Cloudy PBr3, freshly distilled
| IUPAC name
| Other names
|Molar mass||270.69 g/mol|
|Appearance||Colorless fuming liquid|
|Density||2.852 g/cm3 (at 15 °C)|
|Melting point||−41.5 °C (−42.7 °F; 231.7 K)|
|Boiling point||173.2 °C (343.8 °F; 446.3 K)|
|Solubility|| Reacts with alcohols, carboxylic acids, esters|
Soluble in acetone, antimony(III) bromide, arsenic(III) chloride, bromoacetic acid, carbon disulfide, chloroform, liq. H2S, liq. SO2
Std enthalpy of
|Safety data sheet||Sigma-Aldrich|
| Phosphorus pentabromide|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Phosphorus tribromide is an inorganic colorless liquid with the formula PBr3. It is a dense liquid which fumes in open air and is used in chemistry to obtain alkyl bromides.
Phosphorus tribromide reacts with water to form hydrobromic acid and phosphorus acid:
- PBr3 + 3 H2O → H3PO3 + 3 HBr
Phosphorus tribromide is colorless liquid, which fumes in air and immiscible with water, though it hydrolyzes slowly in it.
Phosphorus tribromide is sold by various suppliers, but due to its hazards it's almost impossible to obtain as private individual. It's best to make it yourself.
To limit the small fire that happens when you first add red P to the bromine s well as hydrolysis, a good idea is to purge the installation with an inert gas, such as nitrogen, carbon dioxide or argon. While the reaction can be done in neat, a solvent can also be used, such as carbon tetrachloride, carbon disulfide or benzene. This route is recommended if you're substituting red P with white P.
Decomposition of phosphorus pentabromide will give PBr3 and bromine. Adding small amounts of phosphorus to the mixture will greatly improve the yield.
- Make alkyl bromides
- α-bromination of carboxylic acids
Phosphorus tribromide fumes in air to release HBr fumes which are very corrosive and toxic. Wear proper protection when handling the compound.
PBr3 should be kept in teflon sealed glass bottles, in a dry place. Schlenk flasks are also a good storage container.
Phosphorus tribromide should be neutralized with a base, such as calcium hydroxide suspension outside or in a well ventilated area. Since PBr3 is immiscible with water, it will sink to the bottom and not quickly hydrolyze. Lots of HBr fumes will be produced during neutralization. Sodium thiosulfate can also be used as neutralizing agent.
- Matignon, C.; Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences; vol. 130; (1900); p. 1393
- Gladstone, J. H.; Philosophical Magazine (1798-1977); vol. 35; (1849); p. 345 - 355
- Loewig, C.; Das Brom und seine chemischen Verhaeltnisse, Heidelberg 1829, p. 51