R. A. Awl

Autoxidation of Polyunsaturated Triacylglycerols. III. Synthetic Triacylglycerols ·Containing Linoleate and Linolenate

Four triacylglycerols containing linoleate (L) and linolenate (Ln) in specific positions were synthesized to determine the effect of fatty acid position on their relative rates and products of autoxidation. Analyses by reversedphase high performance liquid chromatography (HPLC) showed that autoxidation of L- and Ln-containing triacylglycerols form monohydroperoxides and hydroperoxy epidioxides as the main products. The peroxyl radicals of internal 12- and 13-mono-hydroperoxides of Ln triacylglycerol components cyclized rapidly and their relative triacylglycerol position had no influence on their rates of cyclization. A good linear relation was obtained between total HPLC peak areas (detected at 235 nm) of the main oxidation products and peroxide values. Reversed phase HPLC analyses thus provide a useful method to estimate oxidation of polyunsaturated triacylglycerols. The ratios of Ln to L mono-hydroperoxides were twice the ratios of Ln to L in the triacylglycerol substrates. Ln triacylglycerol components, therefore, oxidized twice as much as the L components. At 40°C, LnLnL oxidized slightly faster than LnLLn with respective induction periods of 45 and 47 hr. LLnL oxidized faster than LLLn with respective induction periods of 56 and 60 hr. Dilinolenoyl-linoleoylglycerols are, therefore, slightly less stable to oxidation when Ln is in the 1,2- than the 1,3-triacylglycerol position. Dilinoleoyl-linolenoylglycerols are less stable when L is in the 1,3- than the 1,2-triacylglycerol position.

Synthesis and characterization of triacylglycerols containing linoleate and linolenate

Triacylglycerols containing linoleate and linolenate found in vegetable oils were synthesized in gram quantities for oxidation studies. Two acylation methods were examined to convert diacylglycerols or monoacylglycerols to the desired triacylglycerols. Acylations with fatty acid and 1,1′-dicyclohexylcarbodiimide in the presence of 4-dimethylaminopyridine were more rapid, gave triacylglycerols of better isomeric purities and generally better overall yields than the acylations with acid chloride in pyridine. The functional and isomeric purity of the synthetic triacylglycerols were investigated by thin-layer and gas-liquid chromatography of the methyl esters, by lipase hydrolysis, and by13C NMR. Quantitative13C NMR provided a valuable tool to determine isomeric structures of the unsaturated triacylglycerols and complemented the lipase hydrolysis method. The triacylglycerols purified by dry column chromatography were obtained in the following respective percent yields, functional and isomeric purities: LLLn, 92.1, 99.4, 98.1; LLnLn, 91.7, 99.2, 97.4; LLnL, 84.2, 99.7, 98.9; and LnLLn 77.5, 97.8, 99.0 (where L=linoleoyl and Ln=linolenoyl glycerol residues). These synthetic triacylglycerols are valuable models to elucidate the interrelationship of unsaturated fatty acids on the oxidative stability of polyunraturated vegetable oils.

Acetal derivatives of methyl 9(10)-formylstearate: Plasticizers for PVC

Several acetals and an enol ether were prepared from methyl 9(10)-formylstearate and characterized with respect to their thermal, spectroscopic and chromatographic properties. These low-melting (below −80 C) compounds were generally compatible as secondary poly(vinyl chloride) plasticizers and imparted low-temperature properties that were intermediate between those obtained with dioctyl phthalate and dioctyl sebacate.

cis-bond-producing hydrogenation of polyunsaturates catalyzed by polymer-complexed Cr(CO)3 catalysts

Abstractcis-Bond-producing chromium carbonyl catalysts were prepared by complexing conventional or macroreticular, styrene-divinylbenzene copolymers or cross-linked poly (vinyl benzoate) with Cr(CO)6. With one exception, these polymer-Cr(CO)3 catalysts were as selective as the corresponding homogeneous arene-Cr(CO)3 complexes for the formation ofcis-monoenes from methyl sorbate and from conjugated, polyunsaturated fatty esters in cyclohexane. Although several of the polymer catalysts were very active when fresh, they all lost activity on recycling. They could not be recycled more than two times before a marked decrease in activity occurred due to loss of Cr, as shown by elemental analysis and infrared absorption in the recovered catalyst. Thermal analysis indicated instability of the polymer complexes at hydrogenation temperatures.

Cis-Unsaturated fatty acid products by hydrogenation with chromium hexacarbonyl

The use of Cr(CO)6 was investigated to convert polyunsaturated fats intocis unsaturated products. With methyl sorbate, the same order of selectivity for the formation ofcis-3-hexenoate was demonstrated for Cr(CO)6 as for the arene-Cr(CO)3 complexes. With conjugated fatty esters, the stereoselectivity of Cr(CO)6 toward thetrans, trans diene system was particularly high in acetone. However, this solvent was not suitable at elevated temperatures required to hydrogenatecis, trans- andcis, cis-conjugated dienes (175 C) and nonconjugated soybean oil (200 C). Reaction parameters were analyzed statistically to optimize hydrogenation of methyl sorbate and soybean oil. To achieve acceptable oxidative stability, it is necessary to reduce the linolenate constituent of soybean oil below 1–3%. When this is done commercially with conventional heterogenous catalysts, the hydrogenated products contain more than 15%trans unsaturation. By hydrogenating soybean oil with Cr(CO)6 (200 C, 500 psi H2, 1% catalyst in hexane solution), the product contains less than 3% each of linolenate andtrans unsaturation. Recycling of Cr(CO)6 catalyst by sublimation was carried through three hydrogenations of soybean oil, but, about 10% of the chromium was lost in each cycle by decomposition. The hydrogenation mechanism of Cr(CO)6 is compared with that of arene-Cr(CO)3 complexes.

