Methyl Oleate Hydroperoxide Research Articles

Dual Catalytic Role of Molybdate Ions for Direct Conversion of Photo-oxidized Fatty Acid Methyl Esters into Keto or Hydroxy Derivatives

An organosoluble ammonium molybdate salt catalytically converts allylic hydroperoxides of fatty acid methyl esters with good selectivities into either their corresponding alcohols or enones depending on the reaction conditions. Whereas a gentle heating of methyl oleate hydroperoxides in toluene at 80 °C mainly provides the enone in a 83/17 ratio, presence of triethylamine at 40 °C reverses this ratio to 7/93 in favor of the alcohol. Extension of the reaction scope to other alkenes like cyclohexene, cyclooctene, α- and β-pinenes, β-citronellol, and 2-octene shows the wide potential applications of the process which lead to relevant oxygenated building blocks, especially oils as a possible alternative of castor oil.

Thermal degradation of single methyl oleate hydroperoxides obtained by Photosensitized oxidation

AbstractA peroxidation mixture containing methyl 9‐ and 10‐hydroperoxy‐trans‐octadecenoates (MOHP) was obtained by singlet oxygen oxidation of methyl oleate. The two hydroperoxides were collected by solid phase extraction and purified separately by high‐performance liquid chromatography. Identification and single‐isomer purity evaluations were carried out by comparing the chromatographic and gas chromatography‐mass spectrometry parameters of the corresponding reduced hydroxy derivatives. Each purified MOHP was thermally degraded and new reaction mechanisms were proposed from the identification of the degradation products. Thermal rearrangement of each hydroperoxide isomer involved an allylic 3‐carbon intermediate before further degradation steps. The two MOHP isomers obtained from singlet oxygen oxidation produced all eight hydroperoxide isomers by thermal degradation in the condensed phase at high temperature (200°C). This result supports the assumption of singlet oxygen as a promoter of the first steps of oxidation of food lipids and also reconsiders the Khan mechanism.

Thermal degradation of single methyl oleate hydroperoxides obtained by photosensitized oxidation

AbstractA peroxidation mixture containing methyl 9‐ and 10‐hydroperoxy‐trans‐octadecenoates (MOHP) was obtained by singlet oxygen oxidation of methyl oleate. The two hydroperoxides were collected by solid phase extraction and purified separately by high‐performance liquid chromatography. Identification and single‐isomer purity evaluations were carried out by comparing the chromatographic and gas chromatography‐mass spectrometry parameters of the corresponding reduced hydroxy derivatives. Each purified MOHP was thermally degraded and new reaction mechanisms were proposed from the identification of the degradation products. Thermal rearrangement of each hydroperoxide isomer involved an allylic 3‐carbon intermediate before further degradation steps. The two MOHP isomers obtained from singlet oxygen oxidation produced all eight hydroperoxide isomers by thermal degradation in the condensed phase at high temperature (200°C). This result supports the assumption of singlet oxygen as a promoter of the first steps of oxidation of food lipids and also reconsiders the Khan mechanism.

Chromatographic determination of position and configuration isomers of methyl oleate hydroxides from corresponding hydroperoxides

Studies of lipid oxidation usually employ such model systems as purified fatty-acid methyl ester. While methyl oleate hydroperoxides (MOPHs) can only be readily separated from the matrix by HPLC, because of their heat-susceptibility and relative instability, these same techniques are unable to separatecis MOHP fromtrans isomers. The present study reports an enhanced, rapid separation method forcis andtrans isomers of methyl oleate hydroxides, as well as HPLC determination of positional isomers per fraction of configuration isomer and isomer identification by gas chromatography-mass spectrometry.

Chromatographic determination of the position and configuration of isomers of methyl oleate hydroperoxides

Oxygen can react with organic substrates (RH) to yield hydroperoxides, which in many instances are the first products of oxidation to be analytically isolated. A study of the structure of hydroperoxides could elucidate the reaction mechanisms activated during the first steps of oxidation processes. The simplest structural model used in the study of oxidation mechanisms of fats is methyl oleate. In this work the structures of methyl oleate hydroperoxides (MOHPs) were determined by gas chromatography—ion-trap detector mass spectrometry (GC—ITD-MS) of the corresponding hydroxystearates (MSHs). The hydroperoxides were reduced to methyl hydroxyoctadecenoates (MOHs), which were separated into the cis and trans fractions by argentation thin-layer chromatography. By hydrogenation of the double bond the cis- and trans-MOHs were reduced to MSHs for GC—ITD-MS analysis. Methods to isolate and determine the positional isomers of MOHPs were tested. The analytical techniques used were preparative high-performance liquid chromatography and GC—ITD-MS, solid-phase extraction-GC—ITD-MS and direct GC—ITD-MS.

