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

Abstract

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 all-t-butyl peroxide on methyl oleate. The reaction is stoiehiometric; 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-tocarbon linkages predominantly and equally at the 8, 9, 10 and 11 carbons of the oleate monomer segments.l~nsaturation was determined by quantitative hydrogenation and far I?V 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, reduetive cleavage followed by gas chromatography of the aldehydes and aldehyde esters. Precise molecular weight of the hydrogenated dimer was determined from the parent 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 ~alue 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 (a to COOCHa) occurs in not more than 5-10% of the molecules. A small amount of cyclic dimer may be present.

Isolation and characterization of dinners formed in used soybean oil

“…4) by gas chromatography gave two unresolved peaks of RRT 2.23 and 2.63. The GC-MS analysis data of the first peak is presented in Table 4 and they are similar to those obtained for the synthetic dehydrodimer of methyl oleate described by Paschke et al (24). In the EI spectrum the parent ion at m/e 590 was not observed, probably because there are many C=C bonds where cleavage could occur.…”

Comparative study of the autoxidation of TAG containing conjugated and nonconjugated C18 PUFA

“…This peak was identified as the dimer of each bitter gourd-ME. Dimeric triolein was used as a standard (14,15). Triolein was obtained from Nu-Chek-Prep (Elysian, MN).…”

Alterações dos óleos de palma e de soja em fritura descontínua de batatas

“…Verificou-se nas duas tabelas, que os polímeros foram formados e que este resultado já era esperado uma vez que a dimerização e polimerização dos ácidos graxos ocorrem fundamentalmente na presença destes ácidos insaturados, mono e poliinsaturados, na ausência de oxigênio a altas temperaturas e na presença de oxigênio a baixas e altas temperaturas (COWAN, 1962;FORMO et al, 1979;FRANKEL, 1991;FRANKEL, 1998;JORGE, 1996;PASCHKE et al, 1964; WHEELER; MILUN; Tabela 4. Composição, g.100 g -1 do óleo, dos ácidos graxos em amostras de óleo de palma, antes da utilização no experimento (inicial) e provenientes de experimentos de frituras descontínuas de batatas com o óleo aquecido por distintos períodos de tempo.…”