Azeotropic water removal

A solution of 11.28 g (40 mmol) of (2S,3S,5S)-2,5-diamino-l,6-diphenyl-3-hydroxyhexane and 4.88 g (40 mmol) of phenylboric acid in 1 liter of toluene was refluxed and the water azeotropically removed with the aid of a Dean Stark trap until the distillate was clear. The solvent was then removed in vacuo to provide the crude desired compound which was used immediately without further purification. 

Spherical silica particles, about 5 pm in diameter, are dried for about 12 hours at 170°C to remove all adsorbed water and then dispersed in 250 ml of dry toluene. The mixture is then refluxed and any remaining water azeotropically removed. The silane reagent is then added and the reaction allowed to proceed at 95°C for about 3 hours. The mixture is then cooled, filtered, washed several times with toluene and methanol and then dried at 60°C over phosphorus pentoxide in vacuo. 

This is an equilibrium process and there are two techniques which are used to drive the reaction to completion. One is to use a large excess of the alcohol. This is feasible for simple and relatively inexpensive alcohols. The second method is to drive the reaction forward by irreversible removal of water. Azeotropic removal of water is one simple method for doing this. Entries 1-4 in Scheme 3.5 are examples of acid-catalyzed esterifications. Entry 5 is the preparation of a diester starting with an anhydride. This is a closely related reaction in which the initial opening of the anhydride ring is followed by an acid-catalyzed esterification. 

Note 2. Prepared by azeotropic removal of water from the commercial, water-containing product by means of benzene. This solvent was removed in a water--pump vacuum and the remaining mass was powdered. The water-containing acid appeared to work much less efficiently as catalyst. 

The reactor effluent, containing 1—2% hydrazine, ammonia, sodium chloride, and water, is preheated and sent to the ammonia recovery system, which consists of two columns. In the first column, ammonia goes overhead under pressure and recycles to the anhydrous ammonia storage tank. In the second column, some water and final traces of ammonia are removed overhead. The bottoms from this column, consisting of water, sodium chloride, and hydrazine, are sent to an evaporating crystallizer where sodium chloride (and the slight excess of sodium hydroxide) is removed from the system as a soHd. Vapors from the crystallizer flow to the hydrate column where water is removed overhead. The bottom stream from this column is close to the hydrazine—water azeotrope composition. Standard materials of constmction may be used for handling chlorine, caustic, and sodium hypochlorite. For all surfaces in contact with hydrazine, however, the preferred material of constmction is 304 L stainless steel. 

Pervaporation is a relatively new process with elements in common with reverse osmosis and gas separation. In pervaporation, a liquid mixture contacts one side of a membrane, and the permeate is removed as a vapor from the other. Currendy, the only industrial application of pervaporation is the dehydration of organic solvents, in particular, the dehydration of 90—95% ethanol solutions, a difficult separation problem because an ethanol—water azeotrope forms at 95% ethanol. However, pervaporation processes are also being developed for the removal of dissolved organics from water and the separation of organic solvent mixtures. These applications are likely to become commercial after the year 2000. 

Another process employs a pH maintained at 4—7 and a catalyst that combines a divalent metal cation and an acid. Water is removed continuously by azeotropic distillation and xylene is recycled. The low water content increases the reaction rate. The dibenzyl ether groups are decomposed by the acid the yield of 2,2 -methylene can be as high as 97% (34). 

Processes to produce boric acid esters are based on the azeotropic removal of water from a mixture of the appropriate alcohol, phenol, or glycol, and boric acid. A suitable hydrocarbon azeotroping agent is used to help remove the water. The water is removed continuously by using a condenser that allows continuous return of the solvent to the reaction vessel. Eor some borate esters, such as the glycol borates, distillation can result in decomposition. 

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. 

Methylhexane [591-76-4] M 100.2, b 90.1 , d 0.678, n 1.38485, n 5 1.38227. Purified by azeotropic distn with MeOH, then washed with water (to remove the MeOH), dried over type 4A molecular sieves and distd. 

