AskDefine | Define thiocyanate

Dictionary Definition

thiocyanate n : a salt of thiocyanic acid; formed when alkaline cyanides are fused with sulfur

User Contributed Dictionary

English

Noun

thiocyanate
  1. any salt or ester of thiocyanic acid; or the -SCN radical or the SCN-1 anion

Translations

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Extensive Definition

Thiocyanate (also known as sulphocyanate or thiocyanide) is the anion, [SCN]−. Common compounds 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]−, where in oxygen is replaced by sulfur. [SCN]− is one of the pseudohalides, due to the similarity of its reactions to that of halide ions. Thiocyanate was formerly 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 latter reaction is catalyzed by the enzyme sulfotransferase known as rhodanase and may be relevant to detoxification of cyanide in the body.

Structure, bonding and coordination chemistry

Thiocyanate shares its negative charge approximately equally between sulfur and nitrogen. Consequently, 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.

Organic thiocyanates

Organic and transition metal derivatives of the thiocyanate ion can exist as "linkage isomers." In thiocyanates, the organic group or metal is attached to sulfur: R−S−C≡N has a S-C single bond and a C-N triple bond . 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 presence of the [Fe(NCS)(H2O)5]2+.

References

thiocyanate in German: Thiocyanate
thiocyanate in Latvian: Rodanīdi
thiocyanate in Polish: Rodanki
thiocyanate in Portuguese: Tiocianato
thiocyanate in Russian: Роданиды
thiocyanate in Chinese: 硫氰酸盐
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