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.

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. It crystallizes in the NaCl motif.