Inverse PTC

Direction of Extraction. The "normal" PT process involves the transfer of a reactive agent from a soHd or aqueous environment into a nonpolar organic solvent. But the exact opposite can be executed extraction from an organic phase into an aqueous phase, for example, for changing selectivities. This "inverse PTC" is done relatively rarely. 

Some hydrogenations can be also carried out under so-called inverse PTC (IPTC) conditions where the function of a PT agent (e.g, cyclodextrin, CD) comprises the transfer of an organic substrate into aqueous phase [44]. Conjugated dienes are reduced with hydrogen to monoolefins in the presence of y9-CD and hydridopentacyanocobaltate anion, generated in situ, in alkaline aqueous solution [45], The same catalytic system is also highly effective for the IPTC reduction of the C=C bond in a,)ff-unsamrated carbonyl compounds [46]. 

Finally, extraction of the important reactive species can be executed in the opposite direction, from organic phase to water. This is called inverse phase-transfer catalysis. Catalysts for such processes are mostly cyclodextrins or modified derivatives thereof. Relatively few applications of this type of PTC have been published. Whereas the present section is concerned only with the organic phase as the location of the proper chemical reaction, important contributions of inverse PTC toward organometallic catalysis are detailed in Section 4.6.2. 

Fig. 2 Mechanisms for inverse- and counter-phase transfer catalyses mixed system of inverse PTC and water-soluble metal catalyst (left) ...

The inverse-PTCs with no steric limitations are hydrophilic phosphine complexes, which are able to transport the lipophilic substrates capable of forming complexes with transition metals. These hydrophilic phosphine complexes differ essentially from the other inverse-PTCs in that they have the functions of both inverse-PTCs and transition metal catalysts by themselves. Therefore we named these catalysts counter-phase transfer catalysts [4]. 

PTC reactions can be broadly classified into two main classes soluble PTC and insoluble PTC (Figure 1). Within each class, depending on the actual phases involved, reactions are further classified as liquid-liquid PTC (LLPTC), gas-liquid PTC(GLPTC), and solid-liquid PTC(SLPTC). In some cases, the PT catalyst forms a separate liquid phase, and this variant of PTC can be grouped along with traditional insoluble PTC, where the PT catalyst is immobilized on a solid support. Other nontypical variants of PTC include inverse PTC (IPTC) and reverse PTC via a reverse transfer mechanism (Halpem et al., 1985). 

Asai et al. (1994) have developed a reaction model for the oxidation of benzyl alcohol using hypochlorite ion in the presence of a PT catalyst. Based on the film theory, they develop analytic expressions for the mass-transfer rate of QY across the interface and for the inter-facial concentration of QY. Recently, Bhattacharya (1996) has developed a simple and general framework for modeling PTC reactions in liquid-liquid systems. The uniqueness of this approach stems from the fact that it can model complex multistep reactions in both aqueous and organic phases, and thus could model both normal and inverse PTC reactions. The model does not resort to the commonly made pseudo-steady-state assumption, nor does it assume extractive equilibrium. This unified framework was validated with experimental data from a number of previous articles for both PTC and IPTC systems. 

A breakthrough in biphasic, Rh(acac)(CO)2-catalyzed hydroformylation is the use of per(2,6-di-0-methyl)-P-cyclodextrin as an inverse PTC. Highly selective reactions of terminal double bonds are observed. 

Inverse PTC extraction of cations for electrophilic reactions by large UpophUic catalyst anions... 

A nontypical variant of PTC is inverse PTC (IPTC). This refers to a class of heterogeneous reactions similar to traditional PTC systems but based on the use of a phase-transfer agent to transfer species from the organic to the aqueous phase. Thus in this case, the main reaction occurs in the aqueous phase. Commonly used inverse PT catalysts include 4-diaminopyridine based compounds, pyridine, pyridine-A -oxides, and different cyclodextrin derivatives. 

Recently, Bhattacharya (1996) developed a simple, general framework for modeling PTC reactions in liquid-liquid systems. The main feature of this analysis is that it can model complex multistep reactions in both aqueous and organic phases and is thus applicable to both normal and inverse PTC reactions. It does not resort to the commonly made pseudo-steady-state assumption nor does it assume extractive equilibrium. 

