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IUPAC name
Other names
Methyl acetylene
74-99-7 YesY
ChemSpider 6095
EC Number 200-828-4
Jmol 3D model Interactive image
MeSH C022030
PubChem 6335
Molar mass 40.0639 g/mol
Appearance Colorless gas[1]
Odor Sweet[1]
Density 0.53 g/cm3
Melting point −102.7 °C (−152.9 °F; 170.5 K)
Boiling point −23.2 °C (−9.8 °F; 250.0 K)
Vapor pressure 5.2 atm (20°C)[1]
Explosive limits 1.7%-?[1]
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 1000 ppm (1650 mg/m3)[1]
REL (Recommended)
TWA 1000 ppm (1650 mg/m3)[1]
IDLH (Immediate danger)
1700 ppm[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Propyne (methylacetylene) is an alkyne with the chemical formula CH3C≡CH. It was a component of MAPP gas—along with its isomer propadiene (allene), which was commonly used in gas welding. Unlike acetylene, propyne can be safely condensed.[2]

Production and equilibrium with propadiene[edit]

Propyne exists in equilibrium with propadiene, the mixture of propyne and propadiene being called MAPD:


The coefficient of equilibrium Keq is 0.22 at 270 °C or 0.1 at 5 °C. MAPD is produced as a side product, often an undesirable one, by cracking propane to produce propene, an important feedstock in the chemical industry.[2] MAPD interferes with the catalytic polymerization of propene.

Laboratory Methods[edit]

Propyne can also be synthesized on laboratory scale by reducing 1-propanol,[3] allyl alcohol or acetone[4] vapors over magnesium.

Use as a rocket fuel[edit]

European space companies have researched using light hydrocarbons with liquid oxygen as a relatively high performing liquid rocket propellant combination that would also be less toxic than the commonly used MMH/NTO (monomethylhydrazine/nitrogen tetroxide). Their research showed[citation needed] that propyne would be highly advantageous as a rocket fuel for craft intended for low Earth orbital operations. They reached this conclusion based upon a specific impulse expected to reach 370 s with oxygen as the oxidizer, a high density and power density—and the moderate boiling point, which makes the chemical easier to store than fuels that must be kept at extremely low temperatures. (See cryogenics.)

Organic chemistry[edit]

Propyne is a convenient three-carbon building block for organic synthesis. Deprotonation with n-butyllithium gives propynyllithium. This nucleophilic reagent adds to carbonyl groups, producing alcohols and esters.[5] Whereas purified propyne is expensive, MAPP gas could be used to cheaply generate large amounts of the reagent.[6]

Propyne, along with 2-butyne, is also used to synthesize alkylated hydroquinones in the total synthesis of vitamin E.[7]


  1. ^ a b c d e f g "NIOSH Pocket Guide to Chemical Hazards #0392". National Institute for Occupational Safety and Health (NIOSH). 
  2. ^ a b Peter Pässler, Werner Hefner, Klaus Buckl, Helmut Meinass, Andreas Meiswinkel, Hans-Jũrgen Wernicke, Günter Ebersberg, Richard Müller, Jürgen Bässler, Hartmut Behringer, Dieter Mayer, "Acetylene" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim 2007 (doi:10.1002/14356007.a01 097.pub2).
  3. ^ Keiser, Edward & Breed, Mary (1895). "The Action of Magnesium Upon the Vapors of the Alcohols and a New Method of Preparing Allylene". The Journal of the Franklin Institute. CXXXIX: 304–309. doi:10.1016/0016-0032(85)90206-6. Retrieved 20 February 2014. 
  4. ^ Reiser, Edward II. (1896). "The preparation of Allylene, and the Action of Magnesium upon Organic Compounds". The Chemical News and Journal of Industrial Science. LXXIV: 78–80. Retrieved 20 February 2014. 
  5. ^ Michael J. Taschner, Terry Rosen, and Clayton H. Heathcock (1990). "Ethyl Isocrotonate". Org. Synth.  ; Coll. Vol. 7, p. 226 
  6. ^ US patent 5744071, Philip Franklin Sims, Anne Pautard-Cooper, "Processes for preparing alkynyl ketones and precursors thereof", issued 1996-11-19 
  7. ^ Reppe, Walter; Kutepow, N & Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English 8 (10): 727–733. doi:10.1002/anie.196907271. Retrieved 26 December 2013. 

External links[edit]