Characterization of unsaturated fatty acids by gas-liquid chromatography

The equivalent chain length (ECL) has been determined on 79 methyl esters of unsaturated fatty acids and on 7 ethyl esters by gas chromatography. Ethylene glycol succinate (EGS), diethylene glycol succinate, β-cyclodextrin acetate and Apiezon L were chosen as the liquid phases to be used. For methyl esters of mono- and polyenoic acids, the differences between ECL on EGS and ECL on Apiezon L approximate 0.84 per double bond. For positional isomers, the ECL on both EGS and Apiezon L are usually greater for the isomer having the longer proximal end of the molecule (smallest ω value). In these terms a triple bond is approximately equal to three double bonds. Esters of nonconjugated dienoic and trienoic acids of the same chain length are not separable on Apiezon L if their proximal structures are the same. This also applies to tetraenoic and pentaenoic acids of the same chain length and the same proximal structure. Conjugation of double bonds, either with the ester carbonyl group or with themselves, yields ECL values on Apiezon L greater than the number of carbon atoms in the acid. Monounsaturated and nonconjugated polyunsaturated esters have ECL values on Apiezon L lower than the number of carbon atoms of the acid. The ECL values of ethyl esters of 18 and 20 carbon acids are greater than the corresponding methyl esters on Apiezon L. Presented at the Chicago meeting of the American Oil Chemists’ Society, Oct. 13, 1964.     

Hydrozirconation for unsaturated fatty acid derivatives

In the hydrozirconation reaction, developed by Schwartz and coworkers,bis(π-cyclopentadienyl) zirconium hydridochloride Cp₂-Zr(H)Cl, is added to the double bond of an olefin. The organozirconium intermediate can be functionalized by reaction with a variety of electrophiles such as oxygen, halogens, acetyl chloride and carbon monoxide. Furthermore, the double bond can be reformed by treatment with a hydride acceptor such as triphenylmethyl tetrafluoroborate. When a short-chain internal olefin is hydrozirconated, the initially formed alkylzirconium intermediate is rapidly isomerized to a compound in which the zirconium moiety is bound to the sterically least hindered position, which most often is the terminal position. The isomerization occurs rapidly at room temperature in contrast to the corresponding organoboron or aluminum compounds, which slowly positionally rearrange only at elevated temperatures. Because of the facile isomerization of internal alkylzirconium compounds to the terminal ones, we investigated application of the reaction to unsaturated fatty acids such as oleic and erucic acids. However, reactions on long-chain alkenes (such as oleic acid) are frequently much slower than those conducted on shorter-chain alkenes, and attention must be given to optimizing the reaction conditions if good yields are to be obtained. It would also be necessary to find an easily removable protecting group for the carboxylic function, as Cp₂Zr(H)Cl reduces carboxylic acids to alcohols. We found that the 4,4-dimethyl-2oxazoline function is a suitable protecting. group, and therefore synthesized the oxazolines from oleic acid and erucic acid. Hydrozirconation of the 4,4-dimethyl-2-oxazoline of oleic acid followed by oxidation witht-butyl hydroperoxide and conversion to methyl esters, gave methyl 3-hydroxy and methyl 18-hydroxy stearate in 13% and 17% yield, respectively. The relatively low yield is due to competing hydrogenation, the mechanism of which is discussed. Recent results indicate that the carboxyl group can be protected ast-butyl esters in the hydrozirconation and that oleyl alcohol derivatives can also be used. To understand the isomerization pattern in hydrozirconation, the reaction with α,β- and β,γ-unsaturated fatty acid oxazolines is discussed. Possibilities of making the hydrozirconation reaction catalytic by binding of the hydrozirconation reagent to a solid support as well as the synthetic potential in combining hydrozirconation with the olefin metathesis reaction are briefly reviewed.     

