Phosphorus trioxide is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the molecular formula P₄O₆. Although the molecular formula suggests the name tetraphosphorus hexaoxide, 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 Adamantane is an organic compound with a formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the ...

. It is formally the

anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...

phosphorous acid Phosphorous acid (or phosphonic acid (singular)) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in th ...

, H₃PO₃, but cannot be obtained by the dehydration of the acid. A white solid that melts at room temperature, it is waxy, crystalline and highly toxic, with garlic odour.

Preparation

It is obtained by the combustion of phosphorus in a limited supply of air at low temperatures. :P₄ + 3 O₂ → P₄O₆ By-products include red phosphorus suboxide.

Chemical properties

Phosphorus trioxide reacts with water to form

, reflecting the fact that it is the anhydride of that acid. : P₄O₆ + 6 H₂O → 4 H₃PO₃ It reacts with

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...

to form H₃PO₃ and phosphorus trichloride. : P₄O₆ + 6 HCl → 2 H₃PO₃ + 2 PCl₃ With chlorine or bromine it forms the corresponding phosphoryl halide, and it reacts with iodine in a sealed tube to form diphosphorus tetraiodide. P₄O₆ reacts with

ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...

at 195 K to give the unstable compound P₄O₁₈.. Reaction of phosphoprus trioxide with ozone

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

disproportionation reaction In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...

, 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.

As a ligand

Phosphorus-trioxide-iron-tetracarbonyl-complex-from-xtal-3D-balls

P₄O₆ is a ligand for transition metals, comparable to

phosphite The general structure of a phosphite ester showing the lone pairs on the P In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of a ...

. An illustrative complex is P₄O₆·Fe(CO)₄. With BH₃, a dimeric adduct is produced: : Adduct of phosphorus oxide with BH3

References

{{DEFAULTSORT:Phosphorus Trioxide Sesquioxides Adamantane-like molecules Phosphorus oxides Phosphorus(III) compounds Tricyclic compounds