Produkte der Dimerisierung ungesättigter Fettsäuren III: Trennung dimerer Fettsäuren mittels GC und HPLC — Nachweis aliphatischer und verzweigter Dicarbonsäuren

Products of the Dimerisation of Unsaturated Fatty Acids III: Separation of Dimeric Fatty Acids with the Aid of GC and HPLC — Identification of Branched Aliphatic Dicarboxylic Acids From dimers produced by dimerisation of pure oleic acid we obtain by freezing small amounts of compounds, which can be separated further by GC. The separated compounds are isomers with a molecular weight of 594. They are saturated branched aliphatic dicarboxylic acid esters. They are obviously produced by en-reaction followed by hydrogenation. A much more effective separation than by GC is possible by HPLC, using a detector based on light scattering. Thus the dimeric fatty esters can be separated into four fractions: the first fraction consists of aromatics, the second obviously of alicyclic and unsaturated dicarboxylic acids, the third and fourth consist of aliphatic dicarboxylic acid esters of MW 594. Fatty acids obtained by dimerisation of a starting material rich in linoleic acid contain large amounts of aromatic compounds, those which are obtained by dimerisation of starting material rich in oleic acid contain rather high amounts of aliphatic dicarboxylic acids and practically no aromatic compounds.     

Produkte der Dimerisierung ungesättigter Fettsäuren XII: Die Dimerisierung von Konjuensäure

Products of Dimerisation of Unsaturated Fatty Acids XII: The Dimerisation of Conjugated Fatty Acids Dimeric fatty acids obtained by the clay-catalyzed dimerisation of the conjugated fatty acid (mixture of 9,11-octadecadienoic acid and 10,12-octadecadienoic acid) can be separated via HPLC in form of their dimethylates in three fractions in accordance with results obtained by separation of dimeric fatty acids of linoleic acid. The first fraction of aromatic dimeric fatty acids with the molecular weight 586 mainly contains compounds with a tetrasubstituted ring system. The second fraction, consisting of alicyclic unsaturated dimeric fatty acids, is characterized by the molecular weight 590 and a cyclohexene ring system. The third fraction corresponds to alicyclic saturated dimeric fatty acids. Dimeric fatty acids resulting of a Diels-Alder-reaction were detected neither in the end products nor as products in the early phase of the dimerisation. The results obtained by the investigation of the dimerisation of conjugated fatty acids are similar to those of the dimerisation of linoleic acid. Consequently a Diels-Alder-reaction is not involved in the formation of dimeric fatty acids. Although conjugated fatty acids are predominated to undergo a Diels-Alder-reaction no such products could be detected. This result strengthens the thesis that the dimerisation of unsaturated fatty acids is initiated by a cationic mechanism. The composition of the dimeric fatty acid using conjugated fatty acids is more uniform than that of usual mixtures of linoleic and linolenic acid. This provides evidence that a modification of the educt fatty acids can yield new structures of the dimerisation products.     

Produkte der Dimerisierung ungesättigter Fettsäuren XI: Die Fraktion der alicyclischen Dimerfettsäuren

Products of Dimerisation of Unsaturated Fatty Acids XI: The Fraction of Alicyclic Dimeric Acids Dimeric fatty acids can be separated as their dimethylates by HPLC-chromatography [W. Link, G. Spiteller, Fat Sci. Technol. 92 , 135 (1990)]. The main fraction of dimeric fatty acids obtained by the dimerisation of linoleic acid consists of alicyclic unsaturated dimeric fatty acids with the molecular weights 588 and 590. The structures of these compounds remained unknown until now. This fraction was subjected to hydrogenation, epoxidation and dehydrogenation with SeO₂ and Pd/C. The investigation of the reaction products provided evidence that these dimeric acids are a mixture of the following compounds: Dimeric acids with a 6-ring and one double bond and dimeric acids with two 6-rings and a double bond could be identified. In both types of compounds the double bond can be either situated in the ring as well as outside the ring. In dimeric acids containing two rings this ring system can be condensed or separated by a C-chain. Besides dimeric acids with two 6-rings dimeric acids with one 6-ring and one 5-ring were found. Essential contributions to these deductions were obtained by an investigation of model compounds and model fractions.     

