Separation of saturated/unsaturated fatty acids

Fatty acid mixtures can be separated into one fraction rich in saturated fatty acids and the other rich in unsaturated acids. Since saturated fatty acids have a higher melting point than unsaturated, liquid mixture to be fractionated is cooled to a temperature at which the larger part of the saturated acids crystallize, while the greater part of unsaturated acids remain in liquid form. Different industrial methods to separate the two phases are described. The oldest and simplest method is slowly to cool and crystallize the mixture in shallow pans to form cakes which then are pressed in presses of different design. By applying high pressure, the liquid olein is thus squeezed out from the cake, leaving the stearin fraction behind. A new process to separate the phases is to mix an aqueous solution, containing a wetting agent, with the crystallized fatty acid mixture. The stearin crystals are thus wetted and transferred into the aqueous phase, which then can be separated from the olein phase in a centrifuge. The stearin/aqueous suspension is heated to melt the stearin, which can then be separated in a second centrifuge. Other methods to improve phase separation use organic solvents, among which are methanol, acetone, methyl formate and propane. In the solvent fraction process, the miscella has to be cooled to a lower temperature than in the aforementioned methods, due to the solubility effect of the solvents. The solvents are removed by distillation from the fraction. Typical operation results with different types of raw materials are given. The advantages and disadvantages of the different methods are discussed.     

Maleyl esters of monoglycerides of saturated fatty acids

Esterification between maleic anhydride and monoglycerides of saturated fatty acid has been studied. The nature of reaction vessels, temperature and reaction time have been evaluated in view of the product distribution in the final product. Concentration of monoesters (half-esters) diesters and dimers has been calculated and related to the reactants’ ratio, time and temperature of the esterification.     

Addition of chlorine to unsaturated fatty acids and esters

Summary Methyl oleate, oleic acid, and ethyl linoleate were chlorinated with elemental chlorine at temperatures near −20°C. Approximately quantitative yields of the addition products were obtained, with little or no concurrent substitution. The products prepared in this manner had not previously been reported in the pure state. Two new compounds, ethyl tetrachlorostearate and tetrachlorostearic acid, were prepared. Methyl dichlorostearate was found to distil with no apparent decomposition at 190–200°C. under pressures below 1 mm. Removal of the chlorine atoms required more drastic conditions that removal of bromine atoms from the same positions and was accompanied by complicating side reactions. Journal Paper No. 755 of the Purdue University Agricultural Experiment Station, Lafayette, Ind.     

The rates of oxidation of unsaturated fatty acids and esters

The rates of autoxidation of oleic acid, ethyl oleate, linoleic acid, 10,12-linoleic acid, ethyl linoleate, trilinolein, pentaerythritol linoleate, dipentaerythritol linoleate, elaidolinolenic acid, linolenic acid, ethyl linolenate, trilinolenin, and methyl arachidonate have been studied by oxygen uptake in a Warburg respirometer and the results are compared with the rates of enzymatic oxidation of lipoxidase substrates. The increase in the number of double bonds in a fatty acid by one increases the rate of oxidation of the fatty acid or its esters by at least a factor or two. Earlier findings that acids oxidize more rapidly than their esters have been confirmed. The initial rates of lipoxidase oxidation of ethyl linoleate, ethyl linolenate, and methyl arachidonate were found to be essentially the same.     

Quantitative structure-property relationships for normal saturated and unsaturated fatty acids

Quantitative structure-property relationships, a technique of deriving properties of compounds from knowledge of their structures, has been applied to aliphatic carboxylic acids, an industrially important group of compounds. Equations have been developed from the molecular connectivity of the first order and the molar refraction as inputs which, on testing with data of seven properties, yielded average absolute deviations ranging between 0.9 and 6.7%. The compounds studied ranged between C₁ and C₃₀ for saturated and C₃ to C₂₂ for unsaturated fatty acids. The properties studied are normal melting and boiling points, critical temperature and pressure, and heats of fusion, combustion and formation.     

Esterification rates of some saturated and unsaturated fatty acids with glycerol

Esterification rates of eight commonly occurring fatty acids were studied at 180C using equivalent and equimolar amounts of glycerol with and without a cosolvent. The esterification with equivalent amounts of glycerol without cosolvent followed second order kinetics and proceeded at a similar rate for all acids examined. Esterifications with equimolar amounts of glycerol were kinetically complex and their speed depended on the solubility of glycerol in individual fatty acids.     

