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.
Organic thiocyanates are valued building blocks. They allow to access efficiently various sulfur containing functional groups and scaffolds.
Synthesis
Several synthesis routes exist,
the most common being the reaction between alkyl halides and alkali thiocyanate in aqueous media. Illustrative is the preparation of isopropyl thiocyanate by treatment of
isopropyl bromide
2-Bromopropane, also known as isopropyl bromide and 2-propyl bromide, is the halogenated hydrocarbon with the formula CH3CHBrCH3. It is a colorless liquid. It is used for introducing the isopropyl functional group in organic synthesis. 2-Bromopropa ...
with
sodium thiocyanate
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 synthes ...
in boiling ethanol. 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 In organic synthesis, cyanation is the attachment or substitution of a cyanide group on various substrates. Such transformations are high-value because they generate C-C bond. Furthermore nitriles are versatile functional groups.
Cyanation to f ...
of some
organosulfur compound
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...
s. Sulfenyl thiosulfates (RSSO
3−) react with alkali metal cyanides to give thiocyanates with displacement of sulfite. This approach has been applied to allyl thiocyanate:
:
:
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:
[
:
Some arylthiocyanates can also often be obtained by thiocyanogenation, i.e. the reaction of ]thiocyanogen
Thiocyanogen, (SCN)2, is a pseudohalogen derived from the pseudohalide thiocyanate, CNsup>−. This hexatomic compound exhibits C2 point group symmetry and has the connectivity NCS-SCN. The oxidation ability is greater than bromine. It reacts w ...
. This reaction is favored for electron-rich aromatic substrates.[
]
Structure
In methyl thiocyanate, and distances are 116 and 176 pm. By contrast, and distances are 117 and 158 pm in isothiocyanate]s.[ 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°.
]
Reactions
Organic thiocyanates are hydrolyzed to thiocarbamates in the Riemschneider thiocarbamate synthesis.
Some thiocyanates isomerize to the isothiocyandates. This reaction is especially rapid for the allyl isothiocyanate:[
:
]
See also
* Isothiocyanate, isomers of organic thiocyanates with the formula R−N=C=S
* Methyl thiocyanate, the simplest organic thiocyanate
References
{{Thyroid hormone receptor modulators
Functional groups