View source for Isothiocyanate

{{Short description|1=Chemical group (–N=C=S)}}
[[Image:Isothiocyanate group.svg|thumb|right|upright=1.1|alt=General structure of an isothiocyanate.|General structure of an isothiocyanate.]]

In [[organic chemistry]], '''isothiocyanate''' is a [[functional group]] as found in compounds with the formula {{chem2|R\sN\dC\dS}}.  Isothiocyanates are the more common isomers of [[organic thiocyanates|thiocyanate]]s, which have the formula {{chem2|R\sS\sC\tN}}.  

==Occurrence==
Many isothiocyanates from plants are produced by [[enzymatic]] conversion of metabolites called [[glucosinolate]]s. A prominent natural isothiocyanate is [[allyl isothiocyanate]], also known as [[mustard oil]]s. 

[[Cruciferous vegetable]]s, such as [[bok choy]], [[broccoli]], [[cabbage]], [[cauliflower]], [[kale]], and others, are rich sources of [[glucosinolate]] precursors of isothiocyanates.<ref name="lpi">{{cite web |title=Isothiocyanates |url=https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/isothiocyanates |