Journal of Flow Chemistry最新文献

Selective oxidation of hydroxymethylfurfural to diformylfuran was performed in 3D-printed milli-scale porous reactors using pure oxygen in mild operating conditions (T = 60° C, P = 1 atm) and the homogeneous TEMPO/TBN catalytic system. Three different configurations were tested, where a rotation (θ = 22.5°) and/or an inclination (φ = 45°) of the fibers are introduced. An empty tube and a packed bed were also tested as a reference. Out of these designs, the reactor with both parameters varied simultaneously (INSP1) exhibited the highest performance, achieving an efficiency of up to 80%. The maximum conversion of 18.2% was attained for a residence time of 160 s, despite existing mass transfer limitations for this flow rate. The selectivity to DFF was 100% for all the 3D-printed reactors. On the contrary, the packed bed resulted in the highest efficiency, but at the expense of selectivity. Additional oxidation products have been retained in the packing, blocking thus the packed bed after a few hours of operation. The kinetic constant was found based on a (0,1)-order kinetic model from batch experiments. The kinetic information was utilized to evaluate the performance of the 3D-printed porous reactors from a mass transfer and reaction engineering aspect. The 3D-printed reactors were operating almost in kinetic control for total flow rates above 1 mL/min (Ha < 0.3). However, the associated short residence time resulted in small conversion. The 3D-printed reactors show significant potential when operating at higher flow rates. The low conversions can be countered by increasing the residence time, either with multiple passes or by operating them in series.

Herein, an efficient eco-friendly protocol is reported for the continuous synthesis of enaminones using a microreactor device in the presence of a catalytic amount of cerium (III) trichloride (1 mol%) in Propylene carbonate (PC) as a non-toxic solvent. Moreover, continuous separation of the corresponding product, and recycling of the catalyst-solvent system with water is another promising advantage of this technique. Indeed, the separation of the product by water allows any required catalyst and solvent to be reapplied in the next run. In addition, this microfluidic system enabled turnover frequency (TOF) of up to 2940 h⁻¹ for the corresponding products. The employment of these environment friendly facilitates produce the products with an excellent isolated yield up to 98%. This method performs efficiently, and would extent future applications of continuous organic, inorganic and biochemical reactions in green chemistry.

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The application of a flow reactor under ultrasonic irradiation enabled the fast synthesis of new spiro-fused indoles in a one-pot methodology. The exploitation of the reactivity of biobased building blocks, including acrylic acids and formamides, was essential to achieve such highly functionalized molecular targets. A four-step process with a 2–3 min residence time, and no aqueous work-up, created spiro[indoline-succinimides], spiro[indole-pyrrolo-succinimides] and spiro[indole-pyrido-succinimides] with high overall yields.

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A novel method based on periodic change of two-phase velocity for the droplet coalescence in microchannels is proposed. The feasibility of the method is justified by investigating the droplet coalescence in several combinations of the velocity pairs. Once the droplet pairs have been generated, the frequency of the droplet coalescence can be divided into a liquid slug of continuous phase dominated region and a real velocity ratio dominated region. Since the liquid slug between the droplet pairs and the real velocity ratio of the droplet pairs are determined by the flow rate ratios, the critical value of the flow rate ratio is determined to distinguish whether the frequency of the droplet coalescence is liquid slug dominated or real velocity ratio dominated. Compared with the traditional passive method, the droplet pairs are alternatively generated by the periodic change of the two-phase velocity. The velocity gradient of the droplet pairs can be generated spontaneously which avoids the introduction of an expansion structure. The mixing performance inside the coalesced droplet is improved due to the reorganized inner circulation when the droplets is coalesced. The quantitative mixing of the reagents can be achieved to satisfy special application needs by a precise control of the volume of the droplet pairs.

Sustainable synthesis of acrolein, a key chemical intermediate, from biomass-derived glycerol is highly attractive. However, conventional catalysts for the dehydration of glycerol suffer from low acrolein selectivity and high deactivation tendency. Herein, a novel green catalyst (HPW/T_0.6 S-COOH) was prepared and employed in the dehydration of glycerol in a continuous flow reactor. The performance of different catalysts and the effects of reaction conditions (reaction temperature, N₂ flow rate, and glycerol concentration) were examined. The HPW/T_0.6 S-COOH catalyst provides the best glycerol conversion of 96.38% and acrolein selectivity of 92.01%. The NH₃-TPD and pyridine-FTIR results indicate that the Brønsted acid site is more susceptible to acrolein, while the weak strength acid site effectively prevents the further reaction of acrolein, providing practical insights for the rational design of efficient and continuous synthesis of acrolein catalysts.

A continuous flow approach for the generation of phenyl glucosazone from glucose and phenyl hydrazine is reported giving the pure target in 53% isolated yield. This thermal process generates the target product as an insoluble material that causes reactor fouling via adhering to the reactor walls. To overcome this issue a segmented flow approach was realised whereby streams of air and the reaction solution were combined in a T-piece and directed through the heated reactor coil. The resulting micro-mixing prevented reactor fouling and blocking and allowed for multi-hour reactions to generate the desired target in high yield. The value of the phenyl glucosazone product was demonstrated via its oxidative cyclisation into 2H-phenyl-1,2,3-triazoles which represent important heterocyclic scaffolds.

The design and implementation of flow technique helps organic chemists to resolve numerous challenges that are encountered during various catalytic reactions. Flow technologies, which offer solutions for technical and/or chemical issues, have gained popularity over the last two decades in the field of organic chemistry. The selectivity, efficiency, and safety of the entire process has been accelerated by flow reactors as they improve mass and heat transfer, speeds up the mixing of the reaction, and they offer exact control of the reaction parameters. This review mainly describes the utilization of flow chemistry in reactions involving organiozinc reagent, particularly Negishi coupling. The Negishi coupling of organozinc reagent is a valuable tool for the formation of C-C bond with functional group tolerance and are used extensively in total synthesis. This review also portrays a comparative study of organozinc reagents prepared using different procedures. A study of the effect of different catalysts over the same reaction is also carried out. An overview of different flow techniques that are employed has also been incorporated.