HCn

Hydrogen cyanide (HCN) is a colorless, highly toxic chemical that is gaseous at room temperature and highly volatile. It has a faint bitter almond odor that some people can detect, though odor perception varies. In water, HCN is a weak acid with a pKa around 9.2, existing mainly as HCN in neutral solution and as cyanide (CN−) under basic conditions.

The molecule is linear, with the structure H–C≡N. The cyano group (−CN) is the reactive feature responsible for much of its chemistry. HCN is reactive toward electrophiles and forms a variety of nitrile compounds, serving as a key building block in organic synthesis.

Industrial production and uses: Hydrogen cyanide is manufactured on a large scale by catalytic processes that combine ammonia, methane (or other hydrocarbons), and oxygen, such as the Andrussow process. It is a versatile precursor to nitrile compounds, including adiponitrile and acrylonitrile, which are used to produce polymers such as nylon and polyacrylonitrile. It can also be generated in smaller quantities for specialized syntheses and has historically seen use in fumigants and other applications under strict controls.

Safety and handling: HCN is extremely toxic; inhalation can rapidly inhibit cellular respiration and be fatal at sufficient concentrations. It is volatile and flammable, requiring strict containment, proper ventilation, continuous monitoring, and appropriate personal protective equipment. Exposure is tightly regulated, and safety protocols are essential in all uses and handling of the substance.