Produkte der Dimerisierung ungesättigter Fettsäuren VII: Kinetische Untersuchung der Mono- und Dimeren,die bei der Dimerisierung von Ölsäure entstehen

Products of the Dimerisation of Unsaturated Fatty Acids VII: Kinetic Studies about the Dimerisation of Oleic Acid The withdrawing of samples from a mixture of 95% oleic and 5% linoleic acid during dimerisation showed that oleic acid is first transferred into elaidic acid and its corresponding isomers with different positions of the double bond. Only these compounds are able to react to ?isostearic acids”? being found in the monomeric fraction. These findings were proven by the dimerisation of pure elaidic acid which gave identical products in identical quantities. Primary dimerisation products of this mixture of 95% oleic and 5% linoleic acid are formed by reaction of two molecules of linoleic acid or one molecule of linoleic acid with one molecule of oleic acid. The reaction products are partly of cyclic, partly of alicyclic structure. Isomerisation and hydrogenation occur only in the last period of the dimerisation process.     

Produkte der Dimerisierung ungesättigter Fettsäuren X: Identifizierung von Estoliden in der Anfangsphase der Dimerisierung

Products of the Dimerisation of Unsaturated Fatty Acids X: Identification of Estolides in Early Phase of the Dimerisation Dimeric fatty acids, obtained by dimerisation of the conjugated fatty acid (mixture of 9,11-Octadecadienoic acid and 10,12-Octadecadienoic acid) in presence of the catalyst molybdenum pentachloride and tin dichloride, could be separated after methylation with diazomethane. The isolated fraction of methyl-9-octadecanoyloxy-octadecanoat resp. methyl-10-octadecanoyloxy-octadecanoat and methyl-9-octadec-9-enoyloxy-octadecanoat resp. methyl-10-octadec-9-enoyloxy-octadecanoat was characterized. It could be shown that these estolides can be saponified to stearic acid, oleic acid and 9- resp. 10-hydroxyoctadecanoic acid. Thus saponification can serve as an unambiguous proof of estolide components. Analogous estolides could be identified in the early phase of the clay-catalyzed dimerisation of oleic and linoleic acid. The detection of estolides shows that at low dimerisation temperature at first hydroxy fatty acids are formed which are subsequently esterified with unsaturated fatty acids. In the final products of the dimerisation estolides are absent, because their formation is suppressed by higher temperatures.     

Produkte der Dimerisierung ungesättigter Fettsäuren V: Die Aromatenfraktion dimerer Fettsäuren

Products of Dimerisation of Unsaturated Fatty Acids V: The Aromatic Fraction of Dimeric Acids The aromatic fraction of dimeric fatty acid esters can be separated according to a decreasing grade of unsaturation by HPLC using an UV-recorder. Hydrogenation experiments of the collected fractions allowed the determination of the number of rings. If the aromatic fraction are oxidized with KMnO₄ using a phase-transfer catalyst benzene 1,2,4- and 1,3,5-tri-, 1,2,4,5-and 1,2,3,5-tetra- and the pentacarboxylic acid were obtained as main products. Consequently we have to conclude that the catalyst causes intramolecular extensive migration of alkyl chains. Finally 2,3-dihydrobenzofurantetracarboxylic acids with different position of the carboxylic groups were detected in the mixture of oxidation products.     

