Ethenone

Ethenone

Names
Preferred IUPAC name Ethenone[1]
Other names Ketene Carbomethene Keto-ethylene
Identifiers
CAS Number	463-51-4^Y
3D model (JSmol)	Interactive image
Beilstein Reference	1098282
ChEBI	CHEBI:48003^Y
ChemSpider	9643^Y
ECHA InfoCard	100.006.671
EC Number	207-336-9
PubChem CID	10038
RTECS number	OA7700000
UNII	LEP3SM032A^Y
CompTox Dashboard (EPA)	DTXSID1052113
InChI InChI=1S/C2H2O/c1-2-3/h1H2^Y Key: CCGKOQOJPYTBIH-UHFFFAOYSA-N^Y InChI=1/C2H2O/c1-2-3/h1H2 Key: CCGKOQOJPYTBIH-UHFFFAOYSA-N InChI=1/C2H2O/c1-2-3/h1H2 Key: CCGKOQOJPYTBIH-UHFFFAOYAO
SMILES O=C=C
Properties
Chemical formula	C2H2O
Molar mass	42.037 g/mol
Appearance	Colourless gas
Odor	penetrating
Density	1.93 g/cm^3
Melting point	−150.5 °C (−238.9 °F; 122.6 K)
Boiling point	−56.1 °C (−69.0 °F; 217.1 K)
Solubility in water	decomposes
Solubility	soluble in acetone ethanol ethyl ether aromatic solvents halocarbons
Vapor pressure	>1 atm (20°C)[2]
Refractive index (nD)	1.4355
Thermochemistry
Heat capacity (C)	51.75 J/K mol
Std enthalpy of formation (ΔfH^⦵298)	-87.24 kJ/mol
Hazards
NFPA 704 (fire diamond)	4 4 1
Flash point	−107 °C (−161 °F; 166 K)
Explosive limits	5.5-18%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1300 mg/kg (oral, rat)
LC50 (median concentration)	17 ppm (mouse, 10 min)[3]
LCLo (lowest published)	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)[3]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 0.5 ppm (0.9 mg/m^3)[2]
REL (Recommended)	TWA 0.5 ppm (0.9 mg/m^3) ST 1.5 ppm (3 mg/m^3)[2]
IDLH (Immediate danger)	5 ppm[2]
Safety data sheet (SDS)	External MSDS
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

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 an important reagent for acetylations.^[4][5]

Properties

Ethenone is a highly reactive gas (at standard conditions) and has a sharp irritating odour. It is only reasonably stable at low temperatures (−80 °C). It must therefore always be prepared for each use and processed immediately, otherwise a dimerization to diketene occurs or it reacts to polymers that are difficult to handle. The polymer content formed during the preparation is reduced, for example, by adding sulfur dioxide to the ketene gas.^[6] Because of its cumulative double bonds, ethenone is highly reactive and reacts in an addition reaction H-acidic compounds to the corresponding acetic acid derivatives. It does for example react with water to acetic acid or with primary or secondary amines to the corresponding acetamides.

Preparation

Ethenone is produced by thermal dehydration of acetic acid at 700–750 °C in the presence of triethyl phosphate as a catalyst:^[7][8]

CH₃CO₂H → CH₂=C=O + H₂O

It has also been produced on a laboratory scale by the thermolysis of acetone at 600–700 °C.^[9][10]

CH₃COCH₃ →CH₂=C=O + CH₄

This reaction is called the Schmidlin ketene synthesis.^[11]

On a laboratory scale it can be produced by the thermal decomposition of Meldrum's acid at temperatures greater than 200 °C.^{[citation needed]}

History

When passed through heated pipes or electrically heated metal (like copper) wires at 500-600 °C in the presence of carbon disulfide, acetone decomposes into methane and ethenone, with 95% yield.^[12][13] Ethenone was discovered at the same time by Hermann Staudinger (by reaction of bromoacetyl bromide with metallic zinc)^[14][15] The dehydration of acetic acid was reported in 1910.^[16]

The thermal decomposition of acetic anhydride was also described.^[17]

