Mixed-solvent systems

Unlike earlier sulfonated styrene/divinylbenzene copolymers, these sulfonated gels can he run in virtually any solvent from water and buffers to pure organics as well as most any mixed solvent systems desired. In aqueous systems they absorb water and in organic solvents they stay swollen by imbibing organic solvents. 

Figures 13.30-13.53 demonstrate the use of various mobile phases for polymer SEC using standard mixed-bed DVB columns. Once again these applications demonstrate that PDVB gels will easily tolerate virtually any solvent or mixed solvent system.

Another issue important to the success of this chiral titanium reagent 31 was the discovery of a marked solvent effect. When the fumaric acid derivative is reacted with isoprene in the presence of 10 mol% of the titanium reagent 31 in toluene, poor optical purity results (36-68% ee). Interestingly the optical purity of the adduct greatly increased in the order benzene, toluene, xylenes, and mesitylene, with 92% ee obtained in the last. Mesitylene is difficult to remove, because of its high boiling point, and other solvents were screened in detail. As a result, the mixed solvent system toluene petroleum ether (1 1) was discovered to be very effective. 

As already indicated, ion exchange resins are osmotic systems which swell owing to solvent being drawn into the resin. Where mixed solvent systems are used the possibility of preferential osmosis occurs and it has been shown that strongly acid cation and strongly basic anion resin phases tend to be predominantly aqueous with the ambient solution predominantly organic. This effect (preferential water sorption by the resin) increases as the dielectric constant of the organic solvent decreases. 

In mixed solvent systems the difference in the solvating abilities of solvent molecules S and S2 causes a selective solvation of cations and anions [119,120],... 

Mel poisoning in isobutylene polymerization with r-BuX/Me3Al systems was studied using mixed solvent systems containing various proportions of MeG and Mel. Results, together with experimental details and materials used are reported in Fig. 2. 

Mixed solvent systems containing water are included below even in case water is only a minor constiment, molten salts are listed after liquid solvent-based systems. 

A mixed solvent system of an IL with organic solvent sometimes gave very nice results LundelP reported that enhanced enantioselectivity was obtained when lipase-catalyzed acylation was carried out in a mixed solvent system of [emim][TFSI] with t-BuOMe (1 1), while poor enantioselectivity was recorded for that in the pure [emim][TFSI] solvent (Fig. 11). 

Griengl reported the first example of hydroxynitrile lyase-catalyzed cyanohydrin formation in a mixed solvent system of [bmim][BF4] and buffer (pH 3.7) (1 1) (Fig. 19). In the reaction, a mixed solvent system was essential, but excellent results were obtained. 

The solubihty parameter theory can be also used for the mixed-solvent systems. The total-solubility parameter 8, is given by the sum of the individual solubihty parameters in terms of the volume fractions (pj in the mixture, according to Equation 4.6 ... 

The effects of pH and of mixed solvent systems have been described by Tongaree et al. [13]. 

A similar technique, the so-called spontaneous emulsification solvent diffusion method, is derived from the solvent injection method to prepare liposomes [161]. Kawashima et al. [162] used a mixed-solvent system of methylene chloride and acetone to prepare PLGA nanoparticles. The addition of the water-miscible solvent acetone results in nanoparticles in the submicrometer range this is not possible with only the water-immiscible organic solvent. The addition of acetone decreases the interfacial tension between the organic and the aqueous phase and, in addition, results in the perturbation of the droplet interface because of the rapid diffusion of acetone into the aqueous phase. 

Drug solubility can be increased by the use of solubilizing agents, such as those listed in Table 2, and by nonaqueous solvents or mixed solvent systems, to be... 

NB. Mixed solvent systems are shown as e.g. acn-aq (0.01 M) where the number in parentheses indicates the concentration of the lesser constituent ITO-Indium/tin oxide-coated glass, Ar- Solutions purged with argon, Ar atm - Experiment performed under an argon atmosphere, N2 atm - Experiment performed under a nitrogen atmosphere b All potentials are measured vs. SCE unless otherwise stated ... 

NB. Mixed solvent systems are shown as e.g. acn-aq (0.01 M) where the number in parentheses indicates the concentration of the lesser constituent... 

Compounds of the porphyrin series, like other aromatic compounds, have a strong tendency to aggregate in solution. In general, aggregation is favoured by increased concentration and by an increased proportion of the poor solvent in a mixed solvent system.67-70 The aggregate shows reduced fluorescence and reduced PDT activity with respect to the monomer.71... 

Bis(indolyl)nitroethanes are obtained readily in 7-10 min in high yields (70-86%) on fine TLC-grade silica gel (5-40 pm) by Michael reaction of 3-(2 -nitrovinyl) indole with indoles. The same reaction reported requires 8-14 h for completion at room temperature [77]. Several functionalized resins have been prepared from Merrifield resin via a MW-assisted procedure that utilized mixed solvent system to facilitate the swelling of resins and coupling with microwaves [78], These resins can function as solid supports or polymeric scavengers in solid phase synthesis. 

Suppose, after all this, you still haven t found a solvent. Look again. Perhaps your compound completely dissolved in ethanol at room temperature, and would not dissolve in water. AHA Ethanol and water are miscible (i.e., they mix in all proportions) as well. You will have to perform a mixed-solvent recrystallization (see Working with a Mixed-Solvent System ). 

WORKING WITH A MIXED-SOLVENT SYSTEM—THE GOOD PART 103... 

If, after sufficient agony, you cannot find a single solvent to recrystallize your product from, you may just give up and try a mixed-solvent system. Yes, it does mean you mix more than one solvent, and recrystallize using the mixture. It should only be so easy. Sometimes, you are told what the mixture is and the correct proportions. Then it is easy. 

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