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Fatty Acid Methyl Esters with Two Vicinal Alkylthio Side Chains and Their NMR Characterization

Knothe, Gerhard, Steidley, Kevin R.
The journal of the American Oil Chemists' Society 2017 v.94 no.4 pp. 537-549
alkenes, carbon, catalysts, diastereomers, dimethyl disulfide, fatty acid methyl esters, iodine, mass spectrometry, monounsaturated fatty acids, nuclear magnetic resonance spectroscopy, protons
The addition reaction of dimethyl disulfide (DMDS) to double bonds in alkenes and monounsaturated fatty acid esters in the presence of iodine or other catalysts to give bis(methylthio) derivatives has largely served analytical purposes in mass spectrometry with scattered reports on the addition of other disulfides to alkenes also existing. In this work, this iodine-catalyzed reaction was expanded to include the addition of other dialkyl disulfides (RSSR; R=ethyl, propyl, butyl, iso-propyl) besides DMDS to the double bonds in monounsaturated fatty acid methyl esters with 16, 18, 20, and 22 carbon atoms in the fatty acid chain to give the corresponding methyl 1,2-bis(alkylthio)alkanoates. The products are obtained in high to moderate yield after a facile purification procedure and are analytically characterized not only by mass spectrometry but also ¹H and ¹³C NMR. The threo and erythro diastereomers obtained from (Z) and (E) fatty acid methyl esters, respectively, can be easily distinguished by the NMR shifts of the protons and carbons in and close to the 1,2-bis(alkylthio) moiety. Various other effects in the NMR spectra are discussed. The 1,2-bis(alkylthio) derivatives of a symmetrical alkene, 7(E)-tetradecene, serve to confirm the NMR assignments besides NMR techniques such as 2D correlations and DEPT. The compounds may show properties of interest for various applications.