr(CO)₆, and Mo(CO)₆ and mesitylene-Mo(CO)₃ showed no significant activity toward conjugated substrates. When Cr(CO)₆ and Mo(CO)₆ were irradiated at 2537 Å they caused the geometric isomerization of methyl sorbate without hydrogenation, but had no effect on methyl linoleate. A hydrogenation mechanism is proposed for Cr(CO)₆ that involves CH₃CN- and H₂-Cr(CO)₃ complexes as intermediates for the stereoselective 1,4-addition of hydrogen totrans,trans-conjugated dienes.     

Bifunctional copper catalysts. Part II. Stereoselective synthesis of (-)-menthol starting from (+)-citronellal

The one-step transformation of (+)-citronellal into (-)-menthol has been realised with yield ∼90% and stereoselectivity up to 80% under mild conditions in the presence of Cu/SiO₂ by exploiting the presence of acidic and hydrogenation sites on the catalyst surface, the unusual reducibility of an olefinic bond under these conditions and the chemoselectivity of the process. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis and characterization of iron(II) and iron(III) complexes with a tridentate O,N,O′-ligand

The coordination chemistry of the ligand precursor 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol (1a) to iron(II) acetate was studied. In dependence of the added co-ligand different complex geometries were observed. In case of 4-dimethylaminopyridine (DMAP) as co-ligand an octahedral iron(II) complex was found with an O,N,O′-coordination of the tridentate ligand (1a-2H), in which the ligand is planar, the oxygen donors are trans to each other, and the nitrogen donor is in a cis position. The other coordination sites on the iron center are occupied by DMAP ligands. In contrast to that, with triphenylphosphane as the co-ligand an oxidation process took place, which revealed an octahedral iron(III) complex with a comparable geometry for the tridentate ligand (O,N,O′-coordination, 1a-2H) demonstrating the usefulness of 1a-2H to stabilize different oxidation states. The additional coordination sites are occupied by one triphenylphosphane oxide and ethoxide ligands. Interestingly, the ethoxide ligands act as bridging ligands to form a bimetallic complex.     

Highly selective partial hydrogenation of 1,3-butadiene on platinized-platinum electrode in ethylenediamine at open circuit

It was found that platinized-platinum ethylenediamine (EDA) is extremely selective (ca 93%) for the partial hydrogenation of 1,3-butadiene, given three isomeric butenes in a ratio of 1-butene: trans-2-butene: cis-2-butene = 13.2:2.5:1. Such a highly selective partial hydrogenation would be due to a specific adsorption of EDA on pt-Pt giving rise to the replacement of the adsorbed butenes which were formed from the partial hydrogenation of 1,3-butadiene.     

Isomerization during hydrogenation. IV. Methyl eleostearate

Summary The hydrogenation of methyl eleostearate with and without solvent has been studied. The data indicate the stepwise addition of two moles of hydrogen to the conjugated triene to produce equimolar amounts of 9-, 10-, 11-, 12-, and 13-octadecenoates. Additional evidence for thecis-9,trans-11,trans-13 structure of α-eleostearic acid was obtained. Presented at annual meeting, American Oil Chemists’ Society, Apr. 23–25, 1956, Houston, Tex.     

Hydrogenation of canola oil as affected by chlorophyll

Chlorophyll was added to refined and bleached canola oil before hydrogenation, and the effects on hydrogena-tion rate, fatty acid composition and the percentagetrans isomers were determined. The hydrogenation rate was greatly slowed down by chlorophyll under selective (200 C and 48 kPa) and nonselective conditions (165 C and 303 kPa). Higher levels of chlorophyll reduced the reaction rate more than the lower levels under both conditions. Dropping points were slightly higher for the nonselectively hydrogenated samples than for the selectively hydrogenated ones. Addition of 1 mg/kg or more chlorophyll decreased the solid fat content under nonselective conditions. Addition of chlorophyll reduced thetrans isomer content under nonselective conditions. Nonselective conditions also resulted in a greater decrease of 18:3 and faster production of 18:0 than selective conditions at all levels of chlorophyll addition.     

Infrared absorption of methylcis-9,trans-11-, andtrans-10,cis-12-octadecadienoates

The ratio of absorptivity at 10.2 µm and 10.6 µm differs between methylcis-9,trans-11-, andtrans-10,cis-12-octadecadienoates. For thecis-9,trans-11-ester, a_10.2 µm/a_10.6 µm is in the range of 1.1–1.2; for thetrans-10,cis-12-ester, it is 1.3–1.4. These differences in absorptivities are great enough to affect significantly compositions calculated from IR absorption.