simple method of preparation of methyl trans-10,cis-12- and cis-9,trans-11-octadecadienoates from methyl linoleate

• Published in: Journal of the American Oil Chemists' Society 1998, Vol.75 (12), p.1749-1755
• Main Authors: Berdeaux, O, Voinot, L, Angioni, E, Juanéda, P, Sébédio, J. L
• Format: Article
• Language: English
• Subjects: 4,4‐dimethyloxazoline derivative; Aliphatic compounds; Chemistry; conjugated linoleic acid; Conjugated linoleic acid (CLA); Exact sciences and technology; GC‐FTIR; GC‐MS; hydrazine reduction; isomerization; isomers; Life Sciences; linoleic acid; low‐temperature crystallization; NMR; Organic chemistry; Preparations and properties; silver nitrate‐thin layer chromatography
• ISSN: 0003-021X; 1558-9331
• DOI: 10.1007/s11746-998-0327-x

Pure conjugated isomers of linoleic acid were prepared on a large scale by alkali-isomerization of purified methyl linoleate. The methyl esters of alkali-isomerized linoleic acid contained mainly the methyl cis-9,trans-11- and trans-10,cis-12-octadecadienoates (44 and 47%, respectively). These two isomers were then separated and purified by a series of low-temperature crystallizations from acetone. The isomeric purity obtained for the cis-9,trans-11-octadecadienoate isomer was >90% and that of the trans-10,cis-12-octadecadienoate isomer was 89 to 97%. The isolated yield of the two isomers corresponded to 18 and 25.7%, respectively, of the starting material. The structure of the two isomers was confirmed using partial hydrazine reduction, silver nitrate-thin-layer chromatography of the resulting monoenes and gas chromatography coupled with mass spectrometry of the 4,4-dimethyloxazoline derivatives. Fourier transform infrared spectroscopy of the monoenes gave the confirmation of the geometry of each double bond.