Isothiocyanate

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General structure of an isothiocyanate. Isothiocyanate group.svg
General structure of an isothiocyanate.

In organic chemistry, isothiocyanate is a functional group as found in compounds with the formula R−N=C=S. Isothiocyanates are the more common isomers of thiocyanates, which have the formula R−S−C≡N.

Contents

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. [1]

Structure

The N=C and C=S distances are 117 and 158 pm. [2] By contrast, in methyl thiocyanate, N≡C and C−S distances are 116 and 176 pm.

Typical bond angles for C−N=C in aryl isothiocyanates are near 165°. Again, the thiocyanate isomers are quite different with C−S−C angle near 100°. [3] In both isomers the SCN angle approaches 180°.

Synthesis

Allyl thiocyanate isomerizes to the isothiocyanate: [4]

CH2=CHCH2SCN → CH2=CHCH2NCS

Isothiocyanates can be prepared by degradation of dithiocarbamate salts, e.g. induced with lead nitrate. [5] A related method is tosyl chloride-mediated decomposition of dithiocarbamate salts. [6]

Synthesis of phenyl isothiocyanate Synthesis phenylisothiocyanate 1.svg
Synthesis of phenyl isothiocyanate

Isothiocyanates may also be accessed by the fragmentation reactions of 1,4,2-oxathiazoles. [7] This methodology has been applied to a polymer-supported synthesis of isothiocyanates. [8]

Reactions

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

The reaction of acetophenone enolate with phenyl isothiocyanate. In this one-pot synthesis the ultimate reaction product is a Thiazolidine. This reaction is stereoselective with the formation of the Z-isomer only. ThiazolidineSynthesis.gif
The reaction of acetophenone enolate with phenyl isothiocyanate. In this one-pot synthesis the ultimate reaction product is a Thiazolidine. This reaction is stereoselective with the formation of the Z-isomer only.

Flavor research

Isothiocyanates occur widely in nature and are of interest in food science and medical research. [1] 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. [1] 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. [1]

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.

See also

Related Research Articles

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<span class="mw-page-title-main">Tosyl group</span> Chemical group (–SO₂–C₆H₄–CH₃)

In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or Tos) is a univalent functional group with the chemical formula −SO2−C6H4−CH3. It consists of a tolyl group, −C6H4−CH3, joined to a sulfonyl group, −SO2, with the open valence on sulfur. This group is usually derived from the compound tosyl chloride, CH3C6H4SO2Cl (abbreviated TsCl), which forms esters and amides of toluenesulfonic acid, CH3C6H4SO2OH (abbreviated TsOH). The para orientation illustrated (p-toluenesulfonyl) is most common, and by convention tosyl without a prefix refers to the p-toluenesulfonyl group.

<span class="mw-page-title-main">Allyl group</span> Chemical group (–CH₂–CH=CH₂)

In organic chemistry, an allyl group is a substituent with the structural formula −CH2−HC=CH2. It consists of a methylene bridge attached to a vinyl group. The name is derived from the scientific name for garlic, Allium sativum. In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil and named it "Schwefelallyl". The term allyl applies to many compounds related to H2C=CH−CH2, some of which are of practical or of everyday importance, for example, allyl chloride.

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<span class="mw-page-title-main">Allyl chloride</span> Chemical compound

Allyl chloride is the organic compound with the formula CH2=CHCH2Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a chlorinated derivative of propylene. It is an alkylating agent, which makes it both useful and hazardous to handle.

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<span class="mw-page-title-main">Allyl isothiocyanate</span> Chemical compound

Allyl isothiocyanate (AITC) is a naturally occurring unsaturated isothiocyanate. The colorless oil is responsible for the pungent taste of Cruciferous vegetables such as mustard, radish, horseradish, and wasabi. This pungency and the lachrymatory effect of AITC are mediated through the TRPA1 and TRPV1 ion channels. It is slightly soluble in water, but more soluble in most organic solvents.

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<span class="mw-page-title-main">Sulforaphane</span> Chemical compound

Sulforaphane is a compound within the isothiocyanate group of organosulfur compounds. It is produced when the enzyme myrosinase transforms glucoraphanin, a glucosinolate, into sulforaphane upon damage to the plant, which allows the two compounds to mix and react.

<span class="mw-page-title-main">Sulfoxide</span> Organic compound containing a sulfinyl group (>SO)

In organic chemistry, a sulfoxide, also called a sulphoxide, is an organosulfur compound containing a sulfinyl functional group attached to two carbon atoms. It is a polar functional group. Sulfoxides are oxidized derivatives of sulfides. Examples of important sulfoxides are alliin, a precursor to the compound that gives freshly crushed garlic its aroma, and dimethyl sulfoxide (DMSO), a common solvent.

<span class="mw-page-title-main">Glucosinolate</span> Class of chemical compounds

Glucosinolates are natural components of many pungent plants such as mustard, cabbage, and horseradish. The pungency of those plants is due to mustard oils produced from glucosinolates when the plant material is chewed, cut, or otherwise damaged. These natural chemicals most likely contribute to plant defence against pests and diseases, and impart a characteristic bitter flavor property to cruciferous vegetables.

