What Is Cyanide? Structure, Occurrence, and Its Impact in Daily Life
Cyanide is defined as any compound that contains the monovalent combining group CN. In inorganic cyanides, such as sodium cyanide (NaCN), the cyanide group is present as the negatively charged cyanide ion. The compounds, which are regarded as salts of hydrocyanic acid, are said to be highly toxic. Organic cyanides are generally referred to as nitriles, and in these, the C.N. The group is further connected to the carbon-containing group, such as methyl (CH3) in methyl cyanide, by a covalent bond (otherwise called acetonitrile).
About Cyanide
Hydrocyanic acid, which is also called hydrogen cyanide (HCN), is defined as a highly volatile liquid. HCN is produced using the Andrussow process, which involves mixing ammonia, methane, and oxygen with a platinum metal catalyst. The HCN product can be used to prepare acrylonitrile that is used in the production of synthetic rubber, acrylic fibres, and plastics.
Cyanide chemicals are employed in several chemical processes, including fumigation, case hardening of steel and iron, electroplating, and also the concentration of ores. Substances that can be chemically converted into cyanide in nature are present in certain seeds, such as the seeds of apples (Malus domestica) and the pit of the black cherry (Prunus serotina).
Poisoning of cyanide results from ingesting HCN salts or inhaling HCN. Since cyanide works so rapidly, the speed at which an antidote, such as sodium nitrite, amyl nitrite, or sodium thiosulfate solution, is administered is vital in preventing death.
Nomenclature and Etymology
In the IUPAC nomenclature, organic compounds that contain a –C≡N functional group are referred to as nitriles. Therefore, nitriles are organic compounds. Examples of nitrile are given as acetonitrile, CH3CN, which is also called methyl cyanide. Usually, nitriles do not release cyanide ions. A functional group is having cyanide and hydroxyl bonded to similar carbon known as cyanohydrin. Unlike nitriles, cyanohydrins do release hydrogen cyanide. In inorganic chemistry, salts that contain the C≡N− ion are referred to as cyanides. However, the cyanide ion holds a carbon atom, which is usually not considered organic.
Since it was first obtained by heating the pigment known as Prussian blue, the term is derived from the Greek ‘kyanos’, which means dark blue.
Occurrence
Cyanides are produced by certain fungi, algae, and bacteria, and they are found in many plants. Cyanides are also found in substantial amounts in fruit stones and certain seeds. For example, those of apricots, bitter almonds (almonds cyanide), peaches, and apples. Chemical compounds, which release cyanide are called cyanogenic compounds. Usually, cyanides are bound to sugar molecules in plants in the form of cyanogenic glycosides, and they defend the plant against herbivores. Cassava roots (which are also called Manioc) are an important potato-like food grown in tropical countries (and the base where tapioca is made) also have cyanogenic glycosides.
The Madagascar bamboo, which is called Cathariostachys madagascariensis, produces cyanide as a grazing deterrent. As a result, the golden bamboo lemur, which consumes the bamboo, has gained a high cyanide tolerance.
Toxicity
Several cyanides are particularly poisonous. The cyanide anion is thought to be an inhibitor of cytochrome c oxidase (also known as aa3), which is present in the inner membrane of eukaryotic cells' mitochondria and is the electron transport chain’s fourth complex. Within this protein, it attaches to the iron. The binding of cyanide to this enzyme also prevents the transport of electrons from cytochrome-c to oxygen. Resultantly, the electron transport chain is disrupted, which means that the cell can no longer aerobically produce ATP for energy. Heart and central nervous system tissues, which rely heavily on aerobic respiration, are particularly affected. Histotoxic hypoxia is an example.
Antidote
Hydroxocobalamin reacts with cyanide to produce cyanocobalamin that can be safely eliminated by kidneys. This method has the advantage of avoiding methemoglobin formation. The antidote kit is marketed as Cyanokit and was licenced by the US Food and Drug Administration in 2006.
Cyanide Uses or Applications
Medical Uses
The cyanide compound named sodium nitroprusside is mainly used in clinical chemistry to measure urine ketone bodies, primarily as a follow-up to diabetic patients. On occasion, it is also used in situations of medical emergencies to produce a rapid decrease in blood pressure in humans. Also, it is used as a vasodilator in vascular research. The cobalt present in artificial vitamin B-12 comprises a cyanide ligand as an artifact of the purification process, and this must be removed by the body prior to the vitamin molecule being activated for biochemical use. The copper cyanide compound was briefly used by Japanese physicians to treat leprosy and tuberculosis during World War I.
Pest Control
M44 cyanide devices are used in the U.S. to kill coyotes, including other canids. Also, cyanide is used for pest control in New Zealand, specifically for possums, which is an introduced marsupial that threatens the conservation of native species and spreads tuberculosis amongst cattle. Possums may become bait shy, but the use of the pellets containing the cyanide reduces bait shyness.
