Propadan

Propadan is an unsaturated hydrocarbon with the molecular formula C3H4. It is a member of the alkyne family and is also known as 1,2‑propadiene or propadienyl. The compound exists as a colorless, volatile liquid at room temperature, but it readily vaporises and is usually handled as a gas under pressure. Its physical properties include a boiling point of –34 °C and a melting point of –161 °C, making it a gaseous substance under standard laboratory conditions.

The molecule contains a cumulated double bond system, consisting of two adjacent double bonds and one terminal hydrogen atom on each of the two end carbon atoms. This arrangement gives propadan a high degree of reactivity, particularly in electrophilic addition reactions. It undergoes polymerisation to form polypropadiene, a material used in plastics and coatings. Propadan is also a useful building block in the synthesis of other organic compounds, such as acrylic acid derivatives and certain heterocyclic structures.

Industrial applications of propadan are limited compared with more common alkanes. It is sometimes employed as a protective gas in welding and cutting processes, where it can act as a shielding medium that reduces oxidation of the metal surface. Additionally, propadan is used in laboratory settings as a reagent for functional group transformations, such as alkene synthesis via hydroboration–oxidation or the generation of intermediates for metal‑catalysed cross‑coupling reactions.

Safety considerations for propadan include its flammability and the potential for respiratory irritation. Proper ventilation is necessary to avoid buildup of flammable vapours, and it should be stored in well‑sealed containers that are resistant to high pressure. As with many small alkyne derivatives, propadan can form toxic fumes when burnt, and inhalation of its combustion products should be avoided.