Produkte der Dimerisierung ungesättigter Fettsäuren II: Die Monomerfraktion der Dimerisierung reiner Linolsäure 1. Aromatenfraktion

Products of Dimerisation of Unsaturated Fatty Acids II: The Fraction of Monomeres Obtained by Dimerisation of Pure Linoleic Acid, 1st Fraction of Aromatics The monomeric fraction obtained by dimerisation of pure linoleic acid shows after methylation a much more complex gas chromatogram as the same fraction obtained by dimerisation of oleic acid. Main compounds are p-and m-disubstituted benzene derivatives carrying one alkyl- and one alkylcarboxylic group. Besides stearic acid and stearolactone the same monomethyl branched isostearic acids are produced as observed by dimerisation of oleic acid. In contrast to the latter reaction also isomers of oleic acid could be detected in considerable amounts.     

Produkte der Dimerisierung ungesättigter Fettsäuren IX: Kinetische Untersuchungen zur Dimerisierung von Linolsäure

Products of the Dimerisation of Unsaturated Fatty Acids IX: Kinetic Studies about the Dimerisation of Linoleic Acid To clarify the dimerisation process of linoleic acid, we investigated samples taken in different time intervals. The first reaction step is a water addition at double bonds of the starting material and not double bond isomerisation as previously assumed. The resulting unsaturated monohydroxy fatty acids can cyclize with the second double bond in an intramolecular reaction forming 2,5-disubstituted tetrahydrofuran respectively 2,6-disubstituted tetrahydropyran derivates. Linolenic acid, present nearly always in small amounts in linoleic acid, reacts to first dimerisation products with linoleic acid by formation of a C-C-bond. The aliphatic dimers cyclize in an intramolecular reaction to mono-cyclic compounds. No dimeric acids, which would result from a Diels-Alder-reaction, could be identified. Bicyclic and aromatic dimeric acids can also be found in the early phase of the dimerisation. In the further progress of the reaction isomerisations, hydrogenations and dehydrogenations of the primary reaction products occur, thus the content of aromatic substances increases steadily.     

Kurzfristige Fütterungsversuche mit Methylestern dimerer Fettsäuren

Short-Time Feeding Tests with Methyl Esters of Dimeric Fatty Acids Fatty acid methyl esters ex safflower oil were polymerised at high temperature and separated by distillation. Feeding experiments with rats at a level of up to 50 cal-% in the food showed the highest degree in growth retardation with those fractions which contained esters of dimeric fatty acids. Esters of dimeric fatty acids of well defined structure, were fed to mice per os to determine acute toxicity. With the compounds applied the toxicity was far higher than 20 ml/kg body weight. After feeding radiocarbon labelled dimeric fatty acid esters, it could be shown that a high percentage of the material fed was excreted. However, a small amount is metabolised since ¹⁴CO₂ was observed in the exhaled air, and radioactive monomeric fatty acids were found in the body fat. Finally a small amount of the labelled dimeric fatty acids fed to the rats was recovered from the body fat indicating direct incorporation.     

Quantitative Bestimmung der apolaren dimeren Fettsäuren in Fetten und Ölen

Quantitative Determination of Unpolar Dimeric Fatty Acids in Fats and Oils Fatty acids obtained by saponification of fats followed by removal of unsaponifiables and petroleum ether insoluble oxidized fatty acids, were treated to give urea-adducts. The mixture of fatty acids which did not form adducts was esterified and separated by thin-layer chromatography. It was shown by mass-spectrometry that the methyl esters of unpolar dimeric fatty acids occupied a definite zone in the chromatogram. The methyl esters of unpolar dimeric fatty acids can be quantitatively estimated by charring the chromatogram under standardized conditions and densitometry of the above zone, whereby a test substance is co-chromatographed for comparison. The relative standard deviation in the chromatography and densitometric determination was approximately 10%. The lower limit of detection was at 0.005% of the methyl ester of unpolar dimeric fatty acid. Using dimeric fatty acids lebelled with radioactive carbon, it was proved that approximately up to 90% of the unpolar dimeric fatty acids can be detected by this method.     

