View source for Thiocyanate

{{Short description|1=Ion (S=C=N, charge –1)}}
{{About||organic derivatives|Organic thiocyanates|the binary compound, ScN|Scandium nitride}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 470607017
| ImageFile=Thiocyanate-3D-vdW.png
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| PIN=Thiocyanate<ref>{{cite book |author=[[International Union of Pure and Applied Chemistry]] |date=2014 |title=Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 |publisher=[[Royal Society of Chemistry|The Royal Society of Chemistry]] |pages=784, 1069 |doi=10.1039/9781849733069 |isbn=978-0-85404-182-4}}</ref>
| OtherNames= {{ubl|Rhodanide | Sulfocyanate| Sulphocyanate| Thiocyanide| Cyanosulfanide}} 
|Section1={{Chembox Identifiers
| IUPHAR_ligand = 4529
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 8961
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 84336
| InChI = 1/CHNS/c2-1-3/h3H/p-1
| InChIKey = ZMZDMBWJUHKJPS-REWHXWOFAX
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/CHNS/c2-1-3/h3H/p-1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = ZMZDMBWJUHKJPS-UHFFFAOYSA-M
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 302-04-5
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = O748SU14OM
| PubChem=9322
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 18022
| SMILES = [S-]C#N
| SMILES_Comment = [S-C≡N]<sup>−</sup>
| SMILES1 = S=C=[N-]
| SMILES1_Comment = [S=C=N]<sup>−</sup>
}}
|Section2={{Chembox Properties
| S=1|C=1|N=1
| Formula={{chem2|[SCN]−}}
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|Section3={{Chembox Hazards
| MainHazards=
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| AutoignitionPt =
  }}
  }}

'''Thiocyanates''' are [[salts (chemistry)|salts]] containing the  '''thiocyanate''' [[anion]] {{chem2|[SCN]-}}  (also known as '''rhodanide''' or '''rhodanate'''). {{chem2|[SCN]-}} is the [[conjugate base]] of [[thiocyanic acid]]. Common salts include the colourless salts [[potassium thiocyanate]] and [[sodium thiocyanate]].  [[Mercury(II) thiocyanate]] was formerly used in pyrotechnics.

Thiocyanate is analogous to the [[cyanate]] ion, {{chem2|[OCN]-}}, wherein [[oxygen]] is replaced by [[sulfur]]. {{chem2|[SCN]-}} is one of the [[pseudohalogen|pseudohalide]]s, due to the similarity of its reactions to that of [[halide]] ions. Thiocyanate used to be known as rhodanide (from a [[Greek language|Greek]] word for [[rose]]) because of the red colour of its complexes with [[iron]].

Thiocyanate is produced by the reaction of elemental sulfur or [[thiosulfate]] with [[cyanide]]:

:{{chem2 | 8 CN- + S8 -> 8 SCN- }}
:{{chem2 | CN- + S2O3(2-) -> SCN- + SO3(2-) }}

The second reaction is catalyzed by [[thiosulfate sulfurtransferase]], a hepatic mitochondrial enzyme, and by other sulfur transferases, which together are responsible for around 80% of cyanide metabolism in the body.<ref name="Abraham_al2015">{{cite journal|last1=Abraham|first1=Klaus|last2=Buhrke|first2=Thorsten|last3=Lampen|first3=Alfonso|title=Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans|journal=Archives of Toxicology|date=24 February 2015|volume=90|issue=3|pages=559–574|doi=10.1007/s00204-015-1479-8|pmid=25708890|pmc=4754328}}</ref>

Oxidation of thiocyanate inevitably produces [[hydrogen sulfate]].  The other product depends on [[pH]]: in acid, it is [[hydrogen cyanide]], presumably via [[HOSCN]] and with a [[sulfur dicyanide]] side-product; but in base and neutral solutions, it is [[cyanate]].<ref>{{cite journal|doi=10.1021/ja01463a007|title=The oxidation of thiocyanate ion by hydrogen peroxide II: The acid-catalyzed reaction|first1=I.&nbsp;R.|last1=Wilson|first2=G.&nbsp;M.|last2=Harris|journal=Journal of the American Chemical Society |volume=83|issue=2|pages=286–289|date=January 1, 1961}}</ref>

==Biology==
===Occurrences===
Thiocyanate occurs widely in nature, albeit often in low concentrations.  It is a component of some [[sulfur cycle]]s.

