Potassium cyanide

Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and buffing.

Chemical properties

Potassium cyanide is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase, hence blocking oxidative phosphorylation. This prevents the body from using oxygen and causes death.

Production

Potassium cyanide is produced by treating hydrogen cyanide with a 50% aqueous solution of potassium hydroxide, followed by evaporation of the solution in a vacuum:

HCN + KOH → KCN + H2O

About 50,000 tons of potassium cyanide are produced yearly.

Applications

Gold mining

In gold mining, KCN forms the water-soluble salt gold cyanide along with sodium cyanide (NaCN). The gold can then be removed from the solution with a zinc electrode.

Organic synthesis

KCN is used as a nucleophile in the manufacture of nitriles.

Electroplating

KCN is used in electroplating and as a polishing agent in the preparation of metallic surfaces.

Toxicity

Potassium cyanide is highly toxic. The moist solid emits small amounts of hydrogen cyanide due to hydrolysis, which smells like bitter almonds. Not everyone, however, can smell this odor: the ability to do so is a genetic trait.

References

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