Products of unsaturated fatty acid oxidation catalyzed by hematin compounds

Summary A study has been made of the initial and secondary products resulting from the hematin catalyzed decomposition of hydroperoxides. The initial product was found to be the alkoxy free-radical produced by the homolytic cleavage of the O-OH bond of the hydroperoxide. The system was arranged so that the alkoxy radicals reacted with a hydrogen donor as they were formed to produce the corresponding alcohol. The alcohol was then identified by standard physical and chemical procedures. The secondary products resulting from the hematin catalyzed decomposition of linoleate hydroperoxide in the absence of oxygen were found to be composed principally of oxirane, hydroxyl, and carbonyl compounds. Cleavage of the carbon chain, loss of conjugated double bonnds, and polymerization also took place. Reactions to account for these products were proposed, along with a general mechanism of hematin catalysis.     

Photo-sensitized oxidation of unsaturated fatty acid methyl esters. The identification of different pathways

The photo-sensitized oxidation of methyl linolenate and methyl oleate was studied using erythrosine and riboflavin as sensitizers. The complex mixtures of hydroperoxides obtained were analyzed for the proportion of conjugated products and, after reduction to the corresponding mixtures of hydroxystearates, for the distribution of positional isomers. By comparing the mixtures with that obtained from autoxidation, it was shown that the riboflavin reaction involved the “Type 1” mechanism of photosensitized oxidation which proceded via the formation of diene-radicals and yielded the same positional isomers of hydroperoxides as autoxidation. Thus, mixtures of the 8, 9, 10, and 11 positional isomers of allylic hydroperoxides were formed from oleate and the 9, 12, 13, and 16 isomers of conjugated diene-hydroperoxides from linolenate oxidation. The erythrosine reaction, on the other hand, proceded via the “Type 2”. mechanism which involved singlet oxygen as the oxygenating species. The mixtures of isomers resulting from oxidation involving singlet oxygen were different from those obtained by autoxidation. Oleate oxidation gave rise to a mixture of only the 9 and 10 positional isomers while the mixture obtained from oxidation of methyl linolenate contained non-conjugated hydroperoxide isomers (with the hydroperoxide group at positions 10 and 15) as well as the conjugated—9, 12, 13, and 16—isomers.     

Hydrosilylation of long chain unsaturated fatty acid esters

The addition of a series of silicon hydrides: trichlorosilane, methyldichlorosilane, dimethylchlorosilane, phenyl dichlorosilane, and methyl phenyl chlorosilane to esters of long chain unsaturated fatty acids, such as oleic, linoleic acids, and 10-undecenoic acid, was studied with respect to catalysts, temperature, and solvents. Higher yields were obtained on carrying out the hydrosilylation reactions in the presence of chloroplatinic acid or Pt on C catalysts in bulk without solvent, as compared with peroxide catalysts. The addition reaction with methyl 10-undecenoate, which has a terminal double bond, gave a higher yield than that with methyl oleate. NMR data of the products from methyl 10-undecenoate and methyl oleate, as well as their reduction products with lithium aluminum hydride, have shown that, with the former ester, the silyl moiety added exclusively to the terminal carbon atom, while, with the latter, no migration of the silyl moiety to the terminal carbon atom was observed.     

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.     

Omega-formylalkanoates by ozonization of unsaturated fatty esters

Ozonization of the methyl esters of 11-eicosenoic, linoleic, erucic and linolenic acids gave a number of different homologous methyl ω-formylalkanoates. Complete ozonization of the monounsaturated esters formed C₁₁ and C₁₃ compounds with 90% conversion; partial ozonization of the polyunsaturated esters gave C₁₂ and C₁₅ products with maximum conversions at ca. 75% consumption of fatty ester. Thus, methyl linoleate gave 52 and 23% conversions to the 9- and 12-carbon products, and methyl linolenate gave 29, 27 and 19% conversions to the 9-, 12- and 15-carbon products. Yields of aldehyde or acetal esters in distilled products were 70–90% in preparative-scale experiments. Kinetic analysis showed that ozone attack was essentially random. Methanol was used as a participating solvent. Presented in part at the AOCS Meeting, New Orleans, 1962. A laboratory of the No. Util. Res. & Dev. Div., ARS, USDA.     

Rate studies of unsaturated fatty acid oxidation catalyzed by hematin compounds

Summary Hemoglobin and hematin were found to catalyze the oxidation of homogeneous as well as heterogeneous linoleate systems. The interrelationship of several factors affecting the rates of this reaction were studied. A spectrophotometric method was developed for studying the rate of decomposition of linoleate hydroperoxide by hematin compounds. By using this method, the effects of linoleate hydroperoxide, hemoglobin concentrations, and temperature on the rate of hydroperoxide decomposition was studied. In addition, the catalytic activities of several hemoproteins, metallo-protoporphyrins, and metal chelate compounds were determined. Supported in part by grants from Wm. J. Stange Company, Chicago, and General Foods Corporation, New York.     

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.     

