Thiocyanate

Thiocyanate (also known as rhodanide) is the anion −. 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 (also known as rhodanide) is the anion −. 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, −, wherein oxygen is replaced by sulfur. − 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: 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. 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. 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 valuable building blocks in organic chemistry and they allow to access efficiently various sulfur containing functional groups and scaffolds. Several synthesis routes exist, the most basic being the reaction between alkyl halides and alkali thiocyanate in aqueous media. Organic thiocyanates are hydrolyzed to thiocarbamates in the Riemschneider thiocarbamate synthesis. Thiocyanate is known to be an important part in the biosynthesis of hypothiocyanite by a lactoperoxidase. Thus the complete absence of thiocyanate or reduced thiocyanate in the human body, (e.g., cystic fibrosis) is damaging to the human host defense system. Thiocyanate is a potent competitive inhibitor of the thyroid sodium-iodide symporter. 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. In the early 20th century, thiocyanate was used in the treatment of hypertension, but it is no longer used because of associated toxicity. 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 with thiosulfate to form the metabolite thiocyanate.