Formula : PBr 3 Physical properties: Melting point : -41.5 °C (231.7 K) Boiling point: 173.2 °C (446.4 K) Physical state at room temperature: liquid Colour: colourless Density: 2.852 g/cm 3 Solubility in water: rapid hydrolysis
Laboratory Preparation: PBr 3 is prepared by treating phosphorus with bromine. Reactivity: Phosphorus tribromide, like PCl 3 and PF 3, has both properties of a Lewis base and a Lewis acid. The most important reaction of PBr 3 is with alcohols, where it replaces an OH group with a bromine atom to produce an alkyl bromide. PBr 3 converts carboxylic acids to acyl bromides. PBr 3 is a reasonably strong reducing agent, and the oxidation of PBr 3 with oxygen gas is more vigorous than seen with PCl 3. It gives an explosive reaction that forms P 2 O 5 and Br 2. PBr 3 evolves corrosive HBr, is toxic, and reacts violently with water and alcohols.
Uses: For conversion of primary or secondary alcohols to alkyl bromides As a catalyst for the α-bromination of carboxylic acids On a commercial scale, phosphorus tribromide is used in the manufacture of pharmaceuticals such as alprazolam, methohexital and fenoprofen. It is also a potent fire suppression agent marketed under the name PhostrEx. Used as an analytical reagent to test for sugar and oxygen.
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