|Jmol-3D images||Image 1
|Molar mass||40.06 g mol−1|
|Melting point||−136 °C (−213 °F; 137 K)|
|Boiling point||−34 °C (−29 °F; 239 K)|
|S-phrases||S9, S16, S33|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
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 was 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 Keq = 0.22 (270 °C) at 0.1 K (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.
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