Dimethylformamide, solvent system evaporation

Azido-2 -deoxy-3, 5 -diacetyluridine (1.0 g) is dissolved in 13.9 ml of ethanol-free chloroform, and dry dimethylformamide (0.139 ml) and thionyl chloride (2.2 ml) are added. The solution is heated under reflux for 6.5 hr, cooled to room temperature, evaporated, and dissolved in methanol (60 ml) that is 50% saturated with ammonia. The solution is stirred at room temperature for 5 days. TLC on SiOz (methanol-chloroform, 40 60, v/v) shows the major product to have J2/ 0.62. The solution is evaporated, and the product is separated by preparative TLC in the above system the required band elutes with methanol. The eluate is evaporated and the residue is dissolved in water and applied to a column of Dowex 1X2 (OH ) (1.7 X 21.5 cm). The column is washed with water, and the required product is eluted with methanol-water (30 70, v/v). The solvent is evaporated the remaining gum, dissolved in a little ethanol, yields white crystals when stored at 5°. The yield (determined spectrophotometrically) is 47%, m.p. 215° (decomposition). 

Although most of the reports deal with the preparation of microparticles, nanosized particles and capsules are also accessible, usually by employing ultrasonication to form very small droplets [12] from which the solvent is evaporated. Usually, the continuous phase is an aqueous solution. Inverse systems in which water is the solvent have been reported [13, 14] as well as non-aqueous emulsions [15] such as dimethylformamide-in-paraffin [16], dichoromethane-in-fluorinated solvent for microparticles [17], and formic acid-in-paraffin for... 

Elimination of the solvent from cholesteric solutions of polypeptides is usually not accompanied by destruction of the cholesteric structure. As Fig. 7.4 suggests, only a change in the pitch is observed when the concentration of polymer in the solution increases, and when the solvent is evaporated, the polymer films of polypeptides become colored as soon as the pitch of the cholesteric helix becomes commensurate with the wavelength of the reflected light. The rod-like macromolecules of polypeptides usually lie in the plane of the film and the axes of the cholesteric helices are chaotically positioned in this plane. At the same time, there are data which indicate Ae formation of crystalline films of polypeptides from a number of solvents (for example, the PBG-L-dimethylformamide system) in some cases, the formation of an unordered amorphous structure is also possible (for example, as in the presence of trifluoroacetic acid). 

Researchers studying polypeptide and polypeptide hybrid systems have also processed vesicles using two solvents. This method usually involves a common organic solvent that solubilizes both blocks and an aqueous solvent that solublizes only the hydrophilic block. The two solvents can be mixed with the polypeptide or polypeptide hybrid system at the same time or added sequentially. The choice of organic solvent depends heavily upon the properties of the polypeptide material, and commonly used solvents include dimethylformamide (DMF) [46, 59], methanol (MeOH) [49], dimethyl sulfoxide (DMSO) [50, 72], and tetrahydrofuran (THF) [44, 55]. Vesicles are usually formed when the organic solvent is slowly replaced with an aqueous solution via dialysis or removed through evaporation however, some vesicles have been reported to be present in the organic/aqueous mixture [49]. 

In a related study, polymer-supported triphenyl phosphine was used in palladium-catalyzed cyanations [136]. Commercially available resin-bound triphe-nylphosphine was mixed with palladium(II) acetate in N,N-dimethylformamide to generate the heterogeneous catalytic system under a nitrogen atmosphere. The reagents were then added to the activated catalyst and the mixture was irradiated at 140 °C for 30-50 min (Scheme 16.89). Finally, the resin was removed by filtration and evaporation of the solvent furnished the desired benzonitriles in high yields and excellent purity. 

Solvents used for paint removal are able to dissolve or considerably swell physically drying binders (e.g., vinyl chloride copolymers, cellulose nitrate, polyacrylates) and chemically cross-linked coatings (e.g., oil-based paints, dried alkyd resins, cross-linked polyester-melamine resins, cross-linked epoxy and isocyanate coatings) [14.237]. A combination of dichloromethane with low-boiling ketones or esters is particularly suitable. Small amounts of high-boiling solvents with a low volatility (e.g., tetrahydronaphthalene, solvent naphtha, methyl benzyl alcohol, or benzyl alcohol) are added to these mixtures to retard evaporation and increase the solvency. Modern paint removers do not contain chlorinated hydrocarbons, they are formulated on the basis of high boilers (e.g., dimethylformamide, dimethyl sulfoxide, propylene carbonate, and yV-methylpyrrolidone) in combination with alcohols and aromatics, or consist of aqueous, frequently alkaline or acidic systems. 

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