Cyanide

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Source: Wikipedia, the free encyclopedia.
This article is about the class of chemical compounds. For other uses, see Cyanide (disambiguation).
Not to be confused with Nitrile.

Cyanide anion
Space-filling model of the cyanide anion: carbon bound to smaller nitrogen atom
Names
Preferred IUPAC name
Cyanide
Systematic IUPAC name
Nitridocarbonate(II)
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
UNII
  • InChI=1S/CN/c1-2/q-1
    Key: XFXPMWWXUTWYJX-UHFFFAOYSA-N
  • [C-]#N
Properties
CN−
Molar mass 26.018 g·mol−1
Conjugate acid
 Hydrogen cyanide
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 The cyanide ion CN− is one of the most poisonous chemicals. It may cause death in minutes.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

In

triple-bonded to a nitrogen atom.[1]

In

Hydrocyanic acid, also known as hydrogen cyanide, or HCN, is a highly volatile
liquid that is produced on a large scale industrially. It is obtained by acidification of cyanide salts.

methyl (−CH3). Although nitriles generally do not release cyanide ions, the cyanohydrins
do and are thus toxic.

Bonding

The cyanide ion −C≡N is

isoelectronic with carbon monoxide −C≡O+ and with molecular nitrogen N≡N. A triple bond exists between C and N. The negative charge is concentrated on carbon C.[3][4]

Occurrence

In nature

Removal of cyanide from cassava in Nigeria.

Cyanides are produced by certain

bitter almonds, apricots, apples, and peaches.[5] Chemical compounds that can release cyanide are known as cyanogenic compounds. In plants, cyanides are usually bound to sugar molecules in the form of cyanogenic glycosides and defend the plant against herbivores. Cassava roots (also called manioc), an important potato-like food grown in tropical countries (and the base from which tapioca is made), also contain cyanogenic glycosides.[6][7]

The Madagascar bamboo Cathariostachys madagascariensis produces cyanide as a deterrent to grazing. In response, the golden bamboo lemur, which eats the bamboo, has developed a high tolerance to cyanide.

The

cysteinyl thiocyanate, the CN− donor.[8]

Interstellar medium

The

interstellar space.[9] Cyanogen, (CN)2, is used to measure the temperature of interstellar gas clouds.[10]

Pyrolysis and combustion product

Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-deficient conditions. For example, it can be detected in the exhaust of internal combustion engines and tobacco smoke. Certain plastics, especially those derived from acrylonitrile, release hydrogen cyanide when heated or burnt.[11]

Organic derivatives

Main article:
Nitriles
See also: Isocyanide

In IUPAC nomenclature, organic compounds that have a −C≡N functional group are called nitriles.[12][13] An example of a nitrile is acetonitrile, CH3−C≡N. Nitriles usually do not release cyanide ions. A functional group with a hydroxyl −OH and cyanide −CN bonded to the same carbon atom is called cyanohydrin (R2C(OH)CN). Unlike nitriles, cyanohydrins do release poisonous hydrogen cyanide.

Reactions

Protonation

Cyanide is basic. The pKa of hydrogen cyanide is 9.21. Thus, addition of

acids stronger than hydrogen cyanide to solutions of cyanide salts releases hydrogen cyanide
.

Hydrolysis

Cyanide is unstable in water, but the reaction is slow until about 170 °C. It undergoes hydrolysis to give ammonia and formate, which are far less toxic than cyanide:[14]

CN− + 2 H2O → HCO−2 + NH3

Cyanide hydrolase is an enzyme that catalyzes this reaction.

Alkylation

Because of the cyanide anion's high

methyl chloride). In general, organic cyanides are called nitriles. In organic synthesis, cyanide is a C-1 synthon; i.e., it can be used to lengthen a carbon chain by one, while retaining the ability to be functionalized.[15]

RX + CN− → RCN + X−

Redox

The cyanide ion is a

oxidized by strong oxidizing agents such as molecular chlorine (Cl2), hypochlorite (ClO−), and hydrogen peroxide (H2O2). These oxidizers are used to destroy cyanides in effluents from gold mining.[16][17][18]

Metal complexation

The cyanide anion reacts with

anion
can be attributed to its negative charge, compactness, and ability to engage in π-bonding.

