Phosphorus pentabromide

Phosphorus pentabromide
Names
	IUPAC name phosphorus pentabromide
	Other names phosphorus(V) bromide
Identifiers
CAS Number	7789-69-7 ;
3D model (JSmol)	Interactive image;
ChemSpider	56429 ;
ECHA InfoCard	100.029.260
PubChem CID	62678;
	InChI InChI=1S/Br5P/c1-6(2,3,4)5 Key: QRKVRHZNLKTPGF-UHFFFAOYSA-N ;
	SMILES BrP(Br)(Br)(Br)Br;
Properties
Chemical formula	PBr5
Molar mass	430.49 g/mol
Appearance	yellow solid
Density	3.61 g/cm3
Melting point	ca. 100 °C (decomposes)
Boiling point	106 °C (223 °F; 379 K) (decomposes)
Solubility in water	decomposes
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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	Infobox references

Phosphorus pentabromide is a reactive, yellow solid of formula P Br₅, which has the structure PBr₄⁺ Br⁻ in the solid state but in the vapor phase is completely dissociated to PBr₃ and Br₂. Rapid cooling of this phase to 15 K leads to formation of the ionic species phosphorus heptabromide ([PBr₄]⁺[Br₃]⁻).

It can be used in organic chemistry to convert carboxylic acids to acyl bromides. It is highly corrosive. It decomposes above 100 °C to give phosphorus tribromide and bromine:^[1]

PBr₅ → PBr₃ + Br₂

Reversing this equilibrium to generate PBr₅ by addition of Br₂ to PBr₃ is difficult in practice because the product is susceptible to further addition to yield phosphorus heptabromide (PBr₇).^[2]

Phosphorus pentabromide is a hypervalent molecule with a 3-center 4-electron bond.

References

↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
↑ Popov, A. I.; Skelly, N. E. (1954). "Spectrophotometric Study of Phosphorus Pentabromide in Various Solvents". J. Am. Chem. Soc. 76 (15): 3916–3919. doi:10.1021/ja01644a014.

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[1] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.

[2] Popov, A. I.; Skelly, N. E. (1954). "Spectrophotometric Study of Phosphorus Pentabromide in Various Solvents". J. Am. Chem. Soc. 76 (15): 3916–3919. doi:10.1021/ja01644a014.