Microflow systems approaches

Microwave irradiation has been proven useful in accelerating chemical reactions. A unique approach to multicomponent reactions - the combination of microwave irradiation and microreactors - was developed by Organ and Bremner [25]. The three-component coupling reaction of amino pyrazole with an aldehyde and diketone in a glass capillary tube microflow system (1180 pm i.d.) under microwave irradiation (170 W) proceeded smoothly to give the desired quinolinone in high yield (Scheme 4.16). Without microwave irradiation, the reaction efficiency was very low. 

Suga, S. Okajima, M. Fujiwara, K Yoshida, J., Cation flow method a new approach to electrochemical conventional and combinatorial organic syntheses using electrochemical microflow systems,./. Am. Chem. Soc. 2001, 123, 7941-7942... 

Micromixers are the key elements of microflow systems for flash chemistry because extremely fast mixing is essential for conducting an extremely fast reaction between two reaction components As described in Chapter 6, the conventional approach to mixing often leads to disguised chemical selectivity. Fast mixing by virtue of a short diffusion path in... 

There are many other approaches to industrial applications of flash chemistry, although available information is limited. Let us briefly touch on some examples. The Kolbe-Schmitt synthesis serves as a useful standard method to introduce a carboxyl group into phenols (Scheme 10.6). The Kolbe-Schmitt synthesis has been widely used in industry, and there are many variants of this transformation. Microflow systems can be used for conducting the Kolbe-Schmitt synthesis under aqueous high-pressure conditions.A decrease in reaction times by an order of magnitude (a few tens of seconds instead of minutes) and increase in space-time yields by orders of magnitude can be attained using a microflow system. For example, a microflow system composed of five parallel capillaries (inner volume 9 ml) has a productivity of 555 g/h, whereas the productivity of a macrobatch reactor (IL flask) is 28 g/h. 

Yoshida, Cation Flow Method. A new approach to conventional and combinatorial organic syntheses using electrochemical microflow systems, J. 

Oxidation of primary and secondary alcohols to aldehydes and ketones with DMSO, oxalyl chloride, and a base is knovm as Swem-oxidation. When using oxalyl chloride as the dehydration agent, the reaction must be kept colder than —60°C to avoid side reactions, such as Pummerer rearrangement. In contrast, when trifluoroacetic anhydride is used instead of oxalyl chloride, the reaction can be warmed to —30 °C without side reactions. Microflow systems offer a smart approach for controlling the reaction... 

For basic filter material development wall scale models especially the MicroFlowS approach can be applied. During early development of particulate emission control systems single channel models provide a fast and sufficient means for basic DPF design and sizing analysis. In addition, when applicable... 

FIGURE 2.5 Illustration of a SIA-LOV microflow network as assembled for in-valve sorptive preconcentration using renewable sorbent materials prior to further detection via peripheral analytical instruments. SP, syringe pump HC, holding coil. The inset at the right shows how the sorptive beads are retained within the column positions. (Reprinted with permission from Miro, M., and E. H. Hansen. 2007. Miniaturization of environmental chemical assays in flowing systems The lab-on-a-valve approach vis-a-vis lab-on-a-chip microfluidic devices. Anal. Chim. Acta 600 46-57.)... 

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