Xenon tetroxide

Xenon tetroxide

Names
IUPAC names Xenon tetraoxide Xenon(VIII) oxide
Other names Xenon tetroxide Perxenic anhydride
Identifiers
CAS Number	12340-14-6 N
3D model (Jmol)	Interactive image
ChemSpider	21106492 Y
InChI InChI=1S/O4Xe/c1-5(2,3)4 Y Key: VHWKDFQUJRCZDZ-UHFFFAOYSA-N Y InChI=1/O4Xe/c1-5(2,3)4 Key: VHWKDFQUJRCZDZ-UHFFFAOYAS
SMILES O=[Xe](=O)(=O)=O
Properties
Chemical formula	XeO4
Molar mass	195.29 g mol−1
Appearance	Yellow solid below −36°C
Density	? g cm−3, solid
Melting point	−35.9 °C (−32.6 °F; 237.2 K)
Boiling point	0 °C (32 °F; 273 K) [1]
Structure
Molecular shape	Tetrahedral[2]
Dipole moment	0 D
Thermochemistry
Std molar entropy (So298)	? J.K−1.mol−1
Std enthalpy of formation (ΔfHo298)	+153.5 kcal mol−1 [3]
Hazards
EU classification (DSD)	Explosive (E)
Related compounds
Related compounds	Perxenic acid Xenon trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Xenon tetroxide is a chemical compound of xenon and oxygen with molecular formula XeO₄, remarkable for being a relatively stable compound of a noble gas. It is a yellow crystalline solid that is stable below −35.9 °C; above that temperature it is very prone to exploding and decomposing into elemental xenon and oxygen (O₂).^[4][5]

All eight valence electrons of xenon are involved in the bonds with the oxygen, and the oxidation state of the xenon atom is +8. Oxygen is the only element that can bring xenon up to its highest oxidation state; even fluorine can only give XeF₆ (+6). Two other short-lived xenon compounds with an oxidation state of +8, XeO₃F₂ and XeO₂F₄, are accessible by the reaction of xenon tetroxide with xenon hexafluoride. XeO₃F₂ and XeO₂F₄ can be detected with mass spectrometry. The perxenates are also compounds where xenon has the +8 oxidation state.

Reactions

At temperatures above −35.9 °C, xenon tetroxide is very prone to explosion, decomposing into xenon gas and oxygen with ΔH = −643 kJ/mol:

XeO₄ → Xe + 2 O₂

Xenon tetroxide dissolves in water to form perxenic acid and in alkalis to form perxenate salts:

XeO₄ + 2 H₂O → H₄XeO₆

XeO₄ + 4 NaOH → Na₄XeO₆ + 2 H₂O

Xenon tetroxide can also react with xenon hexafluoride to give xenon oxyfluorides:

XeO₄ + XeF₆ → XeOF₄ + XeO₃F₂

XeO₄ + XeF₆ → XeO₂F₄ + XeO₂F₂

Synthesis

All syntheses start from the perxenates, which are accessible from the xenates through two methods. One is the disproportionation of xenates to perxenates and xenon:

2 HXeO₄⁻ + 2 OH⁻ → XeO₆⁴⁻ + Xe + O₂ + 2 H₂O

The other is oxidation of the xenates with ozone in basic solution:

HXeO₄⁻ + O₃ + 3 OH⁻ → XeO₆⁴⁻ + O₂ + 2 H₂O

Barium perxenate is reacted with sulfuric acid and the unstable perxenic acid is dehydrated to give xenon tetroxide:^[6]

Ba
2XeO
6 + 2 H
2SO
4 → 2 BaSO
4 + H
4XeO
6

H
4XeO
6 → 2 H
2O + XeO
4

Any excess perxenic acid slowly undergoes a decomposition reaction to xenic acid and oxygen:

2 H
4XeO
6 → O
2 + 2 H
2XeO
4 + 2 H
2O

References

• Lide, D. R., ed. (2002). CRC Handbook of Chemistry and Physics (83rd ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0483-0.