SODIUM CYANIDE (NACN): STRUCTURE, PROPERTIES, RISKS, USES - CHEMISTRY - 2025

The sodium cyanide is an inorganic salt formed by a sodium cation Na ⁺ and a cyanide anion CN ^-. Its chemical formula is NaCN. Also known as sodium cyanide, it is a white crystalline solid. It is hygroscopic, that is, it absorbs water from the environment, and its crystals are cubic like sodium chloride NaCl.

When dissolved in water it tends to form hydrogen cyanide HCN. Its solutions dissolve gold and silver easily. This characteristic makes it used to extract gold and silver from its minerals. The solutions used for this purpose are recycled, that is, they are reused several times.

Solid NaCN sodium cyanide. L26. Source: Wikimedia Commons.

However, some of the cyanide manages to escape to certain waste ponds, which represents a danger to wildlife and to humans, as cyanide is very toxic and can cause death.

NaCN is used in the chemical industry as an intermediate to prepare various types of compounds, such as dyes, agricultural chemicals, and drugs or medicines.

Sodium cyanide is a very dangerous compound as it can cause death, so it must be handled with extreme caution.

Structure

Sodium cyanide is made up of a Na + ion and a CN- ion.

Structure of the NaCN sodium cyanide molecule. Arrowsmaster, Source: Wikimedia Commons.

The cyanide ion has a carbon C and a nitrogen N atom joined together by a triple bond.

Ions that make up sodium cyanide NaCN. Epop. Source: Wikimedia Commons.

NaCN has the same crystalline structure as NaCl, so its crystals are cubic.

Nomenclature

-Sodium cyanide

-Sodium cyanide

Properties

Physical state

Hygroscopic white crystalline solid (absorbs water from the environment).

Molecular weight

49.007 g / mol

Melting point

563.7 ºC

Boiling point

1496 ºC

Flashpoint

It is not flammable. But if it is exposed to a fire, HCN hydrogen cyanide and nitrogen oxides are produced.

Density

1,595 g / cm ³ at 20 ºC

Solubility

Very soluble in water: 48 g / 100 mL at 10ºC, 82 g / 100 mL at 35ºC. Slightly soluble in alcohol

Dissociation constant

Hydrolyzes in aqueous solution generating hydrogen cyanide HCN. The constant of this hydrolysis is K _h = 2.5 x 10 ^-5.

pH

Aqueous NaCN solutions are strongly alkaline

Chemical properties

When dissolved in water, it separates into its Na ⁺ and CN ^- ions. In aqueous solution, the cyanide ion CN ^- takes a proton H ⁺ from the water H ₂ O, forming HCN and an ion OH ^-, so the solution becomes alkaline.

CN ^- + H ₂ O → HCN + OH ^-

For this reason, its aqueous solutions decompose rapidly when stored, forming hydrogen cyanide HCN.

It is corrosive towards aluminum. Their solutions readily dissolve gold Au and silver Ag in the presence of air.

It is a chelating agent since the cyanide anion CN ^- can easily bind to other metals, such as silver, gold, mercury, zinc, cadmium, etc.

It has a faint smell of bitter almonds.

Risks

It must be handled with great care. It is a highly poisonous compound, inhibits important metabolic processes, and leads to death by ingestion, inhalation, absorption through the skin or contact with the eyes.

If inhaled, NaCN dissolves in the mucosa of the respiratory tract and passes into the bloodstream. The cyanide ion of NaCN has a strong affinity for iron in the oxidation state of +3, that is, the ferric cation Fe ³⁺.

When cyanide is absorbed, it reacts rapidly with the Fe ³⁺ of an important enzyme in the mitochondria of cells (cytochrome oxidase), preventing certain processes of its respiration from taking place.

Therefore, cellular respiration is inhibited or slowed down and cytotoxic hypoxia results. It means that cells and tissues are unable to use oxygen, especially brain and heart cells.

In this way, permanent or lethal damage to the body occurs. This can occur in both humans and animals.

If ingested, it causes congestion of the blood vessels and corrosion of the gastric mucosa, in addition to the aforementioned.

NaCN Sodium Cyanide can kill. Author: OpenIcons. Source: Pixabay.

It is not combustible, but in contact with acids, it releases HCN which is highly flammable and toxic.

If it melts with nitrites or chlorates it can explode.

