Anna CHROBOK1, Natalia BARTECZKO1, Alina BRZECZEK-SZAFRAN1
1Silesian University of Technology, Gliwice, Poland
Here we report, the designing of task specific ionic liquids (ILs) dedicated for catalysis in ruthenium-based ring?closing metathesis. This reaction has opened new industrial routes to value-added molecules, especially for pharmaceuticals, agrochemicals, flavors and fragrances, and polymers. To further increase the overall sustainability of the process, there is a considerable interest in a replacing toxic solvents with greener alternatives. Despite two decades of research on metathesis in water, the use of this most benign solvent is still challenging. Low catalyst loadings with high-yielding processes are further requirements for economic and manufacturing-ready olefin metathesis processes. In pharmaceutical applications it is desirable to work with very low ruthenium loadings, with the content in the final active pharmaceutical ingredient less than 10 ppm.
In this work, to address the challenges and seeking for the best recycling strategy, catalytic reactions were carried out homogenously in water with ILs used as surfactants, and heterogeneously, with ILs immobilized on the surface on carbon nanotubes.
In the first approach, to improve the separation of residual ruthenium from the product, we propose a new method for effective aqueous olefin metathesis (RCM of diallylmalonate) with an HG2 catalyst and D-glucose-based ILs as sustainable surfactants. The quantity, structure, and concentration of D-glucose-based ILs were optimized to obtain high product yield and purity. HG2 was used in truly catalytic amounts (0.2 mol%) at 25 °C, enabling the synthesis of product in 180 min. High conversion (88%) and selectivity (100%), with low Ru content in the product, were obtained. Five cycles of a model metathesis reaction could be conducted without the loss of surfactant activity and with low Ru content in the product.
In the second approach two strategies toward the synthesis of heterogeneous ruthenium-catalyst were explored using supported ionic liquid phase (SILP) and supported ionic liquid-like phase (SILLP) with multi-walled carbon nanotube (MWCNT) as a support. Despite lower loading of the IL, the loading of the Ru-catalyst immobilized in the SILLP material was higher. The SILLP catalyst showed enhanced stability in the RCM reaction, giving product with high yield >98.2% in 5 reaction cycles. We found that both the length of the alkyl chain at the IL as well as the anion attached influenced the immobilization and leaching of the Ru-catalyst so as the overall performance of the composite. A comparative study with Ru-complexes immobilized on pristine MWCNTs was conducted to examine the importance of the IL-phase for the construction efficient catalytic system.
In summary, ionic liquid-based strategies are presented as a generic approach to tailoring catalysts as in industrially-relevant reactions to generate both environmentally and economically sustainable processes.
This work was financed by the National Science Centre, Poland (grant no. UMO-2020/39/B/ST8/00693).
1. K. Grela, Olefin Metathesis: Theory and Practice, John Wiley & Sons, Inc. Hoboken, New Jersey, 2014, 608.
2. K. Erfurt, I. Wandzik, K. Walczak, K. Matuszek, A. Chrobok, Green Chem., 2014, 16, 3508.
3. A. Brzeczek-Szafran, K. Erfurt, A. Blacha-Grzechnik, M. Krzywiecki, S. Boncel, A. Chrobok, ACS Sustainable Chem. Eng., 2019, 7, 19880.