Inverse phase-transfer condition

Alternatively, the Sn2 nucleophilic substitution reaction between alcohols (phenols) and organic halides under basic conditions is the classical Williamson ether synthesis. Recently, it was found that water-soluble calix[n]arenes (n = 4, 6, 8) containing trimethylammonium groups on the upper rim (e.g., calix[4]arene 5.2) were inverse phase-transfer catalysts for alkylation of alcohols and phenols with alkyl halides in aqueous NaOH solution to give the corresponding alkylated products in good-to-high yields.56... 

In order to keep the mild conditions, hydroxycarbonylation has been performed in biphasic media, maintaining the catalyst in the aqueous phase thanks to water-soluble mono- or diphosphine ligands. In the presence of the sodium salt of trisulfonated triphenylphosphine (TPPTS), palladium was shown to carbonylate efficiently acrylic ester [19], propene and light alkenes [20,21] in acidic media. For heavy alkenes the reduced activity due to the mass transfer problems between the aqueous and organic phases can be overcome by introducing an inverse phase transfer agent, and particularly dimeihyl-/-i-cyclodextrin [22,23]. Moreover, a dicationic palladium center coordinated by the bidentate diphosphine ligand 2,7-bis(sulfonato)xantphos (Fig. 2) catalyzes, in the presence of tolylsulfonic acid for stability reasons, the hydroxycarbonylation of ethylene, propene and styrene and provides a ca. 0.34 0.66 molar ratio for the two linear and branched acids [24],... 

Quaternary ammonium salts of alkaloids have been used for the synthesis of optically active oxiranes from electron-poor olefins under phase-transfer conditions. The enantiomer yield is inversely proportional to the dielectric constant of the solvent,Asymmetric epoxidation in the presence of catalytic amounts of poly-(S)-amino-acids in a triphase system has been described with optical yields up to 96% ... 

Alkylation of phthalimide anion can be carried out under solid-liquid phase-transfer conditions, using phosphonium salts or ammonium salts. In the reaction systems using hexadecyltributylphosphonium bromide, alkyl bromides and alkyl methanesulfonate are more reactive than alkyl chlorides. Octyl iodide is less reactive than the corresponding bromide and chloride. ( )-2-Octyl methanesulfonate was converted into (S)-2-octylamine with 92.5% inversion. Kinetic resolution of racemic ethyl 2-bromopro-pionate by the use of a chiral quaternary ammonium salt catalyst has been reported. Under liquid-liquid phase-transfer conditions, A -alkylation of phthalimide has been reported to give poor results. ... 

The best results in terms of activity have been obtained with cationic surfactants such as octadecyltrimethylammonium bromide. The normal to branched (njiso) aldehydes ratio was found to be very dependent on the nature of the surfactant. For example, methyl 9-decenoate hydroformylation gave methyl 11-formylunde-canoate with an n/iso aldehydes ratio of 6.1 1, 4.0 1, 2.3 1 and with anionic, amphophilic, and cationic surfactants, respectively. Interestingly, hydroformylation of this substrate has also been achieved successfully with inverse-phase transfer catalysts such as chemically modified /l-cyclodcxtrins. In this approach, the cyclodextrin forms an inclusion complex with methyl 9-decenoate and transfers the alkene into the aqueous phase. Under optimal conditions, the aldehydes are obtained in a 100% yield and in an n/iso aldehydes ratio of 2.3 1 [10]. 

Trotta, F., Phthalic Acid Esters Hydrolysis Under Inverse Phase-Transfer Catalysis Conditions, /. Mol. Cat., 85, L265 (1993). 

The Haloform reaction is catalyzed by cyclodextrins in what the authors label as inverse phase transfer catalysis, 25 but the synthetic utility of this variation remains to be seen. An alternative to the use of halogen is a nitroarene catalyzed oxidation of acetophenone with sodium percarbonate or sodium perborate.26 However, the yields of substituted benzoic acids furnished by this method are mediocre (23-73%) in comparison to the conventional Haloform conditions. Likewise, the Haloform reaction of acetone with iodine in liquid ammonia is without synthetic merit (8-12%).27... 

The reduction of carbonyl compounds in aqueous media has been carried out by a number of reagents under mild conditions. The most frequently used reagent is sodium borohydride, which can also be used using phase-transfer catalysts or inverse phase transfer catalyst in a two phase medium in the presence of surfactants. 

