Ammonium chloride, sublimation

Ammonium chloride sublimes on further heating, leaving pure anhydrous MgCb ... 

Only a few solids have vapor pressures near atmospheric at safe temperatures, among them COz, UF , ZrCL(, and about 30 organics. Ammonium chloride sublimes at 1 atm and 350°C with decomposition into NH3 and HC1, but these recombine into pure NH4C1 upon cooling. Iodine has a triple point 113.5°C and 90.5 Torr it can be sublimed out of aqueous salt solutions at atmospheric pressure because of the entraining effect of vaporized water. 

Ammonium Chloride. Ammonium chloride, which occurs naturally in volcanic material, forms two solid phases. The o -modification (cubic, CsCl type), which is stable at room temperature, changes reversibly to the jS-modification (cubic, NaCl type) at 457.6 K. The slightly hygroscopic ammonium chloride sublimes easily, the dissociation to ammonia and HCl is complete at 520 K. It is very soluble in water. ... 

Sublimation - ammonium chloride sublimes , potassium chloride does not. 

Procedure The sample is placed in a micro test tube and covered with several eg of ammonium chloride. On heating with a low flame, the ammonium chloride sublimes and condenses, in part at least, on the coolor walls of the tube. The treatment is best repeated with a fresh batch of ammonium chloride. Finally, the bottom of the tube is heated strongly so that the ferrous chloride is completely sublimed. After cooling, the sublimate is spotted with several drops of a 2 % alcoholic solution of a,a -dipyridyl. 

Mix 100 g. of ammonium chloride and 266 g. of paraformaldehyde in a 1-litre rovmd-bottomed flask fitted with a long reflux condenser containing a wide inner tube (ca. 2 cm. diameter) the last-named is to avoid clogging the condenser by paraformaldehyde which may sublime. Immerse the flask in an oil bath and gradually raise the temperature. The mixture at the bottom of the flask liquefies between 85° and 105° and a vigorous evolution of carbon dioxide commences at once remove the burner beneath the oil bath and if the reaction becomes too violent remove... 

Sublimation. This process is employed to separate volatile substances from non-volatile impurities. Iodine, arsenic(III) oxide, ammonium chloride and a number of organic compounds can be purified in this way. The material to be purified is gently heated in a porcelain dish, and the vapour produced is condensed on a flask which is kept cool by circulating cold water inside it. 

Simple sublimation is a batch-wise process in which the solid material is vaporised and then diffuses towards a condenser under the action of a driving force attributable to difference in partial pressures at the vaporising and condensing surfaces. The vapour path between the vaporiser and the condenser should be as short as possible in order to reduce mass-transfer resistance. Simple sublimation has been used for centuries, often in very crude equipment, for the commercial production of ammonium chloride, iodine, and flowers of sulphur. 

The volcanic sublimates ", such as sulfur, ammonium chloride, arsenic sulfide, copper chloride, magnetite, may be mentioned in this connection, as well as the minerals accompanying fumarole and hot-spring activity. 

Methyldihydromorphinone. A solution of 2 g of methyldihydrocodeinone in 10 cc of 48% hydrobromic acid is boiled for 25 min. The solution is then diluted with water, made strongly alkaline, and extracted with ether. Add ammonium chloride to precipitate the phenolic product, 1.7 g of brown powder. Sublime (see glossary for instructions) in a high vacuum at 180° to get 1.4 g of white crystals of methyldihydromorphinone. Recrystallize from alcohol to get pure, long needles, mp 243-245°. The hydrochloride form is prepared, as usual, in dry ethanol and recrystallized from the same. This drug is sometimes called Metopon and is active orally. 

Ammonium chloride decomposes to ammonia and HCl when heated. The vapor resulting from sublimation consists of equal volume of NH3 and HCl, and does not consist of molecular NH4CI. (Young, R. D. 1976. Ammonium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd. ed. Vol. 2, p. 521. New York Wiley Interscience.)... 

Alternatively, it may be prepared by heating ammonium chloride with excess sodium fluoride. Ammonium fluoride is obtained by sublimation. 

The product decomposes on sublimation forming mercury(ll) chloride, ammonia, and nitrogen. However, in the presence of ammonium chloride, the same reaction with ammonia with HgCb in aqueous solution yields fusible white precipitate, (NH3)2HgCl2. Similar product also is obtained by reaction of gaseous ammonia with solid mercury(II) chloride. However, the solid mer-cury(II) chloride is more stable than the above infusible product and can be melted without decomposition. 

Some compounds (e.g. ammonium chloride) explosively sublime in the flame, thus enhancing atomization. By adding excess ammonium chloride to all samples and standards, this effect can be used to minimize interferences of types (a) and (c). 

Sal ammoniac (ammonium chloride) had been known from antiquity, it being easily obtained by sublimation from animal refuse (urine) and from coal soot, chimney sweepings, etc. Its virtues seemed to lie in its volatility, that is its spirituality. Here are a few remarks from Lemerys book. 

