Effect of solvents on the reaction in triphase catalysis

It is known that the distribution of organic phase and aqueous phase existing in the porous pellet is affected by a change of the ring substitution (RS) of the polymer support. Wang and Wu prepared three kinds of polymer supports with different numbers of ring 

For a two-phase PTC, it is recognized that the polarity of the organic solvent affects the reaction rate. In general, the reaction rate increases with the augmentation of the polarity of the solvents. Table 13.3.28 shows the effects of the organic solvents on the apparent rate constant, ko pp and A higher value of the apparent rate constant was obtained using 

Triphase catalyst Conditions ClCsHs g H2O g NaOCHjCFj, g (calcd value, g) Swelling volume ratio 

Data obtained from Wang and Wu 50 mL of chlorobenzene, 20 mL of water, 0.059 mole of (NPCh), 0.7 meq of catalyst was used, 20 C 

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Effect of volume of organic solvent and water on the reactions in triphase catalysis... 

Intraparticle diffusion limits rates in triphase catalysis whenever the reaction is fast enough to prevent attaiment of an equilibrium distribution of reactant throughout the gel catalyst. Numerous experimental parameters affect intraparticle diffusion. If mass transfer is not rate-limiting, particle size effects on observed rates can be attributed entirely to intraparticle diffusion. Polymer % cross-linking (% CL), % ring substitution (% RS), swelling solvent, and the size of reactant molecule all can affect both intrinsic reactivity and intraparticle diffusion. Typical particle size effects on the... 

Nevertheless, the separation of the catalyst at the end of the reaction and, if possible, its recycling is often a limiting factor for the application of PTC. The chemical nature of the catalyst makes it at least partially soluble both in polar and apolar solvents and higher catalyst loadings are often used to maximize the effects on the reaction rates. This led very soon to the development of polymer-supported phase transfer catalysts [222], When using insoluble supports, an additional phase is added to the former biphasic system and, accordingly, the term triphase catalysis was coined (Figure 10.8) [223-225],... 

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