Chemistry:Potassium superoxide
 Potassium cations, K+ Superoxide anions, O− 2 | |
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| Names | |
|---|---|
| IUPAC name
Potassium superoxide
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| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| EC Number |
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PubChem CID
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| RTECS number |
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| UN number | 2466 |
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| 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 |
117 J/(mol·K)[4] |
Std enthalpy of
formation (ΔfH⦵298) |
−283 kJ/mol[4] |
| Hazards | |
| Main hazards | Corrosive, oxidizer, reacts violently with water |
| GHS pictograms |  
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| GHS Signal word | Danger |
| H271, H314 | |
| P210, P220, P221, P260, P264, P280, P283, P301+330+331, P303+361+353, P304+340, P305+351+338, P306+360, P310, P321, P363, P370+378, P371+380+375, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other cations
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Potassium superoxide is an inorganic compound with the formula KO
2.[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 CO
2 scrubber, H
2O dehumidifier, and O
2 generator in rebreathers, spacecraft, submarines, and spacesuits.
Production and reactions
Potassium superoxide is produced by burning molten potassium in an atmosphere of excess oxygen.[7]
- K + O
2 → KO
2
The salt consists of K+
and O−
2 ions, linked by ionic bonding. The O–O distance is 1.28 Å.[2]
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 KO
2 + 2 H
2O → 4 KOH + 3 O
2 - 2 KO
2 + 2 H
2O → 2 KOH + H
2O
2 + O
2[9]
It reacts with carbon dioxide, releasing oxygen:
- 4 KO
2 + 2 CO
2 → 2 K
2CO
3 + 3 O
2 - 4 KO
2 + 4 CO
2 + 2 H
2O → 4 KHCO
3 + 3 O
2
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 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 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 highly exothermic reaction with water.
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 and releases 0.75 moles of oxygen.
References
- ↑ "Handbook of Chemistry and Physics 102nd Edition". CRC Press. https://hbcp.chemnetbase.com/faces/contents/ContentsSearch.xhtml.
- ↑ 2.0 2.1 Abrahams, S. C.; Kalnajs, J. (1955). "The Crystal Structure of α-Potassium Superoxide". Acta Crystallographica 8 (8): 503–6. doi:10.1107/S0365110X55001540.
- ↑ "Information card for entry 2310803" (in en). http://www.crystallography.net/cod/2310803.html.
- ↑ 4.0 4.1 Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 978-0-618-94690-7.
- ↑ "Potassium superoxide" (in en). https://pubchem.ncbi.nlm.nih.gov/compound/61541#section=Safety-and-Hazards.
- ↑ Hayyan M.; Hashim M. A.; AlNashef I. M. (2016). "Superoxide Ion: Generation and Chemical Implications". Chem. Rev. 116 (5): 3029–3085. doi:10.1021/acs.chemrev.5b00407. PMID 26875845.
- ↑ Jakob, Harald; Leininger, Stefan; Lehmann, Thomas; Jacobi, Sylvia; Gutewort, Sven (2007). "Peroxo Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a19_177.pub2. ISBN 978-3527306732.
- ↑ Johnson, Roy A.; Adrio, Javier; Ribagorda, María (2007). "Potassium Superoxide". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rp250.pub2. ISBN 978-0471936237.
- ↑ Kumar De, Anil (2007). A Text Book of Inorganic Chemistry. New Age International. pp. 247. ISBN 978-8122413847.
- ↑ Johnson, Roy A.; Adrio, Javier; Ribagorda, María (2001). "Potassium Superoxide". e-EROS Encyclopedia of Reagents for Organic Synthesis. Wiley. doi:10.1002/047084289X.rp250.pub2. ISBN 0471936235.
- ↑ Bohle, D. Scott; Sagan, Elisabeth S. (2004). Tetramethylammonium Salts of Superoxide and Peroxynitrite. Inorganic Syntheses. pp. 36. doi:10.1002/0471653683.ch1.
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