Benzene azeotropic mixtures

Figure 10.2-4 Proposed two-column design for separation of the ethyl acetate-benzene azeotropic mixture.

An azeotropic mixture con tains two or more substances that distill together at a con stant boiling point The benzene-water azeotrope contains 9% water and boils at 69 C... 

Another way to shift the position of equilibrium to favor the formation of ester is by removing water from the reaction mixture This can be accomplished by adding benzene as a cosolvent and distilling the azeotropic mixture of benzene and water... 

The cmde wax is refined by extracting at 90—100°C with an azeotropic mixture of benzene and a mixture of alcohols, typically 85% benzene and 15% methanol (see Distillation, azeotropic and extractive). Distilling the solvent leaves a wax too daddy colored to be used without added refining. 

Esters of low volatility are accesible via several types of esterification. In the case of esters of butyl and amyl alcohols, water is removed as a binary azeotropic mixture with the alcohol. To produce esters of the lower alcohols (methyl, ethyl, propyl), it may be necessary to add a hydrocarbon such as benzene or toluene to increase the amount of distilled water. With high boiling alcohols, ie, benzyl, furfuryl, and P-phenylethyl, an accessory azeotroping Hquid is useful to eliminate the water by distillation. 

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

In a 2-1. flask fitted with a total-reflux, variable-take-off distillation head is placed a solution of 53 g. (0.472 mole) of dihydroresorcinol (Note 1), 2.3 g. of -toluenesulfonic acid monohydrate and 250 ml. of absolute ethanol in 900 ml. of benzene. The mixture is heated to boiling and the azeotrope composed of benzene, alcohol, and water is removed at the rate of 100 ml. per hour. When the temperature of the distilling vapor reaches 78° (Note 2), the distillation is stopped and the residual solution is washed with four 100-ml. portions of 10% aqueous sodium hydroxide which have been saturated with sodium chloride. The resulting organic solution is washed with successive 50-ml. portions of water until the aqueous washings are neutral and then concentrated under reduced pressure. The residual liquid is distilled under reduced pressure. The yield of 3-ethoxy-2-cyclohexenone (Note 3), b.p. 66-68.5°/0.4 mm. or 115-121°/11 mm., Mq 1.5015, is 46.6-49.9 g. (70-75%). 

FIGURE 8.41 The temperature composition diagram of a minimum-boiling azeotrope (such as ethanol and benzene). When this mixture is fractionally distilled, the (more volatile) azeotropic mixture is obtained as the initial distillate. 

A procedure that has been widely used for spray residues is the separation of the residue from the sample by extraction with an organic solvent, usually benzene. After most of the solvent has been removed, the residue is treated with sodium and isopropyl alcohol and the chloride ion is estimated by standard methods. Carter 10) has determined in this manner DDT residues on a number of crops, and he has recommended the adoption by the Association of Official Agricultural Chemists of the method as a tentative one for DDT 11). Koblitsky and Chisholm 42) have determined DDT in soil samples by the sodium-isopropyl alcohol procedure after removing the DDT by extraction with an azeotropic mixture of two volumes of benzene and one volume of isopropyl alcohol. 

The reaction of phenyldisilanes PhnSi2H8 n and phenyltrisilanes PhnSi3H8 n with hydrogen halides [5] poses an inherent problem which is the formation of azeotropic mixtures between benzene (generated during the reaction) and the halosilanes. The use of mesityldisilanes and 1-naphthyldisilanes completely avoids these difficulties. 

Ionic liquids have also been applied in transfer hydrogenation. Ohta et al. [110] examined the transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in the ionic liquids [BMIM][PF6] and [BMIM][BF4]. These authors compared the TsDPEN-coordinated Ru(II) complexes (9, Fig. 41.11) with the ionic catalyst synthesized with the task-specific ionic liquid (10, Fig. 41.11) as ligand in the presence of [RuCl2(benzene)]2. The enantioselectivities of the catalyst immobilized by the task-specific ionic liquid 10 in [BMIM][PF6] were comparable with those of the TsDPEN-coordinated Ru(II) catalyst 9, and the loss of activities occurred one cycle later than with catalyst 9. 

