Sodium superoxide

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Sodium superoxide
Oxidised sodium after improper storage under contaminated hexane showing an orange crust of sodium superoxide.
IUPAC name
sodium(I) superoxide
Other names
sodium superoxide
3D model (JSmol)
RTECS number
  • WE2860010
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
Basicity (pKb) N/A
72.1 J/mol K
115.9 J/mol K
-260.2 kJ/mol
-218.4 kJ/mol
R-phrases (outdated) R35
S-phrases (outdated) S1/2, S26, S37/39, S45
NFPA 704 (fire diamond)
Flash point Non flammable
Related compounds
Other anions
sodium oxide
sodium peroxide
Other cations
potassium superoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.


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 ammonia:

Na(in NH3) + O2 → NaO2

It is also produced, along with sodium peroxide, when sodium is stored under inappropriate conditions (e.g. in dirty or partially halogenated solvents)[citation needed].


The product is paramagnetic, as expected for a salt of the O
anion. It hydrolyses readily to give a mixture of sodium hydroxide, oxygen and hydrogen peroxide.[3] It crystallizes in the NaCl motif.


  1. ^ Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. DOI: 10.1021/acs.chemrev.5b00407
  2. ^ Stephen E. Stephanou, Edgar J. Seyb Jr., Jacob Kleinberg "Sodium Superoxide" Inorganic Syntheses 1953; Vol. 4, 82-85.
  3. ^ Sasol Encyclopaedia of Science and Technology , G.C. Gerrans, P. Hartmann-Petersen , p.243 "sodium oxides" , google books link