Chemoenzymatic epoxidation of unsaturated fatty acid esters and plant oils

In the presence of an immobilized lipase fromCandida antacrtica (Novozym 435^R) fatty acids are converted to peroxy acids by the reaction with hydrogen peroxide. In a similar reaction, fatty acid esters are perhydrolyzed to peroxy acids. Unsaturated fatty acid esters subsequently epoxidize themselves, and in this way epoxidized plant oils can be prepared with good yields (rapeseed oil 91%, sunflower oil 88%, linseed oil 80%). The hydrolysis of the plant oil to mono- and diglycerides can be suppressed by the addition of a small amount of free fatty acids. Rapeseed oil methyl ester can also be epoxidized; the conversion of C=C-bonds is 95%, and the composition of the epoxy fatty acid methyl esters corresponds to the composition of the unsaturated methyl esters in the substrate. Based partly on a lecture at the 86th AOCS Annual Meeting & Expo, San Antonio, Texas, May 7–11, 1995.     

Monocarbonyl compounds from catalytic decomposition of autoxidized unsaturated fatty acid esters

Monocarbonyl compounds formed by the decomposition of autoxidized triolein, methyl linolenate, and methyl arachidonate were converted into their 2,4-dinitrophenylhydrazone derivatives and analyzed by thin layer and paper chromatographies. From decomposition of autoxidized triolein with acid-washed Fuller’s earth alkanals were the only monocarbonyl products found, whereas, with metal catalysts or heat, 2-alkenals were the primary products. Autoxidized methyl linolenate and methyl arachidonate decomposed with metal catalysts or heat yielded 23–55% of 2,4-alkadienals but minor amounts with acid-washed Fuller’s earth. The differences in distribution of monocarbonyl products were attributed to a selective course of scission of the hydroperoxides that depended upon the conditions of decomposition.     

The reaction of nonconjugated unsaturated fatty acid esters with maleic anhydride

Summary 1. The non-conjugated unsaturated fatty acid esters react with maleic anhydride at 200° C. or above. 2. At 200° C., methyl oleate reacts with almost 1 mole, methyl linoleate with 2 moles, and methyl linolenate with 2.5 moles of maleic anhydride, when an excess of anhydride is present. Methyl stearate reacts negligibly. 3. Methyl oleate reacts without affecting unsaturation. 4. The first molecule of anhydride reacting with methyl linoleate reacts mostly to saturate one double bond, while the second one adds on without affecting unsaturation. 5. The first two molecules of anhydride reacting with methyl linolenate react mostly to saturate one double bond each, while the third molecule adds on without affecting unsaturation. 6. The possible structures of the reaction products have been discussed. Presented before the American Oil Chemists’ Society at their meeting in Chicago, October 8–10, 1941. Now associated with the Southern Regional Research Laboratory, New Orleans, Louisiana. A cooperative organization participated in by the Bureaus of Agricultural Chemistry and Engineering and Plant Industry of the U. S. Department of Agriculture, and the Agricultural Experiment Stations of the North Central States of Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.     

Cis-Trans isomerization of unsaturated fatty acid methyl esters without double bond migration

Trans isomerization of monoenoic and dienoic fatty acid methyl esters has been carried out with thiols and diphenylphosphine in the presence of azobisisobutylnitrile. The equilibrium mixture contained 75–80%trans double bonds and there was no migration of the double bonds.     

Hydrogenation of unsaturated fatty acid methyl esters using decalin for hydrogen transfer

A laboratory procedure was developed for hydrogenation of methyl esters of unsaturated fatty acids using decalin as a hydrogen-transfer agent and 10% Pd/C as catalyst. The esters of 10-undecenoic, oleic, elaidic, stearolic, linoleic, cycloaliphatic C₂₁ di-, C₂₂ tri- and C₃₆ dicarboxylic acids, and a mixture of hydrnocarpic, chaulmoogric and gorlic acids were hydrogenated. Chromatographic and spectral analyses showed complete saturation. This procedure is simple, requiring no external source of hydrogen.     

Hydrogenation of unsaturated fatty acid methyl esters with diimide from hydroxylamine-ethyl acetate

Methyl esters of 10-undecenoic, oleic, linoleic and castor oil fatty acids were hydrogenated with hydroxylamine-ethyl acetate reagent under nitrogen, without change in position and configuration of double bonds. The fatty acid ester was also found to participate in the generation of diimide. No hydrazide was formed.     

Interaction of tocored with unsaturated fatty esters

Tocored, an oxidation product of tocopherol and its model, 2,2,7,8-tetramethyl-5,6-chromanquinone reacted with methyl linoleate at an elevated temperature to form an adduct with isomerized linoleate. Oxidation of tocored in fatty esters produced a variety of products, depending on the degree of unsaturation of the esters. With methyl palmitate no addition product was detected but tocopurple and tocoreddimer were identified as minor products irrespective of the degree of saturation. A mechanism involving the interaction of tocored with lipid radicals to yield an adduct as the consequence of antioxidative action of tocored is postulated.     

