Polymerization of drying oils. III. Some observations on reaction of maleic anhydride with methyl oleate and methyl linoleate

Summary Adducts of maleic anhydride with methyl oleate, methyl linoleate, and monomeric distillate have been prepared. Reaction of the adducts with ethylene diamine gave a linear, soluble polyamide in the case of the oleate adduct, but gelation occurred at a low degree of reaction with other adducts. The linoleate adduct was separated into monomeric and polymeric components. It is suggested that this polymeric component is responsible for the rapid gelation of polyamides from the adducts of methyl linoleate and monomeric distillate. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Kinetics of hydrogenation of conjugated triene and diene with nickel,palladium, platinum and copper-chromite catalysts

A mixture of methyl linoleate and alkali-conjugated methyl linoleate was reduced with nickel, palladium, platinum and copper-chromite catalysts. The course of hydrogenation was followed by gas liquid chromatography of samples withdrawn at intervals. Relative rate constants of reactants and inermediates were calculated by a computer. Conjugated linoleate was 10–18 times more reactive than methyl linoleate with all catalysts except platinum, which showed no selectivity at 60 C. At 150 C conjugated diene reacted four times faster than methyl linoleate with platinum catalyst. A conjugated diene-to-stearate shunt was observed with palladium and platinum catalysts. When β-eleostearate was hydrogenated with the same catalysts, 50–97% of the triene was reduced directly to monoene with all catalysts except copper chromite, which selectively reduced conjugated triene to conjugated diene. On the basis of present kinetic data and previous knowledge about the mode of hydrogen addition to conjugated systems, a scheme has been proposed to account for the products formed during hydrogenation of methyl linolenate. ARS, USDA.     

Reaction of Maleic Anhydride with cis-Isolated Unsaturated Fatty Acid Esters

The structures of maleic anhydride adducts of essentially pure oleic, linoleic and linolenic methyl esters have been determined. The cleavage of the methyl oleate adduct yields a product with a succinyl structure, with or without shift of the double bond; four isomeric structures are possible. The first adduct of maleic anhydride with methyl linoleate is a succinyl derivative followed by a shift into the conjugated isomer with which the second maleic anhydride reacts via a 1–4 Diels Alder addition to yield a second adduct having a cyclohexene structure. The first two moles of maleic anhydride add to methyl linolenate to form di-succinyl derivatives followed by a shift into conjugated diene and triene. The third maleic anhydride adds via a 1–4 addition to yield a disuccinyl and one 1–4 adduct. A number of isomers are possible for the linoleate and linolenate adduct.     

Selective hydrogenation with copper catalysts: V. Kinetics and mechanism at high pressure

The mechanism of hydrogenation at 900~950 psi with copper-chromite catalyst was investigated with pure methyl esters as well as their mixtures. A comparison of double bond distribution intrans-monoenes formed during hydrogenation of linoleate and alkali-conjugated linoleate revealed that 85~95% of the double bonds in linoleate conjugated prior to hydrogenation. The mode of hydrogen addition to conjugated triene and diene at high pressure is similar to that at low pressure but positional and geometric isomerizations of unreduced conjugated esters were less at high pressure. Geometric isomerization of methyl linoleate and linolenate was considerable at high pressure whereas it was negligible at low pressure. The absence of conjugated products during hydrogenation of polyunsaturated fatty acid esters resulted from their high reactivity. Conjugated dienes are 12 times more reactive than the triene, methyl linolenate, and 31 times more reactive than the diene, methyl linoleate. The products of methyl linolenate hydrogenation were the same as those predicted by the conjugation mechanism. Presented at the 70th Annual Meeting of the American Oil Chemists' Society, San Francisco, April 29~May 3, 1979.     

Differences in Oxidation Kinetics Between Conjugated and Non-Conjugated Methyl Linoleate

The oxidation kinetics of conjugated methyl linoleate was compared with that of non-conjugated methyl linoleate under mild oxidation conditions (30 °C in the dark). Samples of methyl 9-cis,11-trans-linoleate, methyl 10-trans,12-cis linoleate and methyl 9-cis,12-cis linoleate were assayed separately and in mixtures. For comparative purposes, methyl α-linolenate and methyl oleate were also used. Two complementary analytical approaches were selected to monitor the progress of oxidation, (1) the traditional follow-up of residual substrate by gas liquid chromatography, and (2) an analytical procedure by high-performance size-exclusion chromatography (HPSEC) for direct measurement of the oxidation compounds formed. The HPSEC method enabled us to quantitate oxidized monomers, dimers and polymers concomitantly in a rapid and direct analysis. Results showed that conjugated methyl linoleate samples oxidized later than their non-conjugated counterparts, and showed a very different oxidation pattern. Thus, formation of oxidized monomers was negligible and the first and major compounds formed were polymerization products. Also, under the conditions used, non-conjugated and conjugated methyl linoleate samples in 1:1 mixtures led to decreased oxidation rate of non-conjugated methyl linoleate and increased oxidation rate of conjugated methyl linoleate. This study supports the view that oxidation kinetics of conjugated dienes differ substantially from that of methylene-interrupted dienes.     

