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Cyanide

From Wikipedia, the free encyclopedia
This article is about the class of chemical compounds. For other uses, seeCyanide (disambiguation).
Not to be confused withNitrile.
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 26.018g·mol−1
Conjugate acid Hydrogen cyanide
Hazards
Occupational safety and health(OHS/OSH):
Main hazards
 The cyanide ionCN−is one of the most poisonous chemicals. It may cause death in minutes.
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).

Inchemistry,cyanide(fromGreekkyanos'dark blue') is achemical compoundthat contains aC≡Nfunctional group.This group, known as thecyano group,consists of acarbonatomtriple-bondedto anitrogenatom.[1]

Ininorganiccyanides, the cyanide group is present as the cyanide anion−C≡N.This anion isextremely poisonous.Solublesaltssuch assodium cyanide(NaCN) andpotassium cyanide(KCN) are highly toxic.[2]Hydrocyanic acid,also known as hydrogen cyanide, or HCN, is a highlyvolatileliquid that is produced on a large scale industrially. It is obtained by acidification of cyanide salts.

Organiccyanides are usually callednitriles.In nitriles, the−C≡Ngroup is linked by a singlecovalent bondto carbon. For example, inacetonitrile(CH3−C≡N), the cyanide group is bonded tomethyl(−CH3). Although nitriles generally do not release cyanide ions, thecyanohydrinsdo and are thus toxic.

Bonding

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The cyanide ion−C≡Nisisoelectronicwithcarbon monoxide−C≡O+and with molecularnitrogenN≡N. A triple bond exists between C and N. The negative charge is concentrated oncarbonC.[3][4]

Occurrence

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In nature

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Removal of cyanide fromcassavainNigeria.

Cyanides are produced by certainbacteria,fungi,andalgae.It is anantifeedantin a number of plants. Cyanides are found in substantial amounts in certain seeds and fruit stones, e.g., those ofbitter almonds,apricots,apples,andpeaches.[5]Chemical compounds that can release cyanide are known as cyanogenic compounds. In plants, cyanides are usually bound tosugarmolecules in the form of cyanogenicglycosidesand defend the plant againstherbivores.Cassavaroots (also called manioc), an importantpotato-like food grown in tropical countries (and the base from whichtapiocais made), also contain cyanogenic glycosides.[6][7]

TheMadagascarbambooCathariostachys madagascariensisproduces cyanide as a deterrent to grazing. In response, thegolden bamboo lemur,which eats the bamboo, has developed a high tolerance to cyanide.

Thehydrogenaseenzymes contain cyanideligandsattached to iron in their active sites. The biosynthesis of cyanide in theNiFe hydrogenasesproceeds fromcarbamoyl phosphate,which converts tocysteinylthiocyanate,theCN−donor.[8]

Interstellar medium

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Thecyanide radical•CN has been identified ininterstellar space.[9]Cyanogen,(CN)2,is used to measure the temperature ofinterstellar gas clouds.[10]

Pyrolysis and combustion product

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Hydrogen cyanide is produced by the combustion orpyrolysisof certain materials under oxygen-deficient conditions. For example, it can be detected in theexhaustofinternal combustion enginesandtobaccosmoke. Certainplastics,especially those derived fromacrylonitrile,release hydrogen cyanide when heated or burnt.[11]

Organic derivatives

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Main article:Nitriles
See also:Isocyanide

InIUPAC nomenclature,organic compoundsthat have a−C≡Nfunctional groupare callednitriles.[12][13]An example of a nitrile isacetonitrile,CH3−C≡N.Nitriles usually do not release cyanide ions. A functional group with a hydroxyl−OHand cyanide−CNbonded to the same carbon atom is calledcyanohydrin(R2C(OH)CN). Unlike nitriles, cyanohydrins do release poisonoushydrogen cyanide.

Reactions

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Protonation

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Cyanide is basic. The pKaof hydrogen cyanide is 9.21. Thus, addition ofacidsstronger than hydrogen cyanide to solutions of cyanide salts releaseshydrogen cyanide.

