Phosphorus pentabromide

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Phosphorus pentabromide
Other names
Phosphorus(V) bromide
Molar mass 430.49 g/mol
Appearance Yellow crystalline solid
Density 3.61 g/cm3
Melting point 103.7 °C (218.7 °F; 376.8 K) (decomposes)
Boiling point Decomposes
Solubility Reacts with alcohols, carboxylic acids
Soluble in AsCl3, bromine, liq. HBr, liq. HCl, liq. H2S, phosphoryl chloride, liq. SO2
sparingly soluble in benzene, carbon disulfide, carbon tetrachloride
-253.6 kJ/mol
Safety data sheet Sigma-Aldrich
Related compounds
Related compounds
Phosphorus tribromide
Phosphoryl bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Phosphorus pentabromide is a reactive, unstable, yellow solid chemical compound with the formula PBr5. This compound has the structure PBr4+Br in the solid state, but in the vapor phase is completely dissociated to PBr3 and Br2.



Phosphorus pentabromide rapidly hydrolyzes in water to release hydrobromic and phorphorous acids.

Addition of elemental phosphorus to this liquid chemical will cause it to convert to PBr3.

Upon excess bromination or cooling below 15 K, it converts to phosphorus heptabromide, which is a red solid.


Phosphorus pentabromide is a yellowish crystalline solid, which breaks down to PBr3 and Br2 upon heating. PBr5 readily hydrolyzes in moist air. It is soluble in anh. HCl, HBr, H2S, but less so in benzene, CS2, carbon tet.


PBr5 is sometimes sold by chemical suppliers, but due to its hazards it's difficult to get hold of.


Can be prepared by reacting PBr3 and bromine in equimolar amounts, at room temperature. Excess bromine will cause it to convert to PBr7. Petroleum ether can be used as a reaction solvent.

During the synthesis of phosphorus tribromide, small amounts of phosphorus pentabromide will be formed. To separate the pentabromide, the PBr3 and excess bromine are removed with a vacuum pump and condensed in a cold trap.




Phosphorus tribromide reacts with water and its fumes are very corrosive, as well as toxic. Wear proper protection when handling the compound.


In Schlenk flasks, at low temperatures. Periodically check for decomposition.


Phosphorus pentabromide should be neutralized with a base, such as calcium hydroxide suspension outside or in a well ventilated area. Lots of HBr fumes will be produced during neutralization. Sodium thiosulfate can also be used as neutralizing agent, as it neutralizes bromine more effectively than bases.


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