Isothiocyanate

Occurrence

Many isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. A prominent natural isothiocyanate is allyl isothiocyanate, also known as mustard oils.

Cruciferous vegetables, such as bok choy, broccoli, cabbage, cauliflower, kale, and others, are rich sources of glucosinolate precursors of isothiocyanates.

Structure

The and distances are 117 and 158 pm. By contrast, in methyl thiocyanate, and distances are 116 and 176 pm.

Typical bond angles for in aryl isothiocyanates are near 165°. Again, the thiocyanate isomers are quite different with angle near 100°. In both isomers the angle approaches 180°.

Synthesis

Allyl thiocyanate isomerizes to the isothiocyanate: :

Isothiocyanates can be prepared by treating organic dithiocarbamate salts with lead nitrate or tosyl chloride. :[[File:Synthesis phenylisothiocyanate 1.svg|center|frameless|upright=2.7|Synthesis of phenyl isothiocyanate]]

Isothiocyanates may also be accessed by the fragmentation reactions of 1,4,2-oxathiazoles. This methodology has been applied to a polymer-supported synthesis of isothiocyanates.

Reactions

Isothiocyanates are weak electrophiles, susceptible to hydrolysis. In general, nucleophiles attack at carbon:

Electrochemical reduction gives thioformamides.

Flavor research

Isothiocyanates occur widely in nature and are of interest in food science and medical research. Vegetable foods with characteristic flavors due to isothiocyanates include bok choy, broccoli, cabbage, cauliflower, kale, wasabi, horseradish, mustard, radish, Brussels sprouts, watercress, papaya seeds, nasturtiums, and capers. These species generate isothiocyanates in different proportions, and so have different, but recognizably related, flavors. They are all members of the order Brassicales, which is characterized by the production of glucosinolates, and of the enzyme myrosinase, which acts on glucosinolates to release isothiocyanates.

• Sinigrin is the precursor to allyl isothiocyanate
• Glucotropaeolin is the precursor to benzyl isothiocyanate
• Gluconasturtiin is the precursor to phenethyl isothiocyanate
• Glucoraphanin is the precursor to sulforaphane

Uses

Phenyl isothiocyanate, is used for amino acid sequencing in the Edman degradation.

Coordination chemistry

Isothiocyanate and its linkage isomer thiocyanate are ligands in coordination chemistry. Thiocyanate is a more common ligand.

References

References

1. (1 April 2017). "Isothiocyanates". Micronutrient Information Center, Linus Pauling Institute, Oregon State University.
2. (2008). "Structure and polarized IR spectra of 4-isothiocyanatophenyl 4-heptylbenzoate (7TPB)". Chemical Physics.
3. (1999). "The chemistry of thiocyanic esters". Tetrahedron.
4. (1971). "The Preparation and Isomerization of Allyl Thiocyanate. An Organic Chemistry Experiment". Journal of Chemical Education.
5. Dains FB. (1926). "Phenyl Isothiocyanate".
6. (2007). "Isothiocyanates from tosyl chloride mediated decomposition of in situ generated dithiocarbamic acid salts". The Journal of Organic Chemistry.
7. (2009). "Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles". Organic Letters.
8. (2007). "Polymer-supported thiobenzophenone : a self-indicating traceless 'catch and release' linker for the synthesis of isothiocyanates". Tetrahedron Letters.
9. (2005). "Improved approaches in the synthesis of new 2-(1, 3-thiazolidin-2Z-ylidene)acetophenones". Arkivoc.
10. (1977). "The Chemistry of Cyanates and Their Thio Derivatives". Wiley.