Monophasic solvent

Several monophasic solvent systems are useful for the separation of carbohydrate mixtures, and in all those listed in Table 9.3 the smallest solute molecules have the fastest mobility. Thus pentoses have higher RF values than hexoses, followed by disaccharides and oligosaccharides. 

Table 9.3 Some monophasic solvents for thin-layer chromatography of carbohydrates...

The enzymatic synthesis of polyphenols was carried out not only in the monophasic solvents but in interfacial systems such as micelles, reverse micelles, and biphasic and Langmuir trough systems, p-Phenylphenol was polymerized in an aqueous surfactant solution to give the polymer with a narrower molecular weight distribution in comparison with that obtained in the aqueous 1,4-dioxane.20... 

Recently, the attractive direct enantioselective hydrogenation of 6 to (S)-7 has met with some success. Thus, the Lonza group showed that the dihydrogen phosphate salt of the chemically rather labile imine 6 can be hydrogenated with Ir-fer-rocenyldiphosphine catalysts in a two-phase solvent system with up to 89% ee (Table 2, entry 3) [12]. Similar results were achieved in our laboratories with the hydrogen sulfate salt of 6 and an Ir catalyst derived from a sterically bulky f-Bu-DIOP ligand in a monophasic solvent system (Table 1, entry 4) [13]. Chemose-... 

Resell CM, Terreni M, Fernandez-Lafuente R et al. (1998) A criterion for the selection of monophasic solvents for enzymatic synthesis. Enzyme Microb Technol 23 64-69 Roy JJ, Abraham TE (2004) Strategies in making cross-linked enzyme crystals. Chem Rev... 

Jessop and coworkers [46] recently developed a method of using switchable additives for hydroformylation, which allows homogeneous catalysis to take place in a monophasic solvent mixture with subsequent catalyst/product separation occurring in a biphasic solvent mixture. The method overcomes the traditional mass-transfer issues that accompany biphasic reactions, and tolerates alkenes of lower water solubility better than traditional aqueous/organic biphasic catalysis. 

From these results, the Institut Fran ais du Petrole (IFF) has developed a biphasic version of its established monophasic Dimersol process , which is offered for licensing under the name Difasol process [98]. The Difasol process uses slightly acidic chloroaluminate ionic liquids with small amounts of allcylaluminiums as the solvent for the catalytic nickel center. In comparison to the established Dimersol process , the new biphasic ionic liquid process drastically reduces the consumption of Ni-cata-lyst and allcylaluminiums. Additional advantages arise from the good performance obtained with highly diluted feedstodcs and the significantly improved dimer selectivity of the Difasol process (for more detailed information see Section 5.3). 

The authors correlate the observed catalytic activity with the solubility of the 1,3-butadiene feedstock in the ionic liquid, which was found to be twice as high in the tetrafluoroborate ionic liquid as in the corresponding hexafluorophosphate system. It is noteworthy that the same reaction in a monophasic systems with toluene as the solvent was found to be significantly less active (TOF = 240 h ... 

To eliminate the need to recover the product by distillation, researchers are now looking at thermomorphic solvent mixtures. A thermomorphic system is characterized by solvent pairs that reversibly change from being biphasic to monophasic as a function of temperature. Many solvent pairs exhibit varying miscibility as a function of temperature. For example, methanol/cyclohexane and n-butanol/water are immiscible at ambient temperature, but have consolute temperatures (temperatures at which they become miscible) of 125°C and 49°C, respectively (3). 

MPVs Monophasic vesicles SPLVs prepared with water-miscible solvent 14... 

Lin and coworkers disclosed that, at room temperature, nonenzymatic chemical addition was still observed in a water-organic solvent biphasic reaction system, though the volume of aqueous phases was relative small. Lin developed a method of preparing an active enzyme meal that contained essential water to retain its power for catalysis and found a new catalytic reaction system by application of the prepared meal in a nonaqueous monophasic organic medium (Figure 5.7). There was no problem over a wide range of temperature (from 0-30 °C) when the reactions were carried out under micro-aqueous conditions [50]. 

C02 as adjustable-solvent In this case, the reaction is carried out in scCOz under truly monophasic conditions and the catalyst is selectively precipitated through a change in temperature and/or pressure. Again, product isolation is achieved by SCF extraction. 

The Eyring plot for the monophasic [Fe(CN)g] oxidation of spinach plasto-cyanin in 50 50 (v/v) MeOH-HjO mixed solvent over the extended temperature range 25 to —35 °C, pH 7.0, 1 = 0.10 M(NaCl), exhibits a marked downward curvature. Fig. 6 [105]. The rate constant at 25 °C of 1.04xl0 M" s compares with the value in Table 4 of 8.0 x 10 s . A plot of first-order... 

Enzyme catalysis in nonconventional media can be divided into a number of different categories depending on whether the aqueous and organic phases are miscible or immiscible and whether the biocatalyst is dissolved or not. In this section, only free enzymes will be considered. Thus, the field can be simplified to just two categories, depending on whether the solvent is water miscible or immiscible (systems employing water-immiscible solvents, where water is present in quantities that are below its solubility limit, have been considered as monophasic) ... 

