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Phosphorus pentabromide

Topic: Chemistry

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Phosphorus pentabromide
Names
IUPAC name
Tetrabromophosphanium bromide
Other names
  • Pentabromo-λ5-phosphane[1]
  • Pentabromophosphorane[1]
  • Phosphorus(V) bromide[1]
  • Phosphorus pentabromide
  • Tetrabromophosphonium bromide
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 232-186-6
UNII
UN number 2691
Properties
PBr
5
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 CCl
4 and CS
2
Hazards[1]
Main hazards Causes severe skin burns and eye damage
GHS pictograms GHS05: Corrosive
GHS Signal word Danger
HH314Script error: No such module "Preview warning".Category:GHS errors
PP260Script error: No such module "Preview warning".Category:GHS errors, PP264Script error: No such module "Preview warning".Category:GHS errors, PP280Script error: No such module "Preview warning".Category:GHS errors, PP301+P330+P331Script error: No such module "Preview warning".Category:GHS errors, PP302+P361+P354Script error: No such module "Preview warning".Category:GHS errors, PP304+P340Script error: No such module "Preview warning".Category:GHS errors, PP305+P354+P338Script error: No such module "Preview warning".Category:GHS errors, PP316Script error: No such module "Preview warning".Category:GHS errors, PP321Script error: No such module "Preview warning".Category:GHS errors, PP363Script error: No such module "Preview warning".Category:GHS errors, PP405Script error: No such module "Preview warning".Category:GHS errors, PP501Script error: No such module "Preview warning".Category:GHS errors
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Phosphorus pentabromide is the inorganic compound with the formula PBr
5. 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 [PBr
4]+
Br−
 (tetrabromophosphonium bromide). The [PBr
4]+
] 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 PBr
3 and Br
2. Rapid cooling of the vapor to 15 K gives a mixture of phosphorus tribromide and the similarly ionic phosphorus heptabromide (tetrabromophosphonium tribromide or [PBr
4]+
[Br
3]−
).[4]

PBr5 can be synthesized with high purity by bromination of a solution of PBr3 in CS2:[5]

PBr
3 + Br
2 → PBr
5

Addition of Br
2 to PBr
3 is complicated because phosphorus pentabromide can further convert to phosphorus heptabromide, which features the tribromide ion:[5]

PBr
5 + Br
2 → [PBr
4]+
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]

Triphenylphosphine dibromide, (C
6H
5)
3PBr
2

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "Phosphorus pentabromide". https://pubchem.ncbi.nlm.nih.gov/compound/Phosphorus-pentabromide. 
  2. ↑ 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. 
  3. ↑ 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. 
  4. ↑ Corbridge, D. E. C. (2013) (in en). Phosphorus: Chemistry, Biochemistry and Technology, Sixth Edition. CRC Press. pp. 154. ISBN 978-1-4398-4088-7. https://books.google.com/books?id=5ufh9rM5ko0C&q=rapid+cooling+of+pbr5&pg=PA154. 
  5. ↑ 5.0 5.1 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. https://doi.org/10.1021/ja01644a014. 
  6. ↑ Allen, C. Freeman; Kalm, Max J. (1958). "2-Methylenedodecanoic Acid". Organic Syntheses 38: 47. doi:10.15227/orgsyn.038.0047. 

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