Phosphorus pentabromide
Chemical compound
From Wikipedia, the free encyclopedia
Phosphorus pentabromide is the inorganic compound with the formula PBr5. It is a yellow ionic solid that is used in organobromine compounds. The compound participates in diverse equilibria, especially in the presence of additional bromine.
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| Names | |
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| IUPAC name
Tetrabromophosphanium bromide | |
| Other names | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.029.260 |
| EC Number |
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PubChem CID |
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| UNII | |
| UN number | 2691 |
CompTox Dashboard (EPA) |
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| Properties | |
| PBr5 | |
| Molar mass | 430.494 g·mol−1 |
| Appearance | Yellow crystalline solid[1] |
| Density | 3.61 g/cm3 |
| Melting point | ca. 100 °C (decomposes) |
| Boiling point | 106 °C (223 °F; 379 K) (decomposes) |
| Reacts with water | |
| Solubility | Decomposes in ethanol Soluble in CCl4 and CS2 |
| Hazards[1] | |
| Occupational safety and health (OHS/OSH): | |
Main hazards |
Causes severe skin burns and eye damage |
| GHS labelling: | |
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| Danger | |
| H314 | |
| P260, P264, P280, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P363, P405, P501 | |
| Related compounds | |
Related compounds |
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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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Synthesis and structure
Unlike phosphorus pentachloride, solid phosphorus pentabromide is an ionic compound. Its structural formula is [PBr4]+Br− (tetrabromophosphonium bromide). The [PBr4]+] cation is tetrahedral.[2] According to X-ray crystallography, the P-Br bond lengths are 215 picometers.[3]
In the vapor phase, it dissociates into PBr3 and Br2. Rapid cooling of the vapor to 15 K gives a mixture of phosphorus tribromide and the similarly ionic phosphorus heptabromide (tetrabromophosphonium tribromide or [PBr4]+[Br3]−).[4]
PBr5 can be synthesized with high purity by bromination of a solution of PBr3 in CS2:[5]
- PBr3 + Br2 → PBr5
Addition of Br2 to PBr3 is complicated because phosphorus pentabromide can further convert to phosphorus heptabromide, which features the tribromide ion:[5]
- PBr5 + Br2 → [PBr4]+Br−3
Organic chemistry
Phosphorus pentabromide is used in organic chemistry to convert carboxylic acids to acyl bromides.[6]
Safety
Phosphorus pentabromide is a skin irritant and a source of bromine, a strong oxidant.[1]
Related compounds
Triphenylphosphine dibromide, (C6H5)3PBr2
