Potassium superoxide
Unit cell of potassium superoxide
  Potassium cations, K+
  Superoxide anions, O−2
Names
IUPAC name
Potassium superoxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.574
EC Number
  • 234-746-5
RTECS number
  • TT6053000
UN number 2466
  • InChI=1S/2K.O2/c;;1-2/q2*+1;-2 ☒N
    Key: XXQBEVHPUKOQEO-UHFFFAOYSA-N ☒N
  • InChI=1/2K.O2/c;;1-2/q2*+1;-2
    Key: XXQBEVHPUKOQEO-UHFFFAOYAV
  • [K+].[O-]=O
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
Structure
Body-centered tetragonal[1][2]
Thermochemistry
117 J/(mol·K)[3]
−283 kJ/mol[3]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Corrosive, oxidizer, reacts violently with water
GHS labelling:[4]
GHS03: OxidizingGHS05: Corrosive
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)
NFPA 704 four-colored diamond
3
0
3
W
OX
Related compounds
Other cations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

Potassium superoxide is an inorganic compound with the formula KO2.[5] 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.

Production and reactions

Potassium superoxide is produced by burning molten potassium in an atmosphere of excess oxygen.[6]

K + O2 → KO2

The salt consists of K+ and O−2 ions, linked by ionic bonding. The O–O distance is 1.28 Å.[1]

Reactivity

Potassium superoxide is a source of superoxide, which is an oxidant and a nucleophile, depending on its reaction partner.[7]

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[8]

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

Potassium superoxide finds only niche uses as a laboratory reagent. 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.[9]

Ion exchange with tetramethylammonium hydroxide gives tetramethylammonium superoxide, a yellow solid.[10]

Applications

The Russian Space Agency has had success using potassium superoxide in chemical oxygen generators for its spacesuits and Soyuz spacecraft. KO2 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 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.

References

  1. 1 2 Abrahams, S. C.; Kalnajs, J. (1955). "The Crystal Structure of α-Potassium Superoxide". Acta Crystallographica. 8 (8): 503–6. doi:10.1107/S0365110X55001540.
  2. ↑ "Information card for entry 2310803". Crystallography Open Database. Retrieved 28 July 2022.
  3. 1 2 Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 978-0-618-94690-7.
  4. ↑ "Potassium superoxide". pubchem.ncbi.nlm.nih.gov. Retrieved 14 December 2021.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ Kumar De, Anil (2007). A Text Book of Inorganic Chemistry. New Age International. p. 247. ISBN 978-8122413847.
  9. ↑ 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.
  10. ↑ Bohle, D. Scott; Sagan, Elisabeth S. (2004). Tetramethylammonium Salts of Superoxide and Peroxynitrite. Inorganic Syntheses. p. 36. doi:10.1002/0471653683.ch1.
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