Microwave batch reactors

Fig. 10.1 Microwave batch reactor 1. micro-wave cavity, 2. magnetron, 3. stirring bar, 4. alir minum plate, 5. magnetic stirrer, 6. IR pyrometer, 7. switch on/off, 8. watercooler.

A complementary, more advanced, laboratory-scale microwave batch reactor for synthesis and kinetics studies was developed by Strauss et al. [113] (Fig. 10.2). 

Fig. 10.2 Schematic diagram of the microwave batch reactor 1. reaction vessel, 2. retaining cylinder, 3. top flange, 4. cold finger, 5. pressure meter, 6. magnetron, 7. power meters, 8. power supply, 9. stirrer, 10. fiber optic thermometer,...

In another example of differential heating, a two-phase water/chloroform system (1 1 by volume) was heated in a microwave batch reactor (MBR)65. About 40 s after commencement, the temperatures of the aqueous and organic phases were 105 and 48°C, respectively, because of the differences in the dielectric properties of each solvent. A sizeable differential could be maintained for several minutes before cooling was begun. Differential heating is particularly advantageous for Hofmann eliminations. In a typical example,... 

A laboratory scale microwave batch reactor (MBR) was developed for synthesis or kinetics studies65. The MBR has a capacity of 25-200 ml and is capable of operating at up to 260°C and up to 10 MPa (100 atm), although in practice, pressures in excess of 5 MPa are seldom used. Aspects of the system are depicted schematically in Figs. 9.1 and 9.2 and an embodiment, fabricated in the CSIRO laboratories, is illustrated in... 

Robotically operated microwave batch reactors incorporating several of the design features of the MBR and an earlier prototype, but with a lower capacity (2-5 ml) have been developed commercially for rapid synthesis, primarily of candidates for drug discovery. These systems can operate under atmospheric or elevated pressure, the upper limits of which are dependent upon individual designs. 

As discussed in this chapter, the scope of demonstrated applications now extends from the sub-milligram level for radio-tracer work to the kilogram scale for preparative chemistry. Commercial microwave batch reactors have been introduced to accommodate such requirements. Continuous reactors have also been produced for use with dry media or liquid-phase reactions and these allow higher throughputs. 

The preparative Claisen rearrangement was studied in aqueous media at temperatures up to 300 °C. The experiments were conducted in the recently created pressurized microwave batch reactor and in conventional heated autoclaves. It was found that allyl phenyl ether isomerizes in water during 10 min at 240 °C to give the ortho-Claisen rearrangement product in 84% conversion . 

The CSIRO Microwave Batch Reactor (MBR). The laboratory-scale MBR (5), is illustrated schematically below (Figure 1). With this system, reactions could be performed under carefully controlled heating, at temperatures up to 260 °C and/or pressures up to 10 MPa (100 atmospheres), and then rapidly cooled. 

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