Ethylene and dimethyl acetals from hydroformylated linseed, soybean, and safflower methyl esters as plasticizers for polyvinyl chloride

Dimethyl and ethylene acetals of polyformylated unsaturated fatty esters were prepared, characterized, and evaluated as polyvinyl chloride plasticizers. Dimethyl acetals were prepared with trimethyl orthoformate as a water scavenger in the acid catalyzed acetalation reaction. With ethylene acetals, water was removed azeotropically. Although the acetals prepared were mixtures, molecular distillation gave diacetal esters of 80–90% purity and triacetal esters of 80–95% purity. The samples were characterized by gas liquid chromatography and by IR and NMR spectra. Compared to di-2-ethylhexyl phthalate as a plasticizer for polyvinyl chloride, the triacetal esters (both dimethyl and ethylene acetals) gave less migration and at least equivalent volatility characteristics; the triacetals also gave equivalent compatibility and strength, but somewhat less desirable low temperature and heat stability properties. The diacetal esters also had good compatibility, equivalent strength, somewhat better low temperature, but less desirable migration and volatility properties.

Poly(amide-acetals) and poly(ester-acetals) from polyol acetals of methyl 9(10)-formylstearate: Preparation and physical characterization

Condensation polymers were prepared from the pentaerythritol acetal of methyl 9(10)-formylstearate by reaction with diamines and with ethylene glycol. The glycerol acetal was self-condensed to a poly(ester-acetal) and also copolymerized with caprolactam. A novel step growth, addition polymerization was carried out with ethylene bis[9(10)-methoxymethylenesterate] and pentaerythritol. Physical and spectral (infrared and nuclear magnetic resonance) properties of the various products were determined. In general, the long C8–C9 side chains in the polymers of the pentaerythritol acetal of methyl 9(10)-formylstearate reduced crystallinity to such a degree that, unlike polymers from methyl azelaaldehydate pentaerythritol acetal, they were soluble in the more ordinary solvents, e.g., chloroform and tetrahydrofuran.

Cyclic fatty esters: Hydroperoxides from photosensitized oxidation of methyl 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoate

Abstract Diunsaturated C-18 cyclic fatty acid (CFA) methyl esters were previously synthesized as models of compounds formed in heat-abused vegetable oils. The oxidation of methyl 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoate ( l ) was investigated to prepare oxygenated derivatives of CFA. Hydroperoxides resulting from photosensitized oxidation of l at 0°C in CH 2 Cl 2 solution with methylene blue were separated chromatographically. The hydroperoxides and their hydroxy derivatives were characterized spectrally (IR, UV, 1 H-NMR and 13 C-NMR) and by capillary GC-MS. Components of the hydroperoxide mixture were also identified and quantified by capillary GC-MS without fractionation by HPLC. The main primary oxidation products (85%) were identified as allylic hydroperoxides with the hydroperoxy group located mainly on carbons 9, 12 and 13. The 8-hydroperoxide also expected from the ene addition reaction with singlet oxygen was found only in small amounts. The addition of singlet oxygen is, therefore, regiospecific for C-9 of the chain double bond. Photosensitized oxidation of l provides an effective way of preparing oxygenated CFA derivatives for further analytical and biological evaluations.

Poly(amide-acetals) and poly(ester-acetals) from 9(10)-formylstearic acid as stationary phases for gas chromatography

Diesters from the reaction product of methyl 9(10)-formylstearate with pentaerythritol were condensed with diols and diamines to produce the respective linear poly(ester-acetals) and poly(amide-acetals). Like those derived from methyl azelaaldehydate, these polymers have latent crosslinking sites at the acetal bond and, when crosslinked on an acidic diatomaceous support, form useful stationary phases bonded to the support surface for gas chromatography. Unlike that derived from methyl azelaaldehydate, the linear poly(amide-acetal) from methyl 9(10)-formylstearate is soluble in solvents, so that column packings are more easily prepared and advantage can be taken of the more polar nature of the poly(amide-acetal). The stationary phases derived from the formylstearate have a continuous operating range from at least −60 C to 190–220 C with no detectable amount of phase bleed. Bleeding gradually increases, but the packings are still useful in dual column, compensated systems to 290 C. The poly(amide-acetal) derived from formylstearate has intermediate polarity, whereas the poly(ester-acetal) counterpart is relatively nonpolar. Polarity of the poly(ester-acetal) was greatly increased, whereas that of the poly(amide-acetal) was slightly lowered by adding dimethyl 1,4-cyclohexanedicarboxylate as a comonomer. Compounds of widely different polarities were separated with good resolution and adequate efficiency on these packings during programed or isothermal gas chromatography.

Cr(CO)3-complexed, silica-bonded polyphenylsiloxane as a stereoselective catalyst for hydrogenation of sorbate and soybean methyl esters

A silica-bonded complex was prepared by reacting polyphenylsiloxane with silylated Chromosorb and then with Cr(CO)6. This complex catalyzed stereoselective hydrogenation of sorbate tocis-3-hexenoate. Soybean methyl esters were hydrogenated at 210 C in cyclohexane to form products high incis unsaturation. The recovered catalyst could be recycled once with methyl sorbate. IR showed decreased Cr(CO)3 in the recovered catalysts, and the hydrogenation products contained inactive Cr.