===Biochemistry===
[[Thiocyanate hydrolase]]s catalyze the conversion of thiocyanate to [[carbonyl sulfide]]<ref>{{cite journal |doi=10.1021/ja057010q |title=Thiocyanate Hydrolase is a Cobalt-Containing Metalloenzyme with a Cysteine-Sulfinic Acid Ligand |date=2006 |last1=Katayama |first1=Yoko |last2=Hashimoto |first2=Kanako |last3=Nakayama |first3=Hiroshi |last4=Mino |first4=Hiroyuki |last5=Nojiri |first5=Masaki |last6=Ono |first6=Taka-aki |last7=Nyunoya |first7=Hiroshi |last8=Yohda |first8=Masafumi |last9=Takio |first9=Koji |last10=Odaka |first10=Masafumi |journal=Journal of the American Chemical Society |volume=128 |issue=3 |pages=728–729 |pmid=16417356 }}</ref> and to [[cyanate]]:<ref>{{cite journal|doi=10.1073/pnas.1922133117 |title=Trinuclear Copper Biocatalytic Center Forms an Active Site of Thiocyanate Dehydrogenase |date=2020 |last1=Tikhonova |first1=Tamara V. |last2=Sorokin |first2=Dimitry Y. |last3=Hagen |first3=Wilfred R. |last4=Khrenova |first4=Maria G. |last5=Muyzer |first5=Gerard |last6=Rakitina |first6=Tatiana V. |last7=Shabalin |first7=Ivan G. |last8=Trofimov |first8=Anton A. |last9=Tsallagov |first9=Stanislav I. |last10=Popov |first10=Vladimir O. |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=10 |pages=5280–5290 |doi-access=free |pmid=32094184 |bibcode=2020PNAS..117.5280T |pmc=7071890 }}</ref>
:{{chem2|SCN-  +  H2O  +  H+  ->  SCO  +  NH3}}
:{{chem2|SCN-  +  H2O   ->  OCN-  +  H2S}}

===Medicine ===
Thiocyanate<ref name="pmid17404297">{{ cite journal |author1=Pedemonte, N. |author2=Caci, E. |author3=Sondo, E. |author4=Caputo, A. |author5=Rhoden, K. |author6=Pfeffer, U. |author7=di Candia, M. |author8=Bandettini, R. |author9=Ravazzolo, R. |author10=Zegarra-Moran, O. |author11=Galietta, L. J. | title = Thiocyanate Transport in Resting and IL-4-Stimulated Human Bronchial Epithelial Cells: Role of Pendrin and Anion Channels | journal = Journal of Immunology | year = 2007 | volume = 178 | issue = 8 | pages = 5144–5153 | pmid = 17404297 | doi=10.4049/jimmunol.178.8.5144|doi-access=free }}</ref> is known to be an important part in the biosynthesis of [[hypothiocyanite]] by a [[lactoperoxidase]].<ref name="pmid17204267">{{ cite journal |author1=Conner, G. E. |author2=Wijkstrom-Frei, C. |author3=Randell, S. H. |author4=Fernandez, V. E. |author5=Salathe, M. | title = The Lactoperoxidase System Links Anion Transport to Host Defense in Cystic Fibrosis | journal = FEBS Letters | year = 2007 | volume = 581 | issue = 2 | pages = 271–278 | pmid = 17204267 | pmc = 1851694 | doi = 10.1016/j.febslet.2006.12.025 }}</ref><ref name="pmid6340603">{{ cite journal |author1=White, W. E. |author2=Pruitt, K. M. |author3=Mansson-Rahemtulla, B. | title = Peroxidase-Thiocyanate-Peroxide Antibacterial System Does not Damage DNA | journal = Antimicrobial Agents and Chemotherapy | year = 1983 | volume = 23 | issue = 2 | pages = 267–272 | pmid = 6340603 | pmc = 186035 | doi=10.1128/aac.23.2.267}}</ref><ref name="pmid352945">{{ cite journal |author1=Thomas, E. L. |author2=Aune, T. M. | title = Lactoperoxidase, Peroxide, Thiocyanate Antimicrobial System: Correlation of Sulfhydryl Oxidation with Antimicrobial Action | journal = Infection and Immunity | year = 1978 | volume = 20 | issue = 2 | pages = 456–463 | pmid = 352945 | pmc = 421877 | doi = 10.1128/IAI.20.2.456-463.1978 }}</ref> Thus the complete absence of thiocyanate or reduced thiocyanate<ref name="pmid18519245">{{ cite journal | author1 = Minarowski, Ł. | author2 = Sands, D. | author3 = Minarowska, A. | author4 = Karwowska, A. | author5 = Sulewska, A. | author6 = Gacko, M. | author7 = Chyczewska, E. | title = Thiocyanate concentration in saliva of cystic fibrosis patients | journal = Folia Histochemica et Cytobiologica | year = 2008 | volume = 46 | issue = 2 | pages = 245–246 | pmid = 18519245 | doi = 10.2478/v10042-008-0037-0 | url = http://versita.metapress.com/content/12805r021413m867/fulltext.pdf | doi-access = free }}{{Dead link|date=June 2018 |bot=InternetArchiveBot |fix-attempted=no }}</ref> in the human body, (e.g., [[cystic fibrosis]]) is damaging to the human host defense system.<ref name="pmid17082494">{{ cite journal |author1=Moskwa, P. |author2=Lorentzen, D. |author3=Excoffon, K. J. |author4=Zabner, J. |author5=McCray, P. B. Jr. |author6=Nauseef, W. M. |author7=Dupuy, C. |author8=Bánfi, B. | title = A Novel Host Defense System of Airways is Defective in Cystic Fibrosis | journal = American Journal of Respiratory and Critical Care Medicine | year = 2007 | volume = 175 | issue = 2 | pages = 174–183 | pmid = 17082494 | pmc = 2720149 | doi = 10.1164/rccm.200607-1029OC }}</ref><ref name="pmid19918082">{{ cite journal | author = Xu, Y.; Szép, S.; Lu, Z. | title = The antioxidant role of thiocyanate in the pathogenesis of cystic fibrosis and other inflammation-related diseases | journal = Proceedings of the National Academy of Sciences of the United States of America | year = 2009 | volume = 106 | issue = 48 | pages = 20515–20519 | pmid = 19918082 | pmc = 2777967 | doi = 10.1073/pnas.0911412106 |bibcode = 2009PNAS..10620515X | last2 = Szep | last3 = Lu | doi-access = free }}</ref>

