Investigation of the effect of microflow reactor diameter on condensation reactions in l-proline-immobilized polymer monoliths

The effect of monolith structure and monolith reactor inner diameter on the residence time distribution (RTD), and the relationship between RTD and the catalytic efficiency of the asymmetric aldol addition reaction between p-nitrobenzaldehyde and cyclohexanone were examined. A monolith column containing L-proline as a catalyst was prepared using poly(ethylene glycol) (PEG) as the porogen. The monolith column prepared with PEG with a molecular weight of 6000 Da displayed a narrow pore size distribution and showed a controlled RTD. The performance of monolith reactors with different inner diameters (micro- and millireactors, 0.53 and 4.00 mm) was compared: the microreactor displayed a narrower RTD and a higher turnover number for the asymmetric aldol addition reaction than the millireactor. The different linear flow velocities in the microreactor did not affect the catalytic reaction efficiency and enantioselectivity, demonstrating that the RTDs can be controlled regardless of the flow velocity.