Phosphorus trioxide

Phosphorus trioxide

Phosphorus in orange, oxygen in red
Names
Other names Phosphorus(III) oxide Phosphorus sesquioxide Phosphorous oxide Phosphorous anhydride Tetraphosphorous hexoxide
Identifiers
CAS Number	1314-24-5 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:37372 Y
ChemSpider	109897 Y
PubChem	123290
InChI InChI=1S/O6P4/c1-7-2-9-4-8(1)5-10(3-7)6-9 Y Key: VSAISIQCTGDGPU-UHFFFAOYSA-N Y InChI=1/O6P4/c1-7-2-9-4-8(1)5-10(3-7)6-9 Key: VSAISIQCTGDGPU-UHFFFAOYAV
SMILES O1P3OP2OP(OP1O2)O3
Properties
Chemical formula	P4O6
Molar mass	219.88 g mol−1
Appearance	colourless monoclinic crystals or liquid
Density	2.135 g/cm3
Melting point	23.8 °C (74.8 °F; 296.9 K)
Boiling point	173.1 °C (343.6 °F; 446.2 K)
Solubility in water	reacts
Acidity (pKa)	9.4
Structure
Molecular shape	See Text
Dipole moment	0
Related compounds
Other anions	Phosphorus trisulfide
Other cations	Dinitrogen trioxide Arsenic trioxide Antimony trioxide
Related compounds	Phosphorus pentoxide Phosphorous acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Phosphorus trioxide is the chemical compound with the molecular formula P₄O₆. Although it should properly be named tetraphosphorus hexoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, and its usage continues today. This colorless solid is structurally related to adamantane. It is formally the anhydride of phosphorous acid, H₃PO₃, but cannot be obtained by the dehydration of the acid. It is a white, waxy, crystalline and highly toxic solid.

It is obtained by the combustion of phosphorus in a limited supply of air at low temperature.

By-products include red phosphorus suboxide.

Phosphorus trioxide reacts with water to form phosphorous acid, reflecting the fact that it is the anhydride of that acid.

It reacts with hydrogen chloride to form H₃PO₃ and phosphorus trichloride.

With chlorine or bromine it forms the corresponding phosphoryl halide, and it reacts with iodine in a sealed tube to from diphosphorus tetraiodide.

When P₄O₆ is allowed to react with ozone at 195 K in dichloromethane, the highly unstable compound P₄O₁₈ is formed.

P₄O₁₈ decomposes above 238 K in solution with the release of O₂ gas. Decomposition of dry P₄O₁₈ is explosive.

P₄O₆ is converted into the mixed P(III)P(V) species P₄O₈ when heated in a sealed tube at 710 K, with the side product being red phosphorus.

P₄O₆ is a ligand for transition metals, comparable to phosphite. Tetracarbonyl(tetraphosphorus hexaoxide)iron, P₄O₆·Fe(CO)₄, is an example of a complex containing the phosphorus trioxide cage as a ligand. Its molecular structure as determined by single-crystal X-ray diffraction is shown below: