Hydrochloric acid azeotropic mixtures

The residue was subjected to azeotropic operation with toluene two times, and ether was added to the residue. The precipitate derived from trioxane was removed by filtration and washed with ether, and the combined ethereal solutions were concentrated under reduced pressure. The residue was dissolved in ethyl acetate, and the solution was washed with water and aqueous saturated solution of sodium chloride, was dried, and was concentrated to give 4 g of an oily material. The oily material was dissolved in 20 ml of methanol and to the solution was added 20 ml of aqueous 1 N solution of sodium hydroxide, and the mixture was stirred for 14 hours at room temperature. After removal of methanol under reduced pressure, water was added to the mixture, and this solution was acidified to pH 3 with aqueous 2 N hydrochloric acid. The mixture was extracted five times with ethyl acetate, and the ethyl acetate extract was dried and concentrated to give 3.5 g of crude crystals. After addition of ethanol to the crude crystals, the crude crystals were filtered. The filtrate was concentrated, and to the residue was added ethanol and ethyl acetate, and precipitate was collected by filtration. The combined amount of the crude crystals was 1.6 g. After the combined crude crystals were methylated with diazomethane, the reaction product was dissolved in 20 ml of ethyl acetate. To this solution was added 1.5 g of sodium acetate and 300 mg of 10% palladium-carbon, and the mixture was stirred for 2 hours under hydrogen. Then, the reaction product was filtered, and after addition of aqueous saturated solution of sodium hydrogen carbonate to the filtrate, the mixture was extracted two times with ethyl acetate. The extract was washed with an aqueous saturated solution of sodium chloride, dried, and concentrated to give 1.3 g of crude crystals. The crude crystals were recrystallized from ethyl acetate to yield 765 mg of the title compound (melting point 134-135°C, yield 43%). 

Metal chlorides which are not readily salted out by hydrochloric acid can require high concentrations of HCl for precipitation. This property is used to recover hydrogen chloride from azeotropic mixtures. A typical example is the calcium chloride [10043-52-4] addition used to breakup the HCl—H2O azeotrope and permit recovery of HCl gas by distillation (see Distillation, azeotropic and extractive). 

Although less common, azeotropic mixtures are known which have higher boiling points than their components. These include water with most of the mineral acids (hydrofluoric, hydrochloric, hydrobromic, perchloric, nitric and sulfuric) and formic acid. Other examples are acetic acid-pyridine, acetone-chloroform, aniline-phenol, and chloroform-methyl acetate. 

If, for example, a mixture of ethanol and water is distilled, the concentration of the alcohol steadily increases until it reaches 96 per cent by mass, when the composition of the vapour equals that of the liquid, and no further enrichment occurs. This mixture is called an azeotrope, and it cannot be separated by straightforward distillation. Such a condition is shown in the y — x curves of Fig. 11.4 where it is seen that the equilibrium curve crosses the diagonal, indicating the existence of an azeotrope. A large number of azeotropic mixtures have been found, some of which are of great industrial importance, such as water-nitric acid, water-hydrochloric acid, and water-alcohols. The problem of non-ideality is discussed in Section 11.2.4 where the determination of the equilibrium data is considered. When the activity coefficient is greater than unity, giving a positive deviation from Raoult s law, the molecules of the components in the system repel each... 

What is the solubility of hydrogen chloride in water What is the composition of an azeotropic mixture of hydrochloric acid with water What is called an azeotropic mixture of liquids and how does it differ from the pure liquids ... 

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. 

In a similar method a well-defined excess of water ( H20/ Nd >5/1) is applied in combination with an excess of carboxylic acid. In this route either Nd oxide or Nd carbonate are used as Nd sources. The excess of water is necessary to start the reaction. In a patent given by Huang et al. the reaction is also kicked by the addition of diluted hydrochloric acid. The reaction is performed in a temperature and time range of 80-150°C/2-4h. At the end of the reaction the mixture separates easily into two clear phases which do not contain unreacted Nd2C>3. Centrifugation is not necessary to achieve phase separation. Water is removed from the upper phase by azeotropic distillation. The water content of the dried Nd-carboxylate solution is below 2000 ppm [217,218]. 