Natural occurrence

Ethenone has been observed to occur in space, in comets or in gas as part of the interstellar medium.^[18]

Use

Ethenone is used to make acetic anhydride from acetic acid. Generally it is used for the acetylation of chemical compounds.^[19]

Reactions with ammonia, water, ethanol, and acetic acid

Mechanism of the above reactions

Ethenone reacts with methanal in the presence of catalysts such as Lewis acids (AlCl₃, ZnCl₂ or BF₃) to give β-propiolactone.^[20] The technically most significant use of ethenone is the synthesis of sorbic acid by reaction with 2-butenal (crotonaldehyde) in toluene at about 50 °C in the presence of zinc salts of long-chain carboxylic acids. This produces a polyester of 3-hydroxy-4-hexenoic acid, which is thermally^[21] or hydrolytically depolymerized to sorbic acid.

Ethenone is very reactive, tending to react with nucleophiles to form an acetyl group. For example, it reacts with water to form acetic acid;^[22] with acetic acid to form acetic anhydride; with ammonia and amines to form ethanamides;^[23] and with dry hydrogen halides to form acetyl halides.^[24]

The formation of acetic acid likely occurs by an initial formation of 1,1-dihydroxyethene, which then tautomerizes to give the final product.^[25]

Ethenone will also react with itself via [2 + 2] photocycloadditions to form cyclic dimers known as diketenes. For this reason, it should not be stored for long periods.^[26]

Hazards

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 show ethenone is toxicologically identical to phosgene.^[27][19]

The formation of ketene in the pyrolysis of vitamin E acetate, an additive of some e-liquid products, is one possible mechanism of the reported pulmonary damage^[28] caused by electronic cigarette use.^[29] A number of patents describe the catalytic formation of ketene from carboxylic acids and acetates, using a variety of metals or ceramics, some of which are known to occur in e-cigarette devices from patients with e-cigarette or vaping product-use associated lung injury (EVALI).^[30][31]

Occupational exposure limits are set at 0.5 ppm (0.9 mg/m³) over an eight-hour time-weighted average.^[32] An IDLH limit is set at 5 ppm, as this is the lowest concentration productive of a clinically relevant physiologic response in humans.^[33]