Copolymerization of methyl esters of unsaturated C18 fatty acids

In order to assay the possibilities of making high polymers from linseed oil, the copolymerizations of styrene with the methyl esters of oleic, linoleic, linolenic, and conjugated linolenic acids were studied at 60–130C and copolymerizations of the last three esters with acrylonitrile were studied at 60C. Appropriate free radical initiators were employed in all cases. The esters without conjugated unsaturation show little tendency to enter a copolymer with styrene, but copolymers containing up to 40% by weight of conjugated linoleate can be obtained. Linoleic, linolenic, and conjugated linoleic esters copolymerize readily with acrylonitrile. Products containing up to 45 mole %, 80 wt %, of the conjugated ester can be made. However, methyl eleostearate, with three conjugated double bonds, inhibits the polymerization of both styrene and acrylonitrile. Quantitative comparisons of the behaviors of the esters are made through the copolymerization equation. The probable performance of these and other vinyl monomers in copolymerization with linseed oil is discussed. Presented at the Symposium on Recent Advances in Drying Oil Chemistry, Division of Organic Coatings and Plastics Chemistry, Am. Chem. Soc. meeting in Washington, 1962.     

Different metabolism of saturated and unsaturated long chain plasma free fatty acids by intestinal mucosa of rats

During fat absorption, unsaturated long chain fatty acids are esterified at a higher rate than saturated fatty acids of similar chain length. This phenomenon has been attributed to differences in the binding affinity of fatty acids to a cytosolic fatty acid-binding protein. As intestinal mucosa utilizes plasma free fatty acids as well, we investigated whether long chainplasma free fatty acids of different degree of saturation are metabolized also at different rates.³H-Palmitic and¹⁴C-linoleic acid complexed to rat serum were injected rapidly into a tail vein of fasting rats. One, 2 and 4 min later there was no difference between³H and¹⁴C-radioactivity in intestinal mucosa, suggesting equal initial uptake of the two labeled fatty acids from plasma. Despite their equal uptake, the incorporation of the isotopes into ester lipids was significantly different, however: at 2 min, 53.1±3.9% of³H and 73.8±4.6% of¹⁴C were recovered in ester lipids. Phospholipids and triglycerides accounted for most of the mucosal³H and¹⁴C. At 4 min, a similar distribution of isotopes in intestinal mucosal metabolites was found. These data show that despite equal initial uptake by intestinal mucosa unsaturated long chain fatty acids taken up from plasma are esterified to a higher and oxidized to a lower extent than saturated plasma free fatty acids. Unsaturated plasma free fatty acids, therefore, may provide a more important source of fatty acids for endogenous intestinal lipoprotein lipids than saturated plasma free fatty acids. It is speculated that the fatty acid binding protein might be operative not only in the intracellular transport and metabolism of luminal fatty acids but of plasma free fatty acids as well.     

Comparison of radiolytic compounds from saturated and unsaturated triglycerides and fatty acids

Formation of certain radiolysis products from palmitic acid, oleic acid, tripalmitin and triolein has provided a means for comparing the radiolytic effects in saturated and unsaturated triglycerides and fatty acids. These substances were chosen to represent the major constituents of fat found in beef. Fractionation and concentration of radiolytic compounds from the irradiated samples was accomplished by the means of size exclusion chromatography. Quantitative and qualitative analyses were performed using a combined GC/MS computer system. In addition to the primary radiolytic compounds, recombination products of relatively high molecular weight and various propanediol diesters from the corresponding glyceryl moities were identified. Quantitative analyses indicated a greater yield of various radiolytic compounds from free fatty acids than from the corresponding triglycerides. Similarly, radiolytic compounds were produced in greater quantities from the saturated fats than the unsaturated fats. Most of the radiolytic compounds identified in this study have not been previously reported.     

Wide-line NMR spectra of some saturated and unsaturated long chain fatty acids

Wide-line NMR spectra were obtained on a series of homologous normal long chain fatty acids: decanoic, lauric, myristic, palmitic, stearic and behenic as well as three isostructural unsaturated acids: elaidic,trans-5-eicosenoic and brassidic. Also included are NMR spectra of metastable forms of both the saturated and unsaturated acids. NMR parameters are correlated with carbon chain length, crystal long spacing and density. Polymorphic forms are distinguished on the basis of line width and second moment differences. Presented in part at the Meeting of the Society for Applied Spectroscopy, October, 1970, New Orleans, La. So. Market. Nutr. Res. Div., ARS, USDA.     

