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An asymmetric Paternò–Büchi-type photoreaction between 2,3-dimethyl-2-butene and benzoylformic acid ester with a chiral menthyl auxiliary was studied in a continuous-flow microcapillary reactor. The fluorinated ethylene propylene (FEP) microcapillary reactor using normal one-layer flow mode gave oxetane products with better efficiency than the batch system. In addition, the slug flow mode in microcapillary reactor using inactive reagent, N2 gas or H2O, improved the reaction efficiency dramatically because of synergistic light dispersion, stirring and thin layer film effects. The reaction efficiencies under each condition were discussed as energy efficiencies calculated from reactors' parameters.
Carbon dioxide chemistry is an area of continuing growth in recent times, due to socioeconomic and environmental reasons. Several methods have now been reported for obtaining N-methylation on primary and secondary amines directly from CO2. We have translated in two microfluidic setups (Slug Flow [SF] and Tube-in-Tube [TiT]) a ruthenium (Ru)-catalyzed process previously reported using a pressure vessel. Here, we demonstrate how the SF approach is more efficient but requires more input to reach a steady state, while the TiT system is less efficient but more tuneable.We have tested these processes on three model amines and two radiopharmaceutical precursors that are routinely used in 11C chemistry. The microfluidic processes tested are also potentially more efficient than the pressure vessel counterpart, in terms of amount of Ru catalyst needed (1% vs. 10%) and projected reaction completion time.
Abstract
The diastereoselective [2+2] photocycloaddition of ethylene to a chiral cyclohexenone was studied in a continuous flow microcapillary reactor. In all cases examined, the microcapillary reactor gave higher conversions and selectivity than the batch system, even after shorter irradiation times. These findings were explained by the superior temperature control, favorable light penetration, and generation of a gas–liquid slug flow with improved mass transfer in the microreactor.
Based on previous work studying complex microreactors, it was desired to further improve the mixing efficiency by varying the mixing unit design for fast liquid—liquid reactions. Different flow regimes were studied, including slug flow, parallel flow, and drop flow. The two-phase hydrolysis of 4-nitrophenyl acetate in sodium hydroxide solution was used to evaluate the overall volumetric mass transfer coefficients (K org a) as a function of the average rate of energy dissipation (ε) for each microreactor design and all flow regimes. The liquid—liquid systems investigated used n-butanol or toluene as the organic phase solvent and a 0.5-M NaOH aqueous solution. The use of surfactant was also investigated with the toluene—water system. All microreactor geometry designs were based on contraction—expansion repeating units with asymmetric obstacles to aid the breakup of slugs and desynchronize the recombination of split streams. The investigated designs were chosen to avoid the formation of the parallel flow regime, contrary to curvature-based mixing-unit designs. The microreactor design can then be optimized to reduce the ε required to reach drop flow, since K org a has been found to be constant at equal ε for a given solvent system in this flow regime, regardless of the reactor selection. Additionally, the “3/7th” scaleup rule was applied and confirmed with the LL-Triangle mixer. It was found that, for low interfacial-tension systems (i.e., n-butanol—water), the onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers.
Journal 2012 , 179 , 330 – 337 . “ Direct carbonylation of nitrobenzene to phenylisocyanate using gas-liquid slug flow in microchannel ” Takebayashi , Y. , Sue , K. , Yoda , S. , Furuya , T. , Mae , K. Chemical
, T. Adschiri * Chemical Engineering Science 2013 , 85 , 50 – 54 . “ Slug flow of ionic liquids in capillary microcontactors: fluid dynamic intensification for solvent extraction ” F. Scheiff ,* A. Holbach , D. W. Agar
-dispersion process in constrictive microchannels ” X. Wang *, K. Wang , A. Riaud , X. Wang , G. Luo * Chemical Engineering Journal 2014 , 254 , 443 – 451 . “ An online method to measure mass transfer of slug flow in a microchannel
transfer catalyzed Wittig reaction in the microtube reactor under liquid–liquid slug-flow pattern ” E. Sinkovec , M. Krajnc Organic Process Research & Development 2011 , 15 , 817 – 823 . “ Ozonolysis in Flow Using Capillary
production of ethyl pyruvate using gas-liquid slug flow in microchannel ” T. Yasukawa , W. Ninomiya , K. Ooyachi , N. Aoki , K. Mae Chemical Engineering Journal 2011 , 167 , 527 – 530 . “Novel Process Window for the safe and
, Y. Zhang , J.-l. Shi , Y.-x. Song , Z. Yao Industrial & Engineering Chemistry Research 2015 , 54 , 7565 – 7570 “ Enzymatic fatty acid hydroxylation in a liquid–liquid slug flow microreactor ” I. Iliuta , A. Garnier
