D. H. Wheeler

Cis, Trans Isomerism of the Eleostearate Isomers

SummaryThe cis, trans isomers of the conjugated trienes present a difficult problem for complete determination of structure.Several methods of attack have been outlined, and application of two of them have been made to α and β eleostearic acids, α and β licanic acids, and to pseudoeleostearic acid.These results indicate the following structures: α eleostearic: cis-9, trans-11, trans-13 β eleostearic: trans-9, trans-11, trans-13 pseudoeleostearic: trans-10, trans-12, trans-14 α licanic: 4-keto, cis-9, trans-11, trans-13 β licanic: 4-keto, trans-9, trans-11, trans-13

Evidence for hydroperoxide formation in the autoxidation of methyl linolenate

Summary1. The results of chemical, spectral, and distillation analyses on the isolated oxidized fractions of three samples of methyl linolenate autoxidized at 0°C. to peroxide values from 600 to 760 m.e./kg. indicated that about 60% of the products consisted of cis,transconjugated diene methyl octadecatrienoate-monohy-droperoxide.2. A product was isolated from the reduced peroxide concentrates which consisted of about 90% cis,trans- conjugated diene methyl monohydroxyoctadecatrienoate.3. Analytical micromolecular distillation analyses showed that the total oxidized material isolated from samples of autoxidized methyl linolenate contained only about 15% polymeric material under the conditions of autoxidation employed in this study.4. Linolenate was shown to be similar to linoleate in forming a cis,trans-conjugated monomeric monohydroperoxide as a major initial product of autoxidation at 0°C.

Dimer acid structures. the thermal dimer of methyl 10-trans, 12-trans, linoleate

Thermal dimerization of the conjugated 10-trans, 12-trans linoleate (250C, 5 hr) produced a dimer whose structure is shown to be that of the Diels-Alder reaction between two molecules of monomer, with one molecule acting as diene, and either one of the two double bonds of the second molecule acting as dieneophile. This produces four skeletal isomers of a tetrasubstituted (1,2,3,4) cyclohexene structure with α-β unsaturation on one chain. The isomers formed depend on whether the 10 or the 12 double bond acts as dieneophile, and whether the monomers add “head to head” or “head to tail.” Evidences for the structures include chemical analyses, ozonolysis, nuclear magnetic resonance, IR and UV spectrometry and particularly mass spectrometry of the distilled dimer, of the completely hydrogenated dimer, and of the aromatized dimer formed by catalytic dehydrogenation. The hydrogenated dimer can be separated into two components by TLC. These are probably related to “head to head” vs. “head to tail” addition.

Thermal polymerization of unsaturated fatty esters normal methyl linoleate

Summary1.Debromination methyl linoleate has been polymerized at 290° and 300° for varying periods, and analysis has been made for monomer, dimer, trimer, normal, and conjugated linoleate.2.The disappearance of normal linoleate follows a first order reaction rate with values of K=0.10 hr.−1 at 300° and 0.05 hr.−1 at 290°.3.Polymerization of mixtures of normal and conjugated linoleate indicate that dimer may be formed by their reaction with each other.4.The value for K, the first order reaction velocity constant for disappearance of normal linoleate, decreases to a limiting value on dilution with methyl stearate. This limiting value is about one-fourth that obtained on undiluted linoleate.5.The above facts are qualitatively explained by assuming that the mechanism of dimerization of normal linoleate is extensively: N»C relatively slow N+C→D relatively rapid.

Dimer acid structures. The thermal dimer of normal linoleate, methyl 9-cis, 12-cis octadecadienoate

The thermal dimer (290C) of normal methyl linoleate and its hydrogenated form have been examined by mass spectrometry. Parent mass peaks of the hydrogenated dimer show the presence of monocyclic, bicyclic, and tricyclic structures.The monocyclic structure is formed via the conjugation-Diels-Alder mechanism.The bicyclic structure is best explained by an extension of the hydrogen transfer free radical coupling mechanism. The noncyclic dehydrodimer resulting from free radical coupling undergoes a relatively rapid intramolecular cyclization to a bicyclic structure, probably by an interval Diels-Alder reaction. A model noncyclic dehydro-linoleate dimer was shown to give a bicyclic dimer as the predominant structure under thermal dimerization conditions.The tricyclic dimer may result from intramolecular alkylation of the bicyclic structures.

The Unsaturated Fatty Acids of the Alga Chlorella

HE purpose of this paper is to elucidate further the composition of the unsaturated fatty acids of the fresh water alga Chlorella pyrenoidosa grown in pure culture in pilot plant quantities. In 1948 Milner (1) had shown the effect of certain environmental conditions on the yield of Chlorella and its lipid content. An excellent discussion of these results and the economic aspects of the problem appeared in 1951 (2) in this journal. Significant to us was the observation that the cell yield increased with increased nitrogen content of nutrient media but that the cells thus obtained had a low content of fatty acid. These however were highly unsaturated as indicated by iodine numbers of over 160. Restriction of nitrogen in the media gave poor yield of C hlorella, but the fatty acid content of the cells increased tenfold to over 60%. Iodine number of the fatty acids dropped to 125. The one sample which we examined was the low-lipid, high-iodine number type. The sample was obtained from Arthur D. Little Inc. Pilot plant studies at the laboratory were apparently aimed at high cell and high protein yields. Milner found that the fatty acids were almost all of C~s and C~s chain length, tte noted that the iodine number of the C~6 fraction indicated at least 17% of triene fatty acids. Polyunsaturated C~6 fatty acids are relatively rare. Heyes and Sborland (3) have re