13C nuclear magnetic resonance of mono-and dihydroxy saturated and unsaturated fatty methyl esters

¹³C nuclear magnetic resonance spectra were obtained for methyl esters oferythro- andthreo-9,10-dihydroxystearates, for 12-hydroxy-cis- andtrans-9-octadecenoates, and forthreo-12,13-dihydroxy-cis-andtrans-9-octadecenoates.Erythro andthreo compounds may be distinguished easily by the difference in the chemical shifts of the carbons alpha to the hydroxy-bearing carbons. Monohydroxy compounds are easily distinguished fromvicinal dihydroxy compounds by differences in chemical shifts of both the hydroxy-bearing carbons and of the carbons alpha to them. The presence of a hydroxy-bearing carbon beta to a double bond results in the two carbons of the double bond of a hydroxy-bearing carbon beta to a double bond results in the two carbons of the double bond having different chemical shifts, with the numerical values being different for thecis andtrans isomers. The chemical shift of a carbon alpha to both a doubly bonded carbon and a hydroxy-bearing carbon is influenced both by the geometry of the double bond and the number of hydroxy-bearing carbons. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

Gas chromatography-mass spectrometry of methyl esters of unsaturated oxygenated fatty acids

Silylation of hydroxyl groups in methyl esters of unsaturated hydroxy acids provides compounds that give mass spectra which can be readily interpreted, whereas spectra of underivatized esters are extremely difficult to evaluate. The relationship of the double bond(s) to the trimethylsiloxy (TMS) group results in specific mass spectral patterns. In esters that have the TMS group separated from the double bond by one methylene group, the ions caused byα-cleavage at the TMS group on the side closest to the olefinic group are much more abundant than those produced fromα-cleavage on the other side of the TMS group. In esters that have the TMS group and the double bond separated by two methylene groups,α-cleavage ions are approximately equal. When the TMS group and the double bond are allylic, no fragmentation results between them. Cleavage does occur on either side of this system, and those ions resulting from cleavage alpha to the TMS group are in greatest abundance. Silylation of esters that have a conjugated diene or ene-yne system adjacent to a hydroxyl group also gives derivatives amenable to gas chromatographymass spectrometry. In these esters, large peaks are observed that arise fromα-cleavage at the TMS group and at the other end of the olefinic system. No fragmentation between the TMS group and the sites of unsaturation occurs. Unsaturated epoxy methyl esters produce spectra difficult to interpret. When the epoxide is converted to methoxy-hydroxy derivatives by BF₃-methanol, the spectrum locates the position of the epoxide group. Silylation of the hydroxyl group produces a compound that gives a less complicated spectrum which also locates the original epoxy group. Mass spectrometry of a series of unsaturated keto-esters, without derivatization, provides spectra that are easily interpretable. Presented at the AOCS Meeting, Los Angeles, April 1972. N. Market. Nutr. Res. Div., ARS, USDA.     

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.     

Hydroformylation of unsaturated fatty esters

Unsaturated fatty esters and vegetable oils were hydroformylated with H₂ and CO (3500–4600 psi) and Co₂(CO)₈ to give fatty aldehydes at 100–110 C and fatty alcohols at 175–190 C. Yields of distillable C₁₉ oxo products varied from 42% to 84%. Distilled products contained from 50% to 90% branched isomers and from 4% to 16% linear isomers. The proportion of linear isomers increased at higher reaction temperatures and in the presence of tributylphosphine-cobalt carbonyl complex. Linear and branched hydroxy products were separated by silicic acid column, thin-layer, and gas-liquid chromatography. The linear hydroxy product (from oleate and linoleate) was identified as methyl 19-hydroxynonadecanoate by nuclear magnetic resonance and mass spectrometry. Isomeric branched products were analyzed by mass spectrometry as the diester derivatives. They were identified as a mixture of 5- to 13-carbomethoxy methyl octadecanoate. Presented at the AOCS-AACC Joint Meeting, Washington, D.C., March 1968. No. Utiliz. Res. Dev. Div., ARS, USDA. Bureau of Mines, U.S. Dept. of Interior.     

Fatty acids: part 27. Olefin inversion involving unsaturated fatty esters

Unsaturated long chain fatty esters gave the corresponding bromochloro ester derivatives when treated with N-bromosuccinimide and hydrogen chloride. Treatment of the intermediate halo esters with sodium iodide furnished the same positional unsaturated fatty ester isomers, but of opposite geometric configuration. This olefin isomerization method was found to be high yielding, stereospecific and to cause no double bond migration.     

Vapor-liquid equilibrium data for fatty acids and fatty methyl esters at low pressures

Conclusions The experimental vapor-liquid equilibrium data obtained with a mixture of methyl esters, and a mixture of a fatty acid and the corresponding methyl ester, were in agreement with calculated Raoult’s law data at a pressure of 4.0±0.2 mm. Hg. The system lauric acid-myristic acid was observed to be non-ideal or not obeying Raoult’s law at a pressure of 4.0±0.2 mm. Hg. An average rate of polymer formation of 0.23% per hour at 155–170° C. was determined for mixtures of lauric acid and myristic acid. The above work shows the feasibility of obtaining useful vapor-liquid equilibrium data for fatty materials at low pressures. A portion of this work was submitted by one of the writers, J.A.M., as a partial fulfillment for the degree of M. Ch. E. at the City College of the City of New York.     

