Vacuum, water aspirator

After the initial boiling ofthe liquid subsides (ca. 2 h), a vacuum (water aspirator) is applied to remove further acetic acid. After treating under vacuum, argon is readmitted to the flask and the system left for a further 10 min. This cycle of evacuation and heating under argon is continued for about 2 h until no more liquid is collected. 

Pump manufacturers express vacuum in aspirated feet of water in a ver r -i (0 psia = -33.9 feet of water). The pharmaceutical and chemical indue r Pascals (100,000 Pascals = atmospheric pressure) and the term TO C. conglomeration of values and conversion n, causes confusion. In ( ... 

A solution of 30 g (0.1 mole) of 17j5-hydroxy-5a-androstan-3-one (androstano-lone), 20 ml of pyrrolidine and 200 ml of benzene is heated at reflux temperature for 2.5 hr under a Bidwell-Sterling water trap. The benzene solution is evaporated to dryness in a rotating evaporator connected to a water aspirator. The white cake which remains is broken up and dried further by immersing the flask in a water bath at 60-75° and evacuating the flask with a mechanical vacuum pump. After 0.5 hr the solid cake is broken up again and dried for another 0.5 hr at 60-75°. The enamine (9) obtained should smell only faintly of pyrrolidine. 

A solution of 25.8 g. (0.20 mole) of 4-amino-2,2,4-trimethyl-pentane (ierf-octylamine) (Note 1) in 500 ml. of C.P. acetone is placed in a 1-1. three-necked flask equipped with a Tru-Bore stirrer and a thermometer and is diluted with a solution of 30 g. of magnesium sulfate (Note 2) in 125 ml. of water. Potassium permanganate (190 g., 1.20 moles) is added to the well-stirred reaction mixture in small portions over a period of about 30 minutes (Note 3). During the addition the temperature of the mixture is maintained at 25-30° (Note 4), and the mixture is stirred for an additional 48 hours at this same temperature (Note 5). The reaction mixture is stirred under water-aspirator vacuum at an internal temperature of about 30° until most of the acetone is removed (Note 6). The resulting viscous mixture is steam-distilled approximately 500 ml. of water and a pale-blue organic layer are collected. The distillate is extracted with pentane, the extract is dried over anhydrous sodium sulfate, and the pentane is removed by distillation at atmospheric pressure. The residue is distilled through a column (Note 7) at reduced pressure to give 22-26 g. (69-82%) of colorless 4-nitro-2,2,4-trimethylpentane, b.p. 53-5473 mm., < 1.4314, m.p. 23.5-23.7°. 

Pyridinecarboxaldehyde (nicotinaldehyde) was supplied by Aldrich-Europe, Beerse, Belgium. The checkers purified this reagent by fractional distillation, b.p. 95-97° (15 mm.). The submitters stress that 3-pyridinecarboxaldehyde should be completely free from contamination by the acid. They stirred 150 g. of the aldehyde with 100 g. of potassium carbonate and 300 ml. of ethanol for 12 hours, filtered the suspended solid, and fractionally distilled the filtrate through a 30-cm. Vigreux column using a water aspirator. However, the checkers found that the recovery of aldehyde from this procedure was very low, and recommend vacuum distillation instead. 3-Pyridinecarboxaldehyde is a powerful skin irritant and should be handled with protective gloves. 

Beakers 10 to 1000-ml. volumetric flasks 1-ml. volumetric pipet, serological pipet steam bath vacuum desiccator vacuum pump and water aspirator are also required. 

The hexane is evaporated completely at room temperature by placing the cells in a vacuum desiccator attached to a water aspirator. The evaporation requires 10 to 20 minutes. A drop of oily residue remains. This evaporation is handled conveniently by placing the cells in a beaker containing a 2.5-cm. level of mineral oil at room temperature and transferring the whole to the desiccator. The oil bath prevents excessive cooling of the hexane solution during the evaporation. 

Considerable dissolved hydrogen chloride is liberated at this point and passes into the water aspirator. A mechanical vacuum pump should not be used at this stage because it would be damaged by corrosion. 

B. Pyridine-N-oxide. The acetic acid solution is evaporated on the steam bath under the pressure of a water aspirator, and the residue (180-190 g.) is distilled at a pressure of 1 mm. or less in an apparatus suitable for collecting a solid distillate (Note 5). The vacuum pump must be protected with a Dry Ice trap capable of holding about 60 ml. of acetic acid, which distils as the pyridine-N-oxide acetate dissociates at low pressure. Heat is provided by an oil bath, the temperature of which is not allowed to rise above 130° (Note 6). The product is collected at 100-105°/1 mm. (95-98°/0.5 mm.). The yield is 103-110 g. (78-83%) of colorless solid, m.p. 65-66° (sealed capillary). The base is deliquescent and must be stoppered immediately. 

The solution is cooled to room temperature and is washed with a few milliliters of benzene into a single-necked flask. The solvent is removed with a rotary evaporator connected to a water aspirator vacuum gentle heat is supplied from a steam bath. The residue is cooled to room temperature before air is admitted. About 200 ml. of hexane is added and stirred with the residue to extract most of the carborane. The brownish tar which remains undissolved is allowed to settle and the solution is decanted. A second extraction of the tar with 40 ml. of hexane converts the residue to a solid which is removed by filtration. The solid is washed on the filter with an additional 40 ml. of hexane. The combined hexane extracts are filtered and then washed in a separatory funnel with four 100-ml. portions of a chilled aqueous 10% sodium hydroxide solution, followed by four 100-ml. portions of water. After the yellow hexane solution has been dried over anhydrous magnesium sulfate and filtered, the solvent is removed by use of a rotary evaporator connected to a water aspirator. The carborane is washed with a small amount of pentane into a 300-ml. single-necked flask which is attached to an alembic column as pictured in Fig. 13. 

