Phase-transfer catalysis continuous flow

Weng, H.-S. Wang, C.-M. Wang, D.-H., A Preliminary Study on a Continuous Flow Stirred Vessel Reactor for Tri-Liquid-Phase Phase Transfer Catalysis. Ind. Eng. Chem. Res. 1997, 36,3613. 

In fact, since the leaving group, methyl carbonate, decomposes (reaction 3), the base is restored and can be used in truly catalytic amounts. This feature allows utihzation of continuous-flow (c-f) procedures (i.e. gas-liquid phase-transfer catalysis, GL PTC, and continuously stirred tank reactor, CSTR ). 

Tundo, P., G. Moraglio, and F. Trotta, Gas-Liquid Phase Transfer Catalysis A New Continuous Flow Method in Organic Synthesis, Ind, Eng. Chem. Res., 28, 881 (1989). 

Gas-liq. phase transfer catalysis under continuous flow... 

Dimethyl carbonate can be used for methylation of nitrogen in amine compounds at a temperature of 180°C under continuous-flow gas-liquid phase-transfer catalysis conditions (which involve transfer of organic ionic reactant species between water and an organic phase) as shown below for the methylation of aniline ... 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

Applications of microreactors to biphasic catalytic reactions constitute a topac of interest. The benefits of having an exceedingly high surface-to-volume ratio and efficient mass-transfer in microchannels have led many researchers to study continuous flow systems using microreactors for catalytic reactions. The excellent mass transfer characteristics within and between the catalyst carrier phase and reaction medium, together with the minimal catalytic pore diffusion resistances at the micrometer scale, make such biphasic catalysis an attractive alternative to conventional catalysis operation (Wieflmeier, 1996 Rahman et al., 2006). 

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