Thiocyanate

Thiocyanate
IUPAC name

thiocyanate
Other names

sulphocyanate, thiocyanide
Identifiers
PubChem 9322
ChemSpider 8961 Y
ChEBI CHEBI:18022 N
ChEMBL CHEMBL84336 N
Jmol-3D images Image 1
Properties
Molecular formula CNS-
Molar mass 58.0824
 N (verify) (what is: Y/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Thiocyanate (also known as rhodanide) is the anion [SCN]−. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates. Mercury(II) thiocyanate was formerly used in pyrotechnics.

Thiocyanate is analogous to the cyanate ion, [OCN]−, wherein oxygen is replaced by sulfur. [SCN]− is one of the pseudohalides, due to the similarity of its reactions to that of halide ions. Thiocyanate used to be known as rhodanide (from a 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:

8 CN− + S8 → 8 SCN−
CN− + S2O32− → SCN− + SO32−

The second reaction is catalyzed by the enzyme sulfotransferase known as rhodanase and may be relevant to detoxification of cyanide in the body.

Contents

Structure, bonding and coordination chemistry

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 ambidentate ligand. [SCN]− can also bridge two (M−SCN−M) or even three metals (>SCN− or −SCN<). Experimental evidence leads to the general conclusion that class A metals (hard acids) tend to form N-bonded thiocyanate complexes, whereas class B metals (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(NH3)5(NCS)]Cl2 and [Co(NH3)5(SCN)]Cl2.[1]

Organic thiocyanates

Organic and transition metal derivatives of the thiocyanate ion can exist as "linkage isomers." In thiocyanates, the organic group (or metal ion) is attached to sulfur: R−S−C≡N has a S-C single bond and a C-N triple bond.[2] In isothiocyanates, the substituent is attached to nitrogen: R−N=C=S has a S-C double bond and a C-N double bond:

Organic thiocyanates are hydrolyzed to thiocarbamates in the Riemschneider thiocarbamate synthesis.

Test for iron(III)

If [SCN]− is added to a solution containing iron (III) ions (Fe3+), a blood red solution is formed due to the formation of [Fe(NCS)(H2O)5]2+.

Biological chemistry of thiocyanate in medicine

Thiocyanate[3] is known to be an important part in the biosynthesis of hypothiocyanite by a lactoperoxidase.[4][5][6] Thus the complete absence of thiocyanate[7] or reducted thiocyanate[8] in the human body, (e.g., cystic fibrosis) is of high importance in the human host defense system.[9][10]

Thiocyanate is a metabolite of sodium nitroprusside, after rhodanese catalyses its reaction with thiosulfate.

References

  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419.  p. 326
  2. ^ Guy, R. G. "Syntheses and Preparative Applications of Thiocyanates" in "Chemistry of Cyanates and Their Derivatives," vol II. Patai, S., (Editor), John Wiley, 1977. New York
  3. ^ Pedemonte N, Caci E, Sondo E, Caputo A, Rhoden K, Pfeffer U, Di Candia M, Bandettini R, Ravazzolo R, Zegarra-Moran O, Galietta LJ (April 2007). "Thiocyanate transport in resting and IL-4-stimulated human bronchial epithelial cells: role of pendrin and anion channels". J. Immunol. 178 (8): 5144–53. PMID 17404297. 
  4. ^ Conner GE, Wijkstrom-Frei C, Randell SH, Fernandez VE, Salathe M (January 2007). "The lactoperoxidase system links anion transport to host defense in cystic fibrosis". FEBS Lett. 581 (2): 271–8. doi:10.1016/j.febslet.2006.12.025. PMC 1851694. PMID 17204267. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1851694. 
  5. ^ White WE, Pruitt KM, Mansson-Rahemtulla B (February 1983). "Peroxidase-thiocyanate-peroxide antibacterial system does not damage DNA". Antimicrob. Agents Chemother. 23 (2): 267–72. PMC 186035. PMID 6340603. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=186035. 
  6. ^ Thomas EL, Aune TM (May 1978). "Lactoperoxidase, peroxide, thiocyanate antimicrobial system: correlation of sulfhydryl oxidation with antimicrobial action". Infect. Immun. 20 (2): 456–63. PMC 421877. PMID 352945. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=421877. 
  7. ^ Childers M, Eckel G, Himmel A, Caldwell J (2007). "A new model of cystic fibrosis pathology: lack of transport of glutathione and its thiocyanate conjugates". Med. Hypotheses 68 (1): 101–12. doi:10.1016/j.mehy.2006.06.020. PMID 16934416. 
  8. ^ Minarowski Ł, Sands D, Minarowska A, Karwowska A, Sulewska A, Gacko M, Chyczewska E (2008). "Thiocyanate concentration in saliva of cystic fibrosis patients". Folia Histochem. Cytobiol. 46 (2): 245–6. doi:10.2478/v10042-008-0037-0. PMID 18519245. 
  9. ^ Moskwa P, Lorentzen D, Excoffon KJ, Zabner J, McCray PB, Nauseef WM, Dupuy C, Bánfi B (January 2007). "A novel host defense system of airways is defective in cystic fibrosis". Am. J. Respir. Crit. Care Med. 175 (2): 174–83. doi:10.1164/rccm.200607-1029OC. PMC 2720149. PMID 17082494. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2720149. 
  10. ^ Xu Y, Szép S, Lu Z (December 2009). "The antioxidant role of thiocyanate in the pathogenesis of cystic fibrosis and other inflammation-related diseases". Proc. Natl. Acad. Sci. U.S.A. 106 (48): 20515–9. doi:10.1073/pnas.0911412106. PMC 2777967. PMID 19918082. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2777967. 
Oxides and related
Other ionic compounds