Biphasic range

The material was chiral-nematic and had an apparent glass transition at 276 K and a clearing point at 325.2 K, as judged by DSC measurements. The clearing point was very sharp, the biphasic range being 0.5 K as determined by optical microscopy. 

Figure 2.9 shows the experimental results of the PBLG/dimethyl formamide(DMF)-methanol system (Nakajama et ai, 1968). The axial ratios were 150 and 350, respectively, and the x value was controlled by varying the concentration of methanol. The more methanol the greater is x It was shown that for small concentrations of methanol, the biphasic range is narrow. As the volume fraction of methanol increases (up to 0.10-0.12) the biphasic range becomes wider. 

In Table II are listed some characteristic features of supercooling at the l/N transition for various polydisperse samples of DDA-9 and AZA-9. The corresponding values obtained for p-azoxyanisole (PAA), a low molecular mass nematic, are listed for comparison. Table II shows that the phase transitions are broad in polydisperse samples of relatively low molecular mass. The DSC peaks become sharper and the biphasic range Tc-T2j narrower with increasing mo lecular weight as reported previously. For values of Mn>12,000-15,000, the transitions are sharp. 

Figure 6.5(a) Textures observed for polymer (6.1) (n = 10, M - 18 700) on heating to the isotropic phase at 1°C min All micrographs focus on the same area of the same sample. Biphasic range 143-162°C. (Reprinted with permission from [42]. Copyright 1994 American Chemical Society.)... 

It is noteworthy that a clear enhancement of selectivity for the linear hydro-formylation product is observed only with cdpp (Table 5.2-1, entry e). With all other ligands, the n/iso ratios are in the 2 to 4 range. While this is in accordance with known results in the case of PPI13 (entry a) and dppe (entry c) (in comparison to monophasic hydroformylation [69]) and also with reported results in the case of Natppts (entry b in comparison to the biphasic hydroformylation of 1-pentene in [BMIM][PF(3] [46]), it is more remarkable for the bidentate metallocene ligand dppf... 

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

This arrangement ensures more efficient overall catalyst utilization and a significant increase in the yield of octenes. As an example, dimer selectivity in the 90-92 % range with butene conversion in the 80-85 % range can be obtained with a C4 feed containing 60 % butenes. Thanks to the biphasic technique, the dimerization... 

In comparison with classical processes involving thermal separation, biphasic techniques offer simplified process schemes and no thermal stress for the organometal-lic catalyst. The concept requires that the catalyst and the product phases separate rapidly, to achieve a practical approach to the recovery and recycling of the catalyst. Thanks to their tunable solubility characteristics, ionic liquids have proven to be good candidates for multiphasic techniques. They extend the applications of aqueous biphasic systems to a broader range of organic hydrophobic substrates and water-sensitive catalysts [48-50]. 

Room temperature ionic liquids are air stable, non-flammable, nonexplosive, immiscible with many Diels-Alder components and adducts, do not evaporate easily and act as support for the catalyst. They are useful solvents, especially for moisture and oxygen-sensitive reactants and products. In addition they are easy to handle, can be used in a large thermal range (typically —40 °C to 200 °C) and can be recovered and reused. This last point is particularly important when ionic liquids are used for catalytic reactions. The reactions are carried out under biphasic conditions and the products can be isolated by decanting the organic layer. 

Anaphylactic reactions may exhibit a biphasic pattern. Different studies indicated a wide variation regarding the incidence of biphasic reactions. These range from 3 to 20% regarding the incidence of biphasic reactions. The time from the initial symptoms to the onset of the secondary reaction varied from >1 up to 47 h [36]. 

Recently, great advancement has been made in the use of air and oxygen as the oxidant for the oxidation of alcohols in aqueous media. Both transition-metal catalysts and organocatalysts have been developed. Complexes of various transition-metals such as cobalt,31 copper [Cu(I) and Cu(II)],32 Fe(III),33 Co/Mn/Br-system,34 Ru(III and IV),35 and V0P04 2H20,36 have been used to catalyze aerobic oxidations of alcohols. Cu(I) complex-based catalytic aerobic oxidations provide a model of copper(I)-containing oxidase in nature.37 Palladium complexes such as water-soluble Pd-bathophenanthroline are selective catalysts for aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic... 

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]. 

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