Desiccators, calcium chloride vacuum

Drying of crystals. Whenever possible crystals should be dried in a smdl vacuum desiccator containing a suitable desiccant. The latter depends upon the nature of the solvent used c/. p. 19). However for most purposes anhydrous calcium chloride is satisfactory. If a hydrocarbon has been used in the recrystallisation, a few thin fresh shavings of paraffin wax are efficacious. 

The beat method of drying, if time permits, is to place the crystals in a desiccator containing an appropriate substance (usually anhydrous calcium chloride, silica gel, or concentrated sulphuric acid) to absorb the solvent. More eflicient and more rapid drying is obtained with the aid of a vacuum desiccator (see Section 11,38 and Fig. 77, 38, 1). 

An alternative procedure is to leave the syrupy residue in a vacuum desiccator over anhydrous calcium chloride and siUca gel, and to Alter ofl the successive Crops of crystals as they separate. These are washed with light petroleum, b.p. 40-60°, spread on a porous tile and recrystallised. 

Heat a suspension of 22 g. of the diacetate in a mixture of 120 ml. of concentrated hydrochloric acid, 190 ml. of water and 35 ml. of alcohol under reflux for 45 minutes. Cool the mixture to 0°, filter the solid with suction, and wash with water. Purify the crude aldehyde by rapid steam distillation (Fig. II, 41, 3) collect about 1500 ml. of distillate during 15 minutes, cool, filter, and dry in a vacuum desiccator over calcium chloride. The yield of pure o-nitrobenzaldehyde, m.p. 44—45°, is 10 g. The crude solid may also be purified after drying either by distillation under reduced pressure (the distillate of rather wide b.p., e.g., 120-144°/3-6 mm., is quite pure) or by dissolution in toluene (2-2-5 ml. per gram) and precipitation with light petroleum, b.p. 40°-60° (7 ml. per ml. of solution). 

To prepare crystalline monoperphthalic acid, place the thoroughly dry ethereal solution (4) in a distilling flask equipped with a capillary tube connected with a calcium chloride or cotton wool drying tube, and attach the flask to a water pump. Evaporate the ether without the application of heat (ice will form on the flask) to a thin syrup (about 150 ml.). Transfer the syrup to an evaporating dish, rinse the flask with a little anhydrous ether, and add the rinsings to the syrup. Evaporate the remainder of the ether in a vacuum desiccator over concentrated sulphuric acid about 30 g. of monoperphthalic acid, m.p. 110° (decomp.), is obtained. 

Prepare acetophenonephenylhydrazone by warming a mixture of 20 g. of acetophenone (Section IV, 136) and 18 g. of phenylhydrazine on a water bath for 1 hour. Dissolve the hot mixture in 40 ml. of rectihed spirit, and shake or stir to induce crystallisation. Cool the mixture in ice, filter and wash with 12 ml. of rectified spirit. Dry in a vacuum desiccator over anhydrous calcium chloride for at least half an hour. The yield of phenylhydrazone, m.p. 105-106 , is 28 g. 

Place an intimate mixture of 125 g. of powdered, anhydrous zinc chloride and 26-5 g. of acetophenonephenylhydrazone in a tall 500 ml. beaker in an oil bath at 170°. Stir the mixture vigorously by hand. After 3-4 minutes the mass becomes hquid and evolution of white fumes commences. Remove the beaker from the bath and stir the mixture for 5 minutes. Then stir in 100 g. of clean, white sand in order to prevent solidification to a hard mass. Digest the mixture for 12-16 hours on a water bath with 400 ml. of water and 12 ml. of concentrated hydrochloric acid in order to dissolve the zinc chloride. Filter off the sand and the crude 2-phenylindole, and boil the solids with 300 ml. of rectified spirit. Treat the hot mixture with a little decolourising carbon and filter through a pre-heated Buchner funnel wash the residue with 40 ml. of hot rectified spirit. Cool the combined filtrates to room temperature, filter off the 2-phenylindole and wash it three times with 10 ml. portions of cold alcohol. Dry in a vacuum desiccator over anhydrous calcium chloride. The yield of pure 2-phenylindole, m.p. 188-189°, is 16 g. 

Methods for removing water from solids depends on the thermal stability of the solids or the time available. The safest way is to dry in a vacuum desiccator over concentrated sulfuric acid, phosphorus pentoxide, silica gel, calcium chloride, or some other desiccant. Where substances are stable in air and melt above 100°, drying in an air oven may be adequate. In other cases, use of an Abderhalden pistol may be satisfactory. 

The mixture is stirred at room temperature for an additional 60 hours (Note 4), during which time the calcium chloride tulie may become spent and need replacement. The viscous, light-yellow liquid product is transferred to a large crystallizing dish and dried in a vacuum desiccator over soda-lime for about 24 hours (Note 5). 

