Drying liquids, azeotropic distillation

This versatile solvent has good chemical stability in the absence of acids and bases which catalyse the cleavage of the lactam ring. It is most conveniently dried by initial azeotropic distillation with previously dried benzene or toluene as described for DMF, and the residual liquid is shaken with barium oxide, the desiccant is removed and the solvent is fractionally distilled under reduced pressure (c. 20 mm). The pure solvent has b.p. 94-96 °C/20 mmHg, or 202 °C/760mmHg. 

Allyl alcohol forms an azeotropic mixture with water, and the mixture is a homogeneous liquid. Therefore, to obtain dry allyl alcohol, ternary azeotropic distillation and dehydration are required. 

Vinylidene chloride (VDC) is prepared commercially by the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess (2—10%) (3,9). A continuous liquid-phase reaction at 98—99°C yields 90% VDC. Caustic gives better results than lime. Vinylidene chloride is purified by washing with water, drying, and fractional distillation. It forms an azeotrope with 6 wt % methanol (10). Purification can be achieved by distillation of the azeotrope, followed by extraction of the methanol with water an inhibitor is usually added at this point. Commercial grades contain 200 ppm of the monomethyl ether of hydroquinone (MEHQ). Many other inhibitors for the polymerization of vinylidene chloride have been described in patents, but MEHQ is the one most often used. The inhibitor can be removed by distillation or by washing with 25 wt % aqueous caustic under an inert atmosphere at low temperatures. 

Tellurium Tetrabutoxide1 10 g (135 mmol) of butanol are added to 2.71 g (7.4 mmol) of tellurium tetraisopropoxide and the mixture is diluted with benzene. After the exothermic reaction has subsided, the mixture is heated under reflux for 2 h and then the isopropanol/benzene azeotrope is distilled from the mixture at 12°. Excess butanol and benzene arc distilled off, the residue is dried under reduced pressure at 20°, and the resultant colorless liquid is distilled yield 2.9 g (92%) b.p. 150°/ 0.8 torr. 

Azeotropic distillation is a useful technique for removing water from organic solutions. For example, toluene and water form an azeotrope having a composition of 86.5 wt % of toluene and 13.5 wt % water, and so distillation of a mixture of these two effectively removes water from a mixture. This technique is used in the Experimental Procedure of Section 18.4 for driving an equilibrium in which water is being formed to completion. Azeotropic distillation may also be used to dry an organic liquid that is to be used with reagents that are sensitive to the presence of water. This application is found in the Experimental Procedure of Section 15.2, in which anhydrous p-xylene is required for a Friedel-Crafts alkylation reaction. 

Place the recovered toluene that was obtained from the azeotropic distillation and from removal from the reaction mixture into the container for nonhalogenated organic liquids. Flush the sodium bicarbonate wash down the drain. Use a small amount of recovered toluene to rinse the pot residue from the simple distillation of the product into the container for nonhalogenated organic liquids. After residual solvent has evaporated from the sodium sulfate on a tray in the hood, place the drying agent in a container for nonhazardous waste. 

Efficient enzymatic conversion can be achieved even though most of the reactants are present as solids, provided that there is a liquid phase in which the reaction can occur. This approach has been successfully used for carbohydrate ester synthesis with synthesis of glucose esters of fatty acids between C12 and C18 as typical examples [34]. It is important that the substrates dissolve during the reaction, and often the products precipitate as they are formed, which can be an advantage due to a favourable effect on the equilibrium position. Candida antarctica lipase B is an efficient catalyst in this system and solvents used (in moderate amounts) include ethyl methyl ketone, acetone or dioxane. In order to increase the ester yield, water formed in the reaction can be removed by azeotropic distillation and the solvent (e.g. ethyl metyl ketone) can after condensation be dried by pervaporation, giving a practically useful complete process [35]. 

Liquid pyridine and alkylpyridines are considered to be dipolar, aprotic solvents, similar to dimethylformarnide or dimethyl sulfoxide. Most pyridines form a significant azeotrope with water, allowing separation of mixtures of pyridines by steam distillation that could not be separated by simple distillation alone. The same azeotropic effect with water also allows rapid drying of wet pyridines by distillation of a small forecut of water azeotrope. 

Dimethyl-2-oxazoline is commercially available from Columbia Organic Chemicals, 912 Drake Street, Columbia, South Carolina, or may be prepared as follows. In a 250-ml., three-necked flask is placed 89.14 g. (1.0 mole) of 2-amino-2-methyl-l-propanol, and the flask is cooled in an ice bath. The amine is carefully neutralized with 52.3 g. (1.0 mole) of 90.6% formic acid over a 1-hour period. A magnetic stirring bar is added, the flask is fitted with a short path distillation head, and the reaction mixture is placed in a silicon oil bath which is rapidly heated to 220-250°. The azeotropic mixture of water and oxazoline distills over a period of 2-4 hours and is collected in an ioe-cooled flask containing ether. The aqueous layer is separated, saturated with sodium chloride, and extracted with three 50-ml. portions of ether. The combined ethereal extracts are dried over potassium carbonate, filtered to remove the drying agent, and the ether is removed at 35-40° at atmospheric pressure. The 4,4-dimethyl-2-oxazoline is collected as the temperature rises above 85°. The yield is 56.7-62.7 g. (57—63%) of a colorless mobile liquid, b.p. 99-100° (758 mm. Hg). 

---