|Preferred IUPAC name
Hydrogen bromide
|Systematic IUPAC name
|Molar mass||80.91 g·mol−1|
|Density||3.6452 kg/m3 (0 °C, 1013 mbar)|
|Melting point||−86.9 °C (−124.4 °F; 186.2 K)|
|Boiling point||−66.8 °C (−88.2 °F; 206.3 K)|
|221 g/100 mL (0 °C)
204 g/100 mL (15 °C)
193 g/100 mL (20 °C) 130 g/100 mL (100 °C)
|Solubility||soluble in alcohol, organic solvents|
|Vapor pressure||2.308 MPa (at 21 °C)|
Refractive index (nD)
|Dipole moment||820 mD|
|350.7 mJ K−1 g−1|
|198.696-198.704 J K−1 mol−1|
Std enthalpy of
|-36.45--36.13 kJ mol−1|
|GHS signal word||DANGER|
|P261, P280, P305+351+338, P310|
|S-phrases||(S1/2), S7/9, S26, S45|
|US health exposure limits (NIOSH):|
|TWA 3 ppm (10 mg/m3)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Hydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and hydrobromic acid are, therefore, not the same, but they are related. Commonly, chemists refer to hydrobromic acid as "HBr", and this usage, while understood by most chemists, is imprecise and can be confusing to the non-specialist.
At cold temperature, HBr is a nonflammable gas with an acrid odor, fuming in moist air because of the formation of carbon monoxide.
HBr is very soluble in water, forming hydrobromic acid solution, which is saturated at 68.85% HBr by weight at room temperature. Aqueous solutions that are 47.6% HBr by weight form a constant-boiling mixture (reverse azeotrope) that boils at 124.3°C. Boiling less concentrated solutions releases H2O until the constant boiling mixture composition is reached.
Uses of HBr
There are many uses of HBr in chemical synthesis. For example, HBr is used for the production of alkyl bromides from alcohols:
- ROH + HBr → RBr + H2O
- RCH=CH2 + HBr → RCH(Br)–CH3
- RC≡CH + HBr → RC(Br)=CH2
- RC(Br)=CH2 + HBr → RC(Br2)–CH3
HBr has been proposed for use in a utility-scale flow-type battery.
Hydrogen bromide (along with hydrobromic acid) is produced on a much smaller scale than the corresponding chlorides. In the primary industrial preparation, hydrogen and bromine are combined at temperatures between 200-400 °C. The reaction is typically catalyzed by platinum or asbestos.
- 2 KBr + H2SO4 → K2SO4 + 2HBr
Concentrated sulfuric acid is ineffective because HBr formed will be oxidized to bromine gas:
- 2 HBr + H2SO4 → Br2 + SO2 + 2H2O
- 2 Br2 + S + 2 H2O → 4 HBr + SO2
- C10H12 + 4 Br2 → C10H8Br4 + 4 HBr
Alternatively bromine can be reduced with phosphorous acid:
- Br2 + H3PO3 + H2O → H3PO4 + 2 HBr
HBr prepared by the above methods can be contaminated with Br2, which can be removed by passing the gas through Cu turnings or through phenol.
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- Record in the GESTIS Substance Database of the IFA
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- "NIOSH Pocket Guide to Chemical Hazards #0331". National Institute for Occupational Safety and Health (NIOSH).
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- Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Butterworth-Heineman: Oxford, Great Britain; 1997; pp. 809-812.
- Carlin, William W. U.S. Patent 4,147,601, April 3, 1979
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- Ruhoff, J. R.; Burnett, R. E.; Reid, E. E. "Hydrogen Bromide (Anhydrous)" Organic Syntheses, Vol. 15, p.35 (Coll. Vol. 2, p.338).
- Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- WebElements: Hydrogen Bromide