Displacement of the double bonds during hydrogenation of unsaturated fatty acid methyl esters

Summary The displacement of the double bond of several unsaturated fatty acid methyl esters during hydrogenation with a nickel-kieselguhr catalyst at 180°C. was investigated. The analysis of the dicarboxylic acids (obtained by oxidation of the reaction products with KMnO₄ in acetic acid solution) by means of partition chromatography enabled a reliable semiquantitative determination of the position isomers formed. During hydrogenation of methyl esters of oleic, elaidic, petroselinic, and linoleic acid formation of large amounts of position isomers was proved to occur. Migration of the double bonds in both directions took place but was in all cases strongly pronounced in a direction opposite the ester group. The place and configuration (cis or trans) of the double bonds in the starting material apparently were of little importance in this respect. It follows that hydrogenation of fatty acid esters leads to products which are far more complicated, as is generally known. This is especially of importance with respect to the application of hydrogenated fatty oils in the food industries.     

Hydrogenation of unsaturated fatty acids to unsaturated fatty alcohols: III. Comparison of different soap catalyst systems

Copper oleate and cadmium oleate catalysts have been replaced by other metal compounds. Silver was the only metal which could be substituted for copper in the ratio range studied. Using nickel oleate, the degree of saturation of the double bond decreased with increasing cadmium oleate concentration. No comparable substitute was found for Cd. The composition of the final components is influenced by the use of a paraffinic solvent, which also has an effect on the saturation of the double bond. An explanation is given for the behavior of the catalyst when the reaction is not selective and is carried out in a paraffinic solvent. The catalytic system Ag/Cd soaps was also studied kinetically and analytically. The results show that the mechanism of the reaction using silver soap is identical with the one using copper soap.     

Two-step homogeneous conjugation and hydrogenation of methyl esters of unsaturated fatty acids

A new approach to the selective hydrogenation of unsaturated fatty acids is suggested. It consists of a two step process. The first is a selective conjugation of the double bonds, while the second consists of the hydrogenation reaction using a catalyst which is specific to conjugated systems. Potassiumt-butoxide was used as a conjugation catalyst and its activity and selectivity were tested at various concentrations, different molar ratios of catalyst to oil, and in various solvents. Phenanthrene chromium tricarbonyl was used as the hydrogenation catalyst and its activity tested at various concentrations, temperatures and in various solvents. UN Expert, Physical Organic Chemist.     

A simple,rapid micromethod for the determination of the structure of unsaturated fatty acids via ozonolysis

A micromethod for the localization of double bonds in unsaturated fatty acids via ozonolysis employing pyrolytic cleavage of ozonides in the presence of a hydrogenation catalyst is described. Cleavage of the ozonides is carried out in a gasliquid chromatographie instrument in a small glass tube, containing the catalyst, inserted in the top of the column opposite the in input heaters at 225C. Ozonides of methyl esters of straight chain unsaturated fatty acids are cleaved through the action of the catalyst to aldehyde fragments which are swept simultaneously into the column for analysis. The double bond positions are deduced from the chain length of the fragments. The method is demonstrated on methyl oleate, linoleate, linolenate and arachidonate. Presented at the AOCS Meeting, Cincinnati, October, 1965.     

An analysis of separation factors applicable in the gas-liquid chromatography of unsaturated fatty acid methyl esters on a polyester substrate

The employment of gas-liquid chromatography (GLC) separation factors between methyl esters of unsaturated fatty acids is feasible as a means of tentative identification, either between acids of one chain length and differing numbers of double bonds, or between acids of one chain length and the same number of double bonds in differing positions, provided the acid structures are appropriately grouped by end carbon chain. The modification of separation factors by temperature, chain length, number of double bonds, or position of double bonds is apparent from examination of a larger number of examples than was hitherto available. Examples of the usefulness of separation factors in identifying unknowns or predicting retention times are given.     

Kinetics of the hydrogenation of fatty oils

Hydrogenation results for fatty oils were analyzed by using a nonlinear least squares method. The rate of the hydrogenation for diunsaturated fatty groups to monounsaturated groups and the rate of the geometrical isomerizations between monounsaturated groups were found to be half order with respect to hydrogen concentration, whereas the hydrogenation rate of monounsaturated groups was the first order. A detailed reaction mechanism is presented to explain the kinetic behavior.     

