Reaction triphase

Figure 5.17 Schematic diagram of the effect of mixing on the concentration of substrate in the liquid and solid phases of a triphasic reaction a represents a reaction that is limited only by the intrinsic reactivity b represents a reaction that is limited by a combination of intrinsic reactivity and mass transport effects c represents a reaction which is limited by mass transport only...

For a triphasic reaction to work, reactants from a solid phase and two immiscible liquid phases must come together. The rates of reactions conducted under triphasic conditions are therefore very sensitive to mass transport effects. Fast mixing reduces the thickness of the thin, slow moving liquid layer at the surface of the solid (known as the quiet film or Nemst layer), so there is little difference in the concentration between the bulk liquid and the catalyst surface. When the intrinsic reaction rate is so high (or diffusion so slow) that the reaction is mass transport limited, the reaction will occur only at the catalyst surface, and the rate of diffusion into the polymeric matrix becomes irrelevant. Figure 5.17 shows schematic representations of the effect of mixing on the substrate concentration. 

The anaerobic reduction of the trinuclear copper center for ascorbate oxidase with different substrates presents a distinct picture. The reaction with reductate is monophasic with a unimolecular rate constant of 100 sec (18), independent of pH. Rapid freeze-quench EPR experiments indicate that the type-2 EPR signal vanishes more slowly 18). The pulse radiolysis studies of the radicals of lumiflavin, deazaflavin, CO2 ", and MV at pH 7.0 129,130) showed a biphasic behavior with an initial, faster reaction k = 97-127 sec " ) and a final, slower reaction k 2 sec" ) 129). Different results have been obtained by Farver and Pecht 130) with CO2 " as a substrate. They found a triphasic reaction with unimolecular rate constants k = 201 sec S 2 = 20 sec", and ks = 2.3 sec. The first constant is twice that in a study by Kyritsis et al. 129), whereas the third constant is identical. The second constant was not observed in the study. 

Triphasic reactions. For example, fluorous-organic-aqueous phases or two organic phases separated by a fluorous phase in a U-tube reaction flask. ... 

FIGURE 10.22 (See color insert following page 588.) Applications of catalytic membrane reactors as (a) contactors using opposing reactant mode, (b) interfacial contactors for triphasic reactions, and (c) efficient gas-soUd contactor using forced flow mode. 

Figure 27. The Pd/C-catalysed Heck reaction in a triphasic reaction system.

One of the most interesting and green continuous flow techniques to be developed emerged from the ability to perform triphasic reactions, whereby a gas-liquid phase is pumped through a packed ed containing a heterogeneous catalyst. Using this... 

The function of the base in a liquid-solid-liquid triphasic reaction has four aspects (i) reactant (ii) deprotonation of acidic organic compound to become the reactive form (iii) improving the reactive environment in the catalytic pellets, such as swelling volume, imbibed solvent ratio, solubility between two phase, etc. or (iv) reducing the solvation of catalyst and water to upgrade the reactivity of active catalyst in the organic phase. In previous works, it was observed that the reactivity of organic reactant was varied with the concentration of the base concentration in a liquid-liquid phasc-transfcr-cataly cd reaction [48. 50, 73]. In the liquid-solid-liquid triphase reaction, the effect of the base for the reactivity of reactant (or... 

Wu and Lee 42 indicated that the free chloride ions on the active site (measured by Volhard analysis) were at only 50-70 i, of the amount of immobilized content (measured by element analysis). The results of the Volhard analysis method determined the free chloride ions in the bulk solution by the AgNOt titration method. Their results implicHl that the active site in the resin could not react completely w ith organic reactant in the duration of triphase reaction. According to the experimental results, this reaction is a two-zone model (or shell-core model), with the reaction (K-cuiring in the shell zone, and not in the core zone. Therefore, the triphasic reactitm mechanism and the swollen type of the resin can be given in Figure 4. This mechanism can help to understand the reaction phenomenon in the triphasc rcaciion. 

The reaction of (NPCI ) with phenol using a liquid-liquid phase-transfer catalyzed reaction in a batch reactor was reported in our previous work 64, and the intrinsic reaction-rate constants were also obtained. Since the intrinsic reaction-rate constant in a triphase reaction was ditlicult to obtain, we assumed that the intrinsic reaction-rate constants in a liquid-liquid phase-transfer catalyzed reaction w cre the same as those in a triphase reaction in order to discuss the ctTectivcness factor of the catalyst, although they might be differem. The elTectivencss factors calculated are listed in Table 2. The etTcctivcncss factors of SR and FBR are much smaller than 1. It is demonstrated that the triphase reaction was inHuenced by particle dilTusion of the reactant. 

The kinetics of the triphase reaction is complicated and not yet completely described by that of the classical fluid-solid system. These experimental results revealed that it is preferable to use an SR rather than an FBR for a triphase reaction but the reactor volume of SR was much larger than that of FBR. The goal of designing an SR could be to reduce the reactor volume and stop the catalyst from flowing out of the reactor. If no premix was set before an FR, the length of reactor was too short to reduce llte performance of the FR. 

