Sodium superoxide

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Sodium superoxide

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UN number	2547
Template:Longitem	NaO2
Molar mass	54.9886 g/mol
Appearance	Yellow to orange crystalline solid
Density	2.2 g/cm3
Melting point	Template:Chembox CalcTemperatures
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Basicity (pKb)	N/A
Template:Longitem	cubic
Template:Longitem	72.1 J/mol K
Template:Longitem	115.9 J/mol K
Template:Longitem	−260.2 kJ/mol
NFPA 704 (fire diamond)	Template:NFPA 704 diamond
Flash point	Template:Chembox CalcTemperatures
Template:Longitem	sodium oxide sodium peroxide
Template:Longitem	Lithium superoxide Potassium superoxide Rubidium superoxide Caesium superoxide

Sodium superoxide is the inorganic compound with the formula NaO₂. 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:

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.

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

Properties

The product is paramagnetic, as expected for a salt of the Template:Chem/link anion. It hydrolyses readily to give a mixture of sodium hydroxide, oxygen and hydrogen peroxide. It crystallizes in the NaCl motif.