Thiocyanate
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Thiocyanate (also known as sulphocyanate or thiocyanide) is both an anion, [SCN]−, and, in organic chemistry, a functional group, RSCN.
Compounds containing the thiocyanate anion include sodium thiocyanate (NaSCN), potassium thiocyanate (KSCN), and mercury(II) thiocyanate (Hg(SCN)2).
Thiocyanate is analogous to the cyanate ion, [OCN]−, wherein oxygen is replaced by sulfur. [SCN]− is one of the pseudohalogens, 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. Thiocyanates are typically colorless.
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
Thiocyanate is produced by the reaction of elemental sulfur with cyanide:
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- 8CN− + S8 → 8SCN−
In some organisms cyanide is detoxified by this conversion as catalyzed by the enzyme sulfotransferase known as rhodanese.
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
[edit] Test for Iron(III)
![The blood-red coloured complex pentaaqua(thiocyanato-N)iron(III), [Fe(NCS)(H2O)5]2+, highlights the presence of Fe3+ in solution](../../../upload/shared/thumb/1/11/Pentaaquathiocyanatoiron%28II%29-3D-balls.png/200px-Pentaaquathiocyanatoiron%28II%29-3D-balls.png)
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+.
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