Propadiene

Propadiene

Names
IUPAC name Allene
Systematic IUPAC name Propa-1,2-diene (substitutive) Dimethylenecarbon, dimethylenemethane (additive)
Identifiers
CAS Number	463-49-0 Y
Beilstein Reference	1730774
ChEBI	CHEBI:37601 Y
ChEMBL	ChEMBL116960 Y
ChemSpider	9642 Y
EC Number	207-335-3
Gmelin Reference	860
Jmol 3D model	Interactive image Interactive image
MeSH	Propadiene
PubChem	10037
UN number	2200
InChI InChI=1S/C3H4/c1-3-2/h1-2H2 Y Key: IYABWNGZIDDRAK-UHFFFAOYSA-N Y
SMILES C=C=C C(=C)=C
Properties
Chemical formula	C3H4
Molar mass	40.07 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
Vapor pressure	{{{value}}}
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

Propadiene is the organic compound with the formula H₂C=C=CH₂. It is the simplest allene, a compound with conjoined C=C double bonds. 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, the mixture sometimes being called MAPD for methylacetylene-propadiene:

H₃CC≡CH ⇌ H₂C=C=CH₂

for which K_eq = 0.22 at 270 °C or 0.1 at 5 °C. MAPD is produced as a side product, often an undesirable one, of cracking propane to produce propene, an important feedstock in the chemical industry. MAPD interferes with the catalytic polymerization of propene.