Propadiene or allene is the organic compound with the formula H2C=C=CH2. It is the simplest allene or compound with two adjacent carbon double bonds, and can also be identified as allene. As a constituent of MAPP gas, it has been used as a fuel for specialized welding.
|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||40.065 g·mol−1|
|Melting point||−136 °C (−213 °F; 137 K)|
|Boiling point||−34 °C (−29 °F; 239 K)|
|Safety data sheet||External MSDS|
|S-phrases (outdated)||S9, S16, S33|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Production and equilibrium with methylacetyleneEdit
Allene exists in equilibrium with methylacetylene (propyne) and the mixture is sometimes called MAPD for methylacetylene-propadiene:
- H3CC≡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.
- Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 375. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
The name allene, for CH2=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.
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "allenes". doi:10.1351/goldbook.A00238
- Klaus Buckl, Andreas Meiswinkel "Propyne" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.m22_m01