Fatty acid methyl esters with two vicinal alkylthio side chains and their NMR characterization

Authors: Knothe, Gerhard; Steidley, Kevin

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2017
Publication Date: 2/25/2017
Publication URL: https://handle.nal.usda.gov/10113/5755335
Citation: Knothe, G., Steidley, K.R. 2017. Fatty acid methyl esters with two vicinal alkylthio side chains and their NMR characterization. Journal of the American Oil Chemists' Society. 94:537-549.

Interpretive Summary: The production of new materials from renewable resources is essential to replace products made from non-renewable petroleum. In this work, new materials containing new structure elements with sulfur were made from so-called fatty acid methyl esters which in turn are produced from vegetable or other plant oils. Since it is important to know how to analyze these new materials, this work also describes analyses by a method known as nuclear magnetic resonance (NMR). The new materials show interesting properties for various applications.

Technical Abstract: 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.