Among the most important cyanide coordination compounds are the potassium ferrocyanide and the pigment Prussian blue, which are both essentially nontoxic due to the tight binding of the cyanides to a central iron atom.[20] Prussian blue was first accidentally made around 1706, by heating substances containing iron and carbon and nitrogen, and other cyanides made subsequently (and named after it). Among its many uses, Prussian blue gives the blue color to

blueprints, bluing, and cyanotypes
.

Manufacture

Main article: Hydrogen cyanide § Production and synthesis

The principal process used to manufacture cyanides is the

catalyst.[21][22]

2 CH4 + 2 NH3 + 3 O2 → 2 HCN + 6 H2O

Sodium cyanide, the precursor to most cyanides, is produced by treating hydrogen cyanide with sodium hydroxide:[14]

HCN + NaOH → NaCN + H2O

Toxicity

Main article: Cyanide poisoning

Many cyanides are highly toxic. The cyanide anion is an

aerobic respiration, such as the central nervous system and the heart, are particularly affected. This is an example of histotoxic hypoxia.[24]

The most hazardous compound is

ppm, is sufficient to cause death within minutes.[24]

Organic nitriles do not readily release cyanide ions, and so have low toxicities. By contrast, compounds such as trimethylsilyl cyanide (CH3)3SiCN readily release HCN or the cyanide ion upon contact with water.[25]

Antidote

Hydroxocobalamin reacts with cyanide to form cyanocobalamin, which can be safely eliminated by the kidneys. This method has the advantage of avoiding the formation of methemoglobin (see below). This antidote kit is sold under the brand name Cyanokit and was approved by the U.S. FDA in 2006.[26]

An older cyanide antidote kit included administration of three substances:

mitochondrial enzyme rhodanese. Thiocyanate is a relatively non-toxic molecule and is excreted by the kidneys. To accelerate this detoxification, sodium thiosulfate is administered to provide a sulfur donor for rhodanese, needed in order to produce thiocyanate.[27]

Sensitivity

Minimum risk levels (MRLs) may not protect for delayed health effects or health effects acquired following repeated sublethal exposure, such as hypersensitivity, asthma, or bronchitis. MRLs may be revised after sufficient data accumulates.[28]

Applications

Mining

Main article: Gold cyanidation

Cyanide is mainly produced for the

anions to form soluble derivatives, e.g., [Ag(CN)2]− (dicyanoargentate(I)) and [Au(CN)2]− (dicyanoaurate(I)).[14] Silver is less "noble"
than gold and often occurs as the sulfide, in which case redox is not invoked (no O2 is required). Instead, a displacement reaction occurs:

The "pregnant liquor" containing these ions is separated from the solids, which are discarded to a

tailing pond or spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction with zinc dust or by adsorption onto activated carbon. This process can result in environmental and health problems. A number of environmental disasters have followed the overflow of tailing ponds at gold mines. Cyanide contamination of waterways has resulted in numerous cases of human and aquatic species mortality.[29]

Aqueous cyanide is hydrolyzed rapidly, especially in sunlight. It can mobilize some heavy metals such as mercury if present. Gold can also be associated with arsenopyrite (FeAsS), which is similar to

iron pyrite (fool's gold), wherein half of the sulfur atoms are replaced by arsenic. Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide.[citation needed
]

Industrial organic chemistry

The second major application of alkali metal cyanides (after mining) is in the production of CN-containing compounds, usually nitriles. Acyl cyanides are produced from acyl chlorides and cyanide. Cyanogen, cyanogen chloride, and the trimer cyanuric chloride are derived from alkali metal cyanides.