HCIO4). Refluxed with benzene (6mL/g) in a flask fitted with a Dean and Stark trap until all the water was removed azeotropically (ca 4h). The soln was cooled and diluted with dry pentane (4mL/g of AgC104). The ppted AgC104 was filtered off and dried in a desiccator over P2O5 at 1mm for 24h [Radell, Connolly and Raymond J Am Chem Soc 83 3958 1961]. It has also been recrystallised from perchloric acid. [Caution due to EXPLOSIVE nature in the presence of organic matter.]... 

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%). 

A -Dieiiol ethers are also formed by acid-catalyzed reaction of the steroid directly with benzyl alcohol with azeotropic removal of water/ Use of isooctane as azeotropic carrier may improve yields/ ... 

Steroidal A -dienamines are formed with a high degree of selectivity in the presence of 17- or 20-ketones. Preparation of morpholine and pyrrolidine enamines is achieved by azeotropic removal of water with or without a catalyst. Pyrrolidine enamines are also formed efficiently by addition of the base to the hot solution of the ketone in methanol followed by immediate cooling. ... 

Enamines are not easily formed from 17-ketones. A pyrrolidine enam-ine is obtained by acid catalysis accompanied by azeotropic removal of water whereas the morpholine and piperidine enamines do not form under these forcing conditions. 

Aryl bromides were also perfluoroethylated under these conditions [205] The key to improved yields was the azeotropic removal of water from the sodium perfluoroalkylcarboxylate [205] Partial success was achieved with sodium hepta-fluorobutyrate [204] Related work with halonaphthalene and anthracenes has been reported [206 207] The main limitation of this sodium perfluoroalkylcarboxylate methodology is the need for 2 to 4 equivalents of the salt to achieve reasonable yields A trifluoromethylcopper solution can be prepared by the reaction of bis(tri-fluoromethyl)mercury with copper powder in /V-methylpyrrolidone (NMP) at 140 °C [208] (equation 138) or by the reaction of N-trifluoromethyl-A-nitro-sotnfluoromethane sulfonamide with activated copper in dipolar aprotic solvents [209] This trifluoromethylcopper solution can be used to trifluoromethylate aro matic [209], benzylic [209], and heterocyclic halides [209]... 

Nitrone hydrate is converted into nitrone by boiling in benzene with azeotropic removal of water [48] (equation 50). This in situ formation of nitrone is carried out in the presence of various alkenes and alkynes, which undergo cycloaddition with the nitrone [48, 49] (equations 51 and 52). 

The synthetic utility of enamines presupposes their general accessibility. In most cases, ketones are readily converted to enamines by condensation of the carbonyl compound with a secondary amine such as pyrrolidine, morpholine, or piperidine and azeotropic removal of water with a solvent such as benzene (3-19). 

Enamines derived from aldehydes can usually be obtained by the reaction of 2 equivalents of a secondary amine with the carbonyl compound, in the presence of anhydrous potassium carbonate, followed by pyrolytic distillation of the aminal with elimination of one of the amine groups (10,15, 30-36). Ketones are directly converted to enamines under the conditions of aminal formation. The azeotropic removal of water with excess aldehyde has also been described (32,37). 

Ph2CHOH, cat. TsOH, benzene, azeotropic removal of water, 78-83% yield. ... 

To a solution of vanillin in toluene is added nitroethane, butylamine and glacial acetic acid. The mixture is refluxed and the water of reaction is steadily azeotropically removed by distillation. After the theoretical amount of water is distilled out, distillation Is continued to remove excess reactants. The last trace of excess reactants is then removed at room temperature under a vacuum. The product is then triturated with a hydrocarbon solvent such as Skellysolve B and is thus obtained in a crystalline state. In general, however, it is preferred to dissolve the residue directly In toluene for use in the next step, without isolating the 1-(2-nitropropen-1-y I )-4-hydroxy-3-methoxy benzene. 

The solution was then heated at reflux for A hour, cooled to 70°C and 4-methylpentan-2-one (2 liters) added. The water was removed by azeotropic distillation under reduced pressure (260 torrs) and the resultant solution treated with charcoal (10 g) at 50°C. The solution was filtered and cooled to 10°C. N-[2-[ [ [5-dimethylamino)methyl-2-furanyl] methyl] thio] ethyl] -N -methyl-2-nitro-1,1 -ethenediamine (380 g) was filtered off and dried, melting point 69°C to 70°C. 

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