The reaction flask is allowed to cool and the condenser, stirrer, and nitrogen inlet are removed. To the solution is added 100 ml. of absolute ethanol, and a brisk stream of carbon dioxide is passed through the solution to precipitate the excess potassium hydroxide as potassium carbonate. Sufficient carbon dioxide to precipitate the excess potassium hydroxide is conveniently obtained from about 150 g. of Dry Ice. The Dry Ice is powdered and placed in a stoppered 500-ml. filter flask with a line leading into the reaction solution. The insoluble potassium carbonate is filtered and washed with four 50-ml. portions of absolute ethanol. The combined filtrate and washings are evaporated to dryness on a rotary evaporator using a water aspirator vacuum and heat from a steam bath. This yields a solid or semisolid cake containing some residual potassium carbonate. 

A mixture of 2-iodotoluene (8.78 g, 0.04 mol) and trimethyl phosphite (24.8 g, 0.20 mol) was placed in a 45-ml, double-jacketed silica reaction vessel. The mixture was degassed by flushing with dry nitrogen for 5 min and irradiated with a 450-watt Hanovia (Model 679A-10) high-pressure quartz mercury vapor lamp fitted with an aluminum reflector head. The lamp was placed 5 cm from the inner portion of the reaction vessel. The reaction temperature was maintained at 0°C by the circulation of coolant from a thermostatically controlled refrigeration unit. Irradiation was continued at this temperature for 24 h. At the end of this time, the volatile materials were removed with a water aspirator, and the residue was vacuum distilled (96 to 97°C/0.25 torr) to give the dimethyl 2-methylphenylphosphonate (7.28 g, 91%). 

A 1-1., three-necked, round-bottomed flask equipped with a Trubore stirrer, a pressure-equalizing dropping funnel, and a reflux condenser with a drying tube is charged with 350 ml. of acetonitrile (Note 1) and 106.4 g. (0.41 mole) of triphenylphos-phine (Note 2). The flask is cooled in an ice-water bath (Note 3), and 64 g. (0.40 mole) of bromine is added dropwise over a period of ca. 15-20 minutes (Notes 4 and 5). The ice-water bath is removed, and a solution of 54 g. (0.40 mole) of cinnamyl alcohol in 50 mi. of acetonitrile is added in portions over a period of 5-10 minutes with continued stirring (Note 6). The solvent is removed by distillation with the use of a water aspirator (30-40 mm.) and an oil bath until the bath temperature reaches 120°. The water aspirator is replaced by a vacuum pump and the water-cooled condenser with an air condenser, and the distillation is continued with rapid stirring (Notes 7, 8, and 9). Most of the product (Note 10) distills at 91-98° (2-4 mm.), and about 59 g. of product crystallizes in the receiving flask (63-75% yield) (Note 11). 

The residue was distilled with a Kugelrohr apparatus under water aspirator vacuum (approximately 20mbar, 140 °C) to give (,SY)-methyl-(3)-hydroxy-butanoate (105 mg, 99%). 

The water trap is in turn connected to a source of vacuum, most likely, a water aspirator (Fig. 47). 

Suppose, by luck of the draw, you ve had to prepare and purify 1-octanol (B.P. 195°C). You know if you simply distill 1-octanol, you run the risk of having it decompose, so you set up a vacuum distillation. You hook your setup to a water aspirator and water trap and attach a closed-end stick manometer. You turn the water for the aspirator on full-blast and open the stick manometer. After a few minutes, nothing seems to be happening. You pinch the tubing going to the vacuum distillation setup, (but not to the manometer) closing the setup off from the source of vacuum. Suddenly, the mercury in the manometer starts to drop. You release the tube going to the vacuum distillation setup, and the mercury jumps to the upper limit. You have air leaks in your vacuum distillation setup. 

The vacuum adapter is connected to a vacuum source, either a vacuum pump or a water aspirator. Real live vacuum pumps are expensive and rare and not usually found in the undergraduate organic laboratory. If you can get to use one, that s excellent. See your instructor for the details. The water aspirator is used lots, so read up on it. 

If you re going to pull a vacuum in the sublimator, do it now. If the vacuum source is a water aspirator, put a water trap between the aspirator and the sublimator. Otherwise you may get depressed if, during a sudden pressure drop, water backs up and fills your sublimator. Also, start the vacuum slowly. If not, air, entrained in your solid, comes rushing out and blows the crude product all over the sublimator, like popcorn. 

After this period, the dropping funnel and the vacuum takeoff are replaced by the short-path distillation assembly shown in Figure 2. The system is protected by a Drierite tube and the benzene is distilled under reduced pressure (water aspirator). After the benzene is removed, the benzene-containing receiver is replaced with a clean, dry flask, and the system is connected to an eflScient vacuum pump. The pressure in the system is reduced to 0.02 mm., and the flask is immersed deeply in an oil bath (Figure 2) heated to about 200°. After about 1 ml. of fluid forerun is collected, the diethylaluminum cyanide distils at 162° (0.02 mm.) (Note 7) and is collected in a tared 200-ml. receiver by heating the side arm and the adaptor with a stream of hot air or an infrared lamp (Note 8). After all the distillate is collected in the receiver (Note 9), dry nitrogen is admitted to the evacuated apparatus and the receiver is stoppered and weighed. Diethylaluminum cyanide is obtained usually as a pale yellow syrup (Note 10) in 60-80% yield (26.7-35.6 g.) (Note 11). 

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