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Structural formula
Space-filling model
Preferred IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.006.671
EC Number 207-336-9
RTECS number OA7700000
Molar mass 42.037 g/mol
Appearance Colourless gas
Odor penetrating
Density 1.93 g/cm3
Melting point −150.5 °C (−238.9 °F; 122.6 K)
Boiling point −56.1 °C (−69.0 °F; 217.1 K)
Solubility soluble in acetone
ethyl ether
aromatic solvents
Vapor pressure >1 atm (20°C)[1]
51.75 J/K mol
-87.24 kJ/mol
Safety data sheet External MSDS
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −107 °C (−161 °F; 166 K)
Explosive limits 5.5-18%
Lethal dose or concentration (LD, LC):
1300 mg/kg (oral, rat)
17 ppm (mouse, 10 min)[2]
23 ppm (mouse, 30 min)
53 ppm (rabbit, 2 hr)
53 ppm (guinea pig, 2 hr)
750 ppm (cat, 10 min)
200 ppm (monkey, 10 min)
50 ppm (mouse, 10 min)
1000 ppm (rabbit, 10 min)[2]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 0.5 ppm (0.9 mg/m3)[1]
REL (Recommended)
TWA 0.5 ppm (0.9 mg/m3) ST 1.5 ppm (3 mg/m3)[1]
IDLH (Immediate danger)
5 ppm[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ethenone is the formal name for ketene, an organic compound with formula C2H2O or H2C=C=O. It is the simplest member of the ketene class. It is a tautomer of ethynol.


Ethenone is a very poisonous colourless gas at STP and has a sharp irritating odour. It is soluble in acetone, ethanol, ethyl ether, aromatic solvents and halocarbons.


Ethenone can be prepared in the laboratory by pyrolysis of acetone vapor.[3] It is also formed by reacting acetyl chloride with a proton acceptor like trimethylamine.


Ethenone has been observed to occur in space, in comets or in gas as part of the interstellar medium.[4]


Ethenone is very reactive, tending to react with nucleophiles to form an acetyl group. For example, it reacts with water to form acetic acid;[5] with acetic acid to form acetic anhydride; with ammonia and amines to form ethanamides;[6] and with dry hydrogen halides to form acetyl halides.[7]

Ethenone will also react with itself via 2+2 photocycloaddition to form cyclic dimers known as diketenes. For this reason, it should not be stored for long periods.[8]


Exposure to concentrated levels causes humans to experience irritation of body parts such as the eye, nose, throat and lungs. Extended toxicity testing on mice, rats, guinea pigs and rabbits showed that ten-minute exposures to concentrations of freshly generated ethenone as low as 0.2 mg/liter (116 ppm) may produce a high percentage of deaths in small animals. These findings put ethenone in the same order of toxicity as phosgene (0.2–20 mg/liter) and hydrogen cyanide (0.2-0.5 mg/liter). Death is from pulmonary edema and is entirely similar to, but much more rapid than is the case with phosgene poisoning.[9]

Occupational exposure limits are set at 0.5 ppm (0.9 mg/m3) over an eight-hour time-weighted average.[10] An IDLH limit is set at 5 ppm, as this is the lowest concentration productive of a clinically relevant physiologic response in humans.[11]


  1. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0367". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ a b "Ketene". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ C. D. Hurd (1941). "Ketene". Organic Syntheses. ; Collective Volume, 1, p. 330 .
  4. ^ Hudson, Reggie L.; Loeffler, Mark J. (2013). "Ketene Formation in Interstellar Ices: A Laboratory Study". The Astrophysical Journal. 773 (2): 109. doi:10.1088/0004-637x/773/2/109. ISSN 0004-637X. 
  5. ^ Tidwell, p. 11.
  6. ^ Tidwell, p. 560.
  7. ^ ChemSpider
  8. ^ Christoph Taeschler :Ketenes, Ketene Dimers, and Related Substances, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 2010
  9. ^ H. A. Wooster; C. C. Lushbaugh; C. E. Redeman (1946). "The Inhalation Toxicity of Ketene and of Ketene Dimer". J. Am. Chem. Soc. 68 (12): 2743. doi:10.1021/ja01216a526. 
  10. ^ Centers for Disease Control and Prevention (4 April 2013). "Ketene". NIOSH Pocket Guide to Chemical Hazards. Retrieved 13 November 2013. 
  11. ^ Centers for Disease Control and Prevention (May 1994). "Ketene". Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs). Retrieved 13 November 2013.