Phosphorus in orange, oxygen in red
|Jmol-3D images||Image 1|
|Molar mass||219.88 g mol−1|
|Appearance||colourless monoclinic crystals or liquid|
|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|
|Molecular shape||See Text|
|Other anions||Phosphorus trisulfide|
|Other cations||Dinitrogen trioxide
|Related compounds||Phosphorus pentoxide
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
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.
- P4(s) + 3 O2(g) → P4O6(s)
By-products include red phosphorus suboxide.
Phosphorus trioxide reacts with cold water to form phosphorous acid.
- P4O6(s) + 6 H2O(l) → 4 H3PO3(aq)
- P4O6 + 6 HCl → 2 H3PO3 + 2 PCl3
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.
As a ligand
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:
P4O6 can also donate electrons to Lewis bases such as BH3. Adducts with one to two equivalents of BH3 complexed with one mole of P4O6 has been reported. When P4O6 is reacted with one molar equivalent of (CH3)2S•BH3, followed by slow crystallization from the toluene solution at 244K, P8O12(BH3)2 rather than an adduct of P4O6 is formed:
- A. F. Holleman; Wiberg, Egon; Wiberg, Nils (2001). Inorganic Chemistry. Boston: Academic Press. ISBN 0-12-352651-5.
- .Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 473. ISBN 978-0-13-175553-6.
- M. Jansen and J. Clade (November 1996). "Tetracarbonyl(tetraphosphorus hexaoxide)iron". Acta Cryst. C52 (11): 2650–2652. doi:10.1107/S0108270196004398.