Phosphorus pentabromide
| Names | |
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| IUPAC name
Tetrabromophosphanium bromide
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| 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
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Causes severe skin burns and eye damage |
| GHS labelling: | |
| 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).
Infobox references
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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.
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
References
- ^ a b c d e f "Phosphorus pentabromide".
- ^ Gerding, H.; Nobel, P. C. (1958). "The structure of solid phosphorus pentabromide". Recueil des Travaux Chimiques des Pays-Bas. 77 (5): 472–478. doi:10.1002/recl.19580770513.
- ^ Gabes, W.; Olie, K. (1970). "Refinement of the crystal structure of phosphorus pentabromide, PBr5". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 26 (4): 443–444. doi:10.1107/S0567740870002595.
- ^ Corbridge, D. E. C. (2013). Phosphorus: Chemistry, Biochemistry and Technology, Sixth Edition. CRC Press. p. 154. ISBN 978-1-4398-4088-7.
- ^ a b Popov, Alexander I.; Skelly, Norman E. (1954-08-01). "Spectrophotometric Study of Phosphorus Pentabromide in Various Solvents1,2". Journal of the American Chemical Society. 76 (15): 3916–3919. doi:10.1021/ja01644a014. ISSN 0002-7863.
- ^ Allen, C. Freeman; Kalm, Max J. (1958). "2-Methylenedodecanoic Acid". Organic Syntheses. 38: 47. doi:10.15227/orgsyn.038.0047.