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.     

Analyses of lipids and oxidation products by partition chromatography. Fatty acid hydroperoxides

A liquid partition chromatographic method was developed to isolated and determine hydroperoxides in autoxidized fatty acids or their methyl esters. By the use of benzene containing 2 to 4% methanol as the mobile solvent, the hydroperoxides were separated from unoxidized fatty acids or methyl esters and from secondary and polymeric decomposition products. In the analyses of oxidized fatty acids, diethyl ether was necessary to elute the secondary decomposition products. Saponification of autoxidized fatty esters destroyed the peroxides as determined iodometrically, but the resulting acids contained a fraction which was eluted in the same position as hydroperoxide acids. Evidence showed that this fraction is a monomeric hydroxy fatty acid containing conjugated cis-traux and trans-trans unsaturation. Fatty ester hydroperoxides were isolated chromatographically in yields and purity comparable to those reported in the literature by countercurrent distribution. The concentrations of methyl linoleate hydroperoxide determined chromatographically were smaller than indicated by the peroxide value and diene conjugation of the autoxidized methyl linoleate. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.     

碱法异构化亚油酸甲酯制备共轭亚油酸

该文探索在乙二醇溶剂中以氢氧化钠碱法异构化亚油酸甲酯制备共轭亚油酸的方法,适宜的异构化条件为m(氢氧化钠)∶m(亚油酸甲酯)∶m(乙二醇)=1∶5∶8.4,170℃反应4 h,亚油酸甲酯转化率和共轭亚油酸产率分别为92.4%和89.3%。该法比目前常用的亚油酸原料法的优越之处体现在:以氢氧化钠取代常用碱氢氧化钾,降低成本;以亚油酸甲酯取代亚油酸为原料,避免了原料本身大量消耗碱;反应初期避免原料大量皂化,减小了体系的传质阻力,因而减少了溶剂乙二醇消耗量。     

Conjugation of polyunsaturated fats with dimsylsodium

The conjugation of polyunsaturated fatty esters, including soybean oil, trilinolein, soybean methyl esters, and methyl linolenate and linoleate, with the sodium salt of dimethyl sulfoxide (dimsylsodium) as catalyst has been investigated. Methyl esters are ca. 95% conjugated within 2 hr. Glycerides react more slowly but are similarly conjugated within 24 hr. The glyceride linkages are not destroyed as they would be with aqueous or alcoholic alkali. Highly conjugated oils can thus be prepared. ARS, USDA.     

Hydrogen sulfide adducts of methyl oleate and linoleate

Sulfur compounds derived from photochemical addition of hydrogen sulfide to methyl oleate and linoleate were separated by preparative gas chromatography. The major compounds were investigated by NMR, mass and IR spectroscopy and by elemental analysis. The primary product of the methyl oleate reaction was methyl 9(10)-mercaptostearate. Gas chromatograms of the product from methyl linoleate showed four principal peaks. From mass spectra and NMR data, we identified methyl 9-(2-pentyl-1-thiolan-5-yl)nonanoate, methyl 8-(2-hexyl-1-thiolan-5-yl)octanoate and methyl 9-(3-hexyl-1,2-dithiolan-5-yl)nonanoate. Evidence for the formation of methyl mercapto-octadecenoates and methyl dimercaptostearates was also obtained. ARS, USDA.     

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.     

Ion exchange resins and ethyleneimine polymer as antioxidants II: Autoxidation products

The antioxidant effects of ion exchange resins and ethyleneimine polymer on the autoxidation products of methyl linoleate in a heterogeneous reaction system are discussed. Results from analyses of the various autoxidation products from linoleate samples with and without the antioxidants showed that the addi-tion of the antioxidants did not change the original autoxidation mechanism of methyl linoleate. How-ever, the antioxidants did retard the autoxidation in response to their antioxidant activity and, compared with a linoleate control, changed the yields of some autoxidized products such as an increased amount of conjugated diene hydroperoxides in linoleate samples with added ion exchange resins.     

