Propadiene 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. As a constituent of MAPP gas, it has been used as a fuel for specialized welding.
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=CH2for 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.2
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.3 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.45
References
IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "allenes". doi:10.1351/goldbook.A00238 /wiki/International_Union_of_Pure_and_Applied_Chemistry ↩
Klaus Buckl, Andreas Meiswinkel "Propyne" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.m22_m01 /wiki/Doi_(identifier) ↩
Lombardo, Nicholas A; Nixon, Conor A; Greathouse, Thomas K; Bézard, Bruno; Jolly, Antoine; Vinatier, Sandrine; Teanby, Nicholas A; Richter, Matthew J; G Irwin, Patrick J; Coustenis, Athena; Flasar, F Michael (2019-08-20). "Detection of Propadiene on Titan". The Astrophysical Journal Letters. 881 (2): L33. arXiv:1908.07424. doi:10.3847/2041-8213/ab3860. ISSN 2041-8205. https://doi.org/10.3847%2F2041-8213%2Fab3860 ↩
Moreno, R.; Lellouch, E.; Lara, L. M.; Courtin, R.; Bockelée-Morvan, D.; Hartogh, P.; Rengel, M.; Biver, N.; Banaszkiewicz, M.; González, A. (December 2011). "First detection of hydrogen isocyanide (HNC) in Titan's atmosphere". Astronomy & Astrophysics. 536: L12. doi:10.1051/0004-6361/201118189. ISSN 0004-6361. http://www.aanda.org/10.1051/0004-6361/201118189 ↩
Hébrard, E.; Dobrijevic, M.; Loison, J. C.; Bergeat, A.; Hickson, K. M. (May 2012). "Neutral production of hydrogen isocyanide (HNC) and hydrogen cyanide (HCN) in Titan's upper atmosphere". Astronomy & Astrophysics. 541: A21. doi:10.1051/0004-6361/201218837. ISSN 0004-6361. http://www.aanda.org/10.1051/0004-6361/201218837 ↩