Sodium superoxide

Sodium superoxide is the inorganic compound with the formula NaO₂.^[1] This yellow-orange solid is a salt of the superoxide anion. It is an intermediate in the oxidation of sodium by oxygen.

Sodium superoxide

Oxidised sodium after improper storage under contaminated hexane showing an orange crust of sodium superoxide.
Names
IUPAC name sodium superoxide
Other names sodium superoxide sodium dioxide
Identifiers
CAS Number	1313-60-6 Y
3D model (JSmol)	Interactive image
ChemSpider	8305406
PubChem CID	61542
RTECS number	WE2860010
UNII	3GSN3JCJ5K Y
UN number	2547
CompTox Dashboard (EPA)	DTXSID30894055
InChI InChI=1S/Na.HO2/c;1-2/h;1H/q+1;/p-1 Key: TZACNHSIZFFYEH-UHFFFAOYSA-M
SMILES [O-][O].[Na+]
Properties
Chemical formula	NaO2
Molar mass	54.9886 g/mol
Appearance	Yellow to orange crystalline solid
Density	2.2 g/cm3
Melting point	551.7 °C (1,025.1 °F; 824.9 K)
Boiling point	Decomposes
Solubility in water	Decomposes
Basicity (pKb)	N/A
Structure
Crystal structure	cubic
Thermochemistry
Heat capacity (C)	72.1 J/mol K
Std molar entropy (S⦵298)	115.9 J/mol K
Std enthalpy of formation (ΔfH⦵298)	−260.2 kJ/mol
Gibbs free energy (ΔfG⦵)	−218.4 kJ/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H271, H314
Precautionary statements	P210, P220, P260, P280, P303+P361+P353, P305+P351+P338
NFPA 704 (fire diamond)	3 0 1 OX
Flash point	Non flammable
Related compounds
Other anions	sodium oxide sodium peroxide
Other cations	Lithium superoxide Potassium superoxide Rubidium superoxide Caesium superoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

NaO₂ is prepared by treating sodium peroxide with oxygen at high pressures:^[2]

Na₂O₂ + O₂ → 2 NaO₂

It can also be prepared by careful oxygenation of a solution of sodium in cryogenic liquid ammonia:

Na(in NH₃) + O₂ → NaO₂

Although the existence of a sodium oxide higher than peroxide was speculated since 19th century, it was not until 1948 when American chemists were able to definitely synthesize it by the latter method.^[3]

Properties

The product is paramagnetic, as expected for a salt of the O⁻
₂ anion. It hydrolyses readily to give a mixture of sodium hydroxide, oxygen and hydrogen peroxide.^[4] It crystallizes in the NaCl motif.