Potassium Cyanide or KCN is a colorless compound looks similar to sugar and is highly soluble in water. KCN is mostly used is gold mining, organic synthesis, and electroplating purposes. It is also used for chemical gliding and buffing in the jewelry department. KCN is highly toxic in nature. It emits tiny amounts of hydrogen cyanide because of hydrolysis which smells like bitter almonds. It tastes acrid with a burning sensation.
How is it produced?
KCN is produced by adding hydrogen cyanide with an aqueous solution of potassium hydroxide which is then further followed by the solution evaporated in a vacuum. The chemical formula looks like:
HCN + KOH → KCN + H2O
You will be surprised to know that about 50,000 tons of KCN is produced on a yearly basis.
What is the structure of KCN?
When it comes to the aqueous solution, the KCN is dissociated into the hydrated potassium or K+ ions and cyanide or CN- ions. The most common form of solid KCN is stable at the atmospheric pressure and temperature. It also has the similar cubic crystal structure like sodium chloride or NaCl, where each potassium ion is surrounded by 6 cyanide ions and vice versa. Albeit the cyanide ions are diatomic, and less symmetric than chloride, they tend to rotate so fast that their time averaged shape is deemed spherical. When the temperature is low and the pressure is high, this free rotation is obstructed, which results in a less symmetrical crystal shape with cyanide ions organized in sheets.
KCN and NaCN or sodium cyanide is used in organic synthesis for making nitriles and carboxylic acids. It is also used in synthesizing in the hydratoins which is useful in synthetic intermediates when it is reacted with a carbonyl compound like aldehyde or ketone when ammonium carbonate is involved as well. KCN is also useful in a photographic fixer when the process of wet plate collodion process. It also dissolves silver. This is helpful in revealing and stabilizing the image which makes it no longer sensitive to light. Nowadays, the photographers use less toxic filters, but KCN is used nonetheless.
Potassium gold cyanide
When it comes to gold mining, KCN creates a water soluble salt called gold potassium cyanide and potassium hydroxide from gold metal which involves oxygen as well. NaCN uses a similar process to produce sodium gold cyanide (NaAu(CN2)).