Potassium superoxide

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Potassium superoxide
Unit cell of potassium superoxide
Identifiers
CAS number 12030-88-5 YesY
PubChem 61541
ChemSpider 26237 N
EC number 234-746-5
RTECS number TT6053000
Jmol-3D images Image 1
Properties
Molecular formula 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)
Solubility in water decomposes
Structure
Crystal structure Body-centered cubic (O2)
Thermochemistry
Std molar
entropy
So298
117 J·mol−1·K−1[1]
Std enthalpy of
formation
ΔfHo298
−283 kJ·mol−1[1]
Hazards
R-phrases 8-14-34
S-phrases 17-27-36/37/39
Main hazards corrosive, oxidant
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 hazards (white): no codeNFPA 704 four-colored diamond
Related compounds
Other anions Potassium oxide
Potassium peroxide
Other cations Sodium superoxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Potassium superoxide is the inorganic compound with the formula KO2. 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 CO2 scrubber, H2O dehumidifier and O2 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.[2]

K + O2 → KO2

The salt consists of K+ and O2- ions, linked by ionic bonds. The O-O distance is 1.28 Å.[3]

Reactivity[edit]

Hydrolysis gives oxygen gas and base:

4 KO2 + 2 H2O → 4 KOH + 3 O2

Its degradation by carbon dioxide affords carbonates:

4 KOH + 2 CO2 → 2 K2CO3 + 2 H2O

Combinations of these two reaction occur as well:

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 the use of superoxide as a nucleophile, e.g., in the conversion of alkyl bromides to alcohols and acyl chlorides into diacyl peroxides.[4]

Applications[edit]

The Russian Space Agency has had success using potassium superoxide in chemical oxygen generators for its spacesuits and Soyuz spacecraft. KO2 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 KO2 is the absorption of 0.618 kg CO2 per kg of absorbent while 0.380 kg O2 are generated per kg of absorbent. For one KO2 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.[5] 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.[6]

References[edit]

  1. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X. 
  2. ^ Harald Jakob, Stefan Leininger, Thomas Lehmann, Sylvia Jacobi, Sven Gutewort “Peroxo Compounds, Inorganic” Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_177.pub2
  3. ^ Abrahams, S. C.; Kalnajs, J. "The Crystal Structure of α-Potassium Superoxide" Acta Crystallographica (1955) volume 8, pages 503-506. doi:10.1107/S0365110X55001540.
  4. ^ Roy A. Johnson, Javier Adrio, María Ribagorda "Potassium Superoxide" e-EROS Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons. doi:10.1002/047084289X.rp250.pub2
  5. ^ Aerojet Nuclear Company (1975). "An Explosives Hazards Analysis of the Eutectic Solution of NaK and KO2". Idaho National Engineering Laboratory. 
  6. ^ "Y-12 NaK Accident Investigation". U.S. Department of Energy. February 2000. Archived from the original on 2010-05-28.