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1.
The autoxidation of polyunsaturated fatty acids is initiated bothin vivo andin vitro by nitrogen dioxide. The mechanism of the initiation process is believed to involve both addition reactions and hydrogen
atom abstraction reactions, with hydrogen abstraction predominating at low levels of nitrogen dioxide. Therefore low levels
of nitrogen dioxide should react with polyunsaturated fatty acids to give allylic derivatives; in an anaerobic system these
derivations should be allylic nitro and nitrite compounds. Using negative methane chemical ionization mass spectrometry and
other analytical techniques, we have identified these allylic nitrite and nitro compounds from the reactions of low levels
of nitrogen dioxide with methyl linoleate and methyl linolenate in the absence of oxygen. 相似文献
2.
Hiroyuki Shimasaki O. S. Privett Ichiro Hara 《Journal of the American Oil Chemists' Society》1977,54(3):119-123
The formation of fluorescent products in the reaction of methyl linoleate hydroperoxide with glycine in aqueous emulsions
correlated directly with the decrease in diene conjugation and the increase in thiobarbituric acid (TBA) reactive substances.
These correlations also were reflected in the course of the oxidation of methyl linoleate in aqueous emulsions with glycine
and indicated that glycine reacted with products of peroxide decomposition as opposed to intermediates of autoxidation in
hydroperoxide formation. Thin layer chromatography (TLC) and selective solvent extraction demonstrated that the products of
the reaction contained many substances with a fluorescent spectrum similar to those of lipofuscin pigments. When methyl esters
of polyunsaturated fatty acids or other polyunsaturated lipids underwent oxidation adsorbed on silica gel particles, products
with similar fluorescent spectral properties were formed illustrating that fluorescent substances were formed in a variety
of reactions associated with the oxidation of unsaturated lipids. 相似文献
3.
Efforts have been made to characterize the products that result from interactions between L-histidine (free base) and peroxidizing
methyl linoleate (ML) in a model system consisting of reactants dispersed on a filter paper. Imidazole lactic acid and imidazole
acetic acid are identified as breakdown products when histidine is incubated with ML, methyl linoleate hydroperoxide (MLHPO),
or n-hexanal over a period of 3 weeks. Two other reaction products are found to give back histidine upon acid hydrolysis.
These products are though to be Schiff's base compounds which result from the condensation of the histidyl α-amino group and
carbonyl groups of reactive aldehydes formed during ML peroxidation. Most of the detectable reaction products have the imidazole
moiety intact indicating the high relative reactivity of the functional groups, especially the amino group, associated with
the α-carbon. Such high reactivity provides an explanation for the low concentrations of ninhydrin-positive free amino compounds
that are, at best, barely detectable on thin layer chromatography.
Presented at the AOCS Meeting, Chicago, September 1976. 相似文献
4.
A. E. Johnston K. T. Zilch E. Selke H. J. Dutton 《Journal of the American Oil Chemists' Society》1961,38(7):367-371
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. 相似文献
5.
The degradation products formed from methyl linoleate hydroperoxides by reaction with heme were fractionated by Sephadex LH-20
column chromatography and by reverse-phase high performance liquid chromatography, and the ability of each compound to form
fluorescent substances through reaction with amino compound was compared. Maximum formation of fluorescent substances was
obtained from monomeric degradation products with amino compound, but low molecular weight aldehydes such as hexanal, 2-hexenal
and 2,4-decadienal, formed only a small amount of fluorescent substances. However, the major monomeric degradation products
described previously, the hydroxy-, keto- and epoxy-derivatives, do not significantly contribute to the formation of fluorescent
substances through reaction with amino compound. It was suggested that formation of fluorescent substances from lipid peroxides
with amino compound may originate from a precursor present in monomeric degradation products formed from hydroperoxide of
methyl linoleate during lipid peroxidation, and that low molecular weight aliphatic aldehydes are not involved in fluorescent
substance formation. Moreover, the majority of TBA-reactive substances in secondary oxidation products prepared from autoxidized
methyl linoleate are also unrelated to the formation of fluorescent substances through reaction with amino compound. 相似文献
6.
Carbon dioxide was partially removed from a nitrogen stream, which also contained some ethylene, by adsorption on a 4A (Na-A) zeolite. The treated nitrogen stream was then passed over a 13X (Na-X) zeolite bed upon which ethylene and any remaining carbon dioxide were adsorbed. Ethylene was recovered by desorption at 68 Pa pressure into a slow flow of nitrogen as stripping gas. The ethylene concentration in the extracted gas was extremely dependent on the nitrogen flow-rate, whereas the concentration of carbon dioxide remained practically constant. Thus, it was possible to obtain a gas mixture greatly enriched in ethylene with a reasonably low content of carbon dioxide. 相似文献
7.
