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  • Continuous-flow photochemical carbene transfer reactions
    J. Flow Chem. (IF 2.277) Pub Date : 2019-12-20
    Claire Empel, Rene M. Koenigs

    Abstract Photochemistry constitutes an important tool to conduct environmentally benign and efficient transformations in organic synthesis. Conventional batch transformations are limited in productivity and scale due to Beer’s law, which can be easily overcome using flow chemistry approaches. Herein, we report on the continuous-flow photolysis of aryl diazoacetates using a glass microreactor and blue LEDs. Following this methodology, we were able to demonstrate the application of continuous-flow chemistry in photochemical cyclopropanation and rearrangement reactions and demonstrate the scalability of photochemical carbene transfer reactions.

  • Development of a multistep reaction cascade for the synthesis of a sacubitril precursor in continuous flow
    J. Flow Chem. (IF 2.277) Pub Date : 2019-12-03
    Katharina Hiebler, Carina Dertnig, Sebastian Soritz, Manuel C. Maier, Theresa R. Hörmann, Bianca Grabner, Heidrun Gruber-Woelfler

    The active pharmaceutical ingredient sacubitril acts as a neprilysin inhibitor in the body and is administered to patients suffering from high blood pressure and chronic heart failure. In this paper, we report the development of a three-step setup for the synthesis of an advanced sacubitril precursor in continuous flow. The key transformation of our cascade is a Suzuki-Miyaura coupling facilitated by a heterogeneous palladium catalyst. Its implementation in a packed-bed reactor and the application of continuous flow methodologies allow intensification of the cross-coupling reaction compared to batch processing. The subsequent steps for the synthesis of the target molecule involve Boc-deprotection as well as N-succinylation, which have been optimized using the statistical “Design of Experiments” (DoE) approach. In this way, the individual as well as interactive effects of selected parameters on the output of the reactions could be investigated very efficiently. The consecutive performance of the three reaction steps using an integrated setup enabled the synthesis of a late-stage sacubitril precursor in continuous flow with 81% overall yield.

  • A microfluidic platform for screening and optimization of organic reactions in droplets
    J. Flow Chem. (IF 2.277) Pub Date : 2019-12-02
    Pawel Jankowski, Rafał Kutaszewicz, Dominika Ogończyk, Piotr Garstecki

    We report an automated microfluidic system for screening and optimization of chemical reactions performed inside microliter liquid droplets. The system offers precise control over generation, merging and flow of droplet “micro-reactors” and over reaction conditions, including the volumes of the reagents, temperature and time. The high level of control coupled with the ability to quickly screen multiple reaction conditions allow us to thoroughly monitor the impact of input parameters on the yield of the reaction. In addition, the reagent consumption is kept remarkably low. As an exemplary use of our system we demonstrate a comprehensive study of acid-catalyzed (para-toluenesulfonic acid, p-TsOH) model imine formation (condensation of ortho-nitrobenzaldehyde and phenylethylamine) in an organic solvent (ethanol). By use of novel screening methods described herein, we unfold that the acid-catalyzed model imine formation in the organic medium can be considered as an assembly of acid-mediated and non-catalyzed reactions, both of which accelerate with increasing temperature.

  • Stereoselective synthesis of optical isomers of ethyl 4-chloro-3-hydroxybutyrate in a microfluidic chip reactor
    J. Flow Chem. (IF 2.277) Pub Date : 2019-07-06
    Petr Kluson, Petr Stavarek, Vera Penkavova, Hana Vychodilova, Stanislav Hejda, Natalie Jaklova, Petra Curinova

    Ethyl (R)-4-chloro-3-hydroxybutyrate ((R)-CHBE) is a versatile fine chemistry intermediate. It is used as a precursor in the synthesis of several pharmacologically valuable products, including L-carnitine. It is usually produced by means of stereoselective biotechnology methods in enzymatic reactions. An alternative preparation strategy towards ethyl (R)-4-chloro-3-hydroxybutyrate is based on the asymmetric hydrogenation of ethyl 4-chloro-acetoacetate (ECAA) to the optically pure product ((R)-CHBE) over ((S)-Ru-BINAP) catalytic complex. The reaction conditions were optimised first using (R)-Ru-BINAP yielding the (S)-CHBE isomer. All reactions were performed under continuous regime in a microfluidic chip reactor. Three different solvent phases were employed. The methanol/water phase, the ethanol/water phase, and the [N8,222][Tf2N]/methanol/water phase. The attained conversions were total in all cases already at 408 K. The parameter of enantioselectivity ee was 99.4% towards the (S)-CHBE for the system in which (R)-Ru-BINAP was accommodated in [N8,222][Tf2N]/methanol/water phase. In the case of methanol/water experiment the ee parameter reached 92.5%. For ethanol/water ee was 91.8%. The (R)-CHBE isomer over (S)-Ru-BINAP was obtained with ee = 99.3% in the [N8,222][Tf2N]/methanol/water phase at 408 K. For the reactions leading to (S)-CHBE apparent activation energies were evaluated. They were similar for MeOH/water and EtOH/water (110.5 and 110.7 kJ.mol−1). The apparent activation energies corresponding with the [N8,222][Tf2N]/MeOH/water system were much higher (of about 90 kJ.mol−1) reaching the level of 200 kJ.mol−1. The impact of the molecular structure of the main reactant was negligible as appeared from the comparison with hydrogenation of methylacetoacetate (MAA, ~ 200 kJ.mol−1). The effect of the presence of the [N8,222][Tf2N] ionic liquid on the sum of the activation energy dominated. The effectiveness of the enantioselective synthesis was additionally assessed by nuclear magnetic resonance employing the method of enantioselective complexation of the chiral compound with a chiral solvating agent.

  • Continuous synthesis of tetraethyl thiuram disulfide with CO 2 as acid agent in a gas-liquid microdispersion system
    J. Flow Chem. (IF 2.277) Pub Date : 2019-08-27
    JiaYu Hu, Jiaxin Tian, Kai Wang, Jian Deng, Guangsheng Luo

    Herein, a continuous synthetic method of tetraethyl thiuram disulfide (TETD) with CO2 as a weak acid reagent in a gas-liquid microdispersion reaction system has been described. A microdispersion reaction system comprising two microreactors for CO2 absorption and diethyldithiocarbamate acid subsequent oxidation reaction was developed. In the first step, the main products of absorption and oxidation reactions were identified. Next, the yield of TETD and selectivity of sodium diethyldithiocarbamate under different flow rates of raw materials, amount of CO2, aging effect, and pressure in the microreaction system were determined. The yield reached 89.03% based on 60% H2O2 dosage and the selectivity was 92.86% in less than 3 min of residence time, which was more than 30 min in the batch process. The space time yield in the microreaction system was ~20 times of that achieved in the batch process. The study provides a new successful reference for replacing batch synthesis by a continuous process using a microreaction system.

  • The creation and testing of a fully continuous tubular crystallization device suited for incorporation into flow chemistry setups
    J. Flow Chem. (IF 2.277) Pub Date : 2019-08-22
    Bart Rimez, Jean Septavaux, Robin Debuysschère, Benoit Scheid

    The study presents the use of a continuous crystallization device that can be directly incorporated into flow chemistry setups. Inside this device spontaneous nucleation and growth of organic molecules are controlled and maintained, using Aspirin as model molecule. The identification of the optimal crystallization scenario is discussed in view of the chemical stability of Aspirin and based on the determination of the solubility and the metastable zone width corresponding to the presented experimental setups. Physicochemical analyses combined with heat transfer modeling of the solution whilst flowing through a capillary placed inside a thermostated water bath provide the desired cooling profile and hence the degree of supersaturation along the system. The crystalline quality and stability of the crystalline output is evidenced for two different pump setups having distinguished flow patterns to show the independence on the flow stability, an important parameter for the success rate of the complete reaction scheme and in the perspective of operation scale-up. Reproducible output of material with narrow size distributions is obtained throughout all experiments.