<span class="mw-page-title-main">Sinigrin</span> Chemical compound

Sinigrin or allyl glucosinolate is a glucosinolate that belongs to the family of glucosides found in some plants of the family Brassicaceae such as Brussels sprouts, broccoli, and the seeds of black mustard. Whenever sinigrin-containing plant tissue is crushed or otherwise damaged, the enzyme myrosinase degrades sinigrin to a mustard oil, which is responsible for the pungent taste of mustard and horseradish. Seeds of white mustard, Sinapis alba, give a less pungent mustard because this species contains a different glucosinolate, sinalbin.

<span class="mw-page-title-main">Methyl isothiocyanate</span> Chemical compound

Methyl isothiocyanate is the organosulfur compound with the formula CH3N=C=S. This low melting colorless solid is a powerful lachrymator. As a precursor to a variety of valuable bioactive compounds, it is the most important organic isothiocyanate in industry.

<span class="mw-page-title-main">Myrosinase</span> Class of enzymes

Myrosinase is a family of enzymes involved in plant defense against herbivores, specifically the mustard oil bomb. The three-dimensional structure has been elucidated and is available in the PDB.

<span class="mw-page-title-main">Phenyl isothiocyanate</span> Chemical compound

Phenyl isothiocyanate (PITC) is a reagent used in reversed phase HPLC. PITC is less sensitive than o-phthaldehyde (OPA) and cannot be fully automated. PITC can be used for analysing secondary amines, unlike OPA. It is also known as Edman's reagent and is used in Edman degradation.

<span class="mw-page-title-main">Methyl thiocyanate</span> Chemical compound

Methyl thiocyanate is an organic compound with the formula CH3SCN. The simplest member of the organic thiocyanates, it is a colourless liquid with an onion-like odor. It is produced by the methylation of thiocyanate salts. The compound is a precursor to the more useful isomer methyl isothiocyanate (CH3NCS).

<span class="mw-page-title-main">Allyl cyanide</span> Chemical compound

Allyl cyanide is an organic compound with the formula CH2CHCH2CN. Like other small alkyl nitriles, allyl cyanide is colorless and soluble in organic solvents. Allyl cyanide occurs naturally as an antifeedant and is used as a cross-linking agent in some polymers.

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<span class="mw-page-title-main">Transition-metal allyl complex</span>

Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2, which is usually described as two equivalent resonance structures.

<span class="mw-page-title-main">Organic thiocyanates</span>

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.

References

  1. 1 2 3 4 "Isothiocyanates". Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 1 April 2017. Retrieved 14 April 2019.
  2. Majewska, Paulina; Rospenk, Maria; Czarnik-Matusewicz, Bogusława; Kochel, Andrzej; Sobczyk, Lucjan; Dąbrowski, Roman (2008). "Structure and polarized IR spectra of 4-isothiocyanatophenyl 4-heptylbenzoate (7TPB)". Chemical Physics. 354 (1–3): 186–195. Bibcode:2008CP....354..186M. doi:10.1016/j.chemphys.2008.10.024.
  3. Erian, Ayman W.; Sherif, Sherif M. (1999). "The chemistry of thiocyanic esters". Tetrahedron. 55 (26): 7957–8024. doi:10.1016/S0040-4020(99)00386-5.
  4. Emergon, David W. (1971). "The Preparation and Isomerization of Allyl Thiocyanate. An Organic Chemistry Experiment". Journal of Chemical Education. 48 (1): 81. Bibcode:1971JChEd..48...81E. doi:10.1021/ed048p81.
  5. Dains FB; Brewster RQ; Olander CP (1926). "Phenyl Isothiocyanate". Organic Syntheses . 6: 72. doi:10.15227/orgsyn.006.0072 .
  6. Wong, R; Dolman, SJ (2007). "Isothiocyanates from tosyl chloride mediated decomposition of in situ generated dithiocarbamic acid salts". The Journal of Organic Chemistry. 72 (10): 3969–3971. doi:10.1021/jo070246n. PMID   17444687.
  7. O'Reilly, RJ; Radom, L (2009). "Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles". Organic Letters. 11 (6): 1325–1328. doi:10.1021/ol900109b. PMID   19245242.
  8. Burkett, BA; Kane-Barber, JM; O'Reilly, RJ; Shi, L (2007). "Polymer-supported thiobenzophenone : a self-indicating traceless 'catch and release' linker for the synthesis of isothiocyanates". Tetrahedron Letters. 48 (31): 5355–5358. doi:10.1016/j.tetlet.2007.06.025.
  9. Ortega-Alfaro, M. C.; López-Cortés, J. G.; Sánchez, H. R.; Toscano, R. A.; Carrillo, G. P.; Álvarez-Toledano, C. (2005). "Improved approaches in the synthesis of new 2-(1, 3-thiazolidin-2Z-ylidene)acetophenones". Arkivoc. 2005 (6): 356–365. doi: 10.3998/ark.5550190.0006.631 . hdl: 2027/spo.5550190.0006.631 .