Binary freezing point behavior of some saturated and unsaturated fatty acid methyl esters with methyl heptadecanoate

The binary freezing point behavior of methyl heptadecanoate with methyl laurate, methyl myristate, methyl palmitate, methyl stearate, methyl elaidate and methyl petroselaidate have been determined. Both stable and metastable polymorphic forms were observed. Methyl laurate formed a simple eutectic with a region of metastable equilibrium. Methyl myristate formed a simple eutectic of stable equilibrium and a solid solution of metastable equilibrium. Methyl palmitate exhibited a solid solution of metastable equilibrium terminating in a eutectic and a region of discontinuous stable equilibrium. Methyl stearate formed a solid solution of metastable wquilibrium and also continuous stable equilibrium which formed an incongruently melting molecular compound that terminated in a eutectic point. Methyl heptadecanonate with the unsaturated eighteen carbon atom acid methyl esters exhibited only simple eutectic points and a small region of metastable equilibrium. The binary freezing point behavior of the methyl esters in general resemble that of the corresponding ethyl esters. The limited results of mixtures of methyl esters of an odd carbon acid with unsaturated acids indicate an induced stabilizing effect caused by unsaturation in the carbon chain. So. Utiliz. Res. Dev. Div., ARS, USDA.     

Incorporation and distribution of saturated and unsaturated fatty acids into nuclear lipids of hepatic cells

Liver nuclear incorporation of stearic (18∶0), linoleic (18∶2n−6), and arachidonic (20∶4n−6) acids was studied by incubation in vitro of the [1-¹⁴C] fatty acids with nuclei, with or without the cytosol fraction at different times. The [1-¹⁴C] fatty acids were incorporated into the nuclei as free fatty acids in the following order: 18∶0>20∶4n−6≫18∶2n−6, and esterified into nuclear lipids by an acyl-CoA pathway. All [1-¹⁴C] fatty acids were esterified mainly to phospholipids and triacylglycerols and in a minor proportion to diacylglycerols. Only [1-¹⁴C] 18∶2n−6-CoA was incorporated into cholesterol esters. The incorporation was not modified by cytosol addition. The incorporation of 20∶4n−6 into nuclear phosphatidylcholine (PC) pools was also studied by incubation of liver nuclei in vitro with [1-¹⁴C]20∶4n−6-CoA, and nuclear labeled PC molecular species were determined. From the 15 PC nuclear molecular species determined, five were labeled with [1-¹⁴C]20∶4n−6-CoA: 18∶0–20∶4, 16∶0–20∶4, 18∶1–20∶4, 18∶2–20∶4, and 20∶4–20∶4. The highest specific radioactivity was found in 20∶4–20∶4 PC, which is a minor species. In conclusion, liver cell nuclei possess the necessary enzymes to incorporate exogenous saturated and unsaturated fatty acids into lipids by an acyl-CoA pathway, showing specificity for each fatty acid. Liver cell nuclei also utilize exogenous 20∶4n−6-CoA to synthesize the major molecular species of PC with 20∶4n−6 at the sn-2 position. However, the most actively synthesized is 20∶4–20∶4 PC, which is a quantitatively minor component. The labeling pattern of 20∶4–20∶4 PC would indicate that this molecular species is synthesized mainly by the de novo pathway.     

Direct determination of saturated fatty acids in fats,oils, and methyl esters

Summary A direct gravimetric method has been developed for the determination of saturated fatty acids in fats, oils, and methyl esters. The procedure involves methanolysis of the triglycerides to produce methyl esters, followed by oxidation of the unsaturated methyl esters by potassium permanganate. The undesired, acidic oxidation products are removed by alkaline washing and the saturated methyl esters thus isolated are weighed directly. The method is intended for the determination of saturated fatty acids having C₁₆ or longer carbon chains. Small quantities of C₁₄ saturated acids will be included in the determination if present with other higher saturated acids. The method is applicable to both natural and hydrogenated vegetable oils. It is not applicable to oils containing large amounts of C₁₄ and lower saturated acids. Concentrations of saturated acids ranging from 3 to 90% in known glyceride mixtures and from 0.3 to 95% in mixtures of methyl esters were determined with an average difference from the calculated value of 0.8%. Replicate determinations on samples in the 10 to 30% saturates range gave a standard deviation of 0.3 to 0.4%. Presented at the spring meeting, American Oil Chemists’ Society, New Orleans, La., April 28 to May 1, 1957