Because the triphase reaction involves not merely diffusion of a single phase into the solid support, the organic reaction take places in the organic phase, and the ion-exchange reaction occurs in the aqueous phase. The catalyst support is usually lipophilic. The organic phase and aqueous phase fill the catalyst pores to form the continuous phase and the disperse phase, respectively. The interaction between quaternary salts as well as... 

The reactivity of a liquid-solid-liquid triphase reaction (i.e., polymer-supported catalytic reaction) is influenced by the structure of the active sites, particle size, degree of cross-linkage, degree of ring substitution, swollen volume, and spacer chain of a catalyst pellet. In the past, the characteristics of a triphase reaction, subjected to the mass transfer limitation of the reactants and ion-exchange rate in the aqueous phase, have been discussed [146,158,162,178,179]. The ion-exchange rate in the aqueous phase affects the reactivity of the triphase reaction. 

Past efforts have carried out this investigation macroscopically. The planar phase boundary in a classical two-phase system cannot be described for the triphase system. Telford et al. [158] suggested an alternating shell model that requires periodical changes in the liquid phase filling the pores of the catalyst. Schlunt and Chau [150] indicated that the reaction occurred in a thin shell near the particle surface. Tomoi and Ford [142] and Hradil et al. [159] proposed that the droplet of organic (or aqueous) phase collided with the solid catalyst. However, the mechanism and effects of the internal molecular structure of the polymer support with the reaction are seldom discussed. Although some rules were listed in the text and clarified by the experimental results [27,28], the relationship between the reaction mechanism and polymer resin in a liquid-solid-liquid triphase reaction has not been understood completely. Hence, this study aims to discuss the mechanism of a polymer-supported triphase reaction. 

Among the vast scope of PTC application [27,28], approximately 40% of PTC patents involve the hydroxide ion and it has been estimated that approximately 60% of commercial PTC applications involve the hydroxide ion [28]. Many papers [61,76,96,116,164,165] have proposed that the reactivity of a reactant in an organic reaction is influenced by the base concentration. The base concentration plays a crucial role in a PT-catalyzed reaction. However, the base effect for the reactivity of reactant in a triphase reaction was rarely paid attention to. 

Most PTC reactions are carried out on an industrial scale in the batch mode in mixer-settler arrangements. In view of the reactor design in the liquid-solid-liquid PT-catalyzed reaction, Ragaini and coworkers [147-149] reported the use of fixed-bed reactors with a recycling pump or with a recycling pump and an ultrasonic mixer, and emphasized the importance of effluent recycle concept. Schlunt and Chau [150] reported the use of a cyclic slurry reactor, which allowed the immiscible reactants to contact the catalyst sites in controlled sequential steps. However, for triphase reactions in liquid-liquid systems where... 

The substitution reaction of (NPCl2)3 with phenol is a sequential reaction [166,169]. The reaction type is different from the common one-stage reaction. The experimental results can easily demonstrate the relationship between the reaction kinetic limitation and the particle diffusion limitation. In a triphase reaction, the overall kinetic cycle can be broken up into two steps by virtue of the presence of two practically insoluble liquid phases a chemical conversion step in which the active catalyst sites (Resin with phenolate ions) react with the hexachlorocyclotriphosphazene in the organic solvent, and an ion-exchange step in which the attached catalyst sites are in contact with the aqueous phase ... 

FIG. 5 Mechanism of the triphasic reaction (a) and the swollen tyrpe of resin (b). 

JF Tang. Application and Kinetics of Liquid-Solid-Liquid Triphase Reaction Ether-Ester Compound. MS thesis, Yuan-Ze University, Taoyan, Taiwan, 1998. 

Figure 5 Biphasic" catalysis in the classical water/organic (left) and water/COj (right) system. Note that the traditional setup leads to a triphasic reaction system in the presence of a gaseous reactant such as Hj, whereas the HjO/scCOj system remains truly biphasic.

Fluorous reactions in supercritical carbon dioxide (SCCO2) and fluorous triphasic reactions... 

Fluorous biphasic and triphasic reactions are at once similar and different. Like fluorous biphasic reactions (see Section 3.3), fluorous triphasic reactions use a fluorous reaction solvent. However, whereas biphasic reactions use heavy fluorous molecules, triphasic reactions use light fluorous molecules or sometimes no fluorous molecules at all. The reaction and separation occur simultaneously in triphasic reactions. Indeed, the reaction drives the separation in most triphasic processes, whereas a separation follows a reaction in biphasic methods. 

Although a few triphasic reactions have been conducted with water, mostly in the molecular recognition/transport field, synthetic chemists are only just beginning to recognize the potential and advantages of this class of reaction and separation... 

---