Potassium superoxide

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Potassium superoxide

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RTECS number	Template:Unbulleted list
UN number	2466
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	yellow solid
Density	2.14 g/cm3, solid
Melting point	Template:Chembox CalcTemperatures
Template:Longitem	+3230·10−6 cm3/mol
Template:Longitem	Body-centered tetragonal
Template:Longitem	117 J/(mol·K)
Template:Longitem	−283 kJ/mol
NFPA 704 (fire diamond)	Template:NFPA 704 diamond
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Potassium superoxide is an inorganic compound with the formula Template:Chem2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a [[carbon dioxide|Template:Chem2]] scrubber, [[water|Template:Chem2]] dehumidifier, and [[oxygen|Template:Chem2]] generator in rebreathers, spacecraft, submarines, and spacesuits.

Production and reactions

Potassium superoxide is produced by burning molten potassium in an atmosphere of excess oxygen.

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The salt consists of Template:Chem2 and Template:Chem2 ions, linked by ionic bonding. The O–O distance is 1.28 Å.

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:

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It reacts with carbon dioxide, releasing oxygen:

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Theoretically, 1 kg of Template:Chem2 absorbs 0.310 kg of CO₂ while releasing 0.338 kg of Template:Chem2. One mole of Template:Chem2 absorbs 0.5 moles of CO₂ and releases 0.75 moles of oxygen.

Potassium superoxide finds only niche uses as a laboratory reagent. Because it reacts with water, Template:Chem2 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.

Template:Chem2 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.