Propadiene
Organic compound (H2C=C=CH2)
From Wikipedia, the free encyclopedia
Propadiene (/proʊpəˈdaɪiːn/) or allene (/ˈæliːn/) is the organic compound with the formula H2C=C=CH2. It is the simplest allene, i.e. a compound with two adjacent carbon double bonds.[4] As a constituent of MAPP gas, it has been used as a fuel for specialized welding.
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| Names | |||
|---|---|---|---|
| IUPAC name
Allene[1] | |||
| Preferred IUPAC name
Propa-1,2-diene[2] | |||
| Systematic IUPAC name
Propadiene | |||
| Identifiers | |||
3D model (JSmol) |
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| 1730774 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| ECHA InfoCard | 100.006.670 | ||
| EC Number |
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| 860 | |||
| MeSH | Propadiene | ||
PubChem CID |
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| UNII | |||
| UN number | 2200 | ||
CompTox Dashboard (EPA) |
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| Properties | |||
| C3H4 | |||
| Molar mass | 40.065 g·mol−1 | ||
| Appearance | Colorless gas | ||
| Melting point | −136 °C (−213 °F; 137 K) | ||
| Boiling point | −34 °C (−29 °F; 239 K) | ||
| log P | 1.45 | ||
| Hazards | |||
| GHS labelling: | |||
 [3] | |||
| Danger | |||
| H220[3] | |||
| P210, P377, P381, P410+P403[3] | |||
| NFPA 704 (fire diamond) | |||
| Explosive limits | 13% | ||
| 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).
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Production and equilibrium with methylacetylene
Propadiene exists in equilibrium with methylacetylene (propyne) and the mixture is sometimes called MAPD for methylacetylene-propadiene:
- H3C−C≡CH ⇌ H2C=C=CH2
for which Keq = 0.22 at 270 °C or 0.1 at 5 °C.
MAPD is produced as a side product, often an undesirable one, of dehydrogenation of propane to produce propene, an important feedstock in the chemical industry. MAPD interferes with the catalytic polymerization of propene.[5]
Occurrence in space
In 2019 it was announced that propadiene had been detected in the atmosphere of Saturn's moon Titan using the NASA Infrared Telescope Facility.[6] This was the first time that propadiene had been detected in space, and the second structural isomeric pair (paired with propyne) detected in Titan's atmosphere, after HCN-HNC.[7][8]