After 30 minutes the solid sulfinic acid is separated on a fritted-glass filter. The sulfinic acid is dissolved from the filter by a mixture of 750 ml. of ether and 750 ml, of methylene chloride. The solution is dried over calcium chloride and evaporated to dryness under reduced pressure (bath temperature 25°) (Note 5). The residue is suspended in 50 ml. of water, and small portions of dilute ammonia are added to the well-stirred suspension until it has a pH of 9 (Note 6). Insoluble impurities are separated by filtration, and 2-nitrobenzenesulfinic acid is precipitated from the filtrate by adding 5-ml. portions of 6N hydrochloric acid with cooling the sulfinic acid precipitated by each portion of acid is separately collected on a Buchner funnel (Note 7). The acid, a pale yellow solid, is dried on a clay plate in a vacuum desiccator over potassium hydroxide pellets, m.p. 120-125° (dec.), weight 9.4-14.9 g. (50-80%). If the 2-nitrobenzenesulfinic acid is to be used for the hydrogenation of the next step high purity is required, and it is generally advisable to reprecipitate the acid once more in the same way (Note 8). 

The live fireflies are dried over calcium chloride in a vacuum desiccator, and then their lanterns are separated by hand. An acetone powder prepared from the dried lanterns is extracted with boiling water. The cooled aqueous extract is extracted with ethyl acetate at pH 3.0, and the ethyl acetate layer is concentrated under reduced pressure. The concentrated luciferin is adsorbed on a column of Celite-Fuller s earth mixture. The column is washed with water-saturated ethyl acetate, and eluted with alkaline water at pH 8.0-8.5. The aqueous eluate of luciferin is adjusted to pH 3.0 with HCl and luciferin is... 

The beaker is chilled in an ice bath for 1 hour. The crystalline diacetate that separates is collected on a Buchner funnel and washed with three 20-ml. portions of cold water. After drying for 30 minutes on the funnel with suction, the diacetate is dried overnight in a vacuum desiccator containing calcium chloride (Note 4). The dried diacetate weighs 26.7-29.3 g. (83-91%) and melts at 158-159° with decomposition. The purity of the diacetate, determined by the titration method of Lucas, Kennedy, and Formo,3 is 97-98%, which is good enough for most purposes. The purity can be increased to 99-100% by a recrystallization from 5M acetic acid. 

The reaction mixture is allowed to stand for 1 to 2 hours (or overnight, if more convenient) after this interval the solution will have assumed a clear, pale yellow color. The condenser is then set for downward distillation, stirring is resumed, and the solvent is removed by distillation from a steam bath (Note 5). After nearly all the ether has been removed, the distillation is continued under reduced pressure (40-50 mm.) until no further appearance of crystals is noted. The residue, which consists of yellow crystals of the crude product, is then allowed to stand until dry in a vacuum desiccator which contains concentrated sulfuric acid, soda lime, and anhydrous calcium chloride (Note 6). 

The compound gradually turns pink on standing in the air. It should be stored in a tightly stoppered bottle or kept in a vacuum desiccator over calcium chloride. 

In order to dry the air which enters, a straight calcium chloride tube is attached to the tube of the desiccator. The calcium chloride must be firmly held in position at both ends by means of glass wool or, better, cot.on wool. In desiccators which are often carried about the container for the sulphuric acid is filled to the acid level with pieces of glass —small pieces of broken tube, stoppers, and the like—or with small pieces of pumice which have previously been boiled with dilute hydrochloric acid and then dried. Splashing is thus avoided. From time to time the concentrated sulphuric acid is renewed. A special vacuum desiccator must be kept for analytical work. 

A sample of 2.5 g (5.6 mmole) of 2,2 -bipyridinium pentachlorooxomolybdate-(V) is placed in a 100-mL, round-bottomed flask fitted with reflux condenser and a bent guard tube (filled with fused calcium chloride) to avoid entrance of moisture. About 20 mL of ethanol (98%) is added, and the materials are shaken. There is an immediate reddish-pink coloration. The mixture is heated at reflux for about 1 hour, until there is no more evolution of hydrogen chloride (tested with blue litmus paper). The mixture is then filtered through a dry sintered-glass Gooch crucible and washed twice with small quantities of ethanol. The product, a reddish-pink solid, is dried in a vacuum desiccator. Yield 1.5 g (71%). Anal. 

If this preparation is carried out during periods of high humidity it is best to place the product in a vacuum desiccator, which is evacuated several times in order to remove the solvent. Anhydrous calcium chloride may be placed in the bottom of the desiccator. 

A. o-Methylbenzyl acetate. A solution of 29.8 g. (0.20 mole) of 2-methylbenzyldimethylamine 2 and 32.7 g. (0.30 mole) of ethyl bromide in 40 ml. of absolute ethanol is placed in a 500-ml. round-bottomed flask fitted with a reflux condenser capped with a calcium chloride drying tube. The solution is heated under reflux on the steam bath for 1 hour then an additional 10.8 g. (0.10 mole) of ethyl bromide is added and the heating continued for an additional 3 hours. The solvent and residual ethyl bromide are removed at reduced pressure (water aspirator) while the flask is heated in a water bath kept at about 60° (Note 1). The oily residue is treated with about 300 ml. of absolute ether, and on scratching crystallization is induced. The product is collected on a Buchner funnel, washed with two 50-ml. portions of anhydrous ether, and dried in a vacuum desiccator. The yield of colorless 2-methylbenzylethyldimethylammonium bromide is 47.5-49.0 g. (92-95%) (Note 2). It is hygroscopic and should therefore not be exposed to moist air. 

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