  • Development of a continuous flow synthesis of propranolol: tackling a competitive side reaction
    J. Flow Chem. (IF 2.277) Pub Date : 2019-08-14
    Sonia De Angelis, Paolo Celestini, Rosa Purgatorio, Leonardo Degennaro, Gabriele Rebuzzini, Renzo Luisi, Claudia Carlucci

    This work reports the preparation of propranolol according to a flow process. Propranolol has been prepared paying attention to tackle the formation of the by-product tertiary amine, resulting from an additional ring opening of the starting epoxide. Remarkably, the use of catalytic amount of water resulted beneficial for the yield and purity of the desired propranolol, and to substantially reducing the amount of tertiary amine byproduct. The high concentration of the solutions allowed for a productivity of several grams/h.

  • Graphene oxide-catalyzed two-step continuous-flow conversion of aryl amine to unsymmetrical thioether
    J. Flow Chem. (IF 2.277) Pub Date : 2019-11-22
    Prasun Choudhury, Basudeb Basu

    A sustainable continuous-flow protocol for the conversion of aryl amine to unsymmetrical thioether is described. This technique is a two-step process involving graphene oxide (GO) catalyzed diazotization followed by the reaction with aryl/alkyl thiols. The continuous-flow conditions afford the desired thioethers in very good yields, effectively suppressing formation of possible disulfide, a common by-product in conventional process. The flow reaction is carried out under ambient conditions, applied to a variety of aryl amines and aryl/alkyl thiols and found to be scalable. The catalytic activity of the GO bed under continuous-flow conditions is found within standard time range and recyclable for ten consecutive runs without any loss of its performance.

  • Microreactor assisted method for studying isocyanate–alcohol reaction kinetics
    J. Flow Chem. (IF 2.277) Pub Date : 2019-07-10
    Christian Orlando Camacho López, Zsolt Fejes, Béla Viskolcz

    Kinetic parameters of phenyl isocyanate–monoalcohol reactions has been studied using a microreactor system. The monoalcohol components were propan-1-ol, butan-1-ol, propan-2-ol and butan-2-ol. The reactions were conducted in alcohol/THF mixed solvent under pseudo-first-order circumstances at various temperatures. The reaction mixtures were analyzed by off-line HPLC. Reaction rate constants and apparent activation energies have been determined with good precision. The reaction rate constants were higher for the primary alcohols than for the secondary alcohols. Higher apparent activation energy was found for the secondary alcohols compared to the primary ones. The applied technique provides a simple way to study the effects of various factors (e.g. structure of the isocyanate and the alcohol, temperature, solvents, concentration of reagents, catalysis) on the kinetics of the isocyanate–alcohol reactions.

  • Continuous synthesis of plate-like silica microparticles using microfluidics
    J. Flow Chem. (IF 2.277) Pub Date : 2019-05-28
    Mohsen Tamtaji, Aliasghar Mohammadi

    The synthesis of plate-like silica particles, which are of importance for a variety of applications, are mainly based on the widely adopted method of the sol-gel reaction of silicon alkoxides in traditional batch-wise instrumentation. In this study, continuous-flow synthesis of amorphous plate-like silica particles is reported through combining droplet-based microfluidics and the sol-gel reaction of tetraethyl orthosilicate. The reaction was conducted at the surface of oil droplets, comprising tetraethyl orthosilicate (TEOS), suspended in acidic (HCl) water, resulting in silica particles on the surface of the droplets, leaving the device with outlet flow. The synthesized particles had plate-like structure with thickness less than 1 μm and microscale in two other dimensions. The influences of experimental parameters (TEOS and HCl concentrations and the flow rate of aqueous phase) on the silica production rate were examined. With increase in the TEOS and HCl concentrations, the production rate increases monotonically. With increase in the flow rate of aqueous phase, the production rate increases up to a specific flow rate. Beyond the flow rate, the production rate decreases with increase in the flow rate. A phenomenological model is proposed to address the production rate using the droplet-based microfluidic system. In addition, response surface methodology (RSM) was used to statistically model and optimize the production rate. At optimum values for the experimental parameters, the experimentally measured production rate was considerably comparable to that predicted by RSM.

