KCN and
sodium cyanide (NaCN) are widely used in
organic synthesis for the preparation of
nitriles and
carboxylic acids, particularly in the
von Richter reaction. It also finds use for the synthesis of
hydantoins, which can be useful synthetic intermediates, when reacted with a carbonyl compound such as an
aldehyde or
ketone in the presence of
ammonium carbonate. KCN is used as a
photographic fixer in the wet plate
collodion process. The KCN dissolves silver where it has not been made insoluble by the developer. This reveals and stabilizes the image, making it no longer sensitive to light. Modern wet plate photographers may prefer less toxic fixers, often opting for
sodium thiosulfate, but KCN is still used. In the 19th century, cyanogen
soap, a preparation containing potassium cyanide, was used by
photographers to remove
silver stains from their hands.
Potassium gold cyanide In
gold mining, KCN forms the water-soluble salt
potassium gold cyanide (or gold potassium cyanide) and potassium hydroxide from gold metal in the presence of oxygen (usually from the surrounding air) and water: :
Analytical chemistry In analytical chemistry, potassium cyanide is used as complexing agent for chemical analysis of zinc in water and wastewater. The cyanide group complexes zinc and other heavy metals, which is separated and analyzed in a spectro-photometer. ==Toxicity==