Inorganic Chemicals

Formula: AlCl3; MW 133.31; Structure and bonding: an electron-deficient compound, a Lewis acid, occurs as dimer Al2Cl6 in hexagonal crystal form. Above 300 °C, dissociation to monomer AlCl3 begins; completely dissociates to AlCl3 at 1,100°C.

Uses
Aluminum chloride has extensive commercial applications. It is used primarily in the electrolytic production of aluminum. Another major use involves its catalytic applications in many organic reactions, including Friedel-Crafts alkylation, polymerization, isomerization, hydrocracking, oxidation, decarboxylation, and dehydrogenation. It is also used in the production of rare earth chlorides, electroplating of aluminum and in many metal finishing and metallurgical operations.

Physical Properties
White or light-yellow crystalline solid (or amorphous solid depending on the method of production); odor of HCl; hygroscopic; melts at 190°C at 2.5 atm; sublimes at 181.2°C; density 2.44 g/cm3 at 25°C; decomposes in water evolving heat; soluble in HCl; soluble in many organic solvents, including absolute ethanol, chloroform, carbon tetrachloride and ether; slightly soluble in benzene.

Thermochemical Data

ΔH°ƒ(s)      –168.3 kcal/mol
ΔG°ƒ(s)      –150.3 kcal/mol
S°              26.45 cal/deg mol
Hsoln.      –77.7 kcal/mol
Hfus         8.45 kcal/mol

Preparation
Aluminum chloride is made by chlorination of molten aluminum at temperatures between 650 to 750°C;

or by chlorination of alumina (bauxite or clay) at 800°C in the presence of a reducing agent, such as carbon or CO. It can be prepared by similar high temperature chlorination of bauxite in the presence of a chlorinated organic reductant such as CCl4.
A pelletized mixture of clay, lignite and a small amount of NaCl is chlorinated at 900°C, producing gaseous AlCl3 (Toth process). Alternatively, alumina is mixed with about 20% by weight carbon and a small amount of sodium salt. The mixture is chlorinated at 600°C (Bayer process). In the laboratory, anhydrous AlCl3 can be prepared by heating the metal with dry HCl gas at 150°C. The product sublimes and deposits in the cool air condenser. Unreacted HCl is vented out.

Reactions
Reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydro aluminates, Ca(AlH4)2; reacts with hydrides of alkali metals in ether forming aluminum hydride;

Hydrolyzes in chilled, dilute HCl forming aluminum chloride hexahydrate, AlCl3⋅6H2O; reacts violently with water, evolving HCl,

Hazard
Violent exothermic reactions can occur when mixed with water or alkene. Corrosive to skin.

Formula: AlCl3•6H2O; MW 241.31

Uses
The hexahydrate is used in the preparation of deodorant and antiperspirant. Also, it is applied in textile finishing to improve the antistatic characteristics and flammability ratings of various textile materials. Commercially, it is sold as crystalline powder or as a 28% solution in water.

Physical Properties
White or yellowish deliquescent powder; faint odor of HCl; density 2.40 g/cm3; soluble in water and polar organic solvents such as alcohol; aqueous solution acidic.

Preparation
Aluminum chloride hexahydrate is prepared by dissolving Al(OH)3 in conc. HCl and passing gaseous HCl through the solution at 0°C. The precipitate is washed with diethyl ether and dried. Alternatively, it is prepared by hydrolyzing anhydrous AlCl3 in cold dilute HCl.

Reactions
Decomposes to alumina when heated at 300°C;

Reacts with caustic soda solution forming gelatinous precipitate of aluminum hydroxide (hydrous aluminum oxide); yields aluminum monobasic stearate, Al(OH)2[OOC(CH2)16CH3] when its solution is mixed with a solution of sodium stearate.

Formula: NH4Cl; MW 53.49

Synonym: Sal ammoniac

Occurrence and Uses

Ammonium chloride occurs in nature in crevices near volcanoes. Also, it is found in smoke when burning dry camel or donkey dung as fuel. Important applications of this compound include the manufacture of dry cells for batteries; as a metal cleaner in soldering; as a flux in tin coating and galvanizing; in fertilizers; in pharmaceutical applications as a diuretic, or diaphoretic expectorant; and as an analytical standard in ammonia analysis. Also, it is used in freezing mixtures; washing powders; lustering cotton; in safety explosives and in dyeing and tanning.

