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| Names | |||
|---|---|---|---|
| IUPAC name Allene[1] | |||
| Preferred IUPAC name Propa-1,2-diene[2] | |||
| Systematic IUPAC name Propadiene | |||
| Identifiers | |||
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3D model (JSmol) | |||
| 1730774 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
| ||
| ECHA InfoCard | 100.006.670 | ||
| EC Number |
| ||
| 860 | |||
| MeSH | Propadiene | ||
| UNII | |||
| UN number | 2200 | ||
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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) | ||
| logP | 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 theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Propadiene (/proʊpəˈdaɪiːn/) orallene (/ˈæliːn/) is theorganic compound with the formulaH2C=C=CH2. It is the simplestallene, i.e. a compound with two adjacent carbondouble bonds.[4] As a constituent ofMAPP gas, it has been used as a fuel for specializedwelding.
Propadiene exists in equilibrium withmethylacetylene (propyne) and the mixture is sometimes called MAPD formethylacetylene-propadiene:
for whichKeq = 0.22 at 270 °C or 0.1 at 5 °C.
MAPD is produced as a side product, often an undesirable one, ofdehydrogenation ofpropane to producepropene, an importantfeedstock in thechemical industry. MAPD interferes with thecatalyticpolymerization of propene.[5]
In 2019 it was announced that propadiene had been detected in the atmosphere of Saturn's moonTitan using theNASA Infrared Telescope Facility.[6] This was the first time that propadiene had been detected in space, and the secondstructural isomeric pair (paired withpropyne) detected in Titan's atmosphere, afterHCN-HNC.[7][8]
The name allene, forCH2=C=CH2, is retained for general nomenclature only; substitution is allowed, but not by alkyl or any other group that extends the carbon chain, nor characteristic groups expressed by suffixes. The systematic name, propa-1,2-diene, is the preferred IUPAC name.
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