Reactivity Profile
HYDROGEN BROMIDE is an anhydrous (no water) strong acid. Reacts rapidly and exothermically with bases of all kinds (including amines and amides). Reacts exothermically with carbonates (including limestone and building materials containing limestone) and hydrogen carbonates to generate carbon dioxide. Reacts with sulfides, carbides, borides, and phosphides to generate toxic or flammable gases. Reacts with many metals (including aluminum, zinc, calcium, magnesium, iron, tin and all of the alkali metals) to generate flammable hydrogen gas. Reacts violently with acetic anhydride, 2-aminoethanol, ammonium hydroxide, calcium phosphide, chlorosulfonic acid, 1,1-difluoroethylene, ethylenediamine, ethyleneimine, oleum, perchloric acid, b-propiolactone, propylene oxide, silver perchlorate/carbon tetrachloride mixture, sodium hydroxide, uranium(IV) phosphide, vinyl acetate, calcium carbide, rubidium carbide, cesium acetylide, rubidium acetylide, magnesium boride, mercury(II) sulfate, calcium phosphide, calcium carbide.
Air & Water Reactions
Acrid odor, fumes in moist air forming clouds containing hydrobromic acid. Heat of solution large, [Merck, 11th ed., 1989].
Hazard
Toxic by inhalation, strong irritant to eyes
and skin.
Health Hazard
Inhalation causes severe irritation of nose and upper respiratory tract, lung injury. Ingestion causes burns of mouth and stomach. Contact with eyes causes severe irritation and burns. Contact with skin causes irritation and burns.
Fire Hazard
Behavior in Fire: Pressurized container may explode and release toxic, irritating vapor.
Description
Hydrobromic Acid is a strong acid formed by dissolving the
diatomic molecule HBr in water. “Constant-boiling”
hydrobromic acid is an aqueous solution that distills at
124.3°C and contains 47.6% HBr by weight. Hydrobromic
acid has a pKa of 9, making it a stronger acid
than hydrochloric acid, but not as strong as HI, hydroiodic
acid. Hydrobromic acid is one of the strongest
mineral acids known.
Hydrobromic acid is mainly used for the production
of inorganic bromides, especially the bromides of zinc,
calcium, and sodium. It is a useful reagent for generating
organobromine compounds. Certain ethers are
cleaved with HBr. It also catalyzes alkylation reactions
and the extraction of certain ores. Industrially significant
organic compounds prepared from hydrobromic
acid include allyl bromide, tetrabromobis(phenol),
and bromoacetic acid.
Hydrobromic acid can be prepared in the laboratory
via the reaction of Br2, SO2 and water. Another laboratory
preparation involves the production of anhydrous
HBr, which is then dissolved in water.
Hydrobromic acid has commonly been prepared
industrially by reacting bromine with either sulfur or
phosphorous and water. However, it can also be
produced electrolytically. It can also be prepared by
treating bromides with nonoxidizing acids like phosphoric
or acetic acids. Hydrobromic acid is available
commercially in various concentrations and purities.
Physical properties
Colorless gas; fumes in moist air; pungent acrid odor; nonflammable; heav-ier than air; density 2.71 (air=1.0); gas density 3.55 g/L at 25°C; liquefies at-66.4°C; solidifies at -86.8°C; critical temperature 89.8°C; critical pressure84.5 atm; highly soluble in water (saturated aqueous solution contains 66%HBr at 25°C); forms a constant-boiling azeotrope at 47.5% HBr in solution,boiling at 126°C at atmospheric pressure; soluble in alcohol; a 0.10Maqueoussolution is 93% ionized to H+and Br ? ions at 18°C.
Preparation
Hydrogen bromide gas may be produced by combustion of hydrogen inbromine vapor at 37.5°C using a catalyst such as platinized asbestos or pla-tinized silica gel. Unreacted free bromine is removed from the product bypassing the gaseous product mixture over hot activated charcoal. Hydrogenbromide formed may be absorbed in water to obtain the acid; or may be cooledand liquefied for shipment in cylinders.
Hydrobromic acid may be prepared in the laboratory by distillation of asolution of potassium bromide with dilute sulfuric acid:
2KBr + H2SO4 → K2SO4 + HBr
The acid may be prepared by several other methods, as well, including reac-tion of bromine either with sulfur and water; or with phosphorus and water:
2Br2 + S + 2H2O → 4HBr + SO2
Hydrobromic acid also may be prepared by hydrogen exchange with a sodiumor potassium bromide solution when the solution is passed through a cation-exchange resin.
Hydrobromic acid is stored and shipped in drums, tanks, carboys, or bot-tles, labeled as corrosive materials. The anhydrous gas is stored and shippedin cylinders under its vapor pressure.
General Description
Hydrobromic acid solution (HBr) is a clear, yellow or brown colored liquid. Its reaction with K has been studied by a molecular beam technique.
