Inorganic Chemicals

Formula: AlBr3; MW 266.72; Structure: anhydrous AlBr3 is body-centered crystal, exists in dimeric form as Al2Br6 in crystal and also in liquid phases; partially dissociates to monomeric form AlBr3 in gaseous state; mass spectra show the presence of di-, tetra-, and hexameric forms, Al2Br6, Al4Br12, Al6Br18, respectively.

Uses
The anhydrous form is used as a catalyst for the Friedel-Crafts alkylation reaction. Its catalytic activity is similar to anhydrous AlCl3. Commercial applications, however, are few.

Physical Properties
Colorless crystalline solid in anhydrous form; melts at 97.5°C; boils at 256°C; density 3.01 g/cm3 at 25°C; moisture sensitive, fumes in air; soluble in water (reacts violently in cold water, and decomposes in hot water, alcohols, acetone, hexane, benzene, nitrobenzene, carbon disulfide and many other organic solvents).

Preparation
Prepared from bromine and metallic aluminum.

2Al + 3Br2 ——› Al2Br6 (anhydrous)

Thermochemical Properties

AlBr3 (cry)             ΔHƒ°            –126.0 kcal/mo
                             Cp               24.3 cal/degree
AlBr3 (gas)            ΔHƒ°            –101.6 kcal/mo
AlBr3 (aq)              ΔHƒ°            –214.0 kcal/mo
Al2Br6 (gas)          ΔHƒ°            –232.0 kcal/mo
AlBr3 (aq)              S°                –17.8 cal/degre
Al2Br6 (gas)         Hfusion       10.1 cal/g

Chemical Reactions
Decomposes upon heating in air to bromine and metallic aluminum.

Reacts with carbon tetrachloride at 100°C to form carbon tetrabromide;

4AlBr3 + 3CCl4 ——› 4AlCl3 + 3Br4

Reaction with phosgene yields carbonyl bromide and aluminum chlorobromide;

AlBr3 + COCl2 ——› COBr2 + AlCl2Br

Reacts violently with water; absorbs moisture forming hexahydrate,
AlBr3⋅6H2O [7784-27-2]

Chemical Analysis
Elemental composition, Al 10.11% and Br 89.89%; Al analyzed by AA spectrophotometry or colorimetric methods; Br– analyzed by iodometric titration or ion chromatography and then calculated stoichiometrically; solid may be dissolved in an organic solvent and determined by GC/MS, identified by mass ions
(AlBr3 )n where n is 2, 4 and 6.

Toxicity
Skin contact can cause tissue burn. It is moderately toxic by all routes of exposure. LD50 oral (rat and mouse): ~1600 mg/kg.

Formula: NH4Br; MW 97.94; ionic salt, cubic crystal

Uses

Ammonium bromide is used for photography in films, plates, and papers; in fireproofing of wood; in lithography and process engraving; in corrosion inhibitors; and in pharmaceutical preparations.

Physical Properties

White crystal or granule; strong saline taste; no odor; slightly hygroscopic; density 2.429 g/cm3 at 25°C; refractive index 1.712; sublimes at elevated temperatures: vapor pressure 54.75 torr at 300°C and 758.2 torr at 395°C; highly soluble in water: 60.6 g and 75.5 g/100 mL at 0° and 20°C, respectively - solubility increasing approximately 16 to 18 g/100 mL for every 20°C increase in temperature.

Thermochemical Properties

ΔHƒ°(s) –64.73 kcal/mol
ΔGƒ°(s) –41.9 kcal/mol
S° 27 cal/degree mol
Cρ 23 cal/degree mol

Preparation

Ammonium bromide is prepared by treating excess ammonia with bromine:

8NH3 + 3Br2 → 6NH4Br + N2

It may be also prepared by the reaction of ammonia and hydrobromic acid:

NH3 + HBr → NH4Br

NH4Br is also made by the reaction of ammonia with ferrous and ferric bromide, which may be obtained by passing aqueous bromine solution over iron filings.

2NH3 + FeBr2 + H2O → 2NH4Br + FeO
6NH3 + 2FeBr3 + 3H2O → 6NH4Br + Fe2O3

Reactions

Ammonium bromide exhibits acid reaction in aqueous solution; acts as an excellent acid in liquid NH3, undergoing neutralization reactions:

NH Br + NaNH3→NaBr + 2NH3

Contact with metal surfaces produces bromides of the metals; similarly reactions with metal hydroxide bases yield corresponding bromides:

2NH4Br + Ca(OH)2 →CaBr2 + 2NH3 + 2H2O

Ammonium bromide decomposes to ammonia and hydrogen bromide when heated at elevated temperatures:

NH4Br→ NH3+HBr

Chemical Analysis

Elemental composition: Br 81.58%, H 4.12%, N 14.30% Mixed with NaOH solution and distilled; distillate analyzed for ammonia by titration, colorimetry, or electrode method (see Ammonia and Ammonium chloride). Bromide portion of NH4Br in aqueous solution may be analyzed by ion chromatography, or by the colorimetry method in which red to violet color is produced upon treatment with chloramine–T, and phenol red at pH 4.5. The colorimetry test for bromide is subject to interference from oxidizing and reducing agents, chloride, and bicarbonate. NH4Br may then be determined stoichiometrically.