Desiccants, solid

The best method for removing water (and also solvents of relatively low boiling point) adhering to solids is drying under reduced pressure. A vacuum desiccator is used for this purpose several forms are shown in Fig. II, 38, 1. These are fitted with the exception of ( ) either with... 

The solid in the tower may be supported on a Witt filter plate, but a plug of glass wool is satisfactory the plug of glass wool above the solid acts as a filter for fine particles of the desiccant. 

Into a 500 ml. round-bottomed flask, fitted with a reflux condenser, place 42 g. of potassium hydroxide pellets and 120 g. (152 ml.) of absolute ethyl alcohol. Heat under reflux for 1 hour. Allow to cool and decant the liquid from the residual solid into another dry 500 ml. flask add 57 g. (45 ml.) of A.R. carbon dtsulphide slowly and with constant shaking. Filter the resulting almost solid mass, after cooling in ice, on a sintered glass funnel at the pump, and wash it with two 25 ml. portions of ether (sp. gr. 0-720), followed by 25 ml. of anhydrous ether. Dry the potassium ethyl xanthate in a vacuum desiccator over silica gel. The yield is 74 g. If desired, it ma be recrystallised from absolute ethyl alcohol, but this is usually unneceasary. 

Equip a I litre three-necked flask with a mechanical stirrer and a thermometer, and immerse the flask in a bath of ice and salt. Place 306 g. (283 ml.) of acetic anhydride, 300 g. (285 ml.) of glacial acetic acid and 25 g. of p-nitrotoluene in the flask, and add slowly, with stirring, 42 5 ml. of concentrated sulphuric acid. When the temperature has fallen to 5°, introduce 50 g. of A.R. chromic anhydride in small portions at such a rate that the temperature does not rise above 10° continue the stirring for 10 minutes after all the chromium trioxide has been added. Pour the contents of the flask into a 3 litre beaker two-thirds filled with crushed ice and almost fill the beaker with cold water. Filter the solid at the pump and wash it with cold water until the washings are colourless. Suspend the product in 250 ml. of cold 2 per cent, sodium carbonate solution and stir mechanically for 10-15 minutes filter (1), wash with cold water, and finally with 10 ml. of alcohol. Dry in a vacuum desiccator the yield of crude p-nitrobenzal diacetate is 26 g. (2),... 

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). 

The suspension of phenylacetamide may be further hydrolysed to phenylacetic acid by refluxing with stirring until the solid dissolves. The mixture becomes turbid after 30 minutes and the product begins to separate as an oil refluxing is continued for 6 hours, the mixture is cooled first with tap water and then by an ice-water bath for about 4 hours. The crude phenylacetic acid is filtered at the pump, washed with two 50 ml. portions of cold water, and dried in a desiccator. The resulting crude acid melts at 69- 70° it may be purified by recrystallisation from light p>etroleum (b.p. 40-60°) or, better, by vacuum distillation. 

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. 

Anthracene and maleic anhydride. In a 50 ml. round-bottomed flask fitted with a reflux condenser, place 2 0 g. of pure anthracene, I 1 g. of maleic anhydride (Section 111,93) and 25 ml. of dry xylene. Boil the mixture under reflux for 20 minutes with frequent shaking during the first 10 minutes. Allow to cool somewhat, add 0 5 g. of decolourising carbon and boil for a further 5 minutes. Filter the hot solution through a small, preheated Buchner funnel. Collect the solid which separates upon coohng by suction filtration, and dry it in a vacuum desiccator containing paraffin wax shavings (to absorb traces of xylene). The yield of adduct (colourless crystals), m.p. 262-263° (decomp.), is 2-2 g. Place the product (9 10-dihydroanthracene-9 10-cndo-ap-succinic anhydride) in a weU-stoppered tube, since exposure to air tends to cause hydration of the anhydride portion of the molecule. 

Heat a mixture of 49 g. of acetylmethylurea (3) and 50 ml. of concentrated hydrochloric acid, with hand stirring, on a steam bath until it is apparent that no more solid is dissolving (4) and continue the heating for 3—4 minutes longer the total time of heating on the steam bath should be 8-12 minutes. Dilute the solution with 50 ml. of water and cool below 10° in an ice bath. Run in slowly and with stirring a cold saturated solution of 38 g. of A.R. sodium nitrite in 55 ml. of water below the level of the liquid. Keep the mixture in the ice bath for 5-10 minutes, filter the solid at the pump and wash it with 8-10 ml. of ice-cold water. Dry the nitrosomethylurea (pale yellow crystals) in the air or in a. vacuum desiccator (5) the yield is 34 g., m.p. 12 124°. 