Alkylidenecyclopentanones (68 and 69), formed by condensation of the morpholine enamine and the corresponding aldehyde with azeotropic removal of water, may be isomerized to the thermodynamically stable 2-alkyl-2-cyclopentenones by heating with hydrochloric acid in butanol152 (Scheme 56). Condensation of glyoxylic esters with aldehyde enamines gives a mixture of (E)- and (Z)-3-alkyl-4-oxo-2-butenoic esters (70 and 71). The Z-isomers (71) cyclysed to the butenolide (72) under neutral conditions,... 

Cool the solution in an ice bath and very slowly add dry methanol (5 mL) by pipette down the condenser, to quench the excess borane. After the effervescence has ceased, add hydrochloric acid (1 M, 5 mL) and stir the mixture for 10 min. Evaporate the solvents using a rotary evaporator and to the residue add methanol (10 mL) and evaporate again. Repeat this procedure three times to aid removal of trimethyl borate, which forms a low-boiling azeotrope with methanol, b.p. 55°C. 

The ratio of cycHc to linear oligomers, as well as the chain length of the linear siloxanes, is controlled by the conditions of hydrolysis, such as the ratio of chlorosilane to water, temperature, contact time, and solvents (60,61). Commercially, hydrolysis of dimethjidichlorosilane is performed by either batch or a continuous process (62). In the typical industrial operation, the dimethyldichlorosilane is mixed with 22% azeotropic aqueous hydrochloric acid in a continuous reactor. The mixture of hydrolysate and 32% concentrated acid is separated in a decanter. After separation, the anhydrous hydrogen chloride is converted to methyl chloride, which is then reused in the direct process. The hydrolysate is washed for removal of residual acid, neutralized, dried, and filtered (63). The typical yield of cycHc oligomers is between 35 and 50%. The mixture of cycHc oHgomers consists mainly of tetramer and pentamer. Only a small amount of cycHc trimer is formed. 

The most common example of an azeotropic mixture is hydrochloric acid, for which the azeotropic mixture boiling at one atmosphere pressure contains 20.22 per cent (by weight) of hydrogen... 

To decompose the addition compound, immerse the tube in ice-salt mixture and add slowly, by means of a dropper, diluted acid obtained by mixing 5 ml concentrated hydrochloric acid with 5 g of ice. Add only sufficient hydrochloric acid to dissolve the precipitate which forms. Allow to stand until all the residual magnesium has reacted with the acid. The ether layer should have a volume of at least 10-12 ml. If it is le.ss, add ordinary ether to make up this volume. Insert the separatory stopper and remove the aqueous layer. Dry the ether layer by adding 0.5-1 g of anhydrous calcium sulfate. Care must be taken to drj the ether thoroughly, since the carbinol forms an azeotropic mixture with water. Transfer the dry ether mixture to an eight-inch distilling tube, and distill from a water bath until the temperature rises to 70°. Remove the water bath and heat over a small smoky flame. The fraction which boils at 77-84° is collected. 

If a mixture of ethanol and water is distilled, eventually it will form a solution that is 95 % ethanol regardless of the starting composition. Hydrochloric acid and water will form a 20.22 % HCl solution, and chloroform and acetone will form a 65.5 % CHCI, solution. These solutions are called azeotropes (Gr a + zeo to boil, trope more at). Webster s dictionary defines an azeotrope as a liquid mixture that is characterized by a constant maximum or minimum boiling point which is lower or higher than that of any of the components and that distills without change in composition. An azeotropic distillation involves the formation of an azeotrope with at least one of the components of a liquid mixture, which then can be separated more readily because of the resulting increase in the difference between the volatilities of the components of the mixture. Figure 4-1, p. 44, shows the water-ethanol system (A) and the HCl-water system (B). 

The imidic ester hydrochloride (1 mole) is dissolved in an eight- to ten-fold weight of anhydrous ethanol, treated with 2-(diethylamino)ethylamine (1.05 moles), and stirred for 8 h at 40-45°. The alcohol is then removed in a vacuum and the residue is dissolved in water and acidified to Congo Red by hydrochloric acid. After short warming the mixture is cooled and all non-basic material is removed by filtration or by extraction with ether. The solution is then evaporated to dryness at 40° in a vacuum and the last traces of water are distilled off azeotropically with benzene-ethanol. The yield is 75-80%. 

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