Potassium superoxide

Potassium superoxide
Names
K⁺ Superoxide anions, O−2

IUPAC name Potassium superoxide
Identifiers
CAS Number	12030-88-5^Y
3D model (JSmol)	Interactive image
ChemSpider	8329498^Y
ECHA InfoCard	100.031.574
EC Number	234-746-5
PubChem CID	61541
RTECS number	TT6053000
UN number	2466
CompTox Dashboard (EPA)	DTXSID30923314
InChI 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
SMILES [K+].[O-]=O
Properties
Chemical formula	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)
Solubility in water	Hydrolysis
Magnetic susceptibility (χ)	+3230·10⁻⁶ cm³/mol^[1]
Structure
Crystal structure	Body-centered tetragonal^[2]^[3]
Thermochemistry
Std molar entropy (S^⦵₂₉₈)	117 J/(mol·K)^[4]
Std enthalpy of formation (Δ_fH^⦵₂₉₈)	−283 kJ/mol^[4]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Corrosive, oxidizer, reacts violently with water
GHS labelling:^[5]
Pictograms
Signal word	Danger
Hazard statements	H271, H314
Precautionary statements	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)	3 0 3 W OX
Related compounds
Other cations	Lithium superoxide Sodium superoxide Rubidium superoxide Caesium superoxide
Related potassium oxides	Potassium oxide Potassium peroxide Potassium ozonide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references

Chemical compound

Potassium superoxide is an inorganic compound with the formula K O₂.^[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.

Production and reactions

Potassium superoxide is produced by burning molten potassium in an atmosphere of excess oxygen.^[7]

K + O₂ → KO₂

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 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

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.^[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. 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. Potassium superoxide was used in a rudimentary life support system for five mice as part of the Biological Cosmic Ray Experiment on Apollo 17.^[12]

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

^ "Handbook of Chemistry and Physics 102nd Edition". CRC Press.
^ ^a ^b 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". Crystallography Open Database. Retrieved 28 July 2022.
^ ^a ^b Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 978-0-618-94690-7.
^ "Potassium superoxide". pubchem.ncbi.nlm.nih.gov. Retrieved 14 December 2021.
^ 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. p. 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. p. 36. doi:10.1002/0471653683.ch1.
^ Haymaker, Webb; Look, Bonne C.; Benton, Eugene V.; Richard C. Simmonds (1975-01-01). "The Apollo 17 pocket mouse experiment (Biocore)". Biomedical Results of Apollo. NASA-SP-368.