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The self-metathesis of methyl 10-undecenoate as well as its cross-metathesis with methyl acrylate was investigated in detail by a systematic variation of the reaction conditions. Unsaturated ;,;-diesters with a chain length of 20 and 12 carbon atoms were thus obtained, respectively. Four different metathesis catalysts were investigated under solvent-free conditions at catalyst loadings ranging from 0.05 mol% to 1 mol% and at temperatures ranging from 30 °C to 90 °C. In the case of the self-metathesis reactions quantitative conversions were obtained with all catalysts, but the second generation metathesis catalysts revealed high amounts of olefin isomerization side reactions at higher temperatures. Using a small quantity of the hydrogen acceptor 1,4-benzoquinone, the isomerization process was almost completely suppressed. Thus, the second generation catalysts allowed for high conversions at very low catalyst loadings. For the cross-metathesis reaction, an interesting temperature and catalyst loading dependent selectivity was observed with the second generation catalysts. Moreover, due to these optimizations, we were able to run these cross-metathesis reactions with a 1:1 ratio of the reactants and low catalysts loadings. This is an improvement over described literature procedures. Thus, we report on the detailed investigation of the described self- and cross- metathesis reactions leading to practical and optimized reaction conditions for the synthesis of unsaturated ;,;-diesters monomers from renewable raw materials in an efficient catalytic manner.
Due to depleting fossil resources, the ever increasing emission of greenhouse gases and toxic waste, as well as the inefficient utilization of our available resources, we have to implement the principles of green chemistry whenever and wherever possible. Plant oils are already the most important renewable resource for the chemical industry. Due to their inherent double-bond functionality, they offer the possibility of being transformed via several very efficient catalytic processes. Especially, new developments in olefin metathesis allow the chemist to directly polymerize or introduce a variety of functional groups to these renewable resources in an efficient manner. Therefore, olefin metathesis with plant-oil-derived fatty acids and their derivatives can contribute to a sustainable development of our future, since this approach has great potential for the substitution of currently used petrochemicals and a variety of value-added chemical intermediates, especially for the polymer industry, can be derived from these resources in a straightforward fashion. This contribution will address and discuss the most recent developments in this field of research.