Schwab A. W. Gast L. E. Rohwedder W. K. 《Journal of the American Oil Chemists' Society》1975,52(7):236-239
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. 相似文献
8.
S. Koritala 《Journal of the American Oil Chemists' Society》1980,57(9):293-298
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. 相似文献
9.
The epoxidation of methyl linoleate was examined using transition metal complexes as catalysts. With a catalytic amount of
methyltrioxorhenium (4 mol%) and pyridine, methyl linoleate was completely epoxidized by aqueous H2O2 within 4 h. Longer reaction times (6 h) were needed with 1 mol% catalyst loading. Manganese tetraphenylporphyrin chloride
was found to catalyze the partial epoxidation of methyl linoleate. A monoepoxidized species was obtained as the major product
(63%) after 20 h. 相似文献
10.
Methyl linoleate with 5% by weight of methyl palmitate as an internal standard was deposited as a monolayer (20% by weight)
on Silica gel H and oxidized at 7,25, and 40°C. Oxidation was followed by iodometric PV practiced directly on aliquots of
the silica gel. Lower temperatures gave higher PV maxima but after longer times. Oxidation of methyl linoleate at all three
temperatures followed first-order kinetics, and the energy of activation was 15.0 kcal/mol. The products recovered from the
chloroform-acetic acid layer of the peroxide determination were analyzed by GC and identified by El- and CI-MS. Calculation
based on methyl palmitate as an internal standard showed that the total peak area decreased to about 40% that of the original
methyl linoleate when the residual methyl linoleate was reduced to less than 2%. The chief nonscission products (NSP) of linoleate
oxidation were epoxy, hydroxy, hydroxy-epoxy, dihydroxy, and trihydroxy methyl esters. The greatest NSP concentrations were
obtained about the time of the greatest PV, and the yield at 40°C was greater than those at 7 and 25°C. Scission products
(SP) increased rapidly until the greatest PV was reached. After this time, SP declined slightly and plateaued at 40°C, but
at 7 and 25°C, SP continued to increase slowly with further oxidation. 相似文献
11.
Sara P. Fore Robert T. O'Connor Leo A. Goldblatt 《Journal of the American Oil Chemists' Society》1958,35(5):225-230
The reaction of mercaptoacetic acid with methyl linoleate and with linoleic acid was investigated. The reaction proceeded at low and erratic rates, with and without catalysts, such as peroxides at various temperatures, but could be accelerated by use of a large excess of mercaptoacetic acid. Addition of 1 mole of mercaptoacetic acid to 1 mole of methyl linoleate resulted in a product containing about 40% of mono-adduct. Ozonolysis of the purified mono-adduct yielded approximately equimolar quantities of caproic and azelaic acids, indicating that addition occurred about equally at the 9,10- and 12,13-ethylenic bonds. The dicarboxylic acid and the dimethyl ester of the mono-adduct and the tricarboxylic acid and trimethyl ester of the di-adduct of linoleic acid and mercaptoacetic acid were prepared, and the infrared spectra and some physical and chemical characteristics of these products were determined. The infrared spectra of the reaction products were obtained and correlated with functional groups which give rise to them. Bands at about 7.8 and 8.8 μ, commonly observed in long chain acids and esters and ascribed to C−O vibrations, are intensified in the sulfur-containing reaction products, suggesting characteristic absorption of C−S compounds at almost identical wavelengths. The formation of adducts was accompanied by a high degree of isomerization of the unreacted ethylenic bonds from thecis to thetrans form both in the mono-adduct and in unreacted methyl linoleate. The methyl linoleate recovered contained about 12% diene conjugation, but catalytic quantities of mercaptoacetic acid were not effective in inducing conjugation. 相似文献
12.
The hydrogenation of methyl linoleate to methyl oleate and methyl stearate was studied in a 6-inch stirred batch reactor at 121°C and 45 psia. Several particle size fractions of a 1 per cent Pd-carbon catalyst were used to help separate the gas absorption resistance, the external mass transfer resistance, and the internal resistance to pore diffusion and reaction. Corrected to the same concentration of hydrogen, the initial rate of reaction for linoleate was 30 times that for oleate. This difference in reactivity and stronger adsorption of linoleate account for the high selectivity of 50–80. 相似文献
13.
A commercial chemiluminescent nitrogen oxides analyzer performed well in its nitric oxide mode when applied to the combustion products of polyurethane materials, but when test gases were passed through a thermal converter prior to measurement of nitrogen dioxide, serious, interferences was encountered from hydrogen cyanide and other nitrogen compounds. 相似文献
14.