Analysis of fat acid oxidation products by countercurrent distribution methods. V. Low-temperature decomposition of methyl linoleate hydroperoxide

Methylcis, trans diene conjugated linoleate hydroperoxide isolated by counterenrrent distritbution from 4°C, auatoxidation of methyl linoleate was stored in atmospheres of oxygen and of nitrogen at 4°C. in darkenss. Besides manometric changes, infrared and ultraviolet characteristics, peroxide value, diene conjugation, and molecular weights were followed on samples removed at various periods of storage up to 53 days. These same analyses were obtained on fractions obtained by counter-current distributions. Evidence for the reaction that occurs on storage in oxygen may be summarized thus: 1 mole oxygen absorbed by linoleate hydroperoxides destroys 1 molecis, trans diene conjugation, 1/2 mole peroxide group, and 1 mole linoleate hydroperoxide; dimers of varying polarities, scission acids, and isolatedrans bonds are formed. Since to volume changes were observed in the nitrogen storage of methyl linoleate hydroperoxide, changes in chemical and physical characteristics can only be related to time of storage. Storage in nitrogen at 4°C, destroys diene conjugation, peroxides, and linoleate hydroperoxide and produces dimers of varying polaritics, seission neids, and isolatedrans bonds. Destruction of diene conjugation was one-fourth as rapid in a nitrogen atmosphere as in oxygen. While differences in reactions and products were observed between oxygen and nitrogen storage, particularly in rates and in countereurrent distribution patterns, the similarity of products from oxygen and nitrogen storage is remarkable. One methyl linoleate hydroperoxide is formed regardless of storage atmosphere, dimirization and attendant destruction of double bonds and peroxides proceed. This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.     

Chromatographic studies on oxidative and thermal fatty acid dimers

A chromatographic study was carried out to investigate the nature of polymeric products in edible oils. Dimers from low-temp oxidation of methyl linoleate were compared with thermal dimers from high-temp polymerization of conjugated methyl linoleate. The distilled dimers were subjected to liquid-partition chromatographic separations on silicic acid columns as methyl esters, as free acids, and as methyl esters prepared by saponification and reesterification. Chromatographically isolated dimer fractions were also rechromatographed before and after each treatment. When thermal dimer esters are saponified and reesterified, chromatographic recoveries are quantitative, and the expected changes in polarity result; whereas, with oxidative dimer esters, gross changes in polarity occur. Chromatographic separations of dimer esters or their acids fractionate into distinct areas of increasing polarity. Presented at the AOCS Meeting, New Orleans, 1964. Honorable Mention, Bond Award Competition. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, USDA.     

Polymerization of drying oils. V. Further observations on the reaction of unsaturated dibasic anhydrides with methyl linoleate

Summary Adducts of methyl linoleate with itaconic and citraconic anhydrides have been prepared. Each adduct was separated into monomeric and polymeric components. With ethylene diamine, the itaconic and citraconic polymeric adducts gave gelled products at 170° in one hour and 3.5 hours, respectively. The adduct of citraconic anhydride and monomeric distillate gave a tough, tacky resin which did not gel during a reaction time of 20 hours at 170°–180°. The effect of dimethylaniline on the condensation of methyl linoleate and maleic anhydride was studied. Increasing amounts of dimethylaniline were found to promote the formation of a heteropolymer and to decrease the yield of liquid adduct. Presented before the American Oil Chemists’ Society Meeting, May 10–12, 1949, New Orleans, Louisiana. Trainee sponsored by the Government of India, 1947–1948. One of the Laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Deuteration of methyl linoleate with nickel,palladium, platinum and copper-chromite catalysts

Samples taken during deuteration of methyl linoleate with the title catalysts were separated into saturate, monoene and diene fractions. Monoenes were further separated intocis andtrans fractions. A comparison of the double bond distribution in monoenes with those from hydrogenation of alkaliconjugated linoleate indicated that up to 59% of the linoleate was reduced through a conjugated intermediate with nickel catalyst. The respective percentages for palladium and platinum catalysts were 51 and 23. Copper catalysts have previously been shown to reduce linoleate solely through conjugated intermediates. Copper-chromite catalyst showed infinite selectivity for the reduction of linoleate, because stearate did not form. The decreasing order of various catalysts for the selective reduction was copper-chromite>>>Ni at 195 C>Pd>Ni at 100 C>Pt. Computer simulation of platinum reduction indicated that ca. 20% of the linoleate was directly reduced to stearate through a shunt. Geometrical isomers of linoleate were formed during reduction with all catalysts except copper-chromite. Nickel catalyst formed bothtrans,trans- andcis,trans-isomers, as well as nonconjugatable dienes. These isomers were favored at the higher temperature and deuterium was incorporated into them. Palladium and platinum did not isomerize linoleate to nonconjugatable dienes. Because conjugated dienes are more reactive than linoleate, they were not found in appreciable amounts during reduction. Conjugated dienes were the only isomers formed with copper-chromite catalyst. Deuterium was found in these conjugated dienes, which were also extensively isomerized. As a result of isomerization and exchange during reduction of linoleate-as well as further exchange between deuterium and monoenes-a wide distribution of isotopic isomers in monoenes was found with nickel, palladium and platinum catalysts. Since isomerization of monoenes with copper-chromite is negligible, the isotopic distribution of monoenes must be due to exchange of intermediate conjugated dienes followed by addition. Presented at the AOCS Meeting, Ottawa, September 1972. ARS, USDA.     

