Solid support catalysts polymer supports

The immobilization of phase transfer catalysts on solid substrates allows a clean reaction with no contamination of the products by the catalyst. Insoluble polystyrene matrices have been used as a solid support. The polymer matrix does not affect the velocity of the reaction, apart from steric hindrance with respect to the reagents. In the case of immobilization on modified silica the active centre is linked to the support by an alkyl chain of variable length. This length strictly determines the adsorption capacity of the polar support, which then controls the rate of reaction. A three-phase catalytic system is set up. Two distinct phases, containing reagents, come into close... 

High selectivity and difficulty of separation from products are two quintessential characteristics of soluble catalysts. Attempts to retain the catalyst selectivity and alleviate the separation (and corrosion) problems have resulted in the preparation of catalysts consisting of molecular species bonded to solid supports, The common supports are organic polymers and porous inorganic solids, which are discussed in turn in the next two sections. 

In investigating the effect of the amount of water, the contents of other components are fixed. Changing the amount of water affects the volume ratio of organic phase to aqueous phase and the concentration of nucleophile in the aqueous phase. For the reaction of hexacyclotriphosphazene and sodium 2,2,2-trifluoroethanoxide catalyzed by tributylamine immobilized on the solid styrene-chloromethylstyrene polymer support catalyst. As shown in Figure 13.3.12, the reaction rate is decreased with the increase in the amount of water up to a concentration of sodium 2,2,2-trifluoroethanoxide at 2.8 M. Flowever, the reaction rate is then increased with further increase in the amount of water larger than 2.8 M sodium 2,2,2-trifluoroethanoxide. This result indicates that a high concentration of sodium... 

Heterogeneous catalytic reactions usually involve the interaction of gaseous or liquid compounds in the presence of a solid or solid-supported catalyst. Homogeneous catalysts on the other hand are present in the same phase as the reacting components - usually in a solution when metallophosphine catalysts are involved. Difficulties frequently arise in the latter case, with the separation of the reaction products. With polymer-supported catalysts, however, these difficulties are usually removed. 

Slotted plate for catalyst support designed with openings for vapor flow Ion exchanger fibers (reinforced ion exchange polymer) used as solid-acid catalyst None specified Hydrolysis of methyl acetate Evans and Stark, Eiir. Pat. Appl. EP 571,163 (1993) Hirata et al., Jap. Patent 05,212,290 (1993)... 

Chemistry on solid support has gained tremendous importance during the last few years, mainly driven by the needs of the pharmaceutical sciences. Due to the robust and tolerable nature of the available catalysts, metathesis was soon recognized as a useful technique in this context. Three conceptually different, RCM-based strategies are outlined in Fig. 11. In the approach delineated in Fig. 1 la, a polymer-bound diene 353 is subjected to RCM. The desired product 354 is formed with concomitant traceless release from the resin. This strategy is very favorable, since only compounds with the correct functionality will be liberated, while unwanted by-products remain attached to the polymer. However, as the catalyst is captured in this process by the matrix (355), a higher catalyst loading will be required, or ancillary alkenes have to be added to liberate the catalyst. 

As anticipated in the introduction, cross-linked polymers swell, to variable extent, when put in contact with liquids. Therefore, the working state of any cross-linked organic pol5uner under solid-liquid conditions, no matter if it is a catalyst, a support or a carrier for solid state S5mthesis, is the swollen state. In macroreticular CFPs swelling does not involve the whole polymeric mass it is... 

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