Physical Properties

Colorless cubic crystals or white granular powder; saline taste; odorless; hygroscopic; does not melt but sublimes on heating at 340°C; vapor pressure 48.75 torr at 250°C and 251.2 torr at 300°C; density 1.5274 g/cm3 at 25°C; refractive index 1.642; readily dissolves in water, solubility: 229 g and 271 g/L solution at O°C and 20°C, respectively; solubility lowered by alkali metal chlorides and HCl; dissolution lowers the temperature of the solution; sparingly soluble in alcohols (6 g/L at 19°C) and soluble in liquid NH3; insoluble in acetone and ether.

Thermochemical Properties

ΔΗ°ƒ(s) –75.15 kcal/mol
ΔΗ°ƒ(s) [NH3(g) + HCl(g)] –41.9 kcal/mol
ΔG°ƒ(s) –48.51 kcal/mol
S° 22.6 cal/degree mol
Cρ 20.1 cal/degree mol
ΔH°subl (1 atm) 39.6 kcal/mol

Manufacture

Ammonium chloride is produced as a by-product in the Solvay process for manufacture of sodium carbonate:

NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl

NaHCO3 precipitate is filtered out of solution while NH4Cl is obtained by crystallization followed by washing and drying. Ammonium chloride also is produced from spent calcium chloride liquor obtained in ammonia-soda process:

CaCl2 + 2NH3 + CO2 + H2O → Na2SO4 + 2 NH4Cl

It also is made by heating a mixture of slight excess of NaCl solution with ammonium sulfate. The filtrate containing NH4Cl is concentrated and cooled.

NH4Cl crystallizes:

(NH4)2SO4 + 2NaCl → Na2SO4 + 2 NH4Cl

It is produced by direct neutralization reaction of NH3 and HCl combined as gaseous mixtures.

NH3(g) + HCl(g) → NH4Cl(s)

Reactions

NH4Cl is acidic in aqueous solution: the pH of 1%, 3%, and 10% solution at 25°C are 5.5, 5.1 and 5.0, respectively. (Merck 1996. The Merck Index, 12th ed. Rahway, NJ: Merck & Co.) It loses ammonia and becomes more acidic on prolonged exposure or storage. It reacts with iron, copper, nickel and other metals and some of their alloys such as bronze and brass. It reacts with alkalies forming NH3.

NH4Cl + NaOH → NH3 + NaCl + H2O

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 NH4Cl. (Young, R. D. 1976. Ammonium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd. ed. Vol. 2, p. 52l. New York: Wiley Interscience.) Reacts with formaldehyde (neutralized with NaOH) forming examethylenetetramine
and HCl.

NH4Cl + 6 HCHO → C6H12N4 + 4HCl + 6H2O

Reaction with copper(II) chloride at 2:1 ratio produces yellow orthorhombic crystals of cupric ammonium chloride, which reacts with water to form blue dihydrate crystal, ammonium tetrachlorodiaquocuprate(II): heat 2NH4Cl + CuCl2 –––→ (NH4)2 + CuCl4 evaporation A similar complex formation occurs with mercuric chloride, zinc chloride, osmium chloride and platinum (II) and (VI) chlorides, forming mercuric ammonium chloride, (NH4)2•HgCl4, zinc ammonium chloride (NH4)3ZnCl4 or ZnCl2•3NH4Cl, osmium ammonium chloride, (NH4)2OsCl6, platinum ammonium chloride, (NH4)2PtCl4 and platinic ammonium chloride (NH4)2PtCl6, respectively. Similarly, it reacts with palladium chloride to form ammonium chloropalladate, (NH4)2PdCl4. It precipitates out ammonium platinichloride from solution of chloroplatinic acid (Archibald, E. H. 1920. J. Chem. Soc., 117, 1105):

H2PtCl6 + 2NH4Cl → (NH4)2PtCl6 + 2HCl

Neutralization reaction occurs with amide, forming chloride salt and ammonia:

NH4Cl + KNH2 → KCl + 2NH3

Heating with zirconium chloride gives a tetraamine adduct:

4NH4Cl+ZrCl4ZrCl4.4NH3+4HCl

Chemical Analysis

Elemental composition: Cl 66.28%, H 7.54%, N 26.18% Ammonium chloride is analyzed by treatment with formaldehyde (neutralized with NaOH) and the product HCl formed is analyzed by titration using an acid-base color indicator such as phenolphthalein. Alternatively, it may be mixed with caustic soda solution and distilled. The distillate may be analyzed for NH3 by titration with H2SO4; or by colorimetric Nesslerization; or with an ammonia-selective electrode (APHA, AWWA, WEF. 1995. Standard Methods for the Examination of Water and Wastewater. 19th ed. Washington, DC, American Public Health Association). The presence of ammonia or any other ammonium compound would interfere in the test. The moisture content in NH4Cl may be determined by Karl–Fischer method.