Methylacetylene.html



Methylacetylene
IUPAC name	Prop-1-yne
Other names	Methylacetylene Methyl acetylene Propyne
Identifiers
CAS number	74-99-7
SMILES	CC#C
Properties
Molecular formula	C3H4
Molar mass	40.0639 g/mol
Density	0.53 g/cm³
Melting point	-102.7 °C, 170 K, -153 °F
Boiling point	-23.2 °C, 250 K, -10 °F
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Methylacetylene (propyne) is an alkyne with the chemical formula CH₃C≡CH. It is a component of MAPP gas along with its isomer 1,2-propadiene (allene), which is commonly used in gas welding. Unlike acetylene, methylacetylene can be safely condensed.¹

Production and equilibrium with allene

Methylacetylene exists in equilibrium with allene, the mixture of methylacetylene and propadiene being called MAPD:

H₃CC≡CH ⇌ H₂C=C=CH₂

K_eq = 0.22 (270 °C), 0.1 K (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.¹ MAPD interferes with the catalytic polymerization of propene.

Use as a rocket fuel

Research by European space concerns into using light hydrocarbons with liquid oxygen as a relatively high performing propellant combination which would also be less toxic than the commonly used MMH/NTO (monomethylhydrazine/nitrogen tetroxide) systems, showed that propyne would be highly advantageous as a rocket fuel for craft intended for low Earth orbital operations. This conclusion was reached based upon a specific impulse expected to reach 370 s if oxygen is used as oxidizer, a high density, and energy/volume ratio, and the moderate boiling point, which causes the chemical to present fewer problems in storage than for example a fuel that needs to be kept at extremely low temperatures. (See cryogenics.)

Organic chemistry

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.² Whereas purified propyne is expensive, MAPP gas can be used to cheaply generate large amounts of the reagent. ³

References

1. ^ ^{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. 10.1002/14356007.a01 097.pub2
2. ^ Michael J. Taschner, Terry Rosen, and Clayton H. Heathcock (1990). "Ethyl Isocrotonate". Org. Synth.; Coll. Vol. 7: 226. 
3. ^ US5,744,071 (PDF version) (1996-11-19) Philip Franklin Sims, Anne Pautard-Cooper, Processes for preparing alkynyl ketones and precursors thereof. 

• German Aerospace Center
• Nova Chemicals