DETAILED STUDIES OF SELF- AND CROSS-METATHESIS REACTIONS OF FATTY ACID METHYL ESTERS

Self- and cross-metathesis[1] reactions with oleochemicals offer the potential to obtain value added chemical intermediates from plant oil renewable resources.[2,3] Here, the self-metathesis (SM) of methyl undec-10-enoate (1) as well as its cross-metathesis (CM) with methyl acrylate (MA) was investigated in detail by systematically varying the applied reaction conditions. The thus resulting unsaturated α,ω-diesters with a chainlength of 20 and 11 carbon atoms, respectively, have a large potential from the synthesis of polyesters as well as polyamides from plant oil renewable resources.[4] Hence, four different metathesis catalysts were investigated under solvent-free conditions at catalyst loadings ranging from 0.1 to 1 mol % and at temperatures ranging from 30 to 70 °C. All reactions were followed by GC and/or GC-MS in order to evaluate the conversion as well as the selectivity of the reactions. In the case of the SM reactions good to excellent conversions were obtained with all catalysts, but the second generation metathesis catalysts revealed high amounts of olefin isomerisation side-reactions.[5] In general, these SM reactions were highly reproducible, but at low catalyst loadings and low temperatures sometimes large variations in the observed conversions were obtained. This was not the case for the investigated CM reactions. Here, also good conversions and CM yields were observed, if second generation metathesis catalysts were applied. Quite interestingly, these reactions showed a better reproducibility and the olefin isomerisation of the also observed SM products was almost completely suppressed. Moreover, due to these optimizations we were able to run these CM reactions with a 1:1 ratio of the reactants and low catalysts loadings, which is an improvement over described literature procedures.[3]
Thus, in summary, we report on the detailed investigation of the described SM as well as CM reactions leading to new and optimized reaction conditions for the productions of unsaturated α,ω-diester monomers from renewable raw materials.

References:
[1] R. H. Grubbs, Angew. Chem. Int. Ed. 2006, 45, 3760.
[2] A. Rybak, P. A. Fokou, M. A. R. Meier, Eur. J. Lipid Sci. Technol. 2008, 110, 797.
[3] A. Rybak, M. A. R. Meier, Green Chem. 2007, 9, 1356.
[4] M. A. R. Meier, J. O. Metzger, U. S. Schubert, Chem. Soc. Rev. 2007, 36, 1788.
[5] M. Arisawa, Y. Terada, K. Takahashi, M. Nakagawa, A. Nishida, Chem. Rec. 2007, 7, 238.