Produkte der Dimerisierung ungesättigter Fettsäuren VIII: Über die Zusammensetzung der Fraktion der “Intermediates” bei der Fettsäuredimerisierung

Products of Dimerisation Unsaturated Fatty Acids VIII: The Fraction of “Intermediates” Obtained by Dimerisation of Unsaturated Fatty Acids The fraction of “intermediates” which is obtained by dimerisation of unsaturated fatty acid contains straight chain saturated fatty acids with 20-24 carbon atoms as well as methyl branched isomers thereof. The production of these compounds is probably caused by the presence of small amounts of monounsaturated fatty acids with 20-24 carbon atoms in the starting material. The fraction of “intermediates” contains in addition monocarboxylic acids with 36 carbon atoms. These are probably formed after dimerisation by an intramolecular cyclisation reaction under participation of one carboxylic group, followed by hydrogenation of the produced carbonyl group. Finally the formed alcoholic group is eliminated as a water molecule, and the produced double bond is hydrogenated.     

Produkte der Dimerisierung ungesättigter Fettsäuren I: Die Monomerfraktion der Dimerisierung reiner Ölsäure

Products of the Dimerisation of Unsaturated Fatty Acids I: The Fraction of Monomeres Obtained by Dimerisation of Pure Oleic Acid The position of methyl branches in ?isomeric stearic acids”? obtained from the monomeric fraction of the dimerisation of pure oleic acid was determined by their transformation into saturated alcanes. These compounds show mass spectra which allow a clear localisation of the position of the methyl branch. Isomeric stearic acids with a methyl branch between carbon 2 and 5 are missing. Methylheptadecanes with a branch in position 2 to 7 could be separated by GC, while the isomers with a methyl branch in position 8 and 9 turned out to be not separable. The recorded mass spectra proved that heptadecanoic acids with a branch in position 8 to 16 were present in about the same amount, while the isomeres with a branch in position 6 and 7 were produced in the course of the dimerisation only in minute amounts. Fatty acids with two methyl branches could not be detected. The fraction of the monomeres contains traces of dialkyl-substituted cyclohexenones, too. The structures of these compounds were determined by microchemical transformation of the ketones followed by analysis of the reaction mixture by GC/MS.     

Untersuchungen über die Entstehung von Kohlenwasserstoffen in erhitzten gesättigten Fettsäuren und Fettsäureestern

Studies on the Formation of Hydrocarbons in Fatty Acids and Fatty Acid Esters on Heating The investigations on the volatile compounds of the unsaponifiable matter and the steam distillate of heated saturated fatty acids have shown that on heating in the presence of air, along with other substances, hydrocarbons having a chain length 1 to 2 C atoms shorter than the corresponding fatty acids are formed. The splitting proceeds so slowly in the case of esters that even after 4 hrs of heating at 160°C no reaction products could be detected. By heating palmitic acid under the same conditions, except that vacuum was employed, no perceptible quantities of hydrocarbons were found.     

Verhalten der freien Fettsäuren nach tierexperimenteller Verbrennung

Behaviour of Free Fatty Acids After Burning in Animal Experiments The pattern of free fatty acids in the serum of rats after 20% burning was determined in order to elucidate the severe changes resulting from the shock after burning. Gas chromatographic analysis was carried out after 1/2, 1, 6, 24, 48 and 72 hours following burning trauma. For comparison the fatty acid pattern of a control group of unburned animals was examined. Gas chromatographic analysis showed following characteristic changes: 1. An increase of palmitic, stearic, palmitoleic, oleic, linoleic and linolenic acids after 6 hours following burning. 2. A constant level of palmitic acid even after 72 hours. 3. A slight decline of palmitoleic and oleic acids after 48 and 72 hours. 4. An increase of the polyunsaturated linoleic and linolenic acids till 24 hours after burning and a subsequent large decrease. The function of fatty acids, especially linoleic and linolenic acids, as constituents of membranes is of great importance. They determine essentially the membrane permeability. Moreover, the polyunsaturated fatty acids are precursors of prostaglandins, whose role in burning is little investigated. The characteristic change of polyunsaturated fatty acids suggests a relationship with membrane damage, increased thrombocyte aggregation and alterations of lung surfactant. Their steep decline might be caused by autoxidation due to lack of antioxidants, degradation during conversion to energy and incorporation into lipoproteins and membranes. The significance of free fatty acids in catabolism of the cell in severe trauma is unquestionable.     

