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Stereo structural formula of propadiene with explicit hydrogens
Spacefill model of propadiene
Ball and stick model of propadiene
IUPAC name
Systematic IUPAC name
Propa-1,2-diene (substitutive)
dimethylenemethane (additive)
3D model (Jmol)
ECHA InfoCard 100.006.670
EC Number 207-335-3
MeSH Propadiene
UN number 2200
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
Safety data sheet External MSDS
Extremely Flammable F+
R-phrases R12
S-phrases S9, S16, S33
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazards (white): no codeNFPA 704 four-colored diamond
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

Propadiene is the organic compound with the formula H2C=C=CH2. It is the simplest allene or compound with two adjacent C=C double bonds, and can also be identified as allene.[1] As a constituent of MAPP gas, it has been used as a fuel for specialized welding.

Production and equilibrium with methylacetylene[edit]

Allene exists in equilibrium with methylacetylene (or propyne), the mixture sometimes being 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 cracking propane to produce propene, an important feedstock in the chemical industry. MAPD interferes with the catalytic polymerization of propene.[2]


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