Double bond oxidation of unsaturated fatty acids

Different oxidizing agents for performing the cleavage oxidation of the double bond of the unsaturated fatty acids are presented, and their economic performance is analyzed. Ozone and sodium hypochlorite are the most commercially efficient oxidants. Laboratory work for the oxidation of oleic acid to azelaic and pelargonic acids using hypochlorite as oxidant is described. The advantages of working in an emulsion system and using RuCl₃ as a catalyst are discussed, and a possible mechanism of the reaction is presented. A flow sheet for an industrial process based on this concept is proposed. A simulation of a plant using this technology is made by a computerized model, and the economic parameters obtained permit us to conclude that the sodium hypochlorite can be an interesting reagent for industrial oxidations of double bonds in fatty acids.     

Homogeneously catalysed hydrogenation of unsaturated fatty acids to unsaturated fatty alcohols

The use of copper and cadmium oxides or soaps as catalysts for the hydrogenation of unsaturated fatty acids to unsaturated fatty alcohols has been investigated. It is shown that copper soaps homogeneously activate hydrogen. When copper and cadmium oxides are used as catalysts, they react with the acid under formation of a homogeneous soap solution. A continuous reaction system for the preparation of unsaturated fatty alcohols by hydrogenation under the influence of copper and cadmium soaps is described.     

Hydrogenation of unsaturated fatty esters with copper-chromite catalyst: Kinetics,mechanism and isomerization

Hydrogenation of linolenate with copper chromite produced a large amount of conjugated diene and minor amounts of nonconjugatable dienes. The double bonds in conjugated dienes and monoenes were scrambled all along the chain. This product distribution can be explained if it is assumed that conjugation of the double bonds is followed by hydrogenation. In competitive hydrogenation, fatty esters with conjugated double bonds were reduced preferentially over fatty esters with methylene-interrupted double bonds. Isomerization of conjugated double bonds (geometric and positional) occurred more rapidly than reduction. Reduction of conjugated double bonds in the presence of deuterium resulted in a majority of the products containing no deuterium. Most of the added deuterium was incorporated into the unreacted material. Mechanisms are proposed to account for the products formed during the hydrogenation of linolenate, linoleate and their isomers. One of 10 papers to be published from the Symposium “Hydrogenation,” presented at the AOCS Meeting, New Orleans, April 1970. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Reduction of unsaturated fatty acids and fatty alcohols with diimide from hydroxylamine-ethyl acetate

Hydroxylamine has been recently found to react with ethyl acetate to generate diimide in situ. This reaction was used to reduce 10-undecenoic, oleic, linoleic, stearolic, concentrates of ricinoleic, cyclopentene and cyclopropene fatty acids (FA), dehydrated castor oil FA, 10-undecen-1-ol, oleyl alcohol and castor fatty alcohols. Unsaturated FA and their corresponding alcohols reacted in a similar manner. Terminally unsaturated, cyclopropene and cyclopentene FA were more reactive than oleic acid, which, in turn, was more reactive than hydroxymonoenoic acids. Conjugated dienoic FA reduced faster than nonconjugated dienoic acids. Partial hydrogenation using this reagent is particularly advantageous in determining geometry and the position of double bonds in the polyunsaturated FA, as it can be carried out in the absence of oxygen or oxidizing agents unlike hydrazine reductions.     

Esterification kinetics of glycerol with fatty acids in the presence of sodium and potassium soaps

The kinetics of the direct esterification of glycerol with fatty acids in the presence of sodium and potassium soaps, synthesized in situ to obtain modified acylglycerol emulsifiers, were investigated. The effect of temperature, soap concentration and fatty acid hydrocarbon chain length on the concentration of monoacylglycerols in the reaction mixture was examined. The kinetic studies proved that esterification of glycerol with fatty acids by our method is a first order consecutive reaction with monoacylglycerol as stable intermediate product. The corresponding rate constants and activation energies were evaluated. With the known reaction rate constants, the maximum concentration of monoacylglycerol may be calculated. It was stated that the proposed method opens up possibilities for a specific adjustment of the acylglycerol composition and, thus, of the hydrophilic-lipophilic properties and the characteristics of the emulsifier.     