The drying mechanisms of desiccants may be classified as foUows Class 1 chemical reaction, which forms either a new compound or a hydrate Class 2 physical absorption with constant relative humidity or vapor pressure (solid + water + saturated solution) Class 3 physical absorption with variable relative humidity or vapor pressure (soHd or liquid + water + diluted solution) and Class 4 physical adsorption. 

Solid Desiccants. The sohd desiccants used in dynamic appHcations fad into a class caded adsorbents (see Adsorption). Because they are used in large packed beds through which the gas or Hquid to be treated is passed, the adsorbents are formed into soHd shapes that adow them to withstand the static (fluid plus sohd head) and dynamic (pressure drop) forces imposed on them. The most common shapes are granules, extmded pedets, and beads. 

The catalyst is previously prepared in an apparatus for catalytic hydrogenation, in which are placed 0.5 g. of palladous chloride, 3.0 g. of Norite, and 20 ml. of distilled water. The bottle is swept out with hydrogen and then shaken with hydrogen for 2-3 hours at 2-3 atmospheres (40 lb.) pressure. The palladium on carbon is collected on a Biichner funnel, washed with five 50-ml. portions of distilled water, then with five 50-ml. portions of 95% ethanol, and finally twice with ether. Upon drying, about 3 g. of the catalyst is obtained. It is stored in a vacuum desiccator over solid sodium hydroxide. If the reduction of the chloro-lepidine does not proceed normally, the used catalyst should be removed by suction filtration and a fresh 3-g. portion of catalyst added. Failure of the reduction step is usually due to an inactive catalyst or to impurities in the acetic acid or chlorolepidine. The palladium catalysts, prepared as described elsewhere in this volume, are presumably also satisfactory for the reduction of 2-chlorolepidine (p. 77). 

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 phenol (Imol) in 5% aqueous NaOH is treated (while cooling) with benzoyl chloride (Imol) and the mixture is stirred in an ice bath until separation of the solid benzoyl derivative is complete. The derivative is filtered off, washed with alkali, then water, and dried (in a vacuum desiccator over NaOH). It is recrystalUsed from ethanol or dilute aqueous ethanol. The benzoylation can also be carried out in dry pyridine at low temperature ca 0°) instead of in NaOH solution, finally pouring the mixture into water and collecting the solid as above. The ester is hydrolysed by refluxing in an alcohol (for example, ethanol, n-butanol) containing two or three equivalents of the alkoxide of the corresponding alcohol (for example sodium ethoxide or sodium n-butoxide) and a few ca 5-10) millilitres of water, for half an hour to three hours. When hydrolysis is complete, an aliquot will remain clear on dilution with four to five times its volume of water. Most of the solvent is distilled off. The residue is diluted with cold water and acidified, and the phenol is steam distilled. The latter is collected from the distillate, dried and either fractionally distilled or recrystalUsed. 

Benzyltrimethylammonium chloride [56-93-9J M 185.7, m 238-239 (dec). A 60% aq soln was evapd to dryness under vac on a steam bath, and then left in a vac desiccator containing a suitable dehydrating agent. The solid residue was dissolved in a small amount of boiling absolute EtOH and pptd by adding an equal volume of diethyl ether and cooling. After washing, the ppte was dried under vac [Karusch J Am Chem Soc 73 1246 7957]. 

Bromoindole [10075-50-0] M 196.1, m 90.5-91°, 90-92°, pK 16.13 (NH). Purified by steam distn from a faintly alkaline soln. Cool the aqueous distillate, collect the solid, dry in a vacuum desiccator over P2O5 and recryst from aqueous EtOH (35% EtOH) or pet ether-Et20. MeOH 279, 287 and 296 (loge... 

Naphthalene-l-sulfonyl chloride [85-46-1] M 226.7, m 64-67°, 68°, b 147.S°/0.9mm, 147.S°/13mm. If the IR indicates the presence of OH then treat with an equal weight of PCI5 and heat at ca 100° for 3h, cool and pour into ice + H2O, stir well and filter off the solid. Wash the solid with cold H2O and dry the solid in a vacuum desiccator over P2O5 + solid KOH. Extract the solid with pet ether (b 40-60°) filter off any insoluble solid and cool. Collect the crystalline sulfonyl chloride and recryst from pet ether or C6H6 pet ether. If large quantities are available then it can be distd under high vacuum. [Fierz-Davaid and Weissenbach Helv Chim Acta 3 2312 1920.] The sulfonamide has m 150° (from EtOH or H2O). 

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