Flammability and Explosibility
Noncombustible, but contact with metals may produce highly flammable hydrogen
gas.
Materials Uses
Hydrogen bromide does not aggressively attack
common metals of construction while in the
anhydrous state. However, in the presence of
moisture, hydrogen bromide will attack most
metals except platinum and silver. Galvanized
pipe, brass, and bronze should be avoided.
Steel, Monel, and aluminum-silicon-bronze
have proven satisfactory in anhydrous hydrogen
bromide service.
Potential Exposure
Hydrogen bromide gas and its aqueoussolutions are used in the manufacture of organic and inor-ganic bromides; as a reducing agent and catalyst in con-trolled oxidations; in the alkylation of aromatic compounds;and in the isomerization of conjugated diolefins. It is usedas an intermediate for pharmaceuticals, dyes, photographicchemicals.
Physiological effects
Hydrogen bromide is extremely irritating to the
eyes, mucous membranes of the respiratory
tract, and skin. Contact may cause bums. Repeated
short exposures to concentrations of
about 35 ppm can cause irritation to the nose
and throat with mucous production and indigestion.
Inhalation of higher concentrations can
cause pulmonary edema and laryngeal spasm,
and can be fatal. Skin contact with the vapor or
liquid causes severe tissue irritation and necrosis
[2].
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek med-ical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, includ-ing resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medi-cal attention. If victim is conscious, administer water ormilk. Do not induce vomiting. Medical observation isrecommended for 24- 48 h after breathing overexposure, aspulmonary edema may be delayed. As first aid for pulmo-nary edema, a doctor or authorized paramedic may consideradministeringa corticosteroid spray. If frostbite hasoccurred, seek medical attention immediately; do NOT rubthe affected areas or flush them with water. In order to pre-vent further tissue damage, do NOT attempt to remove fro-zen clothing from frostbitten areas. If frostbite has NOToccurred, immediately and thoroughly wash contaminatedskin with soap and water.
storage
Splash goggles and rubber gloves should be
worn when handling this acid, and containers of HBr should be stored in a wellventilated
location separated from incompatible metals. Water should never be
added to HBr because splattering may result; always add acid to water. Containers of
hydrobromic acid should be stored in secondary plastic trays to avoid corrosion of
metal storage shelves due to drips or spills.
Cylinders of hydrogen bromide
should be stored in cool, dry locations, separated from alkali metals and other
incompatible substances.
Shipping
Anhydrous hydrogen bromide requires a shippinglabel of“POISON GAS, CORROSIVE."It falls in HazardClass 2.3. It is a violation of transportation regulations torefill compressed gas cylinders without the express writtenpermission of the owner.Special precautions:Cylinders must be transported in asecure upright position, in a well-ventilated truck.Hydrobromic acid, with > 49% hydrobromic acid requires ashipping label of“CORROSIVE." It falls in Hazard Class 8and Packing GroupII or II.Hydrobromic acid,with not > 49% hydrobromic acidrequires a shipping label of“CORROSIVE.”It falls inHazard Class 8 and Packing GroupII or II.
Purification Methods
A solution of aqueous HBr ca 48% (w/w, constant boiling) is purified by distilling twice with a little red phosphorus, and the middle half of the distillate is taken. (The azeotrope at 760mm contains 47.8% (w/w) HBr.) [Hetzer et al. J Phys Chem 66 1423 1962]. Free bromine can be removed by Irvine and Wilson's method for HI (see above), except that the column is regenerated by washing with an ethanolic solution of aniline or styrene. Hydrobromic acid can also be purified by aerating with H2S, distilling and collecting the fraction boiling at 125-127o. [Heisig & Andur Inorg Synth I 155 1939.] HARMFUL VAPOURS.
Incompatibilities
Hydrobromic acid and hydrogen bromide react violently with many metals with the
generation of highly flammable hydrogen gas, which may explode. Reaction with
oxidizers such as permanganates, chlorates, chlorites, and hypochlorites may
produce chlorine or bromine.
Toxics Screening Level
The screening level for Hydrogen Bromide (HBr) is 70 μg/m3 based on 1 hour averaging.
Waste Disposal
In many localities, hydrobromic acid or the residue from a spill may be disposed of down the drain after
appropriate dilution and neutralization. Otherwise, hydrobromic acid and waste material containing this
substance should be placed in an appropriate container, clearly labeled, and handled according to your
institution's waste disposal guidelines. Excess hydrogen bromide in cylinders should be returned to the
manufacturer. For more information on disposal procedures, see Chapter 7 of this volume.
GRADES AVAILABLE
Hydrogen bromide is typically available in 99.8
percent purity.
Gas purity guidelines have been developed
and published by Semiconductor Equipment
and Materials International and can be found in
the Book of SEMI Standards, Gases Volume.