The effect of dietary vitamin c and e supplementation on the toxicity of methyl oleate hydroperoxide (MOHP), a proposed toxic ozone intermediate

Abstract This study assessed the effects of vitamin E (600 mg/day) and/or vitamin C (one gram/day) supplementation for 4 weeks in adult human male volunteers on the in vitro erythrocyte toxicity of a proposed toxic ozone (O3) intermediate [i.e. methyl oleate hydroperoxide (MOHP)]. The results indicated that neither antioxidant vitamin provided significant (p > 0.05) protection against MOHP‐induced changes in methemoglobin (METHB) and reduced glutathione (GSH) over a wide range of MOHP concentrations.

Effects of Metal Chlorides of Periodic Group V, VI, and VII on the Autoxidation of Methyl Oleate and the Decomposition of Methyl Oleate Hydroperoxide

The effects of MoC5, VCl3, CrCl3·6 H2O, WCl6, and MnCl2 on the autoxidation of pure methyl oleate and decomposition of methyl oleate hydroperoxide at 80°C were evaluated on the basis of changes in characteristic numbers, oxirane oxygen content, and reaction products.The chlorides of Cr, V, and W acted as redox catalysts on the decomposition of hydroperoxide and enhanced the autoxidation of methyl oleate remarkably. The prooxi dant activity of the metal chlorides appeared in the order of Cr > V > W > Mn. Molybdenum chloride accelerated the decomposition of hydroperoxide but inhibited the autoxidation of methyl oleate. Manganese chloride had no effect on either reaction.The products resulting from these two reactions were trans-and cis-epoxyoctadecanoates, hydroxyoctadecenoates, hydroxiyepoxyoctadecanoates, oxooctadecenoates, and cleaved products.

Effects of Metal (periodic group VI) Hexacarbonyls on the Autoxidation of Methyl Oleate and the Decomposition of Methyl Oleate Hydroperoxide

To compare the effects of various metals (periodic group VI) on the autoxidation of methyl oleate and the decomposition of methyl oleate hydroperoxide in methyl oleate, the substrates were kept with metal carbonyls [Mo (CO) 6, Cr (CO) 6 and W (CO) 6] at 80°C.The effects of the catalysts were investigated by observing the changes in peroxide value, iodine value, saponification value, refractive index, molecular weight, and trans isomer content. The identification of autoxidation products of methyl oleate and decomposition products of methyl oleate hydroperoxide were carried out by gas chromatography of trimethylsilyl ether derivatives.Mo (CO) 6 showed marked effect on the autoxidation of methyl oleate and the decomposition of methyl oleate hydroperoxide. The products were found as methyl cis-epoxyoctadecanoate and methyl hydroxyoctadecenoate, which were produced by intermolecular reaction among methyl oleate and methyl oleate hydroperoxide. Moreover, methyl hydroxyepoxyoctadecanoate was also produced by intramolecular reaction of methyl oleate hydroperoxide itself.Cr (CO) 6 showed more marked effect than Mo (CO) 6. The autoxidized products of methyl oleate were identified as methyl trans-epoxyoctadecanoate, methyl cis-epoxyoctadecanoate, methyl hydroxyoctadecenoate and methyl oxooctadecenoate, but methyl hydroxyepoxyoctadecanoate was not produced. Methyl oxooctadecenoate and methyl hydroxyoctadecenoate were produced by decomposition of methyl oleate hydroperoxide in the presence of Cr (CO) 6, but W (CO) 6 showed almost no effects.

