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| Names | |
|---|---|
| Preferred IUPAC name Ethenone[1] | |
| Other names Ketene Carbomethene Keto-ethylene | |
| Identifiers | |
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3D model (JSmol) | |
| 1098282 | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.006.671 |
| EC Number |
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| RTECS number |
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| UNII | |
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| Properties | |
| C2H2O | |
| 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) |
| decomposes | |
| Solubility | soluble inacetone ethanol ethyl ether aromatic solvents halocarbons |
| Vapor pressure | >1 atm (20°C)[2] |
Refractive index (nD) | 1.4355 |
| Thermochemistry | |
| 51.75 J/K mol | |
Std enthalpy of formation(ΔfH⦵298) | −87.24 kJ/mol |
| Hazards | |
| NFPA 704 (fire diamond) | |
| 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/m3)[2] |
REL (Recommended) | TWA 0.5 ppm (0.9 mg/m3) ST 1.5 ppm (3 mg/m3)[2] |
IDLH (Immediate danger) | 5 ppm[2] |
| Safety data sheet (SDS) | External MSDS |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Ethenone is the formal name forketene, anorganic compound with formulaC2H2O orH2C=C=O. It is the simplest member of theketene class. It is an important reagent foracetylations.[4][5]
Ethenone is a highly reactive gas (atstandard conditions) and has a sharp, irritating odour. It is reasonably stable only at low temperatures (−80 °C). It must therefore always be prepared for each use and processed immediately, otherwise a dimerization todiketene occurs, or polymers are formed that are difficult to handle. Its polymerization can be reduced by adding sulfur dioxide.[6] Because of its cumulative double bonds, it adds readily to H-acidic compounds, reacting with water, for example, to form acetic acid, and withprimary orsecondary amines to yield the correspondingacetamides.
Ethenone is produced by thermal dehydration of acetic acid at 700–750 °C in the presence oftriethyl phosphate as a catalyst:[7][8]
It has also been produced on a laboratory scale by thethermolysis ofacetone at600–700 °C.[9][10]
This reaction is called the Schmidlin ketene synthesis.[11]
On a laboratory scale it can be produced by the thermal decomposition ofMeldrum's acid at temperatures greater than 200 °C.[citation needed]
Ethenone was first produced in 1907 by N. T. M. Wilsmore throughpyrolysis ofacetone oracetic anhydride vapours over a hot platinum wire in an apparatus that was later developed by Charles D. Hurd into the "Hurd lamp" or "ketene lamp". This apparatus consists of a heated flask of acetone producing vapours which are pyrolyzed by a metal filament electrically heated to red heat, with a condenser to return unreacted acetone to the boiling flask. Other heating methods have been used and similar methods were used on a larger scale for the industrial production of ketene for acetic anhydride synthesis.[12][13][14]
Ethenone was discovered at the same time byHermann Staudinger (by reaction ofbromoacetyl bromide with metalliczinc)[15][16] The dehydration of acetic acid was reported in 1910.[17]
The thermal decomposition of acetic anhydride was also described.[18]
Ethenone has been observed to occur in space, in comets or in gas as part of the interstellar medium.[19]
Ethenone is used to makeacetic anhydride fromacetic acid. Generally it is used for theacetylation of chemical compounds.[20]
Ethenone reacts withformaldehyde in the presence of catalysts such as Lewis acids (AlCl3, ZnCl2 or BF3) to giveβ-propiolactone.[21] The technically most significant use of ethenone is the synthesis ofsorbic acid by reaction withcrotonaldehyde intoluene at about 50 °C in the presence of zinc salts of long-chain carboxylic acids. This produces apolyester of 3-hydroxy-4-hexenoic acid, which is thermally[22] or hydrolytically depolymerized to sorbic acid.
Ethenone is very reactive, tending to react withnucleophiles to form anacetyl group. For example, it reacts with water to formacetic acid;[23] with acetic acid to formacetic anhydride; with ammonia and amines to form ethanamides;[24] and with dryhydrogen halides to form acetyl halides.[25]
The formation of acetic acid likely occurs by an initial formation of1,1-dihydroxyethene, which thentautomerizes to give the final product.[26]
Ethenone will also react with itself via[2 + 2] photocycloadditions to form cyclicdimers known asdiketenes. For this reason, it should not be stored for long periods.[27]
Ketene cycloadditions can be difficult to control;dichloroketene is typically used instead, followed by dehalogenation withzinc-copper couple.[28]
Exposure to concentrated levels causes humans to experience irritation of body parts such as theeye,nose,throat andlungs. 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 (116ppm) may produce a high percentage of deaths in small animals. These findings show ethenone is toxicologically identical tophosgene.[29][20]
The formation of ketene in thepyrolysis ofvitamin E acetate, an additive of somee-liquid products, is one possible mechanism of the reported pulmonary damage[30] caused by electronic cigarette use.[31]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).[32][33]
Occupational exposure limits are set at 0.5 ppm (0.9 mg/m3) over an eight-hour time-weighted average.[34] AnIDLH limit is set at 5 ppm, as this is the lowest concentration productive of a clinically relevant physiologic response in humans.[35]
Media related toEthenone at Wikimedia Commons
