Propadiene () or allene () is the
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
with the formula . It is the simplest
allene
In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon atoms (, where R is hydrogen, H or some organyl group). Allenes are classified as diene#Classes, cumulated dienes ...
, 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
Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melting, melt the parts together and allow them to cool, causing Fusion welding, fusion. Co ...
.
Production and equilibrium with methylacetylene
Propadiene exists in equilibrium with
methylacetylene (propyne) 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
Catalysis () is the increase in reaction rate, rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst ...
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 (paired with
propyne) detected in Titan's atmosphere, after
HCN-
HNC.
References
{{Authority control
Fuel gas
Alkadienes
Cumulated dienes