Potassium superoxide is the inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. Potassium superoxide is used as a CO
2 scrubber, H
2O dehumidifier and O
2 generator in rebreathers, spacecraft, submarines and spacesuit life support systems.
3D model (JSmol)
|Molar mass||71.096 g·mol−1|
|Density||2.14 g/cm3, solid|
|Melting point||560 °C (1,040 °F; 833 K) (decomposes)|
|Body-centered cubic (O−|
Std enthalpy of
|Main hazards||corrosive, oxidant|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Production and reactions
Potassium superoxide is produced by burning molten potassium in an atmosphere of oxygen.
- K + O
2 → KO
Hydrolysis gives oxygen gas, hydrogen peroxide and potassium hydroxide:
Potassium hydroxide (KOH) absorbing carbon dioxide produces carbonates:
- 2 KOH + CO
2 → K2CO3 + H2O
- KOH + CO
2 → KHCO3
Combining these two reactions produces:
- 4 KO
2 + 2 CO
2 → 2 K2CO3 + 3 O
- 4 KO
2 + 4 CO
2 + 2 H2O → 4 KHCO3 + 3 O
Potassium superoxide finds only niche uses as a laboratory reagent. Because it reacts with water, KO
2 is often studied in organic solvents. Since the salt is poorly soluble in nonpolar solvents, crown ethers are typically used. The tetraethylammonium salt is also known. Representative reactions of these salts involve using superoxide as a nucleophile, e.g., in conversing alkyl bromides to alcohols and acyl chlorides to diacyl peroxides.
The Russian Space Agency has had success using potassium superoxide in chemical oxygen generators for its spacesuits and Soyuz spacecraft. KO
2 has also been used in canisters for rebreathers for fire fighting and mine rescue work, but had limited use in scuba rebreathers because of its dangerously explosive reaction with water; the Russian IDA71 rebreather was designed to be used with potassium hydroxide.
Theoretically, 1 kg of KO
2 absorbs 0.310 kg of CO
2 while releasing 0.338 kg of O
2. One mole of KO
2 absorbs 0.5 moles of CO
2 but only releases 0.75 moles of oxygen gas (O2) molecules. The human body will produce fewer CO
2 molecules than oxygen molecules needed because oxidation of food also needs oxygen to produce water and urea.
Potassium superoxide is a potent oxidizer, and can produce explosive reactions when combined with a variety of substances and compounds, including water, acids, organics, or powdered graphite. Even dry superoxide can produce an impact-sensitive explosive compound when combined with organic oils such as kerosene. In 1999 at Oak Ridge National Laboratory, cleanup of potassium oxides from a NaK metal leak produced an impact-sensitive explosion while saturated with mineral oil.
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