Abstract
We report the construction and use of a vortex reactor which uses a rapidly rotating cylinder to generate Taylor vortices for continuous flow thermal and photochemical reactions. The reactor is designed to operate under conditions required for vortex generation. The flow pattern of the vortices has been represented using computational fluid dynamics, and the presence of the vortices can be easily visualized by observing streams of bubbles within the reactor. This approach presents certain advantages for reactions with added gases. For reactions with oxygen, the reactor offers an alternative to traditional setups as it efficiently draws in air from the lab without the need specifically to pressurize with oxygen. The rapid mixing generated by the vortices enables rapid mass transfer between the gas and the liquid phases allowing for a high efficiency dissolution of gases. The reactor has been applied to several photochemical reactions involving singlet oxygen (1O2) including the photo-oxidations of α-terpinene and furfuryl alcohol and the photodeborylation of phenyl boronic acid. The rotation speed of the cylinder proved to be key for reaction efficiency, and in the operation we found that the uptake of air was highest at 4000 rpm. The reactor has also been successfully applied to the synthesis of artemisinin, a potent antimalarial compound; and this three-step synthesis involving a Schenk-ene reaction with 1O2, Hock cleavage with H+, and an oxidative cyclization cascade with triplet oxygen (3O2), from dihydroartemisinic acid was carried out as a single process in the vortex reactor.
Highlights
Continuous flow chemistry is an increasingly popular alternative to traditional synthetic batch operations in both academic[1,2] and industrial settings.[3,4] As new developments are made in synthetic methodology, fine chemical, and active pharmaceutical ingredient (API) synthesis, there is parallel interest in translating these methodologies to continuous processes.[5]
The vortex reactor described in this study was built in a vertical orientation such that LED blocks could be more arranged around the outside of the reactor.[61]
The rotation speed is adjusted by a control box connected to the motor; the rotation speed can be set between 50−4000 rpm in both a clockwise and anticlockwise direction
Summary
Continuous flow chemistry is an increasingly popular alternative to traditional synthetic batch operations in both academic[1,2] and industrial settings.[3,4] As new developments are made in synthetic methodology, fine chemical, and active pharmaceutical ingredient (API) synthesis, there is parallel interest in translating these methodologies to continuous processes.[5]. 3000 rpm with minimal further growth observed at 4000 rpm, suggesting oxygen saturation of the solution These results are in agreement with the general conclusions of the modeling, which indicates that the flow regime in the reactor is well above the Taylor number for vortices to occur and that at higher speeds the mixing in the reactor will be more vigorous. We employed the vortex reactor in several photochemical reactions involving oxygen; we predicted that the yield should scale with the rotation speed. To confirm that the faster rotation speeds, i.e., 4000 rpm, were the most efficient for reactions to be carried out, two more photochemical reactions involving singlet oxygen were run in the vortex reactor (Scheme 3). The similarity in yield of 8 at the three concentrations of TFA is potentially indicative of greater mixing and mass transfer properties of the vortex reactor and requires further studying as the vortex reactor could be beneficial for other catalyst driven reactions
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