  • Experiments on the magnetic enrichment of rare-earth metal ions in aqueous solutions in a microflow device
    J. Flow Chem. (IF 2.277) Pub Date : 2019-05-29
    K. Kolczyk-Siedlecka, M. Wojnicki, X. Yang, G. Mutschke, P. Zabinski

    An attempt is made to achieve a continuous enrichment of rare-earth metal ions from aqueous solutions in a microflow device by applying magnetic forcing. An aqueous solution containing holmium(III) ions is pumped through a small channel which was exposed to a strong inhomogeneous magnetic field. At the outflow, the near- and far-field parts of the flow are separated and analyzed using UV-Vis spectroscopy. The relative change of ion concentration is determined from the measured absorbance. Results are reported for three different types of flow cells at different flow rates and magnetic field strengths and for a cascaded application of cells. The change of concentration is found to be small, and no clear trend can currently be stated due to the error margin of the concentration measurement.

  • Mixing efficiency and pressure drop analysis of liquid-liquid two phases flow in serpentine microchannels
    J. Flow Chem. (IF 2.277) Pub Date : 2019-06-08
    Jin-yuan Qian, Xiao-juan Li, Zhi-xin Gao, Zhi-jiang Jin

    When fluids flow in microchannels, due to the relative low hydraulic diameter and low flow velocity, the flow is usually laminar flow, which hinders the effective mixing between two liquid-liquid phases. In this paper, the mixing efficiency at both droplet forming stage and droplet moving stage are investigated with the volume of fluid (VOF) method. The user defined scalar (UDS) is defined in the dispersed phase to analyze the mixing efficiency quantitatively. The droplet moves in the microchannel with the constant velocity, while serpentine microchannels are designed with different bend radius ranging. \( \overline{R} \) and εd are defined as the ratio of the bend radius to the width of the microchannel, and the ratio of the dispersed phase velocity to the droplet moving velocity, respectively. They are used for illustrating the effect of the bend radius and the dispersed phase fraction on the mixing efficiency in the droplet. Results indicate that the smaller dispersed phase fraction and smaller bend radius show the better mixing efficiency. However, the droplet production frequency changes in a parabolic trend with the variation of the dispersed phase fraction. The suitable dispersed phase fraction should be less than 0.5 in order to achieve a higher mixing efficiency and higher droplet formation frequency. In addition, the pressure drop in microchannel is increased with the decrease of the bend radius. The pressure drop observed in the micorchannel with square turn (\( \overline{R} \) = 0) and the microchannel with a bend radius of \( \overline{R} \) = 1 is nearly the same. This paper can be referred by someone dealing with the micromixer design and mass transfer in micro scale.

  • Multistep synthesis of a valsartan precursor in continuous flow
    J. Flow Chem. (IF 2.277) Pub Date : 2019-07-31
    Katharina Hiebler, Sebastian Soritz, Kristian Gavric, Sam Birrer, Manuel C. Maier, Bianca Grabner, Heidrun Gruber-Woelfler

    Valsartan is a potent, orally active angiotensin II receptor blocker and is widely used in the treatment of hypertension and chronic heart failure. Herein, we present an approach for the continuous synthesis of a late-stage precursor of valsartan in three steps. The applied synthetic route involves N-acylation, Suzuki-Miyaura cross-coupling and methyl ester hydrolysis. After optimization of the individual steps in batch, they were successfully transferred to continuous flow processes employing different reactor designs. The first step of the synthetic route (N-acylation) as well as the third step (methyl ester hydrolysis) are performed in coil reactor setups. The key step of the reaction cascade (Suzuki-Miyaura cross-coupling) is catalyzed by a heterogeneous palladium-substituted cerium-tin-oxide with the molecular formula Ce0.20Sn0.79Pd0.01O2-δ. The catalyst particles are implemented in an in-house developed packed-bed reactor, which features an HPLC column as fixed-bed. The combination of the individual reaction modules facilitates the consecutive performance of the three reaction steps. Using the developed multistep continuous setup, the targeted valsartan precursor was obtained with up to 96% overall yield.

