Phosphorus pentabromide

Phosphorus pentabromide is a reactive, yellow solid of formula PBr₅, which has the structure [PBr₄]⁺Br⁻ (tetrabromophosphonium bromide) in the solid state but in the vapor phase is completely dissociated to PBr₃ and Br₂. Rapid cooling of this phase to 15 K leads to formation of the ionic species phosphorus heptabromide (tetrabromophosphonium tribromide [PBr₄]⁺[Br₃]⁻).^[2]

Phosphorus pentabromide

Names
IUPAC name Tetrabromophosphanium bromide
Other names Pentabromo-λ5-phosphane[1] Pentabromophosphorane[1] Phosphorus(V) bromide[1] Phosphorus pentabromide Tetrabromophosphonium bromide
Identifiers
CAS Number	7789-69-7 Y
3D model (JSmol)	Interactive image
ChemSpider	56429 Y
ECHA InfoCard	100.029.260
EC Number	232-186-6
PubChem CID	62678
UNII	3D9WIS0BQW Y
UN number	2691
CompTox Dashboard (EPA)	DTXSID6064874
InChI InChI=1S/Br5P/c1-6(2,3,4)5 Y Key: QRKVRHZNLKTPGF-UHFFFAOYSA-N Y
SMILES BrP(Br)(Br)(Br)Br
Properties
Chemical formula	PBr5
Molar mass	430.494 g·mol−1
Appearance	Yellow crystalline solid[1]
Density	3.61 g/cm3
Melting point	ca. 100 °C (decomposes)
Boiling point	106 °C (223 °F; 379 K) (decomposes)
Solubility in water	Reacts with water
Solubility	Decomposes in ethanol Soluble in CCl4 and CS2
Hazards[1]
Occupational safety and health (OHS/OSH):
Main hazards	Causes severe skin burns and eye damage
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H314
Precautionary statements	P260, P264, P280, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P363, P405, P501
Related compounds
Related compounds	Phosphorus pentafluoride Phosphorus pentachloride Phosphorus pentaiodide Phosphorus tribromide Phosphorus heptabromide Phosphoryl bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

It can be used in organic chemistry to convert carboxylic acids to acyl bromides. It is highly corrosive. It strongly irritates skin and eyes.^[1] It decomposes above 100 °C to give phosphorus tribromide and bromine:^[3]

PBr₅ → PBr₃ + Br₂

Reversing this equilibrium to generate PBr₅ by addition of Br₂ to PBr₃ is difficult in practice because the product is susceptible to further addition to yield phosphorus heptabromide [PBr₄]⁺[Br₃]⁻.^[4]