Potassium superoxide
Chemical compound
From Wikipedia, the free encyclopedia
Potassium superoxide is an inorganic compound with the formula KO2.[6] 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 CO2 scrubber, H2O dehumidifier, and O2 generator in rebreathers, spacecraft, submarines, and spacesuits.
Potassium cations, K+ Superoxide anions, O−2 | |
 | |
| Names | |
|---|---|
| IUPAC name
Potassium superoxide | |
| Identifiers | |
3D model (JSmol) |
|
| ChemSpider | |
| ECHA InfoCard | 100.031.574 |
| EC Number |
|
PubChem CID |
|
| RTECS number |
|
| UN number | 2466 |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| KO2 | |
| Molar mass | 71.096 g·mol−1 |
| Appearance | yellow solid |
| Density | 2.14 g/cm3, solid |
| Melting point | 560 °C (1,040 °F; 833 K) (decomposes) |
| Hydrolysis | |
| +3230·10−6 cm3/mol[1] | |
| Structure | |
| Body-centered tetragonal[2][3] | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
117 J/(mol·K)[4] |
Std enthalpy of formation (ΔfH⦵298) |
−283 kJ/mol[4] |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards |
Corrosive, oxidizer, reacts violently with water |
| GHS labelling:[5] | |
  | |
| Danger | |
| H271, H314 | |
| P210, P220, P221, P260, P264, P280, P283, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P306+P360, P310, P321, P363, P370+P378, P371+P380+P375, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other cations |
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Production and reactions
Reactivity
Potassium superoxide is a source of superoxide, which is an oxidant and a nucleophile, depending on its reaction partner.[8]
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[9]
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.[10]
Ion exchange with tetramethylammonium hydroxide gives tetramethylammonium superoxide, a yellow solid.[11]
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.[12]
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.