Factors governing the extent of overoxidation in permanganate oxidation of unsaturated fatty acids

The extent of overoxidation of half-esters of dicarboxylic acids is governed mainly by the nature and proportions of the oxidizing agent employed and not by reaction temperatures. In procedures which produce overoxidation, this occurs mainly at the time of the scission of the double bonds and no method is known to prevent it. The acetone permanganate procedure overoxidizes monocarboxylic acids (MCA), dicarboxylic acids (DCA) and half esters of DCA. The acetic acid-acetone permanganate procedure overoxidizes DCA but not MCA half-esters of DCA or azelaoglycerides. The DCA corresponding to the first double bond in unsaturated fatty acids (UFA) can be isolated quantitatively if the esters or triglycerides are oxidized by the latter procedure.     

Stereospecific hydration of unsaturated fatty acids by bacteria

Three new 10-hydroxy fatty acids, all optically active, have been prepared by the anaerobic microbiological hydration of acis-9 double bond. Substrates that formed these new hydroxy fatty acids are linoleic, linolenic, and ricinoleic acids. The hydroxyl group has the D configuration and the methyl esters are levorotatory. Infrared, mass spectral, specific rotation and ultraviolet data on these compounds were determined. There was no migration of the unreated double bonds at C₁₂ and C₁₅ in linoleic or linolenic acids. The presence of a double bond in the 10-hydroxy fatty acids significantly increased the optical rotation of the methyl esters. The hydratase enzyme showed unusual specificity among Δ⁹ unsaturated acids. While it hydrates methylene interrupted and hydroxy unsaturated acids, it failed to hydrate either 9-decenoic, 12,13-epoxy- or 12-keto-cis-9-octadecenoic acids or sterculic acid. Presented at the AOCS Meeting, San Francisco, April 1969. No. Marketing and Nutrition Res. Div., ARS, USDA.     

Isomeric monoethylenic fatty acids in herring oil

Monoethylenic fatty acids from herring oil were concentrated by chromatography by chromatography on silver nitratesilicic acid columns. Examination of consecutive fractions by open tubular gas chromatography confirmed the preferential elution of longer chain length esters and of esters within one chain length with the double bond closer to the terminal methyl group. Isomeric monoethylenic fatty acids with double bonds in the positions closer to the carboxyl group than the approximate midpoint of the even-numbered fatty acid chains could not be adequately separated by gas chromatography and were determined by ozonolysis. The isomers observed are consistent with primary formation from saturated acids through the action of an enzyme specifically removing hydrogen atoms in positions Δ⁹ and Δ¹⁰ relative to the carboxyl group. Chain extension of particular monoethylenic isomers by two carbon atoms in the C₂₀ and longer chain lengths is apparently influenced by the position of the double bond. This work was carried out in partial fulfillment of MSc requirements at Dalhousie University.     

Enzymatic epoxidation of soybean oil methyl esters in the presence of free fatty acids

Epoxides of soybean oil methyl esters (SMEs) are biodegradable, non‐toxic, and renewable epoxy plasticizers. The objective of the present work was to investigate the effects of free fatty acids on the enzymatic epoxidation of SMEs. The results showed that the epoxidation of SMEs depended on the type of the added free fatty acid. For saturated (≤C_18:0) and monounsaturated free fatty acids, the epoxy oxygen group content (EOC) of SMEs increased with increasing carbon chain length of free fatty acids; for branched‐chain unsaturated free fatty acids, the EOC of SMEs decreased in the presence of hydroxyl group (OH) and hydroperoxide (OOH) of free fatty acids; the EOC of SMEs decreased with increasing number of double bonds of free fatty acids. The maximum EOC and the initial epoxidization rate (V₀) linearly decreased with increasing peroxide value of SMEs. The highest EOC (6.87 ± 0.3%) of SMEs was obtained using behenic acid as reaction material, which was similar with that of stearic acid (EOC 6.75 ± 0.2%).     