The effect of methyl oleate hydroperoxide, a possible toxic ozone intermediate, on human normal and glucose-6-phosphate dehydrogenase-deficient erythrocytes

Erythrocytes of both normal and glucose-6-phosphate dehydrogenase (G-6-PD)-deficient humans responded in a dose-dependent manner to the oxidant stress of methyl oleate hydroperoxide (MOHP) as measured by decreases in G-6-PD activity, increases in methemoglobin (METHB) levels, and decreases in reduced glutathione (GSH). The G-6-PD-deficient erythrocytes displayed a markedly enhanced sensitivity to MOHP-induced decreases in G-6-PD activity and METHB increases while being less sensitive than normal erythrocytes to changes in GSH levels.

The Decomposition of Methyl Oleate Hydroperoxide in Saturated Hydrocarbons and Methyl Esters of Fatty Acid

The Decomposition of Methyl Oleate Hydroperoxide in Saturated Hydrocarbons and Methyl Esters of Fatty Acid

Thermal decomposition of methyl oleate hydroperoxides and identification of volatile components by gas chromatography‐mass spectrometry

AbstractThe role of methyl oleate hydroperoxides as precursors of volatile compounds was investigated by thermal decomposition in the injector port of a gas chromatograph attached to a computerized mass spectrometer. The major volatile compounds identified correspond to those formed from triolein heated in air at 192 C.

Peroxide value determination—Comparison of some methods

AbstractA comparison between the determination of the peroxide value by the methods of Wheeler and Sully (iodometric titration) and that of Stine, et al. (ferric thiocyanate method) was made. Some oxidized vegetable oils, H2O2, t‐butyl hydroperoxide, cumene hydroperoxide, methyl oleate hydroperoxides, and methyl linoleate hydroperoxides were used as substrates. One‐hundred percent of the methyl linoleate hydroperoxides were recovered by the Wheeler reduction, 85% by the Sully method. The Wheeler method was used to reduce the methyl linoleate hydroperoxides to the corresponding hydroxy acids. In the Sully procedure, the hydroxy acids are only intermediates which are dehydrated to octadecatrienoic acids. One equivalent methyl linoleate hydroperoxide oxidized two equivalents of I− (Wheeler) and four equivalents of Fe2+ (Stine, et al.). By way of contrast, H2O2 needs only two equivalents I− or Fe2+ for reduction. The excess consumption of reduction equivalents in the ferric thiocyanate method probably is caused by secondary reactions of the methyl linoleate hydroperoxide acyl residue.

Decomposition of Methyl Oleate Hydroperoxides in vacuo on Exposure to Visible Light and Heat

AbstractMethyl oleate hydroperoxides were decomposed in sealed tubes under vacuum either by exposing to light from a 500 W‐tungsten bulb or by heating in the dark at 63° C. Heat treatment caused a faster reduction in peroxide value than the exposure to light. Free acids, hydrocarbons and epoxy compounds were among the products of decomposition. The formation of similar decomposition products in both the treatments suggests that the mechanism of decomposition is the same.

Reaction of 2,2′-Diphenyl-l-picrylhydrazyl with Hydroperoxides

IT has been reported that the stable free-radical 2,2′-diphenyl-1-picrylhydrazyl (DPPH) is entirely unsatisfactory for most rate measurements of free-radical production1,2. These findings have been confirmed and extended during our investigations on the use of DPPH for the quantitative determination of hydroperoxides of unsaturated fatty acids3. We have found that the rate of the reaction of DPPH with different hydroperoxides depends on the concentration of both reactants. Furthermore, we have discovered that while the rate of the heat-induced decomposition of, for example, methyl oleate hydroperoxides is 0.01 per cent/h, at 70° C, the rate increases a thousandfold in the presence of DPPH4. It was, therefore, concluded that the function of DPPH is not that of a reliable ·OH counting device, which may reflect the primary O-O bond cleavage of long-chain, unsaturated fatty hydroperoxides. For the same reasons, it was thought that the actual chemical reaction between DPPH and hydroperoxides should be different from that previously reported5–8.