Qualitative und quantitative Untersuchung der freien Fettsäuren in Depotfetten und fetthaltigen Erzeugnissen

Qualitative and Quantitative Investigation of Free Fatty Acids in Depot Fats and Fat-Containing Products The free fatty acids (FFA) in the fat of dry sausages were adsorbed on aluminia. After elution the methylesters of the fatty acids were separated on Reoplex (400). The composition of fatty acids released from fats showed distinct differences to the composition of a fat after saponification. Myristic, palmitoleic and linoleic acid had increased in the amount expressed as percentage of fatty acids while the percentage of stearic and possibly palmitic acid had decreased in concentration. The volatile fatty acids (<14 C) increased in the fat of dry sausages, too.     

Untersuchungen über die Entstehung von Kohlenwasserstoffen in UV-bestrahlten Fettsäuren und Fettsäure-Estern

Studies on the Formation of Hydrocarbons in Fatty Acids and Fatty Acid Esters Irradiated with UV Rays The investigation of volatile compounds in unsaponifiable matter and in steam distillates of UV-irradiated saturated fatty acids and fatty acid esters has shown that by irradiation in the presence of air as well as under vacuum, along with other substances, unsaturated hydrocarbons are formed. They are most probably 1,2 alkenes whose chains are shorter than the corresponding fatty acids by 2 C-atoms. The volatile compounds in the unsaponifiable matter of the UV-irradiated oleic acid comprise predominantly of carbonyle compounds.     

Untersuchungen über die Struktur dimerer Fettsäuren I: Struktur dimerer Ölsäure-methylester

Investigation on the Structure of Dimeric Fatty Acids, Part I: Structure of Dimeric Methyl Oleates Monoenoic as well as dienoic dimers were synthesized from methyl oleate and compared thin-layer chromatographically with a mixture of dimers obtained from thermally treated methyl oleate. By this means it was made to appear very likely that the unsaturated components of the mixture of dimers comprise monoenoic and dienoic dimers. The mixture contained, beside 30% saturated dimers, 30% dienoic and 40% monoenoic dimers. By analysis with mass- and NMR-spectra an unequivocal characterization of the ring system in saturated dimers was not possible. The mechanism of the dimerisation is discussed.     

Die prozentuale Zusammensetzung der freien Fettsäuren im Vergleich zum Fettsäuremuster nach Verseifung (Gesamtfettsäuren) bei einigen frischen und gelagerten tierischen Lebensmitteln

Percent Composition of Free Fatty Acids of a Few Fresh and Stored Animal Food Products in Comparison to Their Fatty Acid Pattern after Saponification Depot fat and muscle fat of fresh and stored chickens as well as beef tallow and milk fat were analysed after saponification by gas-liquid chromatography as their methyl esters. The free fatty acids of the same fats were absorbed on alumina and examined for their composition after desorption in the same way. The amount of free fatty acids after lipolysis was not identical with the percentage of fatty acids of the fats. Palmitoleic-, oleic-, and linoleic acid showed an increase, but palmitic and stearic acid a decrease of their amounts in the liberated acids in comparison to the composition of the fatty acids of neutral fats. A remarkable amount of volatile acids could be detected in the free fatty acids only.     

Die unterschiedliche Bedeutung der Fettsäuren in ihrer fungistatischen Wirkung

Significance of Fatty Acids in Their Fungistatic Action The fungistatic action of saturated and unsaturated fatty acids, halogenated fatty acids and esters as well as sulfurcontaining derivatives is reviewed. Fungistatic agents, known since a long time, are propionic acid, caprylic acid and its salts as well as undecylenic acid and its salts. The recently known fatty acid derivatives having fungistatic action are morpholine and piperidine compounds of long chain fatty acids and the new class of aminimides of fatty acids with 14–16 C atoms.