Phosphorus pentabromide

Phosphorus pentabromide
IUPAC name phosphorus pentabromide
Other names phosphorus(V) bromide
Identifiers
CAS number	7789-69-7
PubChem	62678
ChemSpider	56429 Y
Jmol-3D images	Image 1
SMILES BrP(Br)(Br)(Br)Br
InChI InChI=1S/Br5P/c1-6(2,3,4)5 Y Key: QRKVRHZNLKTPGF-UHFFFAOYSA-N Y
Properties
Molecular 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 (decomposes)
Solubility in water	decomposes
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Phosphorus pentabromide is a reactive, yellow solid of formula PBr₅, 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 an ionic species [PBr₄]⁺[Br₃]^-.

It can be used in organic chemistry to convert carboxylic acids to acyl bromides. It is highly corrosive and should be handled with care. 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 PBr₇.^[2]

References

1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
2. ^ Popov, A. I.; Skelly, N. E. (1954). "Spectrophotometric Study of Phosphorus Pentabromide in Various So1vents". J. Am. Chem. Soc. 76 (15): 3916–3919. doi:10.1021/ja01644a014.