Propadiene

Propadiene
Stereo structural formula of propadiene with explicit hydrogens	Spacefill model of propadiene
Names
	Preferred IUPAC name Propadiene
	Other names Allene; Propadiene
Identifiers
CAS Number	463-49-0 ;
3D model (JSmol)	Interactive image;
Beilstein Reference	1730774
ChEBI	CHEBI:37601 ;
ChEMBL	ChEMBL116960 ;
ChemSpider	9642 ;
ECHA InfoCard	100.006.670
EC Number	207-335-3;
Gmelin Reference	860
MeSH	Propadiene
PubChem CID	10037;
UNII	4AV0LZ8QKB ;
UN number	2200
CompTox Dashboard (EPA)	DTXSID1029178 ;
	InChI InChI=1S/C3H4/c1-3-2/h1-2H2 Key: IYABWNGZIDDRAK-UHFFFAOYSA-N ;
	SMILES C=C=C;
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
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220
Precautionary statements	P210, P377, P381, P410+P403
NFPA 704 (fire diamond)	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). verify (what is ?) Infobox references

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.

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Allene exists in equilibrium with methylacetylene (propyne) and the mixture is sometimes 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 dehydrogenation of propane to produce propene, an important feedstock in the chemical industry. MAPD interferes with the catalytic polymerization of propene.^[4]

[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. 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, propadiene, is the preferred IUPAC name.
[2]
Record of Allene in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 17 November 2020.
[3]
IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "allenes". doi:10.1351/goldbook.A00238
[4]
Klaus Buckl, Andreas Meiswinkel "Propyne" in Ullmann's Encyclopedia of Industrial Chemistry, 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.m22_m01

Production and equilibrium with methylacetylene