Two-phase solvent system

The solubility of many steroids in ammonia-tetrahydrofuran-/-butyl alcohol is about 0.06 A/, a higher concentration than has been reported in other solvent systems. Still higher concentrations may be possible in particular cases by suitable variation in the solvent ratios Procedure 3 (section V) describes such a reduction of estradiol 3-methyl ether at a 0.12 M concentration. A few steriods such as the dimethyl and diethyl ketals of estrone methyl ether are poorly soluble in ammonia-tetrahydrofuran-/-buty] alcohol and cannot be reduced successfully at a concentration of 0.06 even with a 6 hour reduction period. The diethyl ketal of estrone methyl ether is reduced successfully at 0.12 M concentration using a two-phase solvent system of ammonia-/-amyl alcohol-methylcyclohexane (Procedure 4, section V). This mixture probably would be useful for any nonpolar steroid that is poorly soluble in polar solvents but is readily soluble in hydrocarbons. 

Countercurrent chromatography (CCC) refers to a chromatographic technique which allows the separation of solutes in a two-phase solvent system subjected to a gravitational field. Two immiscible liquid phases, constituted by one or more solvents or solutions, are submitted to successive equilibria, where the solutes to be separated... 

Finally, Sinou el al. have employed a chiral tetrasulfonated diphosphine as a ligand in the Rh-catalysed reduction of the Schilf base depicted in Scheme 8.34. In the presence of an aqueous-organic two-phase solvent system, a quantitative yield combined with a moderate enantioselectivity of 34% ee were obtained for this reaction. 

Scheme 4.1 Epoxidation catalysts tested in two-phase solvent systems.

As reported by Griengl and coworkers, benzaldehyde, decanal, undecanal, and dodecanal were reacted with HCN in a two-phase solvent system aqueous buffer and ionic liquids 1 -ethyl-3-methylimidazolium tetrafluoroborate, 1 -methyl-3-propylimidazolium tetrafluoroborate, and l-butyl-3-methyl-imidazolium tetrafluoroborate in the presence of the HNLs from Prunus amygdalus and Hevea brasiliensis. When compared with the use of organic solvents as the nonaqueous phase, the reaction rate was significantly increased and the enantioselectivity remained good [51]. 

Table 41.12 Rh-catalyzed enantiomeric hydrogenation of N-acetylphenylethenamine using Rh-complex 2 and Me-BDPMI 3 in a [BMIM][SbF6]//PrOH two-phase solvent systems [103],a)...

Since charcoal is such a good sorbent and is readily available, the solution to some sampling problems is to find a way to increase the recovery of that compound from charcoal. One way is by increasing the solvent/sorbent ratio as discussed in the phase equilibrium section. Two other approaches are the use of mixed solvents and the two-phase solvent system. 

The isolation method of solvent extraction has been suggested as a potentially feasible process to concentrate trace organic compounds from finished drinking water (4). One positive attribute of the solvent extraction method is that its performance for any given compound is theoretically predictable from a partition coefficient of a compound between the water sample and an organic solvent. The partition coefficient can be experimentally determined for any solute in any two-phase solvent system (7, 8). Variables of the extraction procedure such as solvent-to-water ratio and the choice of solvents can be adjusted to achieve optimum recovery. 

Either amine oxides (usually NMO) [11,26] or potassium ferricyanide/potassium carbonate [12,35] are used as cooxidants for catalytic AD. The choice of oxidant carries with it the choice of solvent for the reaction, and the details of the catalytic cycle appear to be quite different depending on which oxidant-solvent combination is used. When potassium fenicyanide/potas-sium carbonate is used as the oxidant, the solvent used for the reaction is a 1 1 mixture of i-butyl alcohol and water [35,36], This solvent mixture, normally miscible, separates into two liquid phases upon addition of the inorganic reagents. The sequence of reactions summarized below in Eqs, 6D.1-6D.5 has been postulated as occurring under these conditions. This reaction sequence is further illustrated in the reaction cycle shown in Scheme 6D.2, which also emphasizes the role of the two-phase solvent system. 

