Dear Colleagues,

Continuous flow (CF) approaches are of considerable current interest, as highly efficient and selective reactions can be performed by the utilization of CF reactors, which are constructed in such a way as to possess pores and tubes in the reactors’ active zone with diameters in the micro and millimeter range. Consequently, the surface-to-volume ratio in microstructured devices is orders of magnitude higher than in conventional batch reactors. Because of this fact, micro- and meso-scale CF reactors offer several advantages over conventional batch technologies, such as faster heat and mass transfer, accurate control over a reaction’s temperature, and a laminar flow profile. These properties crucially influence the experimental setup and the outcome of a CF reaction. Accordingly, contemporary flow technologies do not require the use of large amounts of reagents and solvents and the most important reaction parameters, such as flow rate, temperature, and pressure, can be adjusted and observed in a previously unprecedented way. The reaction outcome changes such that a faster mass transfer results in considerably faster reactions. Furthermore, the more accurate temperature control and faster heat transfer yield more selective reactions that provide higher yields of the desired product. This fact is in accordance with the first principle of the 12 principles of green chemistry defined by Paul Anastas and John Warner, which emphasizes that it is easier to prevent the formation of waste than to handle or eliminate it. Nonetheless, by the utilization of a pressure regulator, high-pressure and/or high-temperature reactions can be carried out too. Accordingly, the reaction parameter space is considerably wider than those of conventional batch technologies, and can be harnessed by the experimental tuning of the CF reaction. Nonetheless, accurate control over the residence time can further broaden the versatility of CF processes and reactions. Additionally, the wide range of applicable immobilized catalysts and reagents further increases the flexibility of CF techniques. The problem of the handling of gaseous and dangerous reagents is safely solved by CF devices too. In addition, the use of CF multistep reactions is currently widespread in industrial drug synthesis.

Dr. Istvan M. Mandity
Guest Editor

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• continuous flow
• packed bed reactor
• residence time
• selectivity
• hazardous reagents.