Accelerated organic photoreactions in flow microreactors under gas-liquid slug flow conditions using N₂ gas as an unreactive substance

In this work, the [2+2] photocycloaddition of carbonyl compounds with olefins, the Paternò-Büchi-type photoreaction, was performed in a flow microreactor under slug flow (two-phase flow) conditions which are constructed by alternatively introducing nitrogen gas as an unreactive substance into the organic reaction phase. The use of N₂ gas-liquid slug flow conditions permitted the organic photoreactions to proceed more efficiently compared to one-phase flow conditions. A detailed investigation of the influence of the flow mode, the viscosity of the solvents, and the segment length (length of each phase) on the efficiency of the photoreaction was conducted. Based on the results, we concluded that these three factors contribute to the improvement in photoreaction efficiency under slug flow conditions using N₂ gas as an unreactive substance. Furthermore, the use of N₂ gas as an unreactive substance was found to be applicable to other Paternò-Büchi-type photoreactions.