Hydrolysis

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Cyanide is unstable in water, but the reaction is slow until about 170 °C. It undergoeshydrolysisto giveammoniaandformate,which are far less toxic than cyanide:[14]

CN−+ 2 H2O → HCO−2+ NH3

Cyanide hydrolaseis anenzymethat catalyzes this reaction.

Alkylation

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Because of the cyanide anion's highnucleophilicity,cyano groups are readily introduced into organic molecules by displacement of ahalidegroup (e.g., thechlorideonmethyl chloride). In general, organic cyanides are called nitriles. In organic synthesis, cyanide is a C-1synthon;i.e., it can be used to lengthen a carbon chain by one, while retaining the ability to befunctionalized.[15]

RX + CN−→ RCN + X−

Redox

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The cyanide ion is areductantand isoxidizedby strongoxidizing agentssuch as molecularchlorine(Cl2),hypochlorite(ClO−), andhydrogen peroxide(H2O2). These oxidizers are used to destroy cyanides ineffluentsfromgold mining.[16][17][18]

Metal complexation

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The cyanide anion reacts withtransition metalsto formM-CN bonds.This reaction is the basis of cyanide's toxicity.[19]The high affinities of metals for thisanioncan be attributed to its negative charge, compactness, and ability to engage in π-bonding.

Among the most important cyanide coordination compounds are thepotassium ferrocyanideand the pigmentPrussian 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 toblueprints,bluing,andcyanotypes.

Manufacture

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Main article:Hydrogen cyanide § Production and synthesis

The principal process used to manufacture cyanides is theAndrussow processin which gaseoushydrogen cyanideis produced frommethaneandammoniain the presence ofoxygenand aplatinumcatalyst.[21][22]

2 CH4+ 2 NH3+ 3 O2→ 2 HCN + 6 H2O

Sodium cyanide, the precursor to most cyanides, is produced by treatinghydrogen cyanidewithsodium hydroxide:[14]

HCN + NaOH → NaCN + H2O

Toxicity

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Main article:Cyanide poisoning

Among the most toxic cyanides are hydrogen cyanide (HCN), sodium cyanide (NaCN), potassium cyanide (KCN), and calcium cyanide (Ca(CN)₂). These compounds are extremely poisonous and require careful handling to avoid severe health risks. The cyanide anion is aninhibitorof theenzymecytochrome c oxidase(also known as aa3), the fourth complex of theelectron transport chainfound in theinner membraneof themitochondriaofeukaryoticcells. It attaches to the iron within this protein. The binding of cyanide to this enzyme prevents transport of electrons fromcytochrome cto oxygen. As a result, the electron transport chain is disrupted, meaning that the cell can no longer aerobically produceATPfor energy.[23]Tissues that depend highly onaerobic respiration,such as thecentral nervous systemand theheart,are particularly affected. This is an example ofhistotoxic hypoxia.[24]

The most hazardous compound ishydrogen cyanide,which is a gas and kills by inhalation. For this reason, an air respirator supplied by an external oxygen source must be worn when working with hydrogen cyanide.[11]Hydrogen cyanide is produced by adding acid to a solution containing a cyanide salt. Alkaline solutions of cyanide are safer to use because they do not evolve hydrogen cyanide gas. Hydrogen cyanide may be produced in the combustion ofpolyurethanes;for this reason, polyurethanes are not recommended for use in domestic and aircraft furniture. Oral ingestion of a small quantity of solid cyanide or a cyanide solution of as little as 200 mg, or exposure to airborne cyanide of 270ppm,is sufficient to cause death within minutes.[24]

Organicnitrilesdo not readily release cyanide ions, and so have low toxicities. By contrast, compounds such astrimethylsilyl cyanide(CH3)3SiCNreadily release HCN or the cyanide ion upon contact with water.[25]

Antidote

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Hydroxocobalaminreacts with cyanide to formcyanocobalamin,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:amyl nitritepearls (administered by inhalation),sodium nitrite,andsodium thiosulfate.The goal of the antidote was to generate a large pool offerriciron (Fe3+) to compete for cyanide with cytochrome a3(so that cyanide will bind to the antidote rather than the enzyme). Thenitritesoxidizehemoglobintomethemoglobin,which competes with cytochrome oxidase for the cyanide ion. Cyanmethemoglobin is formed and thecytochrome oxidaseenzyme is restored. The major mechanism to remove the cyanide from the body is by enzymatic conversion tothiocyanateby themitochondrialenzymerhodanese.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 forrhodanese,needed in order to produce thiocyanate.[27]