Antioxidant Activity of Glycerylphosphatides and Their Hydrolysis Products. IV. Reaction of Methyl Oleate Hydroperoxide Concentrate with Phosphoric Acid and β-Glycerylphosphoric Acid and the Isolation of a Phosphorus-containing, Oil-soluble Product from Autoxidized Methyl Oleate in the Presence of β-Glycerylphosphoric Acid

Antioxidant Activity of Glycerylphosphatides and Their Hydrolysis Products. IV. Reaction of Methyl Oleate Hydroperoxide Concentrate with Phosphoric Acid and β-Glycerylphosphoric Acid and the Isolation of a Phosphorus-containing, Oil-soluble Product from Autoxidized Methyl Oleate in the Presence of β-Glycerylphosphoric Acid

Decomposition of methyl oleate hydroperoxide on the celite/dinitrophenylhydrazine‐hydrochloric acid column

AbstractThe hydroperoxides in oxidised methyl oleate can be converted in high yield into the dinitro‐phenylhydrazones of aldehydes and aldehyde esters by reaction on a Celite/dinitrophenylhydrazine‐hydrochloric acid column. The aldehydes and aldehyde esters formed are the same as those produced during the thermal decomposition of methyl oleate hydroperoxide.The dinitrophenylhydrazones of unsaturated conjugated C18 keto esters are also formed.

Thermal dimerization of fatty ester hypdroperoxides

SummaryWhen autoxidized fatty esters and purified fatty hydroperoxides were decomposed in the absence of oxygen at 210°C., the principal reaction was dimerization of the fatty acid chains with elimination of the hydroperoxide groups. Dimers isolated by molecular distillation (60 to 90% of the polymer) have approximately 1 mole hydroxyl, 0.5 mole carbonyl, and two double bonds per mole of dimer. Diene conjugation in the dimers from polyunsaturated fat hydroperoxides varied from 10 to 23%. The infrared spectra of the dimers were similar to those of the original fatty esters except for one striking band at 2.9 μ, which is attributed to the secondary hydroxyl group. Thecis‐trans diene in the polyunsaturated hydroperoxides was isomerized to thetrans‐trans configuration on dimerization. The methyl oleate hydroperoxide dimer showed only absorption for isolatedtrans double bond. The dimer was not split either by catalytic hydrogenation or by hydrogen iodide, indicating a carbon‐carbon bond between the monomer units. On oxidation with permanganate and periodate, the dimeric acids behaved like a monounsaturated mixture containing double bonds in the C6, C7, C8, C9, and C10 positions in the oleate dimer and in the C8, C9, and C10 positions in the safflower ester dimer. Although the dimers showed no peroxidic oxygen iodometrically with potassium iodide, a reduction occurred with hydriodic acid that may indicate the presence of intramolecular peroxide groups and/or allylic alcohol or carbonyl groups. Bromination with N‐bromosuc‐cinimide and dehydrobromination with N,N‐dimethyl aniline produced no aromatization. Subsequent oxidation of the dehydrobrominated dimer yielded 2.6% residue, which was not aromatic. This evidence indicates that the dimer does not have a six‐membered cyclic structure. Dimerization of the hydroperoxides is suggested as occurring through alkyl or alkoxy hydroperoxide radicals to give carbon‐carbon linked fatty acid dimers and some higher polymeric units.

Detection and measurement of hydroperoxides by near infrared spectrophotometry

SummaryNear‐infrared spectra have been measured on a group of hydroperoxides of fatty acid esters and related substances. Only those substances having an −OOH group were found to absorb at 1.46 and 2.07 μ. Dialkyl peroxides and ozonized unsaturated substances had no such maxima in their near infrared spectra although they had high iodometric peroxide values. In a study of the thermal decomposition of methyl oleate hydroperoxide and a study of the autoxidation of methyl linoleate, the intensity of absorption at 1.46 and 2.07 μ paralleled the iodometric peroxide value.

Reactions of fatty materials with oxygen. IV.1 Quantitative determination of functional groups

SummaryConventional analytical procedures employed in oxidation reactions for the quantitative determination of functional groups have been applied to a series of pure compounds as well as to two synthetic mixtures and to methyl oleate hydroperoxide (estimated purity, 70%). In the absence of peroxide and oxirane groups the analytical procedures are reliable. When peroxides are present, unusually high and variable values for carbonyl oxygen are obtained, and the iodine and saponification numbers are generally unreliable. Determination of hydroxyl oxygen is interfered with by large proportions of oxirane compounds but apparently not by peroxides. Determination of acid number and peroxide and oxirane oxygen is reliable in the presence of all the other functional groups investigated. Techniques for the accurate determination of functional groups when peroxide and oxirane groups are present are described.A modified procedure for the determination of carbonyl oxygen is reported.