Phosphorus pentabromide

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Phosphorus pentabromide
Other names Phosphorus(V) bromide
Molecular formula PBr5
Molar mass 430.49 g/mol
CAS number [7789-69-7]
Density g/cm3
Solubility (water) Decomposes
Melting point ca. 100 °C


Boiling point 106 °C


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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 disociated 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:

PBr5PBr3 + Br2

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