Sensitivity

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

Applications

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Mining

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Main article:Gold cyanidation

Cyanide is mainly produced for theminingofsilverandgold:It helps dissolve these metals allowing separation from the other solids. In thecyanide process,finely ground high-grade ore is mixed with the cyanide (at a ratio of about 1:500 parts NaCN to ore); low-grade ores are stacked into heaps and sprayed with a cyanide solution (at a ratio of about 1:1000 parts NaCN to ore). The precious metals are complexed by the cyanideanionsto 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 (noO2is required). Instead, a displacement reaction occurs:

The "pregnant liquor" containing these ions is separated from the solids, which are discarded to atailing pondor spent heap, the recoverable gold having been removed. The metal is recovered from the "pregnant solution" by reduction withzincdust or byadsorptionontoactivated carbon.This process can result in environmental and health problems. A number ofenvironmental disastershave 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 toiron pyrite(fool's gold), wherein half of the sulfur atoms are replaced byarsenic.Gold-containing arsenopyrite ores are similarly reactive toward inorganic cyanide.[citation needed]

Industrial organic chemistry

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

Medical uses

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The cyanide compoundsodium nitroprussideis used mainly inclinical chemistryto measureurineketone bodiesmainly as a follow-up todiabeticpatients. On occasion, it is used in emergency medical situations to produce a rapid decrease inblood pressurein humans; it is also used as avasodilatorin vascular research. The cobalt in artificialvitamin B12contains 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. DuringWorld War I,a copper cyanide compound was briefly used byJapanesephysicians for the treatment oftuberculosisandleprosy.[30]

Illegal fishing and poaching

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Main article:Cyanide fishing

Cyanides are illegally used to capture live fish nearcoral reefsfor theaquariumand 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

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M44 cyanide devicesare used in the United States to killcoyotesand other canids.[33]Cyanide is also used for pest control inNew Zealand,particularly forpossums,anintroduced marsupial that threatens the conservation of native speciesand spreadstuberculosisamongst cattle. Possums can become bait shy but the use of pellets containing the cyanide reduces bait shyness. Cyanide has been known to kill native birds, including the endangeredkiwi.[34]Cyanide is also effective for controlling thedama 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 asinsecticidesfor 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 poisonarsenicis more common).[39]

Niche uses

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Potassium ferrocyanideis used to achieve a blue color on castbronze sculpturesduring 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 injewelry-making and certain kinds ofphotographysuch assepia toning.

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

Human poisoning

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Main article:Cyanide poisoning

Deliberate cyanide poisoning of humans has occurred many times throughout history.[42] Common salts such assodium cyanideare involatile but water-soluble, so are poisonous by ingestion.Hydrogen cyanideis a gas, making it more indiscriminately dangerous, however it is lighter than air and rapidly disperses up into the atmosphere, which makes it ineffective as achemical weapon.Poisoning by hydrogen cyanide is more effective in an enclosed space, such as agas chamber.Most significantly, hydrogen cyanide released from pellets ofZyklon-Bwas used extensively in theextermination campsofthe Holocaust.

Food additive

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Because of the high stability of their complexation withiron,ferrocyanides (Sodium ferrocyanideE535,Potassium ferrocyanideE536, and Calcium ferrocyanide E538[43]) do not decompose to lethal levels in the human body and are used in the food industry as, e.g., ananticaking agentintable salt.[44]

Chemical tests for cyanide

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Cyanide is quantified bypotentiometric 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

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Because of the notorious toxicity of cyanide, many methods have been investigated. Benzidine gives a blue coloration in the presence offerricyanide.[46]Iron(II) sulfateadded to a solution of cyanide, such as the filtrate from thesodium fusion test,givesprussian blue.A solution ofpara-benzoquinoneinDMSOreacts with inorganic cyanide to form a cyanophenol,which isfluorescent.Illumination with aUV lightgives a green/blue glow if the test is positive.[47]