FAQs on Cyanide: Key Facts, Uses & Safety in Chemistry
1. What is cyanide and what is its chemical formula?
Cyanide is a chemical compound that contains a cyano group (C≡N), which consists of a carbon atom triple-bonded to a nitrogen atom. In chemistry, the term most often refers to the cyanide ion, which has the chemical formula CN⁻. It can exist as simple salts like potassium cyanide (KCN) or as part of more complex molecules.
2. What are the major industrial and chemical applications of cyanide?
Cyanide has several critical applications in various industries. Its primary uses include:
- Mining: It is used extensively in the extraction of gold and silver from their ores through a process called cyanidation.
- Electroplating: Cyanide solutions are used in electroplating to provide a strong, smooth, and corrosion-resistant metal finish.
- Chemical Synthesis: It serves as a key starting material in the manufacturing of various organic compounds, including nylon, acrylics, and certain pharmaceuticals.
- Pest Control: In some regions, it is used under strict regulation for controlling pests.
3. How is the Prussian Blue test used to detect the presence of cyanide ions in a laboratory?
The Prussian Blue test is a classic qualitative analysis method to confirm the presence of cyanide. The process involves adding iron(II) sulfate to the solution suspected of containing cyanide, which forms a ferrocyanide complex. Then, upon adding a small amount of iron(III) salt and acidifying the mixture, the formation of a deep blue precipitate, known as Prussian blue (Ferric ferrocyanide), provides a positive result for cyanide.
4. What are some natural sources of cyanide in the environment?
Cyanide is not only a man-made chemical but also occurs naturally. It is produced by various bacteria, fungi, and algae. More commonly, it is found in the form of cyanogenic glycosides in over 2,000 plant species. Notable examples include the seeds or pits of certain fruits like apples, apricots, and peaches, as well as in cassava roots and raw almonds. In these plants, the cyanide is released only when the seeds are crushed or the plant material is chewed.
5. What are the essential safety precautions for handling cyanide compounds in a chemistry lab?
Due to its high toxicity, handling cyanide requires strict safety measures. Key precautions include:
- Working in a well-ventilated fume hood to prevent inhalation of any dust or gas.
- Wearing appropriate Personal Protective Equipment (PPE), including chemical-resistant gloves, safety goggles, and a lab coat.
- Never allowing cyanides to come into contact with acids, as this reaction produces highly toxic hydrogen cyanide (HCN) gas.
- Having an emergency response plan and ensuring an antidote kit is readily available.
6. Why is the cyanide ion (CN⁻) classified as both a pseudohalide and a strong field ligand?
The cyanide ion has a dual classification due to its unique chemical properties. It is called a pseudohalide because it mimics the behaviour of halide ions (like Cl⁻ or Br⁻) in several ways: it has a single negative charge, it forms an insoluble salt with silver (AgCN), and it can form a dimeric molecule called cyanogen, (CN)₂, similar to Cl₂. It is considered a strong field ligand in coordination chemistry because it forms a very strong coordinate bond with metal ions, causing a large crystal field splitting. This strong interaction significantly influences the magnetic and electronic properties of the resulting metal complexes.
7. How does cyanide's ability to form stable complexes explain its use in gold extraction?
Cyanide's role in gold extraction (the MacArthur-Forrest process) is a perfect example of coordination chemistry in action. Gold is a very unreactive metal. However, cyanide ions are powerful complexing agents that react with elemental gold in the presence of oxygen and water. This reaction forms a highly stable and water-soluble complex ion, the dicyanoaurate(I) ion, [Au(CN)₂]⁻. By converting the solid, unreactive gold into a soluble complex, it can be easily separated (leached) from the crushed ore.
8. At a molecular level, what makes cyanide poisoning so rapid and lethal?
Cyanide's toxicity stems from its ability to shut down cellular respiration. Specifically, the cyanide ion binds with extremely high affinity to the iron atom within cytochrome c oxidase, a crucial enzyme in the mitochondrial electron transport chain. This binding prevents the enzyme from transferring electrons to oxygen, the final step in aerobic respiration. As a result, cells can no longer produce ATP (the body's main energy currency) through this process, leading to rapid oxygen deprivation at the cellular level, cytotoxic hypoxia, and swift cell death, particularly affecting the heart and central nervous system.
9. What is the fundamental difference between an organic cyanide (nitrile) and an inorganic cyanide salt?
The key difference lies in the type of chemical bond. An inorganic cyanide is an ionic salt, such as sodium cyanide (NaCN) or potassium cyanide (KCN), where the cyanide ion (CN⁻) is ionically bonded to a metal cation (like Na⁺ or K⁺). In contrast, an organic cyanide, also known as a nitrile, is a covalent compound where the cyano group (-C≡N) is covalently bonded to a carbon-based group (an alkyl or aryl group), represented as R-C≡N. This difference in bonding leads to vastly different chemical properties, reactivity, and applications.
