Propyne ( methylacetylene) is an alkyne with the chemical formula . It is a component of MAPP gas—along with its isomer propadiene (allene), which was commonly used in gas welding. Unlike acetylene, propyne can be safely Condensation.[Peter Pässler, Werner Hefner, Klaus Buckl, Helmut Meinass, Andreas Meiswinkel, Hans-Jürgen Wernicke, Günter Ebersberg, Richard Müller, Jürgen Bässler, Hartmut Behringer, Dieter Mayer, "Acetylene" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim 2007 ().]
Production and equilibrium with propadiene
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.
[ MAPD interferes with the catalytic polymerization of propene.
]
Laboratory methods
Propyne can also be synthesized on laboratory scale by reducing 1-propanol,
Use as a rocket fuel
European space companies have researched using light hydrocarbons with liquid oxygen, 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 second with oxygen as the oxidizer, a high density and power density—and the moderate boiling point, which makes the chemical easier to store than that must be kept at extremely low temperatures.
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 .
Propyne, along with 2-butyne, is also used to synthesize alkylated in the total synthesis of vitamin E.
The chemical shift of an alkynyl proton and propargylic proton generally occur in the same region of the 1H NMR spectrum. In propyne, these two signals have almost exactly the same chemical shifts, leading to overlap of the signals, and the 1H NMR spectrum of propyne, when recorded in deuteriochloroform on a 300 MHz instrument, consists of a single signal, a sharp singlet resonating at 1.8 ppm.
In Astrophysics
Propyne has been detected in multiple astrophysical objects following its first observation in 1973 in the Galactic Center Molecular cloud Sgr B2 using radio astronomy techniques.
Propyne has been detected by infrared spectroscopy in the Redox of the Solar System in the Solar System, including on Jupiter in 2000
Notes
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