References

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  2. ^"Environmental and Health Effects of Cyanide".International Cyanide Management Institute. 2006. Archived fromthe originalon 30 November 2012.Retrieved4 August2009.
  3. ^Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann.ISBN0-7506-3365-4.[page needed]
  4. ^G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher,ISBN0-13-035471-6.[page needed]
  5. ^"ToxFAQs for Cyanide".Agency for Toxic Substances and Disease Registry.July 2006.Retrieved2008-06-28.
  6. ^Vetter, J. (2000). "Plant cyanogenic glycosides".Toxicon.38(1): 11–36.doi:10.1016/S0041-0101(99)00128-2.PMID10669009.
  7. ^Jones, D. A. (1998). "Why are so many food plants cyanogenic?".Phytochemistry.47(2): 155–162.Bibcode:1998PChem..47..155J.doi:10.1016/S0031-9422(97)00425-1.PMID9431670.
  8. ^Reissmann, Stefanie; Hochleitner, Elisabeth; Wang, Haofan; Paschos, Athanasios; Lottspeich, Friedrich; Glass, Richard S.; Böck, August (2003)."Taming of a Poison: Biosynthesis of the NiFe-Hydrogenase Cyanide Ligands"(PDF).Science.299(5609): 1067–1070.Bibcode:2003Sci...299.1067R.doi:10.1126/science.1080972.PMID12586941.S2CID20488694.Archived(PDF)from the original on 2020-11-23.
  9. ^Pieniazek, Piotr A.; Bradforth, Stephen E.; Krylov, Anna I. (2005-12-07)."Spectroscopy of the Cyano Radical in an Aqueous Environment"(PDF).The Journal of Physical Chemistry A.110(14): 4854–4865.Bibcode:2006JPCA..110.4854P.doi:10.1021/jp0545952.PMID16599455.Archived fromthe original(PDF)on 2008-09-11.Retrieved2008-08-23.
  10. ^Roth, K. C.; Meyer, D. M.;Hawkins, I.(1993)."Interstellar Cyanogen and the Temperature of the Cosmic Microwave Background Radiation"(PDF).The Astrophysical Journal.413(2): L67–L71.Bibcode:1993ApJ...413L..67R.doi:10.1086/186961.
  11. ^abAnon (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.Retrieved10 December2016.
  12. ^IUPAC Gold Booknitriles
  13. ^NCBI-MeSHNitriles
  14. ^abcRubo, Andreas; Kellens, Raf; Reddy, Jay; Steier, Norbert; Hasenpusch, Wolfgang (2006). "Alkali Metal Cyanides".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.i01_i01.ISBN978-3527306732.
  15. ^Pollak, Peter; Romeder, Gérard; Hagedorn, Ferdinand; Gelbke, Heinz-Peter (2000). "Nitriles".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.a17_363.ISBN3-527-30673-0.
  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.Retrieved2 March2021.
  18. ^Botz Michael M. Overview of cyanide treatment methods. Elbow Creek Engineering, Inc.http:// botz /MEMCyanideTreatment.pdf
  19. ^Sharpe, A. G. The Chemistry of Cyano Complexes of the Transition Metals; Academic Press: London, 1976[page needed]
  20. ^Holleman, A. F.; Wiberg, E. (2001).Inorganic Chemistry.San Diego: Academic Press.ISBN978-0-12-352651-9.
  21. ^Andrussow, Leonid(1927). "Über die schnell verlaufenden katalytischen Prozesse in strömenden Gasen und die Ammoniak-Oxydation (V)" [About the quicka catalytic processes in flowing gases and the ammonia oxidation (V)].Berichte der Deutschen Chemischen Gesellschaft(in German).60(8): 2005–2018.doi:10.1002/cber.19270600857.
  22. ^Andrussow, L. (1935). "Über die katalytische Oxydation von Ammoniak-Methan-Gemischen zu Blausäure" [About the catalytic oxidation of ammonia-methane mixtures to cyanide].Angewandte Chemie(in German).48(37): 593–595.Bibcode:1935AngCh..48..593A.doi:10.1002/ange.19350483702.
  23. ^Nelson, David L.; Cox, Michael M. (2000).Lehniger Principles of Biochemistry(3rd ed.). New York:Worth Publishers.pp.668, 670–71, 676.ISBN978-1-57259-153-0.
