Electrochemical microflow reactor

Various electrochemical organic reactions have been carried out using electrochemical microflow reactors. Sometimes, electrolysis can be conducted without intentionally added supporting electrolyte by virtue of the extremely short distance between the anode and the cathode. 

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In the cation flow method an organic cation is generated continuously by low temperature electrolysis using an electrochemical microflow reactor. The cation thus generated is immediately allowed to react with a carbon nucleophile in the flow system. This method, in principle, enables the manipulation of highly reactive organic cations. 

Figure 5.8 Electrochemical microflow reactor for the cation-flow method (a) outside (b) inside (anodic part). Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission...

An electrochemical microflow reactor consisting of a plate-to-plate electrode configuration mounted in a nonconducting housing has been developed. As shown in Figure 7.23, a 75 im thick polyimide foil between the working electrode and the counter electrode defines a unique distance. This polyimide foil contains microstructured slits (250 im wide). 

An electrochemical microflow reactor, which is composed of diflone and stainless steel bodies produced by a mechanical manufacturing technique, is shown in Figure 7.24. The reactor consists of a two-compartment electrochemical cell, which is divided by a PTFE membrane. Carbon felt (7 mm x 7 mm x 5 mm) made of carbon fibers = 10 im) is used as the electrode. 

Figure 7.23 Electrochemical microflow reactor with a plate-to-plate electrode...

Figure 12.9 An electrochemical microflow reactor for the cation flow method.

The generation of the cation can be monitored using an FTIR spectrometer (ATR method) equipped with a low-temperature flow cell attached to the outlet of the electrochemical microflow reactor. The absorption at 1814 cm , which is assigned as the C=0 vibration, increases with increase in the electric current. An interesting application of the cation flow method is continuous sequential combinatorial... 

Recently, microflow systems have attracted significant research interest from both academia and industry [28, 29]. Microflow systems are expected to serve as a much better reaction environment than conventional macrobatch reactors because of the inherent advantages of microspaces, such as fast molecular diffusion by virtue of small sizes and fast heat and mass transfer by virtue of large surface-to-volume ratios. In electroorganic synthesis, the use of a microflow reactor serves as a solution to the problems with conventional macrobatch electrochemical reactors, such as difficulty in mass transfer on the surface of the electrodes and high ohmic drop between the electrodes. 

Electrochemical microflow systems have also attracted significant research interest from the viewpoint of electrolysis without an intentionally added supporting electrolyte, becausethe short distance between the electrodes andthehigh electrode surfaceto reactor volume ratio are advantageous for conductivity and reaction efficiency. 

Oxidation and reduction are fundamental processes in the synthesis of organic and inorganic compounds. Some oxidation and reduction reactions are difficult to control in macro-scale batch reactors and in such cases microflow reactors serve as powerful tools for accomplishing the reactions in a highly controlled manner. This is especially true for many oxidation reactions because of their exothermic nature. It should also be noted that the danger of unexpected explosions can be avoided by the use of microflow reactors because of the small volume and highly efficient heat transfer ability of microflow systems. This chapter provides an overview of oxidation and reduction reactions using chemical, electrochemical and biochemical methods in microflow reactors. 

Electrochemical Microflow Systems, Fig. 4 Galactosidase reaction monitored by fluorescence in a nano-channel reactor (Redrawn from [58])... 

Figure 12.8 A microflow electrochemical reactor having a plate-to-plate configuration.

Using a similar type of the microflow cell, Haswell s group reported the electroreductive coupling of activated olefins and benzyl bromide derivatives (Equation 12.8) [40]. The microflow electrochemical reactor can be easily multiplexed to generate a number of parallel flow cells, which offer the performance of a single cell while increasing the volumetric throughput of the system. 

Oxidation of furans can be also carried out using a ceramic microflow electrochemical reactor (CEM) using H2SO4 as the supporting electrolyte [30]. Scheme 7.7 shows the oxidative methoxylation of methyl 2-furoate. 

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