Frdric Destaillats Paul Angers 《European Journal of Lipid Science and Technology》2005,107(3):167-172
Chemical pathways responsible of the conjugation of linoleic acid during heat treatments such as refining (deodorization), frying or cooking processes have been investigated. For this purpose, methyl linoleate was submitted to oxidative and non‐oxidative thermal conditions. The resulting degradation products were mainly composed of geometrical and conjugated fatty acid isomers. Oxidative conditions were obtained using tert‐butyl hydroperoxide under inert atmosphere, and air. The obtained results from both thermal oxidative conditions were compared to non‐oxidative thermal treatment. Higher levels of conjugated linoleic acid were found when linoleate was heated under oxidative conditions. Two distinct mechanisms responsible for the formation of CLA isomers are proposed and discussed. Evidence of formation of 9,11‐C18:2 and 10,12‐C18:2 acids from 9,12‐C18:2 by a free‐radical chain reaction is provided. The first step consists in the formation of a free radical by abstraction of an active bis‐allylic hydrogen. By delocalization of the initial free radical, two allylic free radicals were stabilized and converted into the corresponding CLA isomers via the abstraction of a hydrogen radical from other linoleic acid or oxygenated species. Kinetic observations confirmed the significance of the bimolecular mechanism. Moreover, the proposed mechanism is supported by several pieces of information from the literature on peroxidation of linoleic acid. Under pure thermal conditions and/or for diluted samples, a second pathway to the formation of CLA from heat‐treated linoleic acid is proposed via an intramolecular rearrangement of the pentadienyl structure. This thermal [1,3]‐sigmatropic rearrangement results in a mixture of 9,11 and 10,12 CLA isomers. The formed cis/trans CLA isomers were readily rearranged by a [1,5]‐sigmatropic shift to yield trans‐8,cis‐10 and cis‐11,trans‐13 CLA isomers, respectively. 相似文献
15.
The reaction between electrochemically generated Fenton's reagent and toluene was studied. The products arising from this reaction system were consistent with a primary hydrogen atom abstraction from the methyl group of toluene to give benzyl radicals.Benzaldehyde was obtained with a current yield higher than 60%; benzyl alcohol was also produced in smaller quantities in some experiments. The dependence of the yields on reagent concentrations, temperature and coulombs passed was examined. On the basis of the experimental results a mechanism is proposed involving peroxy and alkoxy radicals as intermediates. 相似文献
16.
A previous study of autoxidation products by high pressure liquid chromatography (HPLC) of methyl oleate and linoleate was
extended to methyl linolenate. Autoxidized methyl linolenate was fractionated by HPLC either after reduction to allylic alcohols
on a reverse phase system, or directly on a micro silica column. Isolated oxidation products were characterized by thin layer
and gas liquid chromatography and by ultraviolet, infrared, nuclear magnetic resonance and mass spectrometry. Secondary products
from the autoxidation mixtures (containing 3.5–8.5% monohydroperoxides) included epoxy unsaturated compounds (0.2–0.3%), hydroxy
or hydroperoxy-cyclic peroxides (3.8–7.7%), epoxy-hydroxy dienes (<0.1%), dihydroxy or dihydroperoxides with conjugated diene-triene
and conjugated triene systems (0.9–2.9%). Cyclization of the 12- and 13-hydroperoxides of linolenate would account for their
lower relative concentration than the 9- and 16-hydroperoxides. Dihydroperoxides may be derived from the 9- and 16-linolenate
hydroperoxides. Cyclic peroxides and dihydroperoxides are suggested as important flavor precursors in oxidized fats. 相似文献
17.
Methyl linoleate, diluted with an equal weight of methyl laurate, was heated without exclusion of air at 200C for 200 hours.
The reaction mixture was separated by means of molecular distillation, urea adduction, column chromatography, and gas chromatography.
Cyclic and aromatic materials were detected in the nonurea adductable monomer fractions. The dimer was separated into polar
and nonpolar fractions. Analytical data for the nonpolar dimer are consistent with a cyclic Diels-Alder product. Bioassays
showed the nonadductable monomer, the polar dimer, and a fraction of intermediate boiling point to be toxic when administered
to weanling male rats. Urea-adductable fractions, nonpolar dimer, and polymer were not toxic. The concentrations of the toxic
components were so low that the heated linoleate, before fractionation but after removal of the laurate, was not toxic. 相似文献
18.
S. Koritala R. O. Butterfield H. J. Dutton 《Journal of the American Oil Chemists' Society》1973,50(8):317-320
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. 相似文献
19.
A. W. Schwab W. K. Rohwedder L. W. Tjarks L. E. Gast 《Journal of the American Oil Chemists' Society》1973,50(9):364-366
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. 相似文献
20.
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. 相似文献