|Molar mass||40.0639 g/mol|
|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)|
|US health exposure limits (NIOSH):|
|TWA 1000 ppm (1650 mg/m3)|
|TWA 1000 ppm (1650 mg/m3)|
IDLH (Immediate danger
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is: / ?)(|
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.
Production and equilibrium with propadiene
Propyne exists in equilibrium with propadiene, the mixture of propyne and propadiene being called MAPD:
- H3CC≡CH ⇌ H2C=C=CH2
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. MAPD interferes with the catalytic polymerization of propene.
Use as a rocket fuel
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 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.)
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. Whereas purified propyne is expensive, MAPP gas could be used to cheaply generate large amounts of the reagent.
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- NIST Chemistry WebBook page for propyne
- German Aerospace Center
- Nova Chemicals
- CDC - NIOSH Pocket Guide to Chemical Hazards