Oxidative crosslinking of alkyd resins studied with mass spectrometry and NMR using model compounds

The crosslinking of alkyd resins has been studied using ethyl linoleate and methyl ricinoate as model compounds. With quantitative¹³C NMR it was established that ether- and peroxy-crosslinks were formed in roughly equal amounts. Double bonds reacted to give epoxides, endoperoxides, and β-scission into aldehydes. Using SIMS it was established that dimers through pentamers were formed having included several oxygen atoms. After reduction of peroxide (crosslinks) with stannous chloride, the higher oxygen homologues decreased. In the NMR spectrum of the reduced material, peroxide and epoxide signals completely disappeared. High resolution electrospray ionization mass spectra (ESI-MS) yielded evidence regarding the crosslink mechanism. The non-conjugated linoleic acid was found to crosslink by combination of radicals: dimers were having masses 2(M-1). The conjugated linoleic acid crosslinked by addition of radicals to the double bond and disproportionation, yielding masses 2M as well. (M = mass of ethyl linoleate or methyl ricinoate, respectively, including several oxygen atoms.) EIS-MS of oligomers after isotopic exchange enabled estimation of OH and OOH groups. Presented at the 75th Annual Meeting of the Federation of Societies for Coatings Technology, November 3–5, Atlanta, GA. General Analytical and Environmental Chemistry Dept., P.O. Box 9300, 6800 SB Arnhem, The Netherlands. P.O. Box 3, 2157 BA Sassenheim, The Netherlands.     

Prooxidant effects of inorganic chromium compounds in the autoxidation of methyl linoleate

The prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)-oxide > chromium chloride > potassium chromate > chromium (III)-oxide > potassium dichomate. In comparison with the control, additions of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts of hydroperoxides and conjugated dienes and large amounts of hydroxy groups,α,β,γ,δ-unsaturated carbonyls, isolatedtrans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing hydroperoxides derived from the autoxidation of methyl linoleate.     

Oxygen absorption of methyl esters of fat acids,and the effect of antioxidants

Summary The oxygen absorption of methyl linolenate, methyl linoleate, methyl oleate, methyl stearate, the distilled methyl esters of lard, and various mixtures of the four individual methyl esters were measured at 100° C. in the Barcroft-Warburg apparatus. Mixtures of methyl esters absorbed oxygen at a rate which could be approximately predicted from the rate of oxygen absorption of each component and the percentage of each present. The antioxidants nordihydroguaiaretic acid (NDGA), propyl gallate, benzylhydroquinone, α-tocopherol, and their synergistic combinations with citric acid, d-isoascorbyl palmitate, and lecithin were tested with the substrates methyl linoleate, methyl oleate, methyl stearate, and the distilled methyl esters of lard. Citric acid showed marked synergism with each antioxidant. The two most effective were the combinations of citric acid with nordihydroguaiaretic acid and with propyl gallate. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, United States Department of Agriculture.     

Nucleophilic addition of hydrogen sulfide to methyl oleate,methyl linoleate,and soybean oil

Hydrogen sulfide was added to methyl oleate, methyl linoleate, and soybean oil at −70 and 25 C in the presence of boron trifluoride. Major reaction compounds were identified by gas liquid chromatography and mass spectrometry. At −70 C with a 200 molar ratio of hydrogen sulfide to ester, the reactions were complete in 4 hr. Primary reaction product from methyl oleate was methyl 9(10)-mercaptostearate. Methyl linoleate gave ca. equal amounts of methyl 9-(2-pentyl-1-thiolan-5-yl) nonanoate and methyl 8-(2-hexyl-1-thiolan-5-yl) octanoate. At 25 C, the reaction of methyl oleate and linoleate with hydrogen sulfide was less complete, and more side reactions were noted. When equimolar amounts of methyl oleate and methyl 9(10)-mercaptostearate were reacted in the presence of boron trifluoride at 25 C, a new compound was formed, bis(methyl n-octadecanoate 9[10]-yl) sulfide. The addition of liquid hydrogen sulfide to soybean oil at −70 C in the presence of boron trifluoride yields a product which, upon saponification, acidification, and methylation analyzes by gas liquid chromatography as ca. 52% thiolan, 27% mercaptostearate, 10% palmitate, 6% stearate, and 5% unidentified compounds.