Continuous-flow microwave reactor

Current single-mode continuous-flow microwave reactors allow the processing of comparatively small volumes. Much larger volumes can be processed in continuous-flow reactors that are housed inside a multimode microwave system. In a 2001 publication, Shieh and coworkers described the methylation of phenols, indoles, and benzimidazoles with dimethyl carbonate under continuous-flow microwave conditions using a Milestone ETHOS-CFR reactor (see Fig. 3.11) [104]. In a typical procedure, a solution containing the substrate, dimethyl carbonate, 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) base, tetrabutylammonium iodide (TBAI), and a solvent was circulated by a pump through the microwave reactor, which was preheated to 160 °C and 20 bar by microwave irradiation (Scheme 4.31). Under these condi-... 

Scheme 4.31 Methylation of phenols, indoles, and benzimidazoles in a multimode continuous-flow microwave reactor.

Fig. 10.3 Schematic diagram of the continuous-flow microwave reactor ...

Figure 36. Design of continuous flow microwave reactor [64].

Chemat and co-workers have developed a continuous flow microwave reactor that is suitable for homogeneous and heterogeneous reactions127. Although their system had only a small cavity (66 ml), it was possible to treat significant quantities of reagents (30 -330 ml/min). This underscored the feasibility of scaling up the manufacture of fine... 

Figure 16.10 Schematic of a continuous-flow microwave reactor consisting of (a) a liquid column as a pressure regulator, (b) a metal salt solution container, (c) a microwave oven cavity, (d) a metal cluster dispersion receiver and (e) a spiral tube reactor (from [139]).

There is considerable interest in continuous-flow chemistry at the present time, for rapid analog synthesis in medicinal chemistry in addition to scale-up. A true continuous-flow microwave reactor is available in the Milestone FlowSYNTH... 

A number of prototype and bespoke continuous-flow microwave reactors of varying scales have also been fabricated and chemistry reported in them. However, because these are specialized instruments that are not readily available, they will not be discussed further here. 

FIGURE 5.13 Cambrex GENESIS continuous-flow microwave reactor. (Reproduced with permission from Cambrex. Copyright 2009 Camhrex. All rights reserved.)... 

Bagley M.C., Jenkins R.L., Caterina Lubinu M., Mason C., Wood R. A simple continuous flow microwave reactor. J. Org. Chem. 2005 70(17) 7003-7006. 

Choedkiatsakul, I., Ngaosuwan, K., et al., 2015. Biodiesel production in a novel continuous flow microwave reactor. Renewable Energy 83, 25—29. 

Paulus et al. (2007) reported for the first time the use of different continuous-flow microwave reactors for polymerizations, using the cationic ring-opening po-lymerizatiorrs of 2-etlryl-2-oxazoline as a model system. In addition, they correlated the broader molecrrlar-weight distributions with residence time distributions of the continuous-flow reactors using methyl orange as the flow marker. 

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