Batch processing metal-catalyzed reactions

Metal-catalyzed cross-couplings are key transformations for carbon-carbon bond formation. The applicability of continuous-flow systems to this important reaction type has been shown by a Heck reaction carried out in a stainless steel microreactor system (Snyder et al. 2005). A solution of phenyliodide 5 and ethyl acrylate 6 was passed through a solid-phase cartridge reactor loaded with 10% palladium on charcoal (Scheme 2). The process was conducted with a residence time of 30 min at 130°C, giving the desired ethyl cinnamate 7 in 95% isolated yield. The batch process resulted in 100% conversion after 30 min at 140°C using a preconditioned catalyst. 

Short (or discontinuous) fibers are best prepared in a batch process, e.g., in a small cylindrical reaction chamber. The value of the technology, however, lies in its capability to facilitate the growth of continuous (potentially endless) fibers with a recently discovered automatic self-regulating growth mechanism [2], Finally, the diameter of the laser focus determines the diameter of fibers grown by laser assisted chemical vapor deposition, just as the diameter of the metal particles determines the diameter of the whiskers grown by metal catalyzed chemical vapor deposition. 

The partial pressure of CO necessary to maintain Co2(CO)8 in solution rises rapidly with temperature. The decomposition of Co2(CO)g may, however, be kinetically slow in the absence of compounds which could catalyze this conversion (56), and the decomposition process is reported to be autocatalytic (59). Thus, a catalytic reaction was possible in an unstable temperature-pressure region for some time before cobalt metal precipitation became noticeable. Although operation with a metastable catalyst may be possible in short batch experiments, it would be undesirable in a continuous reaction where stability over extended periods is essential. 

In addition, autocatalytic reactions may also be catalyzed by impurities, for example, by heavy metals or acids. As an example, it is known that the decomposition of dihydroxy-diphenylsulfone is catalyzed by iron [2], In a diagram, as represented in Figure 12.17, the maximum allowed iron concentration can easily be defined. This gives a reliable way of establishing a critical limit for the process, which can also easily be checked before a batch is started. 

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