Another way to produce biphenyl derivates using flow was described by Leeke et al. [34] where they performed a Pd catalyzed Suzuki-Miyaura synthesis in the presence of a base. First experiments were carried out in toluene/methanol solvent. A reaction mixture was passed through the encapsulated Pd filled column bed length 14.5 cm (some cases 10 cm) x 25.4 mm id. 45 g of PdEnCat. Base concentration, temperature and flow rate were optimized and at optimum parameters (0.05 M base concentration, 100°C and 9.9 mL/min) the conversion was 74%. Then the reaction was performed under supercritical conditions using supercritical CO2 at high pressure and temperature. After optimizing the concentration of base, flow rate, pressure and temperature, the highest conversion rate (81%) was observed at 166 bar and 100°C where the reactant mixture was monophasic in the supercritical state. This system is able to produce 0.06 g/min of the desired product. 

As an alternative to distillation, extraetion with a eo-solvent that is poorly mis-eible with the ionie liquid has often been used. There are many solvents that can be used to extract product from the ionic liquid phase, whether from a monophase reaction or from a partially miscible system. Typical solvents are alkanes and ethers (15). Supercritical CO2 (SCCO2) was recently shown to be a potential alternative solvent for extraction of organics from ionic liquids (22). CO2 has a remarkably high solubility in ionic liquids. The SCCO2 dissolves quite well in ionic liquids to facilitate extraction, but there is no appreciable ionic liquid solubilization in the CO2 phase in the supercritical state. As a result, pure products can be recovered. For example, about 0.5 mol fraction of CO2 was dissolved at 40°C and 50 bar pressure in [BMIMJPFe, but the total volume was only swelled by 10%. Therefore, supercritical CO2 may be applied to extract a wide variety of solutes from ionic liquids, without product contamination by the ionic liquid (29). 

Monophasic systems in which the ionic liquid acts as both the solvent and the catalyst, e.g. dialkylimidazolium chloroaluminates as Friedel-Crafts catalysts (see later). 

Semiconductor nanoclusters trapped in AOT w/o microemulsions are reported to exhibit longer excited state lifetimes (about 10-100 ns) than those in aqueous solution or in monophasic organic solvents [213]. Clearly the surfactant-nanoparticle interaction is very important not only in restricting growth but also in extending the hfetimes of the excited states. Tata et al. [214] have shown that the removal of water from the micelles leads to a strong increase in fluorescence intensity, and the addition of specific quencher, 4-hydroxythiophenol, leads to variations in quenching efficiencies. 

Most of the oxidants used with these catalysts tend to be water soluble. However, the use of tetrabutylammonium monopersulfate (5) has been reported to provide relatively smooth oxidation with good ee s e.g, 4 -> 6) under monophasic conditions in organic solvents. The enantioselectivity is both substrate and catalyst dependent, with best results being obtained from electron-rich alkenes and Katsuki-type catalysts (c/. 2) <99TL1001>. Che and co-workers <99CC1789> have also reported on the use of an immobilized chromium binaphthyl catalyst, which offers the advantage of simple work-up and catalyst recovery. 

Mixtures of chloroform and methanol have had wide use as lipid extractants (e.g., Bligh and Dyer, 1959). This solvent system allows for extraction of both polar and nonpolar lipids, unlike extraction with hexane (see Basic Protocol 1 and Alternate Protocol 1). Optimum extraction may be achieved when water in the tissue, or that added to the medium, y ields a monophasic solution. Subsequently, additional water and/or chloroform... 

Enzymes as different as yeast alcohol oxidase, mushroom polyphenol oxidase, and horse-liver alcohol dehydrogenase demonstrated vastly increased enzymatic activity in several different solvents upon an increase in the water content, which always remained below the solubility limit (Zaks, 1988b). While much less water was required for maximal activity in hydrophobic than in hydrophilic solvents, relative saturation seems to be most relevant to determining the level of catalytic activity. Correspondingly, miscibility of a solvent with water is not a decisive criterion upon transition from a monophasic to a biphasic solvent system, no significant change in activity level was observed (Narayan, 1993). Therefore, the level of water essential for activity depends more on the solvent than on the enzyme. 

The new cyclosporine formulation (Sandimmun Neoral, Novartis Pharmaceuticals Corporation, East Hanover, NJ) is a self-microemulsifying drug delivery system, which consists of the drug in a lipophilic solvent (corn oil), hydrophilic cosolvent (propylene glycol) surfactant and an antioxidant [37]. Upon contact with GI fluids, Sandimmun Neoral readily forms a homogenous, monophasic microemulsion, which allows the absorption of the drug molecules. Unlike Sandimmun, the formation of this microemulsion is independent of bile salt activity, and indeed, studies have shown that the absorption of cyclosporine from the new formulation is much less dependent on bile flow [38] and is unaffected by food intake [39],... 

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