Potassium superoxide

Reactivity

Potassium superoxide is a source of superoxide, which is an oxidant and a nucleophile, depending on its reaction partner.

Upon contact with water, it undergoes disproportionation to potassium hydroxide, oxygen, and hydrogen peroxide:

4 KO₂ + 2 H₂O → 4 KOH + 3 O₂

2 KO₂ + 2 H₂O → 2 KOH + H₂O₂ + O₂

It reacts with carbon dioxide, releasing oxygen:

4 KO₂ + 2 CO₂ → 2 K₂CO₃ + 3 O₂

4 KO₂ + 4 CO₂ + 2 H₂O → 4 KHCO₃ + 3 O₂

Theoretically, 1 kg of KO₂ absorbs 0.310 kg of CO₂ while releasing 0.338 kg of O₂. One mole of KO₂ absorbs 0.5 moles of CO₂ and releases 0.75 moles of oxygen.

As a laboratory reagent, potassium superoxide only finds niche uses. Because it reacts with water, KO₂ 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 converting alkyl bromides to alcohols and acyl chlorides to diacyl peroxides.

Ion exchange with tetramethylammonium hydroxide gives tetramethylammonium superoxide, a yellow solid.

Applications

The Russian Space Agency has successfully used potassium superoxide in chemical oxygen generators for its spacesuits and Soyuz spacecraft. Potassium superoxide was also used in a rudimentary life support system for five mice as part of the Biological Cosmic Ray Experiment on Apollo 17.

KO₂ has also been used in canisters for rebreathers for firefighting and mine rescue, and in cartridges for chemical oxygen generators on submarines. A flash fire caused by dropping such a cartridge into seawater contributed to the Kursk disaster. This highly exothermic reaction with water is also the reason why potassium superoxide has had only limited use in scuba rebreathers.

Safety

Potassium superoxide when in contact with metallic potassium is a pressure-sensitive explosive that detonates when scratched.