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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 .
In methyl thiocyanate, N≡C and C−S distances are 116 and 176 pm. By contrast, N=C and C=S distances are 117 and 158 pm in isothiocyanates. [7] Typical bond angles for C−S−C are 100°. [3] By contrast C−N=C in aryl isothiocyanates is 165°. Again, the thiocyanate isomers are quite different with C−S−C angle near 100°.
Thiocyanate complexes are not widely used commercially. Possibly the oldest application of thiocyanate complexes was the use of thiocyanate as a test for ferric ions in aqueous solution. [14] The reverse was also used: testing for the presence of thiocyanate by the addition of ferric salts. The 1:1 complex of thiocyanate and iron is deeply red.
The esters of thiocyanic acid have the general structure R−S−C≡N, where R stands for an organyl group. Isothiocyanic acid, HNCS, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a variety of Lewis bases in carbon tetrachloride solution at 25 °C have been reported.
Sodium thiocyanate (sometimes called sodium sulphocyanide) is the chemical compound with the formula NaSCN. This colorless deliquescent salt is one of the main sources of the thiocyanate anion . As such, it is used as a precursor for the synthesis of pharmaceuticals and other specialty chemicals . [ 2 ]
Potassium thiocyanate is the chemical compound with the molecular formula KSCN. It is an important salt of the thiocyanate anion , one of the pseudohalides . The compound has a low melting point relative to most other inorganic salts.
Space-filling model of the thiocyanate ion, [SCN] −. Structure calculated using HF/6-31G* in Spartan '04 Student Edition. Image generated in Accelrys DS Visualizer.
The Hg(SCN) 3− ion can also exist independently and is easily generated from the compounds above, amongst others. [5] Organic halides attack Hg(SCN) 2 to give a mercuric halide and a mixture of the corresponding thiocyanate and isothiocyanate. [6] Mercuric thiocyanate catalyzes HSCN or BrSCN addition (either reagent formed in situ) to alkynes ...