Title: Size-enlargement enhanced catalytic methodology for sustainable synthesis

Abstract:

Among organic transformations, catalyst assisted reactions are the most commonly performed processes. While in case of heterogeneous catalysts they are unambiguous, for homogeneous systems the laborious product purification and recycling of the high value catalysts still call for the design of more flexible and sustainable strategies. The membrane assisted recovery of homogeneous catalysts is feasible with low energy consumption, and its scale-up and implementation in continuous and hybrid processing are relatively straightforward. Still, the efficiency of catalyst separation depends on the absolute catalyst retention by the membrane and on the molecular weight gap between the catalyst and the other components (starting materials, product, side-product). Thus, the size-enlargement of the catalyst is usually required to achieve efficient retention and to avoid catalyst leaching in the membrane separation. This work presents nanofiltration enabled catalyst recycling methodology where the size-enlargement of the catalyst is achieved through covalent anchoring. Cinchona alkaloid based hydrogen bond donor organocatalysts (thiourea and squaramide) were attached to permethyl-β-cyclodextrin and applied in Michael reaction. For the asymmetric addition both alternative and conventional solvents were screened (up to 99% ee), and the enantioselectivities were correlated with the Kamlet-Taft parameters of the solvents.  Continuous organocatalysis was performed in a coiled tube flow reactor connected to a membrane filtration unit (80 g L−1 h−1), allowing complete recovery of the catalyst and 50% solvent recycling. Further development of this catalysis-separation methodology could broaden the alternatives and facilitate the efficient production of enantiopure chemicals. The size-enlarged catalyst recovery procedure has the potential to be successfully applied in other catalytic fields as well, like electro-, or photocatalysis.

Biography:

Péter Kisszékelyi is a fourth year PhD student at the George Oláh Doctoral School, Budapest University of Technology and Economics, Hungary. He works under the supervision of Dr. József Kupai in the Organocatalysis Research Group (www.kupaigroup.com) at the Department of Organic Chemistry and Technology. His research focuses on cinchona-based recyclable organocatalyst design and other sustainable catalytic methodologies.