Sodium cyanide
Encyclopedia
Sodium cyanide is an inorganic compound
with the formula
NaCN. This highly toxic colorless salt is used mainly in gold mining
but has other niche applications. It is an inorganic salt derived from neutralization reactions involving the weak acid
hydrogen cyanide.
Worldwide production was estimated at 500,000 tons in the year 2006. In former times, it was prepared by the Castner-Kellner process
involving the reaction of sodium amide
with carbon at elevated temperatures.
The structure of solid NaCN is related to that of sodium chloride
. The anions and cations are each six-coordinate (potassium chloride
(KCN) has a similar structure). Each Na+ forms pi-bonds to two CN- groups as well as two "bent" Na---CN and two "bent" Na---NC links.
Because the salt is derived from a weak acid, NaCN readily reverts back to HCN by hydrolysis
: the moist solid emits small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts. It is detoxified most efficiently with hydrogen peroxide
(H2O2) to produce sodium cyanate
(NaOCN) and water:
and other precious metals in mining. This application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water, producing the salt sodium gold cyanide (or gold sodium cyanide) and sodium hydroxide:
A similar process uses potassium cyanide
(KCN, a close relative of sodium cyanide) to produce potassium gold cyanide (KAu(CN2)).
Few other methods exist for this extraction process.
, cyanogen chloride
, and many nitrile
s. In organic synthesis
, cyanide, which is classified as a strong nucleophile
, is used to prepare nitrile
s, which occur widely in many specialty chemicals, including pharmaceuticals.
and in collecting jars used by entomologists.
, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis
then occurs as a consequence of anaerobic metabolism.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
NaCN. This highly toxic colorless salt is used mainly in gold mining
Gold mining
Gold mining is the removal of gold from the ground. There are several techniques and processes by which gold may be extracted from the earth.-History:...
but has other niche applications. It is an inorganic salt derived from neutralization reactions involving the weak acid
Weak acid
A weak acid is an acid that dissociates incompletely. It does not release all of its hydrogens in a solution, donating only a partial amount of its protons to the solution...
hydrogen cyanide.
Production and chemical properties
Sodium cyanide is produced by treating hydrogen cyanide with sodium hydroxide:- HCN + NaOH → NaCN + H2O
Worldwide production was estimated at 500,000 tons in the year 2006. In former times, it was prepared by the Castner-Kellner process
Castner-Kellner process
The Castner–Kellner process is a method of electrolysis on an aqueous alkali chloride solution to produce the corresponding alkali hydroxide, invented by American Hamilton Castner and Austrian Karl Kellner in the 1890s....
involving the reaction of sodium amide
Sodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...
with carbon at elevated temperatures.
- NaNH2 + C → NaCN + H2
The structure of solid NaCN is related to that of sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
. The anions and cations are each six-coordinate (potassium chloride
Potassium chloride
The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...
(KCN) has a similar structure). Each Na+ forms pi-bonds to two CN- groups as well as two "bent" Na---CN and two "bent" Na---NC links.
Because the salt is derived from a weak acid, NaCN readily reverts back to HCN by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
: the moist solid emits small amounts of hydrogen cyanide, which smells like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts. It is detoxified most efficiently with hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
(H2O2) to produce sodium cyanate
Cyanate
The cyanate ion is an anion with the chemical formula written as [OCN]− or [NCO]−. In aqueous solution it acts as a base, forming isocyanic acid, HNCO. The cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair...
(NaOCN) and water:
- NaCN + H2O2 → NaOCN + H2O
Sodium gold cyanide
Sodium cyanide is mainly used to extract goldGold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and other precious metals in mining. This application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air and water, producing the salt sodium gold cyanide (or gold sodium cyanide) and sodium hydroxide:
- 4 Au + 8 NaCN + O2 + 2 H2O → 4 Na[Au(CN)2] + 4 NaOH
A similar process uses potassium cyanide
Potassium cyanide
Potassium cyanide is an inorganic compound with the formula KCN. This colorless crystalline compound, 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...
(KCN, a close relative of sodium cyanide) to produce potassium gold cyanide (KAu(CN2)).
Few other methods exist for this extraction process.
Chemical feedstock
Several commercially significant chemical compounds are derived from cyanide, including cyanuric chlorideCyanuric chloride
Cyanuric chloride is the inorganic compound with the formula 3. This colorless solid is the chlorinated derivative of 1,3,5-triazine. It is the trimer of cyanogen chloride...
, cyanogen chloride
Cyanogen chloride
Cyanogen chloride is an inorganic compound with the formula NCCl. This linear, triatomic pseudohalogen is an easily condensed colorless gas. More commonly encountered in the laboratory is the related compound cyanogen bromide, a room-temperature solid that is widely used in biochemical analysis and...
, and many nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s. In organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, cyanide, which is classified as a strong nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
, is used to prepare nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s, which occur widely in many specialty chemicals, including pharmaceuticals.
Niche uses
Being highly toxic, sodium cyanide is used to kill or stun rapidly such as in illegal cyanide fishingCyanide fishing
Cyanide fishing is a method of collecting live fish mainly for use in aquariums, which involves spraying a sodium cyanide mixture into the desired fish's habitat in order to stun the fish...
and in collecting jars used by entomologists.
Toxicity
Cyanide salts are among the most rapidly acting of all known poisons. Cyanide is a potent inhibitor of respirationCellular respiration
Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...
, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis
Lactic acidosis
Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood accompanied by the buildup of lactate especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen , for example...
then occurs as a consequence of anaerobic metabolism.
External links
- Institut national de recherche et de sécurité (1997). "Cyanure de sodium. Cyanure de potassium". Fiche toxicologique n° 111, Paris:INRS, 6pp. (PDF file, in French)
- International Chemical Safety Card 1118
- Hydrogen cyanide and cyanides (CICAD 61)
- National Pollutant Inventory - Cyanide compounds fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- CSST (Canada)
- Sodium cyanide hazards to fish and other wildlife from gold