Photochemical oxidation of fatty acid esters with and without chlorophyll

1. It has been confirmed that the principal products formed in the oxidation of methyl oleate by oxygen under a variety of conditions are predominantlytrans hydroperoxides. However no inversion of the double bond occurs in unoxidized oleate. Hence the conversion ofcis totrans double bonds and peroxide formation occur together in the same molecules.
2. The autoxidation of methyl linoleate at low temperature yields predominantlycis,trans conjugated hydroperoxides. Autoxidation at 25°C., oxidation catalyzed by visible light, or ultraviolet light and copper soap catalyzed oxidation at temperatures appreciably above 0°C., lead to the formation primarily oftrans,trans conjugated hydroperoxides. The inversion of the second double bond in this case appears to be independent of the peroxide-forming reactions.
3. The photochlorophyll oxidation of methyl linoleate leads to the formation of some unconjugated hydroperoxides, some of which containtrans double bonds.
4. Under all of the conditions employed in the present investigation, the oxidation of methyl oleate and linoleate led primarily to the formation of monomeric peroxides which retained most of the unsaturation of the parent compound.

     

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.     

A polarographic investigation of the kinetics of epoxidation of unsaturated fatty acid esters

Summary A polarographic technique which uses a nonaqueous electrolytic solution consisting of 0.25M ammonium acetate in glacial acetic acid is a suitable medium for the investigation of the kinetics of fatty acid ester epoxidations. From the polarographic data the specific reaction rate constants for the perlauric acid epoxidation of vinyl laurate, methyl oleate, and vinyl oleate in benzene at 25°C. were found to be 12, 232, and 270 × 10⁻³ l./mole⁻¹ min⁻¹. The Arrhenius equation for the epoxidations of methyl oleate and vinyl oleate by perlauric acid can be expressed as Presented at the Fall Meeting of the American Oil Chemists' Society, Philadelphia, Pa., Oct. 10, 1955. Senior Fellow, National Renderers Association. Presently member of staff, Eastern Regional Research Laboratory. A laboratory of the Eastern Utilization Research Branch, Agricultural Research Service. United States Department of Agriculture.     

A bulky phosphite-modified rhodium catalyst for the hydroformylation of unsaturated fatty acid esters

A series of hydroformylation experiments was performed with a high-grade and a technical-grade-derived methyl oleate (MO) and a rhodium catalyst modified by the bulky tris(2-tert-butyl-4-methylphenyl)phosphite. In the hydroformylation of pure methyl oleate, relatively high turnover numbers were obtained (400–500 mol/mol/h) under mild conditions (molar ratio MO/Rh=910, 80–100°C and 20 bar; CO/H₂=1:1, solvent toluene), leading to about 95% conversion in 3 h. Fast isomerization occurs under these conditions to produce the trans oleate. Trans oleate reacts more slowly than cis oleate. At temperatures below 50°C, isomerization does not occur. The use of technical-grade methyl oleate, containing 14% 9,12 diene, methyl linoleate (ML), results in lower reaction rates because dienes form stable π-allylic intermediates, which slowly undergo hydroformylation. More severe conditions were applied to obtain higher rates. The rate varied from 50 to 400 mol/mol/h, depending on conditions (molar ratio MO/Rh=910, T=50–120°C, P = 50–80 bar; CO/H₂=1:1–1:6, solvent, toluene). Several isomers of ML were formed during the reaction. Subsequent hydroformylation of these isomers results in a complicated mixture of products. The product mixture consists predominantly of methyl formylstearate, methyl formyloleate, methyl diformylstearate, and some yet unidentified side products. A comparison of the classic triphenylphosphine-modified catalyst and the bulky phosphite-modified catalyst has shown that the latter is several times more active.     

Paper chromatography of unsaturated fatty acid esters as their mercuric acetate addition compounds

Summary A method is described by which unsaturated fatty acid esters can be separated and identified by reversed-phase paper chromatography. The procedure is based upon the formation of the mercuric acetate addition compounds of the esters and the detection of the compounds on the chromatograms, using the sensitive color reaction with diphenylcarbazone. The application of this technique to the analysis of the component unsaturated acids of natural fats has been examined, and tetradecenoic acid in olive oil and hexadecenoic acid in linseed oil both formerly unidentified have been detected as the minor component acids by means of the method. The preliminary investigation on the absorption spectra of diphenylcarbazone complexes derived from the addition compounds has been made to bring the method into quantitative use.     

Alcohols from ozonolysis products of unsaturated fatty esters

1-Nonanol and alkyl 9-hydroxynonanoates were more readily prepared by hydrogenation of the respective isolated aldehydes than by direct hydrogenation of products from reductive ozonolysis of oleate esters. Hydrogenation with nickel catalysts and aprotic solvents reduced the isolated aldehydes in good yield with a minimum of side reactions. Although the noble metal catalyst and hydroxylic solvent systems frequently used in similar reductions were also effective, they required a promoter that fortuitously catalyzed hydrolysis of acetals that formed during hydrogenation. Direct hydrogenation of the ozonolysis products resulted in side reactions and a mixture of products difficult to separate. Presented in part at the AOCS meeting, Chicago, October 1967.