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

Abstract

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 ॅ‐ॆ 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 舠head to head舡 or 舠head to tail.舡 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 舠head to head舡 vs. 舠head to tail舡 addition.

Chemical reactions involved in the deep‐fat frying of foods: VIII. Characterization of nonvolatile decomposition products of triolein

“…After dehydrogenation, all the trans unsaturation absorption disappeared, and a new absorption at 12.25/1, due to the polysubstituted benzene ring, was developed. Similar observation was reported previously on dehydrogenation of cyclic dimers by Paschke et al (8).…”

“…Chemical and physical analysis of fraction 1B2 indicate; that it was a cyclic dimer with two ester groups and two double bonds-one of the double bonds in the ring and the other in the side chain. Such monocyclic dimers can be formed by Diels-Alder reaction and had been reported previously in oils heated under air (8,14,16). The molecular weight and elemental analysis of this fraction (Table IV) agreed with those of a cyclic dimer of methyl linoleate, which should have a theoretical molecular weight of 588, a theoretical C% of 77.6 and a theoretical H% of 11.7.…”

“…Fraction 1B from silic acid column chromatography was further separated by preparative TLC using a 1 mm thick 20 x 20 cm Silica Gel G plate. Approximately 75 mg of fraction 1B was applied to each plate and elution was done with benzene, according to the method of Paschke et al (8). A portion of the plate was sprayed with 2,7-dichlorofluoresceine and viewed under UV light.…”

Quantitative analysis of cyclic dimer fatty acid content in the dimerization product by proton NMR spectroscopy

“…The synthesis of the dimer acid using the fatty acid in vegetable oil followed previous reports [10,12,26,27]. The clay catalyzed method is well known as a better strategy to synthesize the dimer acids than radical coupling method, which inevitably leads to greater amounts of undesirable contents of trimers and higher oligomers [27].…”

Heat-induced changes during processing and use of edible fats

“…If dimerization occurred by this mechanism, absorption due to conjugated dienes would not be expected, and indeed the dimeric fraction from co-polymerization of 9, 11 and 9, 12 methyl octadecadienoate at 300' in an inert atmosphere (which might be expected to cause polymerization by a Diels-Alder mechanism) showed only a single band for transabsorption at 10.3 pm. Moreover, we were unable to aromatize spot B from deodorized CSO either by the bromination-dehydrobromination procedure of Clingman, Rivett & Sutton (1954) or by heating to 275' with palladium-on-charcoal catalyst, a method used by Paschke, Peterson & Wheeler (1964) to demonstrate the presence of a cyclohexene structure in a Diels-Alder type dimer.…”