Absolute (100%) ethanol is often made by adding benzene to the ethanol -water binary azeotrope (two components), to make a ternary azeotrope (three components). This ternary alcohol-water-benzene (18.5 7.4 74.1) azeotrope comes over until all the water is gone, followed by a benzene-ethanol mixture. Finally, absolute ethanol gets its chance to appear, marred only slightly by traces of benzene. 

Cyclohexane, 73 706-711, 797 24 27 air oxidation, 7 558—562, 559t analytical methods for, 73 710 azeotrope with benzene, 3 598t azeotropic mixtures with butyl alcohols, 4 395t... 

In some instances, it is desirable to remove lipids and other so-called extractives before proceeding with polysaccharide separation. This removal is generally accomplished through Soxhlet extraction with an azeotropic mixture of ethanol and benzene.26 2 27... 

Azeotrope formers, generally polar compounds, have the ability to form, with hydrocarbons, nonideal mixtures having vapor pressures higher than either component in the mixture and therefore lower boiling points. Fortunately, different types of hydrocarbons show different degrees of nonideality with a given azeotrope former. For example, benzene and cyclohexane boil at about 176° F., while the methanol-cyclohexane azeotrope boils at 130° F., and the methanol-benzene azeotrope boils at 137° F., a difference of 7° F. Hence, fractionation of a mixture of benzene and cyclohexane in the presence of methanol effectively separates the two hydrocarbons. 

KEYES PROCESS. A distillation patcess involving the addition of benzene to a constant-boiling OS, alcohol-water solution to obtain ahsolute 1100 ) alcohol. On distillation, a ternary azeotropic mixture containing all iltree components leaves the lop of the column while anhydrous alcohol leaves the bottom. The azeotrope tvvhich separates into two layers) is redistilled separately for recovery and reuse ol the henzene and alcohol... 

Commercial grades of DMF may be purified initially by azeotropic distillation with benzene (CAUTION). Distil a mixture of 1 litre of DMF and 100 ml of benzene at atmospheric pressure and collect the water benzene azeotrope which distils between 70 and 75 °C. Shake the residual solvent with powdered barium oxide or with activated alumina (Grade I), filter and distil under nitrogen at reduced pressure collect the fraction having b.p. 76°C/39mmHg or 40°C/10mmHg. The distillate is best stored over a Type 4A molecular sieve. 

Figure 9.20(b) illustrates the use of pervaporation with two distillation columns to break a binary azeotrope such as benzene/cyclohexane. The feed is supplied at the azeotropic composition and is split into two streams by the pervaporation unit. The residue stream, rich in cyclohexane, is fed to a distillation column that produces a pure bottom product and an azeotropic top stream, which is recycled to the pervaporation unit. Similarly, the other distillation column treats the benzene-rich stream to produce a pure benzene product and an azeotropic mixture that is returned to the pervaporation unit. 

The submitters report that /3-methylglutaraldehyde may be isolated at this point from an analogous hydrolysis. The hydrolysis is carried out with 196 g. of 3,4-dihydro-2-methoxy-4-methyl-2H-pyran in 650 ml. of water and 15 ml. of concentrated hydrochloric acid for 3 hours. After neutralization with sodium bicarbonate, the solution is saturated with sodium chloride and extracted continuously with ether for 20 hours. The ether is removed by distillation, and the product is dried thoroughly by azeotropic distillation using a benzene-hexane mixture. Distillation affords /3-methylglutaraldehyde, b.p. 85-86°/15 mm., 1.4307-1.4351. Yields up to 90% have been secured. The aldehyde polymerizes on standing but is stable as a 50% solution in water or ether. The monomer may be recovered by careful destructive distillation of the polymer. 

The synthesis of chlorohydrogendisilanes by reaction of phenylhydrogendisilanes with HC1 in benzene has been complicated by equilibration reactions in the cases of mono-and dichlorodisilanes and by the formation of azeotropic mixtures of the chlorodisilanes with the solvent and the by-product benzene54. This could be overcome by the use of the larger mesityl (Mes) substituent55 (equation 31). 

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