Hydrogen cyanide is a colorless, extremely poisonous gas with the chemical formula HCN, consisting of hydrogen bonded to a carbon–nitrogen triple bond. First isolated in 1782 from Prussian blue dye by Swedish chemist Carl Wilhelm Scheele (who may have died from exposure to it), this deadly compound has a distinctive bitter almond odor that 40% of people cannot detect due to genetics. Despite being one of the most rapidly acting poisons known – interfering with cellular respiration by binding to cytochrome c oxidase – hydrogen cyanide plays vital industrial roles in producing nylon, plastics, and pesticides, with over 1 million tons manufactured annually. Nature also produces HCN in surprising places, from apple seeds and cassava roots to interstellar space, making this simple molecule both a feared poison that has been used in gas chambers and chemical weapons, and an essential building block for life’s chemistry.

Find a review of the 50 most important industrial gases here.

20 Fun Facts About Hydrogen Cyanide

Beyond the basics above, what else should we know about Hydrogen Cyanide? Check out the 20 fun facts below!

1. HCN is the only chemical weapon that’s lighter than air, rising and dispersing quickly which limited its military effectiveness.
2. The carbon-nitrogen triple bond in HCN is the strongest bond in any stable molecule at 1,078 kJ/mol.
3. Cassava root, a staple food for 800 million people, contains enough cyanide precursors to be lethal if not properly processed.
4. Hydrogen cyanide polymerizes explosively into a dark brown solid at room temperature without stabilizers like sulfur dioxide.
5. Cigarette smoke contains 10-400 micrograms of HCN per cigarette, more than any other consumer product.
6. The molecule is perfectly linear and rotates 88.6 billion times per second, creating unique rotational spectra.
7. Some millipedes produce HCN as a defense mechanism, secreting enough to create a visible vapor cloud when threatened.
8. Hydrogen cyanide forms in car fires when polyurethane foam burns, causing more fire deaths than carbon monoxide.
9. The compound exists in Saturn’s moon Titan’s atmosphere, where it forms complex organic polymers in the upper atmosphere.
10. Apple seeds contain amygdalin which releases HCN when chewed – you’d need to eat 200 seeds to risk poisoning.
11. B-12 vitamin contains a cyanide group safely bound to cobalt, making it the only vitamin with a poison component.
12. HCN was likely crucial for origin of life, forming amino acids and nucleotide bases in Miller-Urey type experiments.
13. The bitter almond smell is detectable at 2-10 ppm, but toxic effects begin at 20 ppm with death at 300 ppm.
14. Firefighters’ blood contains special cyanide antidote kits since HCN from burning plastics is a major threat.
15. Hydrogen cyanide boils at 25.6°C (78°F), meaning it can be a liquid on a warm day but gas at room temperature.
16. The Nazis used Zyklon B (HCN absorbed on pellets) in gas chambers, consuming 500 tons during the Holocaust.
17. Gold mining uses 90,000 tons of HCN annually to extract gold via cyanidation, recovering 0.001% gold from ore.
18. Comets contain frozen HCN that sublimates near the Sun, creating spectacular cyan-colored comas visible in telescopes.
19. The molecule absorbs infrared at exactly 3,312 cm⁻¹, allowing satellites to track industrial emissions globally.
20. Some bacteria near gold deposits are immune to cyanide and actually metabolize it, covering themselves in gold nanoparticles.

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