Propadiene

Propadiene or allene is the organic compound with the formula. It is the simplest allene, i.e. a compound with two adjacent carbon double bonds. As a constituent of MAPP gas, it has been used as a fuel for specialized welding.

Production and equilibrium with methylacetylene

Propadiene exists in equilibrium with methylacetylene and the mixture is sometimes called MAPD for methylacetylene-propadiene:
for which at 270 °C or 0.1 at 5 °C.
MAPD is produced as a side product, often an undesirable one, of dehydrogenation of propane to produce propene, an important feedstock in the chemical industry. MAPD interferes with the catalytic polymerization of propene.

Occurrence in Space

In 2019 it was announced that propadiene had been detected in the atmosphere of Saturn's moon Titan using the NASA Infrared Telescope Facility. This was the first time that propadiene had been detected in space, and the second structural isomeric pair detected in Titan's atmosphere, after HCN-HNC.