Obtaining

It can be obtained with sodium Na, ammonia NH ₃ and carbon C. Sodium reacts with ammonia to give sodium amide NaNH ₂:

2 Na + 2 NH ₃ → 2 NaNH ₂ + H ₂ ↑

Sodium amide is heated with charcoal to 600 ° C and produces sodium cyanamide Na ₂ NCN, which is then converted to sodium cyanide with charcoal at 800 ° C:

2 NaNH ₂ + C → 2 H ₂ ↑ + Na ₂ NCN

Na ₂ NCN + C → 2 NaCN

Another method is to melt calcium cyanamide CaNCN and carbon C with sodium carbonate Na ₂ CO ₃:

CaNCN + C + Na ₂ CO ₃ → CaCO ₃ + 2 NaCN

It can also be prepared by passing nitrogen gas N ₂ through a hot mixture of sodium carbonate Na ₂ CO ₃ and powdered carbon C, using iron Fe as a catalyst or accelerator of the reaction:

Na ₂ CO ₃ + 4 C + N ₂ → 2 NaCN + 3 CO ↑

Applications

In the extraction of gold and silver minerals. Consequences

Sodium cyanide has long been used to extract the metals gold and silver from their ores.

The cyanide used in the process is recycled, but something escapes into the waste pond along with the unrecovered heavy metals.

Birds, bats and other animals that drink from these cyanide lagoons have been poisoned.

There are records of a dam in Romania that isolated a waste pond and was damaged by a weather event.

As a consequence, tons of cyanide were released to the Sasar river and nearby aquifer systems such as the Lapus, Somes, and Tisza rivers, ending in the Danube.

This caused a cascade of animal deaths, or in other words, an ecological disaster.

Mining of gold with cyanide in New Zealand around the year 1918. You can see the amount of polluted water, which was discharged into nearby rivers. National Library NZ on The Commons. Source: Wikimedia Commons.

In the production of other chemical compounds

NaCN sodium cyanide is used in the synthesis of various types of organic compounds.

For example, pigments and colorants (including optical brighteners), compounds for use in agriculture or agrochemicals and various pharmaceuticals are prepared.

It is also used to obtain chelating or sequestering agents for metal ions.

Compounds called nitriles are prepared with sodium cyanide NaCN, which when treated with a hot acidic or alkaline aqueous solution allows obtaining carboxylic acids.

Preparation of a carboxylic acid using sodium cyanide NaCN. Roland Mattern. Source: Wikimedia Commons.

It enables the preparation of fatty acids with cyano groups, heavy metal cyanides and hydrocyanic acid or HCN hydrogen cyanide.

In the metals industry

NaCN is used in solutions used in electroplating or electroplating of metals (coating of metals with others) for example zinc.

It is a component of hardened steel. It also works in metal cleaning.

In other uses

Sodium cyanide is an intermediate in the manufacture of nylon.

It is used for the separation of minerals by flotation with foam.

Applications out of use, questioned or very rare

NaCN was used to kill rodents, such as rabbits and rats, and their burrows, and to kill termite nests.

Currently it is used occasionally to eliminate coyotes, foxes and wild dogs. It is used in capsule form as single or multiple doses on rangelands, hunting grounds, and forests.

Due to its extreme toxicity, NaCN should only be used by trained people.

This use is considered very dangerous for humans, but there are those who still use it.

Wildlife should not be eliminated, as these animals already struggle to survive in difficult conditions. Author: MaxWdhs. Source: Pixabay.

In agriculture it was formerly used to fumigate citrus fruit trees and other fruits. It was also used as an insecticide and miticide (eliminator of mites) to be applied after harvest, for non-stored citrus or for the fumigation of trucks used to transport them. It was also used to spray ships, railroad cars, and warehouses.

All of these uses have been questioned due to the high toxicity of sodium cyanide. For this reason, it is no longer used or only very rarely and under very controlled conditions.

References

1. US National Library of Medicine. (2019). Sodium cyanide. Recovered from pubchem.ncbi.nlm.nih.gov.
2. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Fourth Edition. John Wiley & Sons.
3. Hurst, HE and Martin, MD (2017). Toxicology. Cyanide. In Pharmacology and Therapeutics for Dentistry (Seventh Edition). Recovered from sciencedirect.com.
4. Coppock, RW and Dziwenka, M. (2015). Threats to Wildlife by Chemical Warfare Agents. In Handbook of Toxicology of Chemical Warfare Agents (Second Edition). Recovered from sciencedirect.com.
5. Morrison, RT and Boyd, RN (2002). Organic Chemistry. 6th Edition. Prentice-Hall.