Thiocyanate is a potent competitive inhibitor of the thyroid [[sodium-iodide symporter]].<ref name="pmid15572417">{{ cite journal |author1=Braverman L. E. |author2=He X. |author3=Pino S. | title = The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term | journal = J Clin Endocrinol Metab | year = 2005 | volume = 90 | issue = 2 | pages = 700–706 | pmid = 15572417 | doi = 10.1210/jc.2004-1821| url = http://jcem.endojournals.org/content/90/2/700.long |display-authors=etal| doi-access = free }}</ref> Iodine is an essential component of [[thyroxine]]. Since thiocyanates will decrease iodide transport into the thyroid follicular cell, they will decrease the amount of thyroxine produced by the thyroid gland. As such, foodstuffs containing thiocyanate are best avoided by iodide deficient hypothyroid patients.<ref>{{cite web|title=Hypothyroidism|url=http://umm.edu/health/medical/altmed/condition/hypothyroidism|website=umm.edu|publisher=University of Maryland Medical Center|access-date=3 December 2014}}</ref>

In the early 20th century, thiocyanate was used in the treatment of [[hypertension]], but it is no longer used because of associated toxicity.<ref>{{cite journal | title =Toxicity of Thiocyanates Used in Treatment of Hypertension |author1=Warren F. Gorman |author2=Emanuel Messinger |author3=And Morris Herman | journal = Ann Intern Med | year =1949 | volume = 30 | issue = 5 | pages = 1054–1059 | doi = 10.7326/0003-4819-30-5-1054|pmid=18126744 }}</ref> [[Sodium nitroprusside]], a metabolite of which is thiocyanate, is however still used for the treatment of a [[hypertensive emergency]]. [[Rhodanese]] catalyzes the reaction of sodium nitroprusside (like other [[cyanide]]s) with [[sodium thiosulfate|thiosulfate]] to form the metabolite thiocyanate.

==Coordination chemistry==
{{main|Transition metal complexes of thiocyanate}}
[[File:PalenikPdPN SCN NCSic1970.svg|thumb|left|120px|Structure of Pd(Me<sub>2</sub>N(CH<sub>2</sub>)<sub>3</sub>PPh<sub>2</sub>)(SCN)(NCS).<ref name="PalenikClark1970">{{cite journal|last1=Palenik|first1=Gus J.|last2=Clark|first2=George Raymond|title=Crystal and molecular structure of isothiocyanatothiocyanato-(1-diphenylphosphino-3-dimethylaminopropane)palladium(II)|journal=Inorganic Chemistry|volume=9|issue=12|year=1970|pages=2754–2760|issn=0020-1669|doi=10.1021/ic50094a028}}</ref>]]

{{image frame|content=<math chem>\ce{S=C=N^\ominus <-> {^{\ominus}S}-C}\ce{#N}</math>|align=right|width=250|caption=[[Resonance (chemistry)|Resonance structures]] of the thiocyanate ion}}