More recently, two-phase solvent systems, sometimes with temperature-dependent mutual miscibility of the two components, have gained interest as reaction media [149-156]. Having different solubilities for educts, products, reagents, and catalysts, biphasic solvent combinations can facilitate the separation of products from reaction mixtures. Since perfluorohydrocarbons [149-154] and room temperature ionic liquids [155, 156] are immiscible with many common organic solvents, they are particularly suitable for the formation of such biphasic solvent systems see also Section 5.5.13. 

Crownpak CR(+). Chiral separation of gemifloxacin was performed in analytical counter-current chromatography using (- -)-(18-crown-6)-tetra-carboxylic acid as CSP. A successful separation of gemifloxacin enantiomers could be achieved using a two-phase solvent system composed of 1-butanol-ethyl-acetate-bis(2-hydroxyethyl)amino tris (hydroxymethyl)methane acetate buffer with a small amount of CgH4 [19]. 

To overcome a main problem eissociaied with homogeneous catalysis, i.e. the recovery of the catalyst, the latest development in this field comprises the functionalization of catalyst precursor 1—3 with perfluoroalkyl chains to enable catalysis to be carried out in an txganic/perfluorinated two-phase solvent system. It has been demonstrated that this approach allows reuse of the catalyst several times. Recently, an elegant synthetic route towards the enantioselective synthesis of chiral allylic alcohols in which... 

Selective reduction to hydroxylamine can be achieved in a variety of ways the most widely applicable systems utilize zinc and ammonium chloride in an aqueous or alcoholic medium. The overreduction to amines can be prevented by using a two-phase solvent system. Hydroxylamines have also been obtained from nitro compounds using molecular hydrogen and iridium catalysts. A rapid metal-catalyzed transfer reduction of aromatic nitroarenes to N-substituted hydroxylamines has also been developed the method employs palladium and rhodium on charcoal as catalyst and a variety of hydrogen donors such as cyclohexene, hydrazine, formic acid and phosphinic acid. The reduction of nitroarenes to arylhydroxyl-amines can also be achieved using hydrazine in the presence of Raney nickel or iron(III) oxide. ... 

Selective extraction methods using two-phase solvent systems may also be used to enrich fatty acids. Solvent systems such as dimethyl formamide, hexane, and ethylene glycol can form a two-phase system that effectively partitions sunflower oil TAGs rich in linoleic acid from those depleted in linoleic acid (111). TAGs partitioned in this way may contain up to 84.7% linoleic acid. This method would not likely be used in industry because the magnitude of the losses are usually unacceptable. 

Aqueous Two-Phase Solvent Systems for Countercurrent Chromatograp... 

Settling Time of Two-Phase Solvent Systems in Countercurrent Chroma... 

These aqueous two-phase solvent systems are more difficult to handle than organic-based solvent systems, so that the number of applications in the literature is quite small as compared to the other systems. However, these applications are really specific, quite often striking in their separation power, and they truly reveal some unique features of countercurrent chromatography. 

Biotic Dicarboxylic Acids, CCC Separation with Polar Two-Phase Solvent Systems Using a Cross-Axis Coil Planet Centrifuge... 

The cross-axis CPC produces a unique mode of planetary motion, such that the column holder rotates about its horizontal axis while revolving around the vertical axis of the centrifuge.This motion provides satisfactory retention of the stationary phase for viscous, low-interfacial tension, two-phase solvent systems, such as aqueous-aqueous polymer phase systems. Our previous studies demonstrated that the cross-axis CPC equipped with a pair of multiplayer coils or eccentric coil assemblies in the off-center position was very useful for the separation of proteins with polyethylene glycol-potassium phosphate solvent systems.The apparatus is also useful for the separation of highly polar compounds such as sugars,hippuric acid, and related compounds, which require the use of polar two-phase solvent systems. 

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