Applications of Immobilized Catalysts in Continuous Flow Processes

Abstract

As part of the dramatic changes associated with automation in pharmaceutical and agrochemical research laboratories, the search for new technologies has become a major topic in the chemical community. Commonly, high-throughput chemistry is still carried out in batches whereas flow-through processes are rather restricted to production processes, despite the fact that the latter concept allows facile automation, reproducibility, safety, and process reliability. Indeed, methods and technologies are missing that allow rapid transfer from the research level to process development. Continuous flow processes are considered as a universal lever to overcome these restrictions and only recently, joint efforts between synthetic and polymer chemists and chemical engineers have resulted in the first continuous flow devices and microreactors which allow rapid preparation of compounds with minimum workup. Importantly, more and more developments combine the use of immobilized reagents and catalysts with the concept of structured continuous flow reactors. Consequently, the present article focuses on this new research field, which is located at the interface of continuous flow processes and solid-phase-bound catalysts.

A continuous-flow electrophile scavenger prepared by a simple grafting procedure

“…While many continuous-flow syntheses take place in empty capillaries or microchip channels, they frequently require the use of reactive solid supports, such as inorganic or enzymatic catalysts [11,12], organic reagents [3,[13][14][15], or scavengers [16,17]. Polymer-supported scavengers are used to remove an unwanted compound from a solution, and their use enables synthetic chemists to exploit the advantages of solution-phase reactions, while still employing polymeric supports for easy workup and purification of the reactions.…”

Immobilisation of the Pyrphos Ligand on Soluble Hyperbranched Supports and Use in Rhodium‐Catalysed Hydrogenation in Ionic Liquids

“…Pyrboc-Rh 20 55 55 Dendr-(Rh) 4 11 46 29 Dendr-(Rh) 8 7 4 3 2 2 Dendr-(Rh) 16 6 activity of these systems decreases with increasing size of the supporting material which is a very similar behaviour to that of the dendritic catalysts. The activity of PEI 0.8 -{Glutaroyl-pyrphos-RhA C H T U N G T R E N N U N G (NBD) BF 4 } n 16, bearing on average 9 active sites, amounts to a TOF of 37 min À1 which is slightly less than that of {G2}-DAB-dendr-{Glutaroyl-pyrphos-RhA C H T U N G T R E N N U N G (NBD) BF 4 } 8 7.…”

“…[7] The recycling of dendritic catalysts is achieved inter alia by using membrane reactors. [8] Unfortunately, in most cases the catalyst performance deteriorated with time. Another possibility is filtration after precipitation of the catalyst.…”

“…The activity of PEI 0.8 -{Glutaroyl-pyrphos-RhA C H T U N G T R E N N U N G (NBD) BF 4 } n 16, bearing on average 9 active sites, amounts to a TOF of 37 min À1 which is slightly less than that of {G2}-DAB-dendr-{Glutaroyl-pyrphos-RhA C H T U N G T R E N N U N G (NBD) BF 4 } 8 7. PEI 2 -{Glutaroyl-pyrphos-RhA C H T U N G T R E N N U N G (NBD) BF 4 } 17 (26 end groups) exhibits a significantly higher activity (31 min…”

Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

“…[172][173][174][175][176][177][178][179][180][181] For example, their separation of catalyst from reaction products is easy and their potentiality for consecutive recycling steps is accessible for green chemical process. In addition, immobilization on solid phase often causes stabilization of sensitive catalyst.…”