Thiocyanate shares its negative charge approximately equally between [[sulfur]] and [[nitrogen]]. As a consequence, thiocyanate can act as a [[nucleophile]] at either sulfur or nitrogen—it is an [[Ligand#Ambidentate ligand|ambidentate ligand]]. [SCN]<sup>−</sup> can also bridge two (M−SCN−M) or even three metals (>SCN− or −SCN<). Experimental evidence leads to the general conclusion that [[Classes of metals|class A metals]] ([[HSAB theory|hard acids]]) tend to form ''N''-bonded thiocyanate complexes, whereas [[Classes of metals|class B metals]] ([[HSAB theory|soft acids]]) tend to form ''S''-bonded thiocyanate complexes. Other factors, e.g. kinetics and solubility, are sometimes involved, and linkage isomerism can occur, for example [Co(NH<sub>3</sub>)<sub>5</sub>(NCS)]Cl<sub>2</sub> and [Co(NH<sub>3</sub>)<sub>5</sub>(SCN)]Cl<sub>2</sub>.<ref>Greenwood, p. 326</ref> It [SCN] is considered as a weak ligand. ([<nowiki/>[[Isothiocyanate|NCS]]] is a strong ligand)<ref>{{Cite web|title=coordination compounds|url=https://ncert.nic.in/ncerts/l/lech109.pdf}}</ref>
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===Test for iron(III) and cobalt(II)===
{{multiple image
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| image1 = Pentaaquathiocyanatoiron(II)-3D-balls.png
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| image2 = Aqueous_ferric_thiocyanate_(Fe(SCN)n)_hydrate_mix.jpg
| caption2 = The blood-red colored (up) complex [Fe(NCS)(H<sub>2</sub>O)<sub>5</sub>]<sup>2+</sup> (left), indicates the presence of Fe<sup>3+</sup> in solution.
}}

If [SCN]<sup>−</sup> is added to a solution with [[ferric|iron(III) ions]], a blood-red solution forms mainly due to the formation of [[Ferric#Iron(III) salts and complexes|[Fe(NCS)(H<sub>2</sub>O)<sub>5</sub><nowiki>]</nowiki><sup>2+</sup>]], i.e. pentaaqua(thiocyanato-''N'')iron(III). Lesser amounts of other hydrated compounds also form: e.g. Fe(SCN)<sub>3</sub> and [Fe(SCN)<sub>4</sub>]<sup>−</sup>.<ref>Greenwood, p. 1090</ref>

Similarly, Co<sup>2+</sup> gives a blue complex with thiocyanate.<ref>{{Cite journal|last=Uri|first=N|date=1947-01-01|title=The stability of the cobaltous thiocyanate complex in ethyl alcohol-water mixtures and the photometric determination of cobalt|journal=Analyst|volume=72|issue=860|pages=478–481|doi=10.1039/AN9477200478|pmid=18917685|bibcode=1947Ana....72..478U}}</ref> Both the iron and cobalt complexes can be extracted into organic solvents like diethyl ether or amyl alcohol. This allows the determination of these ions even in strongly coloured solutions. The determination of Co(II) in the presence of Fe(III) is possible by adding KF to the solution, which forms uncoloured, very stable complexes with Fe(III), which no longer react with SCN<sup>−</sup>.<ref>{{Cite journal |last=Kolthoff |first=I. M. |date=1930 |title=The Cobalt-Thiocyanate Reaction for the Detection of Cobalt and Thiocyanate |url=http://link.springer.com/10.1007/BF02759120 |journal=Mikrochemie |language=en |volume=8 |issue=S1 |pages=176–181 |doi=10.1007/BF02759120 |issn=0369-0261}}</ref>

Phospholipids or some detergents aid the transfer of thiocyanatoiron into chlorinated solvents like chloroform and can be determined in this fashion.<ref>{{cite journal|last1=Stewart|first1=J.C.|title=Colorimetric determination of phospholipids with ammonium ferrothiocyanate|journal=Anal. Biochem.|date=1980|volume=104|issue=1|pages=10–14|doi=10.1016/0003-2697(80)90269-9|pmid=6892980}}</ref>
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==See also==
* [[Sulphobes]]

==References==
*{{Greenwood&Earnshaw}}

===Citations===
{{Reflist}}

{{Cyanides}}
{{Thiocyanates}}
{{Inorganic compounds of carbon}}
{{Thyroid hormone receptor modulators}}

[[Category:Thiocyanates| ]]
[[Category:Anions]]
[[Category:Sulfur ions]]
[[Category:Concrete admixtures]]