Methylacetylene

Methylacetylene (propyne) is an alkyne with the chemical formula H3C≡CH. It is a component of MAPP gas along with its isomer 1,2-propadiene (allene), which is commonly used in gas welding.

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 370s if oxygen is used as oxidiser, 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.)

Use in organic chemistry
Propyne is a convenient three-carbon building block for synthesis. When propyne is condensed and treated with n-Butyllithium, solid propynyllithium is formed. This nucleophilic reagent can then be added to a carbonyl, producing a secondary alcohol. While purified propyne is expensive, in this reaction it can be replaced with MAPP gas to cheaply generate large amounts of the reagent.