  24. ^abBiller, José (2007)."163".Interface of neurology and internal medicine(illustrated ed.). Lippincott Williams & Wilkins. p. 939.ISBN978-0-7817-7906-7.
  25. ^"MSDS of trimethylsilyl cyanide"(PDF).Gelest Inc. 2008.Archived(PDF)from the original on 2022-10-10.Retrieved2022-08-16.
  26. ^Cyanide Toxicity~treatmentateMedicine
  27. ^Chaudhary, M.; Gupta, R. (2012). "Cyanide Detoxifying Enzyme: Rhodanese".Current Biotechnology.1(4): 327–335.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. ^Kumar, Rahul; Saha, Shouvik; Sarita, Dhaka; Mayur B., Kurade; Kang, Chan Ung; Baek, Seung Han; Jeong, Byong-Hun (2016)."Remediation of cyanide-contaminated environments through microbes and plants: a review of current knowledge and future perspectives".Geosystem Engineering.70(1): 28–40.doi:10.1080/12269328.2016.1218303.S2CID132571397.Retrieved24 April2022.
  30. ^Takano, R. (August 1916)."The treatment of leprosy with cyanocuprol".The Journal of Experimental Medicine.24(2): 207–211.doi:10.1084/jem.24.2.207.PMC2125457.PMID19868035.Retrieved2008-06-28.
  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 ZimbabweABC News,25 September 2013. Retrieved 30 October 2015.
  33. ^Shivik, John A.; Mastro, Lauren; Young, Julie K. (2014)."Animal attendance at M-44 sodium cyanide ejector sites for coyotes".Wildlife Society Bulletin.38(1): 217–220.Bibcode:2014WSBu...38..217S.doi:10.1002/wsb.361.
  34. ^Green, Wren (July 2004)."The use of 1080 for pest control"(PDF).New Zealand Department of Conservation.Retrieved8 June2011.
  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.Retrieved2 September2016.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.Retrieved2 September2016.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.US Congress, House Committee on Ways and Means, US Government Printing Office. 1921. p. 3987.Retrieved2 September2016.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.18 November 2013. Archived fromthe originalon 11 May 2016.Retrieved2 September2016.
  40. ^Taylorson, R.; Hendricks, SB (1973)."Promotion of Seed Germination by Cyanide".Plant Physiol.52(1): 23–27.doi:10.1104/pp.52.1.23.PMC366431.PMID16658492.
  41. ^Mullick, P.; Chatterji, U. N. (1967). "Effect of sodium cyanide on germination of two leguminous seeds".Plant Systematics and Evolution.114:88–91.doi:10.1007/BF01373937.S2CID2533762.
  42. ^Bernan (2008).Medical Management of Chemical Casualties Handbook(4th ed.). Government Printing Off. p. 41.ISBN978-0-16-081320-7.,Extract p. 41
  43. ^Bender, David A.; Bender, Arnold Eric (1997).Benders' dictionary of nutrition and food technology(7th ed.). Woodhead Publishing. p. 459.ISBN978-1-85573-475-3.Extract of page 459
  44. ^Schulz, Horst D.; Hadeler, Astrid; Deutsche Forschungsgemeinschaft (2003).Geochemical processes in soil and groundwater: measurement – modelling – upscaling.Wiley-VCH. p. 67.doi:10.1002/9783527609703.ISBN978-3-527-27766-7.
  45. ^Gail, Ernst; Gos, Stephen; Kulzer, Rupprecht; Lorösch, Jürgen; Rubo, Andreas; Sauer, Manfred (2004). "Cyano Compounds, Inorganic".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.a08_159.pub2.ISBN978-3527306732.
  46. ^Schwenecke, H.; Mayer, D. (2005). "Benzidine and Benzidine Derivatives".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.a03_539.ISBN978-3527306732.
  47. ^Ganjeloo, A; Isom, GE; Morgan, RL; Way, JL (1980). "Fluorometric determination of cyanide in biological fluids with p-benzoquinone*1".Toxicology and Applied Pharmacology.55(1): 103–107.doi:10.1016/0041-008X(80)90225-2.PMID7423496.
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