Cis, trans isomerization of conjugated linoleates by lodine and light

SummaryInfrared and ultraviolet studies have shown that the three geometrically isomeric types of conjugated linoleates (cis, cis; cis, trans; andtrans, trans) are readily equilibrated by dilute iodine and light. Infrared shows that the equilibrium is at 32%cis, trans and 64%trans, trans isomer. Probably no more than 5–10%, if any,cis, cis isomer exists at equilibrium. The equilibrated mixture can be used to determine total conjugation in mixtures of conjugated geometric isomers by either infrared or ultraviolet absorption.

Dimer acid structures. The dehydro-dimer from methyl oleate and Di-t-butyl peroxide

The dehydro-dimer of methyl oleate was prepared and its structure determined as a model of a non-ring dimer for reference in studying the structure of other fatty dimer acids.The dehydro-dimer of methyl oleate is formed by the action of di-t-butyl peroxide on methyl oleate. The reaction is stoichiometric; one mole of DTBP producing one mole of dehydrodimer and two moles of t-BuOH, when excess methyl oleate is used. The dimer was shown to contain two double bonds, and to be formed by carbon-to-carbon linkages predominantly and equally at the 8, 9, 10 and 11 carbons of the oleate monomer segments.Unsaturation was determined by quantitative hydrogenation and far UV absorption. The points of linkage were established by diagnosis of the positions of the involved tertiary carbons of the hydrogenated dimer 1) by chemical oxidation, and 2) by mass spectrometry. Positions of the double bonds were determined by quantitative ozonization, reductive cleavage followed by gas chromatography of the aldehydes and aldehyde esters. Precise molecular weight of the hydrogenated dimer was determined from the parant mass peak at the expected m/e of 594, confirming the non-ring structure. The unhydrogenated dimer showed a parent m/e peak at the expected value of 590.The bridging at the 8 and 10 positions is explained as being due to coupling of radicals with limiting resonance structures resulting from loss of a hydrogen atom from the methylene at position 8. The bridging at the 9 and 11 positions is explained as due to coupling of limiting resonance structures resulting from loss of a hydrogen atom from the methylene at position 11.Mass spectrometric data indicate that the dimerization is a coupling of the expected free radical forms, rather than attack by an oleate free radical on the double bond of an intact oleate molecule, with subsequent loss of hydrogen to form the second double bond in the dimer.Coupling at the 2-position (α to COOCH3) occurs in not more than 5–10% of the molecules. A small amount of cyclic dimer may be present.

Inter- and intramolecular polymerization in heat-bodied linseed oil

Summary1. Linseed oil has been polymerized at 300° for 1.5, 3, and 6 hours. The polymeric glycerides have been separated from the monomeric glycerides, and the derived methyl esters of each fraction have been analyzed for monomer, dimer, and trimer.2. The monomeric glycerides show very little intradimerization, ranging from 1.3 to 6% of their acid groups, or 3 to 4% of the total polymeric acid groups in the whole oil.3. The polymeric glycerides show appreciable intradimerization, from 10 to 20% of their total polymeric acid groups.4. There is no evidence that a shift from intra- to interdimerization is the major cause of the sudden increase in viscosity in the later stages of thermal polymerization.5. The rapid rise in viscosity is due to the nature of the relationship of viscosity to molecular weight and of molecular weight to extent of reaction in the difunctional polymerization system present.

Dimer acid structures: Cyclic structures of clay catalyzed dimers of normal linoleic acid, 9-cis, 12-cis-Octadecadienoic acid

The clay catalyzed dimer of linoleic acid has been examined by mass spectrometry of the unhydrogenated, the partially hydrogenated and completely hydrogenated dimer. The results show that monocyclic, bicyclic and tricyclic structures are present. Monocyclic structures predominate, bicyclic structures are also prominent, and tricyclic structures are relatively minor. The monocyclic structure is believed to arise from a Diels-Alder type addition reaction. The bicyclic structure may result from a free radical coupling followed by intramolecular ring closure. The monocyclic structure in the unhydrogenated dimer appears to be mostly a benzene ring with saturated and unsaturated side-chains. It probably is formed by hydrogen transfer from the Diels-Alder cyclohexene structure first formed. Little, if any, of the Diels-Alder dimer structure as such is present. The catalytic linoleate dimer has a higher ratio of monocyclic to bicyclic dimer than does the noncatalytic (thermal) dimer made from normal (nonconjugated) linoleate, while the thermal dimer of a conjugatedtrans-trans linoleate is exclusively monocyclic. It is suggested that the clay catalyzes conjugation and hence favors the Diels-Alder reaction, and then catalyzes hydrogen transfer to aromatize the cyclohexene ring.