Burning at subatmospheric pressure is accompanied by the evolution of white fumes which solidify upon contact with a cold surface. For the LP3 propellant, it is larger in quantity and increases considerably as soon as the ash starts forming. This smoke was found to contain 25% ammonium perchlorate and 55% ammonium chloride. A trap was installed to determine the amount of smoke evolved per unit mass of propellant as a function of pressure and oxidizer particle size, but the results were inconclusive. The weight of sublimate caught was approximately 20% of the original weight of the propellant. 

Sesquiammino-boron Trichloride, 2BC13.3NH3, is also formed when dry ammonia gas is passed into liquid boron trichloride. The ammine does not fume on exposure to air, is less volatile than ammonium chloride, and may be sublimed without decomposition. Water decomposes it with formation of ammonium chloride, hydrochloric acid, and a borate. Besson 2 described a substance of composition 2BC13. 9NH3, which he obtained from boron phosphino-chloride and ammonia. This is not attacked by moist air and does not lose ammonia below 50° C., but water decomposes it immediately. 

If well-dried ammonia gas is passed over freshly sublimed aluminium chloride ammonia is rapidly absorbed, heat is developed, and the whole mass fuses and then gradually solidities as more ammonia is absorbed, leaving a white voluminous powder of composition A1C13.GNH3 or [A1(NH3)6]C13. Hexammino-aluminium chloride is stable at ordinary temperature and is much less hygroscopic than the chloride. It is decomposed by water with formation of aluminium hydroxide, and when heated in dry air is oxidised, yielding the oxide and ammonium chloride. If heated in an atmosphere of dry hydrogen it loses ammonia and passes into diammino-aluminium chloride, [A1(NH3)2]C13.5 Triammino-aluminium chloride obtained in this way by Persoz was not found by Stillmann and Yoder. 

Antimony pentachloride also unites with ammonia. Two products are formed by passing ammonia gas into cold antimony pentachloride, namely, triammino-antimony pentachloride, [Sb(NH3)3]Cl3, and tetranunino-antimony pentachloride, [Sb(NH3)1]Cl5.1 Triammino-antimony pentachloride is a red substance which decomposes on heating, with formation of a sublimate of composition 3NH4Cl.SbCl5. Tetram-mino-antimony pentachloride is a white volatile substance which decomposes into antimony ammonium chloride. NH4Cl.SbCls, on treatment with hydrochloric acid. 

In 1705, L. Lemery 1 first showed that ammonium chloride exists among the products derived from volcanoes, where he found it admixed with sodium chloride, and this fact was verified by F. Seras in 1737, and by F. de Bonderoy in 1765. Ammonium chloride occurs as a sublimate mixed with other volatile matters in cavities VOL. ii. 2 o... 

Ammonium chloride is also formed by the action of hydrochloric acid on a soln. of ammonia or ammonium carbonate J. G. Qentele 5 made it by the double decomposition of ammonium bicarbonate and sodium, magnesium, calcium, and other chlorides H. J. E. Hennebutte and E. Mesnard, and A. Dubose and M. Heuzey, made it by the action of ammonium bicarbonate or sulphate on the double chloride of iron and calcium and it is made by the action of soln. of ammonium sulphate and sodium chloride when the soln. is cone, the crystals of sodium sulphate separate out and they are removed by suitable shovels the cone. soln. of ammonium chloride which remains is purified by crystallization. Ammonium chloride can also be obtained by sublimation from a dry intimate mixture of the same two salts. A. French made it by the joint action of air and steam on a mixture of salt, pyrites, and carbon or organic matter 2NaCl+4H20-j-S02+C-j-N2=2NH4Cl-i-Na2S04-i-C02. 

The purification of ammonium chloride.—Crude sal ammoniac is usually contaminated with iron or tarry matters, and in consequence, the colour varies from yellow to red it can be purified by heating it in thin layers on an iron plate hot enough to drive off the water and free acid, and to carbonize most of the tarry products. The grey mass is then sublimed. The sublimation is conducted in cast-iron pots lined internally with firebricks, and covered with a lid made of slightly concave plates. The salt to be sublimed is well dried, and heated. The pots hold about half a ton, and the sublimation occupies about five days. The sublimate forms a solid fibrous crust about 4 inches thick. The crust is easily detached from the lid it is then broken up, separated from adhering dirt, and packed for the market in barrels or sacks. W. Hempel 9 proposed converting the crystalline salt into hard stone-like masses by press, between 50° and 100°. 

In order to fix the iron and prevent its volatilization as chloride, F. C. Calvert recommended mixing the product before sublimation with acid calcium phosphate or ammonium phosphate, and M. Adler recommended superphosphate. Kecrystal-lization after treatment of the soln. with animal charcoal has also been recommended. The iron is also said to be removed by treating the soln. with a little chlorine (not an excess), then with ammonia, and finally crystallizing the filtered soln. In his work on at. wt., J. S. Stas purified ammonium chloride as followrs ... 

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