  • Continuous high-pressure operation of a pharmaceutically relevant Krapcho dealkoxycarbonylation reaction
    J. Flow Chem. (IF 2.277) Pub Date : 2019-01-31
    M. C. Rehbein, J. Wolters, C. Kunick, S. Scholl

    The synthesis of the pharmaceutically relevant scaffold 3,4-dihydro-1H-1-benzazepine-2,5-dione via Krapcho dealkoxycarbonylation in a continuous high temperature high pressure coil reactor is investigated and compared to results from batch experiments. In a first step, the continuous reactors residence time distribution (RTD) is characterized, followed by an initial comparison of batch and continuous reactant conversion profiles indicating a very good agreement between both reactors by means of conversion time. Reaction temperature is increased above the solvents atmospheric boiling point in the continuous reactor system to intensify the reaction and increase throughput. Optimal reaction parameters for complete conversion of the starting material in ≤ 3 min reaction time were estimated based on batch kinetics and confirmed by a continuous experiment. The system is able to generate around 12.2 g product per day.

  • Continuous flow production in the final step of vortioxetine synthesis. Piperazine ring formation on a flow platform with a focus on productivity and scalability
    J. Flow Chem. (IF 2.277) Pub Date : 2019-04-30
    Zoltán Boros, László Nagy-Győr, Katalin Kátai-Fadgyas, Imre Kőhegyi, István Ling, Tamás Nagy, Zoltán Iványi, Márk Oláh, György Ruzsics, Ottó Temesi, Balázs Volk

    In this study, the piperazine formation step of vortioxetine synthesis was investigated under continuous flow conditions. The batch variant of this step could be carried out at laboratory scale at 130–135 °C with a long reaction time (27 h) followed by a laborious optimization process, but the formation of a significant amount of side-products could be detected, thus an efficient purification procedure was necessary. In the attempted scale-up of the batch reaction, a complete conversion could not at all be reached, even after elongated reaction times (36 h). The continuous-flow experiments were carried out in a new, purpose-built flow system. The examinations were extended to a wide range of reaction parameters (ratio of solvents, concentration and molar ratio of reagents, geometry of coiled loop reactor, residence time, temperature) and to the feasibility study of scale-up. In the second part of the experiments, the fine-tuning of scaled-up reaction parameters of continuous flow synthesis was carried out using a systematic design of experiments approach. Finally 190 °C reaction temperature and 30 min of residence time led to the highest efficacy in the production of vortioxetine drug substance with high yield and purity.

  • Ethoxylation of p -Fluoronitrobenzene using phase-transfer catalysts under microflow conditions
    J. Flow Chem. (IF 2.277) Pub Date : 2019-02-27
    Hajime Mori, Akane Saito, Yasuhiro Nishiyama

    Nucleophilic aromatic substitution, one of the most common transformation methods for aromatic organic compounds, is often performed under biphasic conditions using a phase-transfer catalyst. Herein, we investigated the synthesis of 4-nitrophenetole from 4-fluoronitrobenzene in a continuous-flow microreactor, which accelerates mass transfer between the two phases. The reaction proceeded smoothly under slug flow conditions and a slight acceleration effect was observed under ambient pressure. By contrast, high temperature and pressure conditions gave the target compound in good yield within a shorter residence time.

  • Efficient continuous flow synthesis of ethyl shikimate: the first step in the synthesis of Tamiflu
    J. Flow Chem. (IF 2.277) Pub Date : 2019-05-09
    Cloudius R. Sagandira, Paul Watts

    Ethyl shikimate is the first intermediate in the synthesis of oseltamivir phosphate (Tamiflu). Commercially, it is synthesised from the esterification of (−)-shikimic acid with ethanol in the presence of SOCl2 in batch. Herein is a comprehensive study on the continuous flow synthesis of ethyl shikimate in >90% yield and less than 10 min residence time. Furthermore due to environmental, health and safety concerns over the use of SOCl2, the use of safer and more environmentally friendly reagents was investigated. Numerous effective continuous flow synthetic procedures for ethyl shikimate have been developed successfully.

  • Metallorganic reactions in the polytropic microreactors
    J. Flow Chem. (IF 2.277) Pub Date : 2019-03-07
    Min Fu, Leslaw Mleczko

    High exothermicity, unstable intermediates, high reaction rates are the features that make metallorganic reactions very challenging, especially in commercial operation. No wonder that there is a large interest for the alternative production technology. This paper reviews a research program by Bayer on metallorganic reactions in microreactors. Selected aspects of use of micro-reaction technology for this reaction class are discussed. Two operational issues, i.e. temperature control and clogging are highlighted. Furthermore, the design concept of a MRT based commercial unit and its economics are discussed.

