Phosphoryl bromide

Phosphoryl bromide, also known as phosphorus oxybromide, is an inorganic compound with the formula POBr3.

Preparation
Phosphoryl bromide is prepared by the reaction between phosphorus pentabromide and phosphorus pentoxide:


 * 3 PBr5 + P2O5 → 5 POBr3

It can also be prepared via the slow addition of liquid bromine to phosphorus tribromide at 0 °C, followed by the slow addition of water and vacuum distillation of the resulting slurry.

Structure and properties
Phosphoryl bromide forms colorless crystals or thin plates with a faint orange tint. Its crystals belong to the orthorhombic space group Pnma, with intermolecular Br–O bridges creating infinite chains within the structure. The intermolecular bonding causes distortions from the C3v symmetry found in the free molecule.

It is stored in sealed glass ampoules.

Uses
Phosphoryl bromide finds use as a specialist brominating agent.

Safety
Phosphoryl bromide reacts violently with water evolving heat, forming phosphoric acid and hydrobromic acid. Reacts with organic compounds to cause fire. Evolves highly toxic and corrosive gases when exposed to fire. When heated to decomposition, it emits highly toxic fumes like bromides, oxybromides and oxides of phosphorus. It is corrosive to metals and tissues.