The azo coupling of 2-naphthol and cresol novolaks was performed as an example for organic reactions in a microsegmented flow system with microspectrophotometric on-line characterization. A lithographically prepared glass/glass chip microreactor was used for the generation of segments and the mixing of reaction partners. The formation of segments and their transport behavior is strongly influenced by the addition of surfactants. The reaction rates were high in alkaline media at room temperature, so that the formation of dyes could be observed by a microscope-video system. The single reaction volumes were in the range between about 0.05 and 1 lL. The spectrum of each segment was registered with a measuring frequency of 45±50 Hz. The residence time of segments inside the optical measurement channels varied between 0.1 and 1.5 s and is in the range of 0.3 s for typical segment sizes of about 150 nL. The single reaction segments containing azo dyes as well as polymerbased azo dyes were stored in segment sequences inside capillary Teflon tubes.
The alkyne, aldehyde, amine A(3)-coupling reaction, a traditional multicomponent reaction (MCR), has been investigated as a two-step flow process. The implicated aminoalkylation reaction of phenylacetylene with appropriate aldimine intermediates was catalyzed by gold nanoparticles impregnated on alumina. The aldimine formation was catalyzed by Montmorillonite K10 beforehand. The performance of the process has been investigated with respect to different reaction regimes. Usually, the A(3)-multicomponent reaction is performed as a "one-pot" process. Diversity-oriented syntheses using MCRs often have the shortcoming that only low selectivity and low yields are achieved. We have used a flow-chemistry approach to perform the A(3)-MCR in a sequential manner. In this way, the reaction performance was significantly enhanced in terms of shortened reaction time, and the desired propargylamines were obtained in high yields.
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