Propadiene

Propadiene or allene 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.[2] 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
Names
Preferred IUPAC name
Propa-1,2-diene[1]
Other names
Allene[1]
Propadiene
Identifiers
CAS Number
3D model (JSmol)
Beilstein Reference
 1730774
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.006.670
EC Number
  • 207-335-3
Gmelin Reference
 860
MeSH Propadiene
PubChem CID
UNII
UN number 2200
CompTox Dashboard (EPA)
Properties
Chemical formula
 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
Safety data sheet External MSDS
EU classification (DSD) (outdated)
 F+
R-phrases (outdated) R12
S-phrases (outdated) S9, S16, S33
NFPA 704 (fire diamond)
4
0
3
Explosive limits 13%
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.[3]

References
  1. 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.
  2. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "allenes". doi:10.1351/goldbook.A00238
  3. Klaus Buckl, Andreas Meiswinkel "Propyne" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.m22_m01
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