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.[3] As a constituent of MAPP gas, it has been used as a fuel for specialized welding.

Production and equilibrium with methylacetylene

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.[4]

References

  1. ^ a b 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, propadiene, is the preferred IUPAC name.
  2. ^ a b c Record of Allene in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 17 November 2020.
  3. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "allenes". doi:10.1351/goldbook.A00238
  4. ^ Klaus Buckl, Andreas Meiswinkel "Propyne" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.m22_m01