An oscillatory plug flow photoreactor facilitates semi-heterogeneous dual nickel/carbon nitride photocatalytic C-N couplings

• Published in: Reaction chemistry & engineering 2020-03, Vol.5 (3), p.597-64
• Main Authors: Rosso, Cristian, Gisbertz, Sebastian, Williams, Jason D, Gemoets, Hannes P. L, Debrouwer, Wouter, Pieber, Bartholomäus, Kappe, C. Oliver
• Format: Article
• Language: English
• Subjects: Carbon; Carbon nitride; Chemical reactions; Couplings; Cross coupling; Nickel; Photocatalysis; Photocatalysts; Plug flow; Recyclability; Residence time distribution; Substrates
• ISSN: 2058-9883; 2058-9883
• DOI: 10.1039/d0re00036a

Carbon nitride materials have emerged as an efficient and sustainable class of heterogeneous photocatalysts, particularly when paired with nickel in dual catalytic cross-coupling reactions. Performing these transformations on larger scales using a continuous process is difficult due to the problems associated with handling solids in flow. By combining an oscillatory pump with a microstructured plug flow photoreactor, a stable suspension of the photocatalyst can be maintained, circumventing clogging of the reactor channels. Through careful tuning of the oscillator properties, the residence time distribution (RTD) was optimized, whilst maintaining a stable catalyst suspension. Short residence times (20 min) were achieved using optimized conditions and the recyclability of the photocatalyst was demonstrated over 10 cycles with no loss of activity. During a stable 4.5 hour scale-out demonstration, the model substrate could be isolated on 12 g scale (90% yield, 2.67 g h −1 ). Moreover, the method was applied for the gram scale synthesis of an intermediate of the active pharmaceutical ingredient tetracaine. Dual nickel/photocatalytic C-N couplings are performed with an organic heterogeneous photocatalyst, in an oscillatory plug flow reactor. Reaction was complete in 20 min residence time, enabling 2.7 g h −1 throughput and 10-fold catalyst recycling.