Catalytic hydroformylation and hydrocarboxylation of unsaturated fatty compounds

The two catalyst systems rhodium-triphenylphosphine and palladium chloride-triphenylphosphine were investigated for the respective hydroformylation and hydrocarboxylation of oleic acid or ester to produce C-19 bifunctional compounds. Compared to conventional cobalt carbonyl for making formylstearate, rhodium-triphenylphosphine permits lower pressures (1000–2000 psi vs. 3000–4000 psi), higher conversions (95% vs. 80%), and no loss of functionality (vs. 15% hydrogenation with cobalt). Although palladium chloride-triphenylphosphine for hydrocarboxylation introduces the carboxyl function directly into the fatty acid chain, CO pressures of 3000–4000 psi and corrosion-resistant equipment are necessary. When applied to polyunsaturated fatty acids, both rhodium and palladium catalyst systems have the outstanding advantage of introducing functionality at each double bond position to produce polyformyl- and polycarboxystearates. Selected formyl derivatives were converted in excellent yield to acetals, to acids and their esters, to hydroxymethyl compounds and their esters, and also to aminomethyl compounds that could be condensed to polyamides. Several of the esters and acetals were effective primary plasticizers for poly(vinyl chloride) that had outstanding low volatility characteristics. Other applications for these new and highly versatile derivatives included rigid urethane foams, urethane-modified coatings, ester lubricants, and a shrink-resist treatment for wool.     

The effect of fatty acid composition on biodiesel oxidative stability

Concerning their environmental impact, native based fuels and lubricants show immense potential. In fact, these products are highly exposed to oxidative processes during storage or application [1, 2]. One way to raise oxidative stabilities is the addition of synthetic antioxidants. Another way may be the modification of the fatty acid composition, since polyunsaturated fatty acids show a much higher proneness to autoxidation. In order to decrease the content of polyunsaturated and to raise the content of saturated components, experiments for fractional distillation and crystallisation as well as for hydrogenation of fatty acid methyl esters have been carried out. In distillation experiments with separation columns the methyl esters performed good separation of the lower‐boiling esters with a chain‐length up to 16C‐atoms, from the C‐18 fraction, causing a degree of saturation up to 75 wt‐% in the distillate. In tests with fractional crystallisation, the rate of saturation could be raised up to 92.8 wt‐%. Using the process of catalytic hydrogenation, a rate of saturation up to 100 wt‐% could be achieved, depending on the duration of the hydrogenation process. By partial hydrogenation of the polyunsaturated components, products with high oxidation stability and low pour point could be produced within relatively short hydrogenation time.     

On the mechanism of the copper‐catalysed hydro‐genation; a reinterpretation of published data

The copper‐catalysed hydrogenation of triglyceride oils differs from the nickel‐catalysed reaction in that copper catalysts only hydrogenate double bonds in methylene interrupted polyunsaturated fatty acid moieties. Accordingly, the copper‐catalysed reaction stops when the triglycerides present in the reaction mixture are only monounsaturated fatty acids and polyunsaturated fatty acids in which the double bonds are separated by more than one methylene group. Copper catalysts thus exhibit a very high oleic acid selectivity. This observation has been explained in the literature by assuming that copper catalysts can only catalyse the hydrogenation of conjugated polyenes and that they are also capable of catalysing the conjugation of methylene interrupted polyenes. Accordingly, the hydrogenation of linolenic acid and linoleic acid moieties starts with their conjugation which is then followed by hydrogen addition to these conjugated acids. For both reactions (conjugation and hydrogenation) the literature assumes the Horiuti‐Polanyi mechanism stipulating the addition of a hydrogen atom to a double bond as the first step. Reinterpretation of the literature data now leads to the hypothesis that the first step in the conjugation mechanism could well be the abstraction of a hydrogen atom from an allylic methylene group rather than the addition of a hydrogen atom to a doubly bonded carbon atom. A conjugated double bond system then results from the addition of a hydrogen atom to the allylic radical formed by the foregoing hydrogen abstraction.