Phosphorus pentabromide

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Phosphorus pentabromide
Phosphorus-pentabromide-xtal-3D-ball-polyhedra.png
Phosphorus(V) bromide.jpg
Identifiers
CAS number 7789-69-7 YesY
PubChem 62678
ChemSpider 56429 YesY
Jmol-3D images Image 1
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 (223 °F; 379 K) (decomposes)
Solubility in water decomposes
Except where noted otherwise, 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 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 the ionic species [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]

PBr5PBr3 + 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[edit]

  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). 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.