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Propadiene

Organic compound (H2C=C=CH2) From Wikipedia, the free encyclopedia

Propadiene

Propadiene (/proʊpəˈdaɪiːn/) or allene (/ˈæliːn/) 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.

Quick Facts Names, Identifiers ...
Propadiene
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Stereo structural formula of propadiene with explicit hydrogens
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Spacefill model of propadiene
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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
EC Number
  • 207-335-3
860
MeSH Propadiene
UNII
UN number 2200
  • InChI=1S/C3H4/c1-3-2/h1-2H2 Y
    Key: IYABWNGZIDDRAK-UHFFFAOYSA-N Y
  • 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[2]
Danger
H220[2]
P210, P377, P381, P410+P403[2]
NFPA 704 (fire diamond)
ThumbHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 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. propaneInstability 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. hydrogen peroxideSpecial hazards (white): no code
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 methylacetylene

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

H3C−C≡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.[4]

Occurrence in Space

In 2019 it was announced that propadiene had been detected in the atmosphere of Saturn's moon Titan using the NASA Infrared Telescope Facility.[5] This was the first time that propadiene had been detected in space, and the second structural isomeric pair (paired with propyne) detected in Titan's atmosphere, after HCN-HNC.[6][7]

References

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