Zhenghui Wen, Diego Pintossi, Manuel Nuño & Timothy Noël
The Noël Research Group at the University of Amsterdam, in collaboration with Vapourtec, recently demonstrated a strategy to increase the sustainability of continuous-flow photocatalytic hydrogen atom transfer (HAT) transformations. They used organic solvent nanofiltration (OSN) to recycle the catalyst and purify the resulting product. The work, published in Nature Communications, utilised the Vapourtec E-Series system with a Vapourtec UV-150 photochemical reactor.
Tetrabutylammonium decatungstate (TBADT) is an extremely versatile HAT photocatalyst, with applications in a wide range of transformations, such as alkylation, arylation, amination, fluorination, sulfinylation and oxygenation. However, the low quantum yield of the catalyst, as well as difficulties in removing and recycling the catalyst, pose challenges when it comes to carrying out TBADT transformations on an industrial scale. In this paper, the authors utilise OSN to reduce TBADT consumption, increase its turnover number, and lower its concentration in the product solution. Unlike other catalyst recovery strategies, OSN eliminates thermal stress for the recovered catalyst because phase transitions (e.g. evaporation) are avoided.
Continuous photocatalytic alkylation and amination reactions were performed in a Vapourtec UV-150 photochemical reactor. To provide enough photon flux, a 365 nm high-power LED was used as light source. Catalyst recovery was shown to be a viable strategy for scaling up the transformation reaction, with no adverse effects on product yields. Reactions performed with in-line TBADT recovery resulted in product yields that were comparable to those obtained with pristine catalyst.
The UV-150 photochemical reactor offers safe, precise and repeatable photochemistry under continuous flow operation. Furthermore, it eliminates scale-up problems that limit traditional batch photochemistry. These key features made the UV-150 Reactor ideal for use in the demonstration of sustainable continuous-flow photocatalytic HAT transformations.
