Sodium superoxide

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	12034-12-7 ;
3D model (JSmol)	Interactive image;
ChemSpider	8305406;
ECHA InfoCard	100.298.059
PubChem CID	61542;
RTECS number	WE2860010;
UNII	3GSN3JCJ5K ;
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). verify (what is ?) Infobox references

Sodium superoxide is the inorganic compound with the formula Na O₂.^[1] This yellow-orange solid is a salt of the superoxide anion. It is an intermediate in the oxidation of sodium by oxygen.

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.

References

^ Hayyan, Maan; Hashim, Mohd Ali; AlNashef, Inas M. (2016-02-15). "Superoxide Ion: Generation and Chemical Implications". Chemical Reviews. 116 (5). American Chemical Society (ACS): 3029–3085. doi:10.1021/acs.chemrev.5b00407. ISSN 0009-2665. PMID 26875845.
^ Stephen E. Stephanou, Edgar J. Seyb Jr., Jacob Kleinberg "Sodium Superoxide" Inorganic Syntheses 1953; Vol. 4, 82-85.
^ Schechter, William H.; Sisler, Harry H.; Kleinberg, Jacob (January 1948). "The Absorption of Oxygen by Sodium in Liquid Ammonia: Evidence for the Existence of Sodium Superoxide". Journal of the American Chemical Society. 70 (1): 267–269. doi:10.1021/ja01181a083. ISSN 0002-7863.
^ Sasol Encyclopaedia of Science and Technology , G.C. Gerrans, P. Hartmann-Petersen , p.243 "sodium oxides" , google books link

[1] Hayyan, Maan; Hashim, Mohd Ali; AlNashef, Inas M. (2016-02-15). "Superoxide Ion: Generation and Chemical Implications". Chemical Reviews. 116 (5). American Chemical Society (ACS): 3029–3085. doi:10.1021/acs.chemrev.5b00407. ISSN 0009-2665. PMID 26875845.

[2] Stephen E. Stephanou, Edgar J. Seyb Jr., Jacob Kleinberg "Sodium Superoxide" Inorganic Syntheses 1953; Vol. 4, 82-85.

[3] Schechter, William H.; Sisler, Harry H.; Kleinberg, Jacob (January 1948). "The Absorption of Oxygen by Sodium in Liquid Ammonia: Evidence for the Existence of Sodium Superoxide". Journal of the American Chemical Society. 70 (1): 267–269. doi:10.1021/ja01181a083. ISSN 0002-7863.

[4] Sasol Encyclopaedia of Science and Technology , G.C. Gerrans, P. Hartmann-Petersen , p.243 "sodium oxides" , google books link

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