Phosphorus trioxide

Structural formula
General
Surname	Phosphorus trioxide
other names	Diphosphorus trioxide Tetraphosphorus hexoxide
Molecular formula	P 4 O 6
Brief description	Waxy, colorless, monoclinic crystals
External identifiers / databases
CAS number 12440-00-5 1314-24-5 10248-58-5 EC number 235-670-5 ECHA InfoCard 100.032.414 PubChem 123290 Wikidata Q411876
properties
Molar mass	109.96 g mol −1 or 219.92 g mol −1
Physical state	firmly
density	2.13 g cm −3
Melting point	23.8 ° C
boiling point	175.3 ° C
solubility	good at benzene and carbon disulfide
Refractive index	1.540 (27 ° C)
safety instructions
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Phosphorus trioxide is an oxide of the element phosphorus . This chemical compound is also known as diphosphorus trioxide . The molecular mass determined in the molten, dissolved and vaporous state corresponds to the empirical formula P ₄ O ₆ . The waxy, colorless crystals are very poisonous .

presentation

Phosphorus trioxide is produced when white phosphorus is burned at low temperatures with a lack of oxygen . A strong development of heat is observed:

${\displaystyle \mathrm {P_{4}+3\ O_{2}\rightarrow P_{4}O_{6}} }$

White phosphorus reacts with oxygen to form phosphorus trioxide.

properties

Physical Properties

Phosphorus trioxide is the anhydride of phosphonic acid . Phosphorus is in the +3 oxidation state. The crystals of this compound have a density of 2.14 g · cm ⁻³ . The melting point is 24 ° C, the boiling point at 175 ° C under a nitrogen - atmosphere . Phosphorus trioxide dissolves in benzene and carbon disulfide .

The structure of phosphorus trioxide is derived from the tetrahedral phosphorus molecule P ₄ . By replacing the six P -P- bonds - the edges of the tetrahedron - respectively by P O -P bonds, we come to the illustrated above molecular structure. The bond lengths of the PO bonds are 164 pm for the molecule in the gas state. The bond angles are 126.4 ° for the POP group and 99.8 ° for the OPO group.

The structure has a high degree of symmetry . In addition to the tetrahedral arrangement of the phosphorus atoms , an octahedral arrangement can be determined for the oxygen atoms . The four faces of the tetrahedral basic structure are framed by four symmetrically linked P ₃ O ₃ six-membered rings. This structure is also found in arsenic (As ₄ O ₆ ) and urotropine (N ₄ (CH ₂ ) ₆ ).

Phosphorus trioxide crystallizes in a monoclinic crystal structure in the space group P 2 ₁ / m (space group no. 11) and the lattice parameters a = 6.43, b = 7.887, c = 6.183 Å and β = 106.01 °.

Chemical properties

Phosphorus trioxide oxidized in air further phosphorus pentoxide :

${\displaystyle \mathrm {P_{4}O_{6}+2\ O_{2}\rightarrow P_{4}O_{10}} }$

Phosphorus trioxide oxidizes to phosphorus pentoxide.

Chemiluminescence is observed during this process under reduced pressure .

Above 210 ° C a decomposition to phosphorus and phosphorus tetroxide takes place:

${\displaystyle \mathrm {4\ P_{4}O_{6}\rightleftharpoons 4\ P+3\ P_{4}O_{8}} }$

Phosphorus trioxide disproportionates to phosphorus and phosphorus tetroxide.

In cold water , phosphorus trioxide is converted to phosphonic acid :

${\displaystyle \mathrm {P_{4}O_{6}+6\ H_{2}O\rightarrow 4\ H_{3}PO_{3}} }$

Phosphorus trioxide reacts with water to form phosphonic acid.

The disproportionation of phosphonic acid becomes relevant in hot water, so that phosphoric acid , phosphine and phosphorus are then obtained as reaction products.

The reaction with hydrogen chloride leads to the formation of phosphonic acid and phosphorus trichloride :

${\displaystyle \mathrm {P_{4}O_{6}+6\ HCl\rightarrow 2\ H_{3}PO_{3}+2\ PCl_{3}} }$

Phosphorus trioxide and hydrogen chloride react to form phosphonic acid and phosphorus trichloride.

Phosphorus trioxide reacts with the halogens chlorine and bromine to form phosphoryl halides , and with iodine to form diphosphorus tetraiodide . The reaction with ozone leads to the ozonide P ₄ O ₁₈ , which slowly decomposes above −35 ° C to form phosphorus pentoxide, releasing oxygen .

${\displaystyle \mathrm {P_{4}O_{6}+4\ O_{3}\rightarrow P_{4}O_{18}} }$

swell

1. ↑ ^{a b} Entry on phosphorus oxides. In: Römpp Online . Georg Thieme Verlag, accessed April 30, 2014.
2. ^ ^{A b c d} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 786.
3. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Liquids, pp. 4-140.
4. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
5. ↑ ^{a b c d e} Ralf Steudel : Chemistry of Non-Metals, Syntheses - Structures - Bonding - Use , 4th edition, 2014 Walter de Gruyter GmbH & Co. KG, Berlin / Boston, ISBN 978-3-11-030439-8 , Pp. 407-408, (accessed via De Gruyter Online).
6. ↑ M. Jansen, M. Voss, HJ Deiseroth: Structural properties of phosphorus oxides in the solid state . In: Angewandte Chemie , 1981 , 93 , pp. 1023-1024, doi : 10.1002 / anie.19810931127 .