Gas-solid-liquid PTC is a particularly interesting variation due to the absence of an organic solvent and the possibility of continuous operation in a plug-flow reactor packed with a solid such as inert alumina spheres. Other atypical variants include inverse PTC, where an organic-soluble reagent is transported by a suitable transfer agent into the aqueous phase, for reaction to occur there. Because of the reverse direction of catalyst transfer, it is appropriately called reverse PTC. Insoluble PTC results when the PT catalyst is immobilized on a solid support and used in a traditional liquid-liquid reaction system, or a three-phase liquid-liquid-liquid (L-L-L) systan is involved where the PT catalyst is concentrated in a third Uqnid phase. 

Relates inversely to the plasma rnicotic pressure (the O lnuk ptc.s.sure created by the plasma proteins within the sasoil. tutc). which tends to hold or prevent the nitration of sal.t and. solutes across the glomerular capilltu-ies into Bonmott i space ... 

To complete the book, four appendices are included. Appendix A contains the Matlab scripts for the most common moment-inversion algorithms presented in Chapter 3. Appendix B discusses in more detail the kinetics-based finite-volume methods introduced in Chapter 8. Einally, the key issues of PTC in phase space, which occurs in systems far from collisional equilibrium, and moment conservation with some QBMM are discussed in Appendix C and Appendix D, respectively. 

New tools for such biphasic reactions are inverse- or counter-phase transfer catalysts, which are able to transport lipophilic molecules from the organic phase into the aqueous phase. An advantage of the inverse- or counter-PTC is its applicability to reactions not only with ionic salts but also with non-ionic reagents soluble in water. Such carriers were first reported by Mathias and Vaidya and by us in 1986 [3, 4], and three types of carriers are known at present. Mathias and Vaidya found that pyridine derivatives react with acid halides in the organic phase to form the pyridinium salts, which transfer into the aqueous phase [3]. This catalysis was... 

It is difficult to verify the counter- or inverse-phase transfer catalysis strictly, because the catalyst more or less acts as a surfactant as well as a normal PTC [13]. However, it should be a positive proof of the counter-PTC to ascertain that the aqueous phase is where the products are formed. 

Selectivity of multiphase reactions catalysed by phase transfer catalysts can be greatly improved by the use of the so called capsule membrane - PTC (CM-PTC) technique. We report here the theoretical and experimental analysis of the CM-PTC and Inverse CM-PTC for exclusively selective formation of benzyl alcohol and benzaldehyde from the alkaline hydrolysis and oxidation of benzyl chloride, respectively. The theoretical analysis shows that it is possible to simultaneously measure rate constant and equilibrium constant under certain conditions. The effects of speed of agitation, catalyst concentration, substrate concentration, nature of catalyst cation, membrane structure, nucleophile concentration, surface area for mass transfer and temperature on the rate of reaction are discussed. 

Inverse capsule membrane phase transfer catalysis (ICM-PTC)... 

There is a merit in having the aqueous phase nucleophile inside the capsule and the organic phase substrate as the bulk outside phase. This way, the capsule can be reused several times and the process can be made economical. The aqueous phase byproduct salt could be washed easily with water, or digested with fresh aqueous solution of the substrate. We have named this process as inverse capsule membrane phase transfer catalysis (ICM-PTC) wherein the locale of the reaction is likely to be outer surface of the capsule. Some aspects of ICM-PTC are also reported in this paper. 

In contrast to the normal and reversed PTC methodologies, in which the chemical transformation takes place in the organic phase, it is reasonable to expect that PTC reactions can also be performed by transferring the organic reactants from the organic phase into the aqueous phase for reaction with a second reactant. Such a complementary methodology is named as inverse phase transfer catalysis (IPTC) by Mathias and Vaidya [124]. Recently, the application of IPTC in organic synthesis has been reviewed by Li et al. [150]. 

The RET gene rearrangement in papillary thyroid carcinoma is caused by an intrachromosomal inversion or by a translocation involving the tyrosine kinase receptor domain of the RET/PTC (papillary thyroid carcinoma) gene resulting the... 

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