Water-soluble calix[n]arenes are powerful receptors for non-polar substrates in aqueous solution. These compounds are promising candidates as carrier molecules for the transport of non-polar substrates through bulk water as well as inverse phase-transfer catalysts, as proven for the Suzuki coupling of iodobenzene with phenyl boronic acid [91]. 1.5-bis(4,4 -bis(perfluorooctyl)penta-l,4-dien-3-one (39) stabilizes palladium 0) nanoparticles (transmission electron microscopy) formed in the reduction of palladium dichloride with methanol. These palladium colloids are soluble in perfluorinated solvents, and they are efficient recoverable catalysts for Suzuki crosscoupling under fluorous biphasic conditions (Equation 69) [92]. 

The cyanide ion is a source of nucleophilic carbon and is only weakly basic. It is thus available as a salt that can be used in water solution. It can be alkylated most readily by nucleophilic substitution under phase-transfer conditions using a quaternary ammonium catalyst (Eq. 7.14, Section 9.6.1) [26]. The alkylations also proceed well under homogeneous conditions in DMSO. Trimethylsilyl ethers may serve as electrophiles and can be prepared in situ from alcohols. Heating an alcohol at 65 °C with sodium cyanide, trimethylchlorosilane, and a catalytic amount of sodium iodide in acetonitrile and DMF gives the nitriles in a single operation [27]. Good yields are obtained with primary, secondary, and tertiary alcohols, and inversion of configuration has been demonstrated in a secondary case. 

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]. 

Clarke S.I., Sawistowski H., Phase inversion of stirred liquiddiquid dispersions under mass-transfer conditions, Trans. Instn. Chem. Engrs. 56 (1978), p. 50-55... 

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. 

Nucleophilic azide ion displacements are enhanced by polar, aprotic solvents (e.g. DMSO) with which high yield, aryl halide displacement to form even mononitrophenyl azides can occur. Phase-transfer catalysis (permitting the use of less polar solvents) or ultrasonication (for activated primary halides) has also been used. Under such conditions, 8 2 inversion of configuration occurs and this has been observed also for alcohols under Mit-sunobu conditions (Triphenylphosphine, Diethyl Azodicarboxy-late, HN3). Retention is possible where a neighboring group is present. ... 

Bunimovich et al. (1995) lumped the melt and solid phases of the catalyst but still distinguished between this lumped solid phase and the gas. Accumulation of mass and heat in the gas were neglected as were dispersion and conduction in the catalyst bed. This results in the model given in Table V with the radial heat transfer, conduction, and gas phase heat accumulation terms removed. The boundary conditions are different and become identical to those given in Table IX, expanded to provide for inversion of the melt concentrations when the flow direction switches. A dimensionless form of the model is given in Table XI. Parameters used in the model will be found in Bunimovich s paper. 

Reactions in a condensed phase are never isolated but under strong influence of the surrounding solvent molecules. The solvent will modify the interaction between the reactants, and it can act as an energy source or sink. Under such conditions the state-to-state dynamics described above cannot be studied, and the focus is then turned to the evaluation of the rate constant k(T) for elementary reactions. The elementary reactions in a solvent include both unimolecular and bimolecular reactions as in the gas phase and, in addition, bimolecular association/recombination reactions. That is, an elementary reaction of the type A + BC —> ABC, which can take place because the products may not fly apart as they do in the gas phase. This happens when the products are not able to escape from the solvent cage and the ABC molecule is stabilized due to energy transfer to the solvent.4 Note that one sometimes distinguishes between association as an outcome of a bimolecular reaction and recombination as the inverse of unimolecular fragmentation. 

Liquid-liquid dispersion involves two phases a continuous phase (one with large volume), and a dispersed phase (one with small volume). When the volume fractions of both phases are nearly the same, phase inversion occurs. In this case, which of the two phases becomes a continuous one depends on the starting conditions as well as the physical properties of the system. The range of volume fraction within which either of two immiscible liquids may be continuous is primarily a function of the viscosity ratio it is not strongly dependent upon vessel characteristics or stirring speed (Selker and Sleicher, 1965). Here we briefly evaluate the minimum speed of rotation required to disperse one phase completely into the other, the interfacial area, and the mass-transfer coefficient in liquid-liquid dispersion. 

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