Medical uses

The cyanide compound

vasodilator in vascular research. The cobalt in artificial vitamin B12 contains a cyanide ligand as an artifact of the purification process; this must be removed by the body before the vitamin molecule can be activated for biochemical use. During World War I, a copper cyanide compound was briefly used by Japanese physicians for the treatment of tuberculosis and leprosy.[30]

Illegal fishing and poaching

Main article: Cyanide fishing

Cyanides are illegally used to capture live fish near coral reefs for the aquarium and seafood markets. The practice is controversial, dangerous, and damaging but is driven by the lucrative exotic fish market.[31]

Poachers in Africa have been known to use cyanide to poison waterholes, to kill elephants for their ivory.[32]

Pest control

dama wallaby, another introduced marsupial pest in New Zealand.[35]
A licence is required to store, handle and use cyanide in New Zealand.

Cyanides are used as insecticides for fumigating ships.[36] Cyanide salts are used for killing ants,[37] and have in some places been used as rat poison[38] (the less toxic poison arsenic is more common).[39]

Niche uses

Potassium ferrocyanide is used to achieve a blue color on cast bronze sculptures during the final finishing stage of the sculpture. On its own, it will produce a very dark shade of blue and is often mixed with other chemicals to achieve the desired tint and hue. It is applied using a torch and paint brush while wearing the standard safety equipment used for any patina application: rubber gloves, safety glasses, and a respirator. The actual amount of cyanide in the mixture varies according to the recipes used by each foundry.

Cyanide is also used in

sepia toning
.

Although usually thought to be toxic, cyanide and cyanohydrins increase germination in various plant species.[40][41]

Human poisoning

Main article: Cyanide poisoning

Deliberate cyanide poisoning of humans has occurred many times throughout history.[42] Common salts such as

Zyklon-B was used extensively in the extermination camps of the Holocaust
.

Food additive

Because of the high stability of their complexation with

table salt.[44]

Chemical tests for cyanide

Cyanide is quantified by potentiometric titration, a method widely used in gold mining. It can also be determined by titration with silver ion. Some analyses begin with an air-purge of an acidified boiling solution, sweeping the vapors into a basic absorber solution. The cyanide salt absorbed in the basic solution is then analyzed.[45]

Qualitative tests

Because of the notorious toxicity of cyanide, many methods have been investigated. Benzidine gives a blue coloration in the presence of

UV light gives a green/blue glow if the test is positive.[47]