References

1. "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 723. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
2. NIOSH Pocket Guide to Chemical Hazards. "#0367". National Institute for Occupational Safety and Health (NIOSH).
3. "Ketene". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
4. Miller, Raimund; Abaecherli, Claudio; Said, Adel; Jackson, Barry (2001). "Ketenes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_063. ISBN 3527306730.
5. Mitzel, Thomas M.; Pigza, Julie A. (2009). "Ketene". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rk000.pub2. ISBN 978-0-471-93623-7.
6. EP 0377438, R. Bergamin et al., issued 1990-06-11, assigned to Lonza AG 
7. Miller, Raimund; Abaecherli, Claudio; Said, Adel; Jackson, Barry (2001). "Ketenes". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a15_063. ISBN 978-3-527-30385-4.
8. Arpe, Hans-Jürgen (2007), Industrielle organische Chemie: Bedeutende vor- und Zwischenprodukte (in German) (6th ed.), Weinheim: Wiley-VCH, pp. 200–201, ISBN 978-3-527-31540-6^{[permanent dead link]}
9. Weygand C (1972). Hilgetag G, Martini A (eds.). Weygand/Hilgetag Preparative Organic Chemistry (4th ed.). New York: John Wiley & Sons, Inc. pp. 1031–1032. ISBN 978-0471937494.
10. Hurd CD, Kamm O (1941). "Ketene in Organic Syntheses". Organic Syntheses. Vol. Collective Vol. 1. p. 330.
11. Schmidlin J, Bergman M (1910). "Darstellung des Ketens aus Aceton" [Preparation of ketene from acetone]. Berichte der Deutschen Chemischen Gesellschaft (in German). 43 (3): 2821–2823. doi:10.1002/cber.19100430340.
12. K.-H. Lautenschläger, W. Schröter, A. Wanninger, "Taschenbuch der Chemie", 20. Aufl. 2006, ISBN 978-3-8171-1761-1.
13. "Ketene". Organic Syntheses. doi:10.15227/orgsyn.004.0039.
14. H. Staudinger H. W. Klever (1908): "Keten. Bemerkung zur Abhandlung zur Abhandlung der HHrn. V.T. Wilsmore und A. W. Stewart". Berichte der deutschen chemischen Gesellschaft, volume 41, issue 1, pages 1516-1517. doi:10.1002/cber.190804101275
15. Tidwell, T. T. (2005), "Ein Jahrhundert Ketene (1905–2005): die Entdeckung einer vielseitigen Klasse reaktiver Intermediate". Angewandte Chemie, volume 117, pages 5926–5933. doi:10.1002/ange.200500098
16. J. Schmidlin, M. Bergman (1910): Berichte der deutschen chemischen Gesellschaft, volume 43, pages 2821- doi:10.1002/cber.19100430340
17. Norman Thomas Mortimer Wilsmore (1907): "Keten". Journal of the Chemical Society, Transactions, volume 91, article CLXXXVIII (188), pages 1938-1941. doi:10.1039/ct9079101938
18. Hudson, Reggie L.; Loeffler, Mark J. (31 July 2013). "Ketene Formation in Interstellar Ices: A Laboratory Study". The Astrophysical Journal. 773 (2): 109. Bibcode:2013ApJ...773..109H. doi:10.1088/0004-637x/773/2/109. hdl:2060/20140010162. S2CID 37437108.
19. Entry on Diketen. at: Römpp Online. Georg Thieme Verlag, retrieved 16. Juni 2014.
20. Hans-Jürgen Arpe, "Industrielle Organische Chemie", 6. Aufl., 2007, WILEY-VCH Verlag, Weinheim, ISBN 978-3-527-31540-6.
21. EP 1295860, D. Decker et al., issued 26. März 2003-03-26, assigned to Nutrinova GmbH 
22. Tidwell, p. 11.
23. Tidwell, p. 560.
24. ChemSpider http://www.chemspider.com/Chemical-Structure.9643.html
25. Nguyen, Minh Tho; Raspoet, Greet (1999). "The hydration mechanism of ketene: 15 years later". Can. J. Chem. 77 (5–6): 817–829. doi:10.1139/v99-090.
26. Christoph Taeschler :Ketenes, Ketene Dimers, and Related Substances, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 2010
27. 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.
28. "The Vaping-Related Lung Disease Outbreak May be Coming to an End". 20 December 2019.
29. Wu, Dan; O’Shea, Donal F. (24 March 2020). "Potential for release of pulmonary toxic ketene from vaping pyrolysis of vitamin E acetate". Proceedings of the National Academy of Sciences. 117 (12): 6349–6355. Bibcode:2020PNAS..117.6349W. doi:10.1073/pnas.1920925117. PMC 7104367. PMID 32156732.
30. Attfield, Kathleen R.; Chen, Wenhao; Cummings, Kristin J.; Jacob, Peyton; O’Shea, Donal F.; Wagner, Jeff; Wang, Ping; Fowles, Jefferson (15 October 2020). "Potential of Ethenone (Ketene) to Contribute to Electronic Cigarette, or Vaping, Product Use–associated Lung Injury". American Journal of Respiratory and Critical Care Medicine. 202 (8): 1187–1189. doi:10.1164/rccm.202003-0654LE. PMID 32551843. S2CID 219919028.
31. U.S. patent No. 5475144. Catalyst and process for synthesis of ketenes from carboxylic acids. Dec 12, 1995. https://patents.google.com/patent/US5475144A/en
32. Centers for Disease Control and Prevention (4 April 2013). "Ketene". NIOSH Pocket Guide to Chemical Hazards. Retrieved 13 November 2013.
33. Centers for Disease Control and Prevention (May 1994). "Ketene". Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs). Retrieved 13 November 2013.

Literature

• Tidwell, Thomas T. Ketenes, 2nd edition. John Wiley & Sons, 2006, ISBN 978-0-471-69282-9.

External links

• Media related to Ethenone at Wikimedia Commons