Propadiene (/prpəˈdn/) or allene (/ˈæln/) 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.

Propadiene
Stereo structural formula of propadiene with explicit hydrogens
Spacefill model of propadiene
Ball and stick model of propadiene
Names
Preferred IUPAC name
Propadiene[1]
Other names
Allene[1]
Propadiene
Identifiers
3D model (JSmol)
1730774
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.670 Edit this at Wikidata
EC Number
  • 207-335-3
860
MeSH Propadiene
UNII
UN number 2200
  • InChI=1S/C3H4/c1-3-2/h1-2H2 checkY
    Key: IYABWNGZIDDRAK-UHFFFAOYSA-N checkY
  • C=C=C
  • C(=C)=C
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:
GHS02: Flammable GHS04: Compressed Gas[2]
Danger
H220, H280[2]
P210, P377, P381, P410+P403[2]
NFPA 704 (fire diamond)
0
4
3
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 methylacetyleneEdit

Allene exists in equilibrium with methylacetylene (propyne) and the mixture is sometimes called MAPD for methylacetylene-propadiene:

 

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]

ReferencesEdit

  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