Phase transfer catalysis applications

Efficient Asymmetric Alkylations via Chiral Phase-Transfer Catalysis Applications and Mechanism... 

Phase transfer catalysis, applications in heterocyclic chemistry, 36, 175 Phenanthridine chemistry, recent developments in, 13, 315 Phenanthrolines, 22, 1 Phenothiazines, chemistry of, 9, 321 Phenoxazines, 8, 83 Photochemistry of heterocycles, 11, I of nitrogen-containing heterocycles, 30, 239... 

Examples of phase-transfer catalysis applications include methylation of benzimidazole in 38yo yield <81AJC1729>, benzylation (76% yield) and tritylation (80%) of the same substrate <85H(23)2895>, and other benzimidazole alkylations <91BSF255>. Tetrabutylammonium sulfate has been used in the aminoalkylation of imidazole (60%) and benzimidazole (50%) with 2-chloroethylamine <91SC535>, while methylene-l,r-diimidazole and other di-imidazoles and -benzimidazoles were made with the appropriate dichloroalkane under phase transfer conditions <83JHC1245, 88JHC771,92H(34)1365>. See also <83CHE1141 >. 

Dolling, U. H., D. L. Hughes, A. Bhattacharya, K. M. Ryan, S. Karady, L. M. Weinstock, V. J. Grenda, and E. J. J. Grabowski, Efficient Asymmetric Alkylations via Chiral Phase-Transfer Catalysis Applications and Mechanism, Phase-Transfer Cctalysis New Chemistry, Catalysts, and AppUcatwns, C. M. Starks, ed., ACS... 

LeGoues FK, Hammar M, Reuter MC, Tromp RM, Majdoub M, Loupy A, Petit A, Roudesli S (1996) Coupling focused microwaves and solvent-free phase transfer catalysis application to the synthesis of new furanic diether. Tetrahedron 52 617-628... 

Thus, aqueous two-phase reactions requiring basic conditions are not candidates for solvent substitution by CO2. These two issues suggest significant potential limitations to the transfer of two-phase reactions from organic/aqueous systems to scC02/aqueous systems in phase transfer catalysis applications, although alternative solvents should be viable for the SCF phase. 

Quaternary ammonium salts compounds of the type R4N" X find application m a technique called phase transfer catalysis A small amount of a quaternary ammonium salt promotes the transfer of an anion from aqueous solution where it is highly solvated to an organic solvent where it is much less solvated and much more reactive... 

C. Starks, Ind. Appl. Surfactants IZ, 77, 165 (1990) C. Starks, ed., Phase-Transfer Catalysis Neir Chemisty, Catalysts and Applications American Chemical Society, Washington, D.C., 1987 E. Dehmlov, Phase-Transfer Catalysis Vedag Chemie, Deerfield Beach, Fla., 1983 M. Halpem, Phase-Transfer Catalysis in Climan s Tnyclopedia of Industrial Chemisty Vol. A19, VCH V6, New York, 1991 M. Halpem, Phase-Transfer Catalysis Commun. 1, 1 (1995). Specialty Sufactants Worldwide in Specialty Chemicals SRI International, Menlo Park, Calif., 1989, pp. 81—94. 

Ch. M. Starks, ed.. Phase Transfer Catalysis. New Chemistry, Catalysts, and Applications, ACS Symposium Series 326, American Chemical Society, Washington, D.C., 1987. 

With the discovery of the crowns and related species, it was inevitable that a search would begin for simpler and simpler relatives which might be useful in similar applications. Perhaps these compounds would be easier and more economical to prepare and ultimately, of course, better in one respect or another than the molecules which inspired the research. In particular, the collateral developments of crown ether chemistry and phase transfer catalysis fostered an interest in utilizing the readily available polyethylene glycol mono- or dimethyl ethers as catalysts for such reactions. Although there is considerable literature in this area, much of it relates to the use of simple polyethylene glycols in phase transfer processes. Since our main concern in this monograph is with novel structures, we will discuss these simple examples further only briefly, below. 

In specific applications to phase transfer catalysis, Knbchel and his coworkers compared crown ethers, aminopolyethers, cryptands, octopus molecules ( krakenmole-kiile , see below) and open-chained polyether compounds. They determined yields per unit time for reactions such as that between potassium acetate and benzyl chloride in acetonitrile solution. As expected, the open-chained polyethers were inferior to their cyclic counterparts, although a surprising finding was that certain aminopolyethers were superior to the corresponding crowns. 

Dietrich, Lehn and Sauvage recognized not only the possibility of enclosing a cation completely in a lipophilic shell, but they also recognized the potential for using such systems for activating associated anions. This is made particularly clear in a paper which appeared some years later One of the original motivations for our work on cryptates rested on their potential use for salt solubilization, anion activation and phase transfer catalysis . This particular application is discussed below in Sect. 8.3. 

Application of phase-transfer catalysis in heterocyclic chemistry 99MI33. 

Interests in the phase transfer catalysis (PTC) have grown steadily for the past several years [68-70]. The use of PTC has recently received industrial importance in cases where the alternative use of polar aprotic solvents would be prohibitively expensive [71-74]. Thus, the potential application of the phase transfer catalyzed aromatic nucleophilic displacement reactions between phenoxide or thiophenoxide and activated systems has... 

Quaternary ammonium compounds (quats) are prepared - by moderate heating of the amine and the alkyl halide in a suitable solvent - as the chlorides or the bromides. Subsequently conversion to the hydroxides may be carried out. Major applications of the quat chlorides are as fabric softeners and as starch cationizing agent. Several bio-active compounds (agrochemicals, pharmaceuticals) possess the quat-structure. Important applications of quat bromides are in phase transfer catalysis and in zeolite synthesis. 

C. M. Stark, C. Liotta and M. Halpen, Phase Transfer Catalysis, Fundamental, Applications and Industrial Perspectives, Chapman Hall, New York, 1994. 

Apart from the study of physicochemical aspects such as ion solvation, and bio-mimetic aspects such as photosynthesis or carrier-mediated ion transfer (Volkov et al., 1996, 1998), there are several areas of potential applications of electrochemical IBTILE measurements comprising electroanalysis, lipophilicity assessment of drugs, phase transfer catalysis, electro-assisted extraction, and electrocatalysis. 

E. V. Dehmlow and S. S. Dehmlow, Phase Transfer Catalysis, 3rd Edition, Verlag Chemie, Weinheim 1992 W. P. Weber and G. W. Gokel, Phase Transfer Catalysis in Organic Synthesis, Springer Verlag, New York, 1977 C. M. Stark, C. Liotta, and M. Halpern, Phase Transfer Catalysis Fundamentals, Applications and Industrial Perspective, Chapman and Hall, New York, 1994. 

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