References

  1. doi:10.1351/goldbook.C01486
    .
  2. ^ "Environmental and Health Effects of Cyanide". International Cyanide Management Institute. 2006. Archived from the original on 30 November 2012. Retrieved 4 August 2009.
  3. ISBN 0-7506-3365-4.[page needed
    ]
  4. ISBN 0-13-035471-6.[page needed
    ]
  5. ^ "ToxFAQs for Cyanide". Agency for Toxic Substances and Disease Registry. July 2006. Retrieved 2008-06-28.
  6. PMID 10669009
    .
  7. PMID 9431670
    .
  8. S2CID 20488694. Archived
    (PDF) from the original on 2020-11-23.
  9. PMID 16599455. Archived from the original
    (PDF) on 2008-09-11. Retrieved 2008-08-23.
  10. doi:10.1086/186961
    .
  11. ^ a b Anon (June 27, 2013). "Facts about cyanide:Where cyanide is found and how it is used". CDC Emergency preparedness and response. Centers for Disease Control and Prevention. Retrieved 10 December 2016.
  12. IUPAC Gold Book nitriles
  13. ^ NCBI-MeSH Nitriles
  14. ^
    ISBN 978-3527306732
    .
  15. ISBN 978-3527306732
    .
  16. ^ Young, C. A., & Jordan, T. S. (1995, May). Cyanide remediation: current and past technologies. In: Proceedings of the 10th Annual Conference on Hazardous Waste Research (pp. 104–129). Kansas State University: Manhattan, KS. https://engg.ksu.edu/HSRC/95Proceed/young.pdf
  17. ^ Dmitry Yermakov. "Cyanide Destruction | SRK Consulting". srk.com. Retrieved 2 March 2021.
  18. ^ Botz Michael M. Overview of cyanide treatment methods. Elbow Creek Engineering, Inc. http://www.botz.com/MEMCyanideTreatment.pdf
  19. ^ Sharpe, A. G. The Chemistry of Cyano Complexes of the Transition Metals; Academic Press: London, 1976[page needed]
  20. ISBN 978-0-12-352651-9
    .
  21. doi:10.1002/cber.19270600857
    .
  22. doi:10.1002/ange.19350483702
    .
  23. ISBN 978-1-57259-153-0
    .
  24. ^
    ISBN 978-0-7817-7906-7
    .
  25. ^ "MSDS of trimethylsilyl cyanide" (PDF). Gelest Inc. 2008. Archived (PDF) from the original on 2022-10-10. Retrieved 2022-08-16.
  26. ^ Cyanide Toxicity~treatment at eMedicine
  27. doi:10.2174/2211550111201040327
    .
  28. ^ Toxicological Profile for Cyanide (PDF) (Report). U.S. Department of Health and Human Services. 2006. pp. 18–19. Archived (PDF) from the original on 2004-03-31.
  29. S2CID 132571397
    . Retrieved 24 April 2022.
  30. PMID 19868035
    . Retrieved 2008-06-28.
  31. ^ Dzombak, David A; Ghosh, Rajat S; Wong-Chong, George M. Cyanide in Water and Soil. CRC Press, 2006, Chapter 11.2: "Use of Cyanide for Capturing Live Reef Fish".
  32. ^ Poachers kill 80 elephants with cyanide in Zimbabwe ABC News, 25 September 2013. Retrieved 30 October 2015.
  33. doi:10.1002/wsb.361
    .
  34. ^ Green, Wren (July 2004). "The use of 1080 for pest control" (PDF). New Zealand Department of Conservation. Retrieved 8 June 2011.
  35. ^ Shapiro, Lee; et al. (21 March 2011). "Effectiveness of cyanide pellets for control of dama wallabies (Macropus eugenii)" (PDF). New Zealand Journal of Ecology. 35 (3). Archived (PDF) from the original on 2015-02-03.
  36. ^ "Sodium Cyanide". PubChem. National Center for Biotechnology Information. 2016. Retrieved 2 September 2016. Cyanide and hydrogen cyanide are used in electroplating, metallurgy, organic chemicals production, photographic developing, manufacture of plastics, fumigation of ships, and some mining processes.
  37. ^ "Reregistration Eligibility Decision (RED) Sodium Cyanide" (PDF). EPA.gov. 1 September 1994. p. 7. Archived (PDF) from the original on 2022-10-10. Retrieved 2 September 2016. Sodium cyanide was initially registered as a pesticide on December 23, 1947, to control ants on uncultivated agricultural and non-agricultural areas.
  38. ^ "Tariff Information, 1921: Hearings on General Tariff Revision Before the Committee on Ways and Means, House of Representatives". AbeBooks.com. US Congress, House Committee on Ways and Means, US Government Printing Office. 1921. p. 3987. Retrieved 2 September 2016. Another field in which cyanide is used in growing quantity is the eradication of rats and other vermin – especially in the fight against typhus.
  39. ^ "Deadliest Poisons Used by Man". PlanetDeadly.com. 18 November 2013. Archived from the original on 11 May 2016. Retrieved 2 September 2016.
  40. PMID 16658492
    .
  41. S2CID 2533762
    .
  42. ISBN 978-0-16-081320-7., Extract p. 41
  43. ISBN 978-1-85573-475-3. Extract of page 459
  44. ISBN 978-3-527-27766-7
    .
  45. ISBN 978-3527306732
    .
  46. ISBN 978-3527306732
    .
  47. PMID 7423496
    .

External links

Wikisource has the text of the 1911 Encyclopædia Britannica article "Cyanide".
Wikimedia Commons has media related to Cyanides.
Safety data (French)
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