Potassium superoxide

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Potassium superoxide
Unit cell of potassium superoxide
Names
IUPAC name
Potassium dioxide
Other names
Potassium superoxide
Identifiers
12030-88-5 YesY
ChemSpider 8329498 N
EC Number 234-746-5
Jmol 3D model Interactive image
PubChem 61541
RTECS number TT6053000
Properties
KO2
Molar mass 71.10 g·mol−1
Appearance yellow solid
Density 2.14 g/cm3, solid
Melting point 560 °C (1,040 °F; 833 K) (decomposes)
decomposes
Structure
Body-centered cubic (O
2
)
Thermochemistry
117 J·mol−1·K−1[1]
−283 kJ·mol−1[1]
Hazards
Main hazards corrosive, oxidant
R-phrases 8-14-34
S-phrases 17-27-36/37/39
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Related compounds
Other anions
Potassium oxide
Potassium peroxide
Other cations
Sodium superoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Potassium superoxide is the inorganic compound with the formula KO
2
.[2] It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide ion. Potassium superoxide is used as a CO
2
scrubber, H
2
O
dehumidifier and O
2
generator in rebreathers, spacecraft, submarines and spacesuit life support systems.

Production and reactions[edit]

Potassium superoxide is produced by burning molten potassium in an atmosphere of oxygen.[3]

K + O
2
KO
2

The salt consists of K+
and O
2
ions, linked by ionic bonds. The O-O distance is 1.28 Å.[4]

Reactivity[edit]

Hydrolysis gives oxygen gas, hydrogen peroxide and potassium hydroxide:

2 KO
2
+ 2H
2
O
→ 2 KOH + H
2
O
2
+ O
2
[5]

Its degradation by carbon dioxide affords carbonates:

4 KOH + 2 CO2 → 2 K2CO3 + 2 H2O

Combinations of these two reactions occur as well:

4 KO
2
+ 2 CO2 → 2 K2CO3 + 3 O
2
4 KO
2
+ 4 CO2 + 2 H2O → 4 KHCO3 + 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 the use of superoxide as a nucleophile, e.g., in the conversion of alkyl bromides to alcohols and acyl chlorides into diacyl peroxides.[6]

Applications[edit]

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 utilized in canisters for rebreathers for fire fighting and mine rescue work, but had limited use in scuba rebreathers because of its dangerously explosive reaction with water. The theoretical capacity of KO
2
is the absorption of 0.618 kg CO2 per kg of absorbent while 0.380 kg O
2
are generated per kg of absorbent. For one KO
2
molecule, it's one CO2 molecule but only 0.75 oxygen molecules. The human body though will produce less CO2 molecules than oxygen molecules needed because oxidation of food also needs oxygen to produce water and urea.

Hazards[edit]

Potassium superoxide is a potent oxidizer, and can produce explosive reactions when combined with a variety of substances, including water, acids, organics, or powdered graphite. Even dry superoxide can produce an impact-sensitive explosive compound when combined with organic oils such as kerosene.[7] In 1999 at Oak Ridge National Laboratory, cleanup of potassium oxides from a NaK metal leak produced an impact-sensitive explosion while saturated with mineral oil.[8]

References[edit]

  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin. p. A22. ISBN 0-618-94690-X. 
  2. ^ Hayyan M., Hashim M.A., AlNashef I.M., Superoxide Ion: Generation and Chemical Implications, Chem. Rev., 2016, 116 (5), pp 3029–3085. DOI: 10.1021/acs.chemrev.5b00407
  3. ^ 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. 
  4. ^ Abrahams, S. C.; Kalnajs, J. (1955). "The Crystal Structure of α-Potassium Superoxide". Acta Crystallographica. 8: 503–6. doi:10.1107/S0365110X55001540. 
  5. ^ Kumar De, Anil (2007). A Text Book of Inorganic Chemistry. New Age International. p. 247. ISBN 978-8122413847. 
  6. ^ 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. 
  7. ^ Aerojet Nuclear Company (1975). "An Explosives Hazards Analysis of the Eutectic Solution of NaK and KO
    2
    ". Idaho National Engineering Laboratory.
     
  8. ^ "Y-12 NaK Accident Investigation". U.S. Department of Energy. February 2000. Archived from the original on 2010-05-28.