Hydrogen bromide
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| Names | |||
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Preferred IUPAC name
Hydrogen bromide
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Systematic IUPAC name
Bromane
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| Identifiers | |||
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3D model (Jmol)
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| 3587158 | |||
| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.030.090 | ||
| EC Number | 233-113-0 | ||
| KEGG | |||
| MeSH | Hydrobromic+Acid | ||
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PubChem CID
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| RTECS number | MW3850000 | ||
| UNII | |||
| UN number | 1048 | ||
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| Properties | |||
| BrH | |||
| Molar mass | 80.91 g·mol−1 | ||
| Appearance | Colorless gas | ||
| Odor | Acrid | ||
| 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) |
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| Solubility | soluble in alcohol, organic solvents | ||
| Vapor pressure | 2.308 MPa (at 21 °C) | ||
| Acidity (pKa) | -8.8 (±0.8); ~−9 | ||
| Basicity (pKb) | ~23 | ||
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Refractive index (nD)
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1.325 | ||
| Structure | |||
| Linear | |||
| 820 mD | |||
| Thermochemistry | |||
| 350.7 mJ K−1 g−1 | |||
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Std molar
entropy (S |
198.696-198.704 J K−1 mol−1 | ||
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Std enthalpy of
formation (ΔfH |
−36.45 – −36.13 kJ mol−1 | ||
| Hazards | |||
| Safety data sheet |
hazard.com |
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| GHS pictograms |
 
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| GHS signal word | DANGER | ||
| H314, H335 | |||
| P261, P280, P305+351+338, P310 | |||
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EU classification (DSD)
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 C |
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| R-phrases | R35, R37 | ||
| S-phrases | (S1/2), S7/9, S26, S45 | ||
| NFPA 704 | |||
| Lethal dose or concentration (LD, LC): | |||
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LC50 (median concentration)
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2858 ppm (rat, 1 hr) 814 ppm (mouse, 1 hr) |
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| US health exposure limits (NIOSH): | |||
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PEL (Permissible)
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TWA 3 ppm (10 mg/m3) | ||
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REL (Recommended)
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TWA 3 ppm (10 mg/m3) | ||
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IDLH (Immediate danger)
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30 ppm | ||
| Related compounds | |||
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Related compounds
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Hydrogen fluoride Hydrogen chloride Hydrogen iodide Hydrogen astatide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |||
Hydrogen bromide is the diatomic molecule with the formula HBr. It is a colorless compound and a hydrogen halide. Hydrobromic acid is a solution of HBr in water. Both the anhydrous and aqueous solutions of HBr are common reagents in the preparation of bromide compounds.
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 azeotrope mixture that boils at 124.3 °C. Boiling less concentrated solutions releases H2O until the constant boiling mixture composition is reached.
Hydrogen bromide and hydrobromic acid are important reagents in the production of inorganic and organic bromine compounds. The free-radical addition of HBr to alkenes gives alkyl bromides:
These alkylating agents are precursors to fatty amine derivatives. Similar free radical addition to allyl chloride and styrene gives 1-bromo-3-chloropropane and phenylethylbromide, respectively.
Hydrogen bromide reacts with dichloromethane to give bromochloromethane and dibromomethane, sequentially:
Allyl bromide is prepared by treating allyl alcohol with HBr:
Although not widely used industrially, HBr adds to alkenes to give bromoalkanes, an important family of organobromine compounds. Similarly, HBr adds to haloalkene to form a geminal dihaloalkane. (This type of addition follows Markovnikov's rule):
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