Solid NaOH Slug‐Flow Platform for Enhanced Mass Transfer in Phase‐Transfer Catalysis

ABSTRACT Aqueous NaOH solutions (NaOH(aq)) form immiscible dual phases with organic phases (Org(l)), promoting various heterogeneous reactions. However, the use of excess NaOH and phasetransfer catalyst ‐(PTC) to enhance mass transfer between immiscible phases can drive undesirable side reactions and necessitate complex purification protocols. To overcome the limitations of traditional catalysis performed with NaOH(aq), a continuous‐flow platform was developed using solid NaOH particles (NaOH(s)), Org(l), and fluorinated oil (F‐oil). F‐oil effectively suppresses the precipitation of NaOH(s), thereby enabling stable slug flow. When the system was applied to gem ‐dichloroaziridination and gem ‐dichlorocyclopropanation reactions, lower amounts of NaOH and phase‐transfer catalyst were required compared with the reported NaOH(aq)–Org(l) processes. Additionally, the reaction time was reduced from 15 to 5 min in the gem ‐dichloroaziridination reaction, and excellent yields of 83%–99% were achieved for the gem ‐dichlorocyclopropanation process. These results imply that rapid mass transfer occurs in the NaOH(s)–Org(l)–F‐oil system. Finally, the mechanisms of phase‐transfer catalysis in the NaOH(aq)–Org(l) and NaOH(s)–Org(l) systems were compared. Notably, the proposed process can be operated stably without NaOH precipitation and is expected to be suitable for application in various organic reactions that use NaOH.