  • Design and application of a modular and scalable electrochemical flow microreactor.
    J. Flow Chem. (IF 2.277) Pub Date : 2018-01-01
    Gabriele Laudadio,Wouter de Smet,Lisa Struik,Yiran Cao,Timothy Noël

    Electrochemistry constitutes a mild, green and versatile activation method of organic molecules. Despite these innate advantages, its widespread use in organic chemistry has been hampered due to technical limitations, such as mass and heat transfer limitations which restraints the scalability of electrochemical methods. Herein, we describe an undivided-cell electrochemical flow reactor with a flexible reactor volume. This enables its use in two different modes, which are highly relevant for flow chemistry applications, including a serial (volume ranging from 88 μL/channel up to 704 μL) or a parallel mode (numbering-up). The electrochemical flow reactor was subsequently assessed in two synthetic transformations, which confirms its versatility and scale-up potential.

  • Multicapillary Flow Reactor: Synthesis of 1,2,5-Thiadiazepane 1,1-Dioxide Library Utilizing One-Pot Elimination and Inter-/Intramolecular Double aza-Michael Addition Via Microwave-Assisted, Continuous-Flow Organic Synthesis (MACOS).
    J. Flow Chem. (IF 2.277) Pub Date : 2013-11-19
    Farman Ullah,Qin Zang,Salim Javed,Aihua Zhou,Christopher A Knudtson,Danse Bi,Paul R Hanson,Michael G Organ

    A microwave-assisted, continuous-flow organic synthesis (MACOS) protocol for the synthesis of functionalized 1,2,5-thiadiazepane 1,1-dioxide library, utilizing a one-pot elimination and inter-/intramolecular double aza-Michael addition strategy is reported. The optimized protocol in MACOS was utilized for scale-out and further extended for library production using a multicapillary flow reactor. A 50-member library of 1,2,5-thiadiazepane 1,1-dioxides was prepared on a 100- to 300-mg scale with overall yields between 50 and 80% and over 90 % purity determined by proton nuclear magnetic resonance (1H-NMR) spectroscopy.

  • Accessing Stereochemically Rich Sultams via Microwave-Assisted, Continuous Flow Organic Synthesis (MACOS) Scale-out.
    J. Flow Chem. (IF 2.277) Pub Date : 2011-11-26
    Michael G Organ,Paul R Hanson,Alan Rolfe,Thiwanka B Samarakoon,Farman Ullah

    The generation of stereochemically-rich benzothiaoxazepine-1,1'-dioxides for enrichment of high-throughput screening collections is reported. Utilizing a microwave-assisted, continuous flow organic synthesis platform (MACOS), scale-out of core benzothiaoxazepine-1,1'-dioxide scaffolds has been achieved on multi-gram scale using an epoxide opening/S(N)Ar cyclization protocol. Diversification of these sultam scaffolds was attained via a microwave-assisted intermolecular S(N)Ar reaction with a variety of amines. Overall, a facile, 2-step protocol generated a collection of benzothiaoxazepine-1,1'-dioxides possessing stereochemical complexity in rapid fashion, where all 8 stereoisomers were accessed from commercially available starting materials.

  • An Automated Process for a Sequential Heterocycle/Multicomponent Reaction: Multistep Continuous Flow Synthesis of 5-(Thiazol-2-yl)-3,4-Dihydropyrimidin-2(1H)-ones.
    J. Flow Chem. (IF 2.277) Pub Date : 2011-08-25
    Nicholas Pagano,Ananda Herath,Nicholas D P Cosford

    The first example of a sequential heterocycle formation/multicomponent reaction using an automated continuous flow microreactor assembly is reported. Consecutive Hantzsch thiazole synthesis, deketalization, and Biginelli multicomponent reaction provides rapid and efficient access to highly functionalized, pharmacologically significant 5-(thiazol-2-yl)-3,4-dihydropyrimidin-2(1H)-ones without isolation of intermediates. These complex small molecules are generated in reaction times less than 15 min and in high yields (39-46%) over three continuous chemical steps.

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上海纽约大学William Glover