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.

We report the development of a scalable continuous Taylor vortex reactor for both UV and visible photochemistry. This builds on our recent report (Org. Process Res. Dev. 2017, 21, 1042) detailing a new approach to continuous visible photochemistry. Here we expand this by showing that our approach can also be applied to UV photochemistry and that either UV or visible photochemistry can be scaled-up using our design. We have achieved scale-up in productivity of over 300× with a visible light photo-oxidation that requires oxygen gas and 10× with a UV induced [2+2] cycloaddition obtaining scales of up to 7.45 kg day-1 for the latter. Furthermore, we demonstrate that oxygen is efficiently taken up in to the reactions of singlet O2 and, for the examples examined, that near-stoichiometric quantities of oxygen can be used with little loss of reactor productivity. Furthermore, our design should scalable to substantially larger size as well as having the potential for scaling-out with reactors in parallel.

Safety warning: Any experiment involving flammable organic solvents and air or pure oxygen is potentially hazardous, especially when partially contained, as is the case of the flask of our reactor. We took the following precautions and encountered no problems but we stress the need for readers to make safety assessments for their own experiments as peripheral circumstances may be different from ours. All experiments were carried out in a fume hood or ventilated enclosure with adequate ventilation and the front lowered. Any obvious sources of ignition were removed. Oxygen was fed from a cylinder fitted with a compliant regulator and was delivered at a maintained pressure of 1 bar using a mass flow controller compatible with oxygen. The equipment was maintained and cleaned free of grease at all times to prevent any incompatibilities with oxygen. Temperatures were kept at ambient. When working above the solvent flash point and LOC, care must be taken to ensure that all possible risks have been considered. Appropriate safeguards and suitable safety measures must be implemented.

Interaction of p‐tert‐butylcalix[8]areneH8 (L8H8) with [NaVO(OtBu)4] (formed in situ from VOCl3) afforded the complex [Na(NCMe)5][(VO)2L8H]⋅4 MeCN (1⋅4 MeCN). Increasing [NaVO(OtBu)4] to 4 equiv led to [Na(NCMe)6]2[(Na(VO)4L8)(Na(NCMe))3]2⋅10 MeCN (2⋅10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)3] with L8H8 afforded the alkali‐metal‐free complex [(VO)4L8(μ3‐O)2] (3); solvates 3⋅3 MeCN and 3⋅3 CH2Cl2 were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert‐butoxide was added to L8H8 and then treated with 2 equiv of VOCl3; crystallisation afforded [(VO2)2Li6[L8](thf)2(OtBu)2(Et2O)2]⋅Et2O (4⋅Et2O). Upon extraction into acetonitrile, [Li(NCMe)4][(VO)2L8H]⋅8 MeCN (5⋅8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)3] and [V(Np‐tolyl)(OtBu)3] and L8H8, afforded [tBuNH3][{V(p‐tolylN)}2L8H]⋅3 1/2 MeCN (6⋅3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1, 3, and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)−1 were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl2]. For copolymerisation, incorporation of propylene was 7.1–10.9 mol % (compare 10 mol % for [VO(OEt)Cl2]), although catalytic activities were lower than [VO(OEt)Cl2].

We report the development of a small footprint continuous electrochemical Taylor vortex reactor capable of processing kilogram quantities of material per day. This report builds upon our previous development of a scalable photochemical Taylor vortex reactor (Org. Process Res. Dev. 2017, 21, 1042; 2020, 24, 201–206). It describes a static and rotating electrode system that allows for enhanced mixing within the annular gap between the electrodes. We demonstrate that the size of the annular gap and the rotation speed of the electrode are important for both conversion of the substrate and selectivity of the product exemplified using the methoxylation of N-formylpyrrolidine. The employment of a cooling jacket was necessary for scaling the reaction in order to manage the heat generated by electrodes at higher currents (up to 30 A, >270 mA cm–2) allowing multimole productivity per day of methoxylation product to be achieved. The electrochemical oxidation of thioanisole was also studied, and it was demonstrated that the reactor has the performance to produce up to 400 g day–1 of either of the corresponding sulfoxide or sulfone while maintaining a very high reaction selectivity (>97%) to the desired product. This development completes a suite of vortex reactor designs that can be used for photo-, thermal-, or electrochemistry, all of which decouple residence time from mixing. This opens up the possibility of performing continuous multistep reactions at scale with flexibility in optimizing processes.

A novel annular flow reactor for UV photochemistry.

We report the use of a simple rotary evaporator as a semi-continuous UV photochemical reactor. By generation of a thin film from the rotation of a flask, better light penetration is achieved, and in this work we used high-power Hg lamps to enable the direct irradiation of molecules with UV light. The intramolecular [2 + 2] photocycloaddition of Cookson’s dione and the intermolecular [2 + 2] photocycloaddition of maleimide with 1-hexyne were used as test reactions to examine the effectiveness of this reactor. High productivities, equivalent to 210 g h–1, were obtained for the simple intramolecular reaction, demonstrating the scalability of the reactor. The effects of flask size, reaction mixture volume, and use of borosilicate or quartz glassware were also investigated.

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