Organic thiocyanates are organic compounds containing the functional group RSCN. the organic group is attached to sulfur: R−S−C≡N has a S–C single bond and a C≡N triple bond.[1]
Organic thiocyanates are valued building blocks. They allow to access efficiently various sulfur containing functional groups and scaffolds.[2]
Several synthesis routes exist,[3] the most common being the reaction between alkyl halides and alkali thiocyanate in aqueous media.[4] Illustrative is the preparation of isopropyl thiocyanate by treatment of isopropyl bromide with sodium thiocyanate in boiling ethanol.[5] The main complication with this route is the competing formation of alkyisothiocyanates. "SN1-type" substrates (e.g., benzyl halides) tend to give the isothiocyanate derivatives.
Some organic thiocyanates are generated by cyanation of some organosulfur compounds. Sulfenyl thiosulfates (RSSO3−) react with alkali metal cyanides to give thiocyanates with displacement of sulfite. This approach has been applied to allyl thiocyanate:[6]
Sulfenyl chlorides (RSCl) also convert to thiocyanates.
Aryl thiocyanates are traditionally produced by the Sandmeyer reaction, which involves combining copper(I) thiocyanate and diazonium salts:[3]
Some arylthiocyanates can also often be obtained by thiocyanogenation, i.e. the reaction of thiocyanogen. This reaction is favored for electron-rich aromatic substrates.[1]
In methyl thiocyanate, and distances are 116 and 176 pm. By contrast, and distances are 117 and 158 pm in isothiocyanates.[7]
Typical bond angles for are 100°.[3] By contrast in aryl isothiocyanates is 165°. Again, the thiocyanate isomers are quite different with angle near 100°.
In both organic thiocyanate and isothiocyanate isomers the angle approaches 180°.
Organic thiocyanates are hydrolyzed to thiocarbamates in the Riemschneider thiocarbamate synthesis.
Electrochemical reduction typically converts thiocyanates to thioates and cyanide, although sometimes it can replace the thiocyanate group as a whole with hydride.[8]
Some thiocyanates isomerize to the isothiocyanates. This reaction is especially rapid for the allyl isothiocyanate:[6]
Likewise, acyl thiocyanates are difficult to synthesize because any excess thiocyanate ion catalyzes isomerization to the acyl isothiocyanate.