Triphase catalysis, described

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

There are various combinations of solvents that lead to the different biphasic and triphasic systems described in Section 2.1 that have found applications in synthesis and catalysis. For practical purposes, it is essential that the catalyst and product... 

Insoluble catalysts offer an important advantage of simple catalyst removal by filtration or centrifugation after the completion of a PTC reaction. Regen [82] demonstrated that quaternary onium cations chemically bound to insoluble resins could act as PTC catalysts and suggested the term triphase catalysis to describe the related PTC reactions. Insoluble PTC catalysts can be grouped into three categories, namely, the resin bound, the inorganic solid bound, and the third-liquid-phase catalysts as described in Section... 

Leznoff has published further on the solid-phase synthesis of insect sex attrac-tants. The advantages and uses of enzymes attached to solid supports have been reviewed. Aspects of triphase catalysis (organic layer-water-polymer) have been discussed by Regen, while advances in phase-transfer catalysis have been reviewed. A crown ether NAD(P)H mimic has been described,bringing synthetic chemists nearer to the objective of artificial enzyme systems. 

In most of the examples described in this section, the catalyst could be reused with little loss of activity. Triphase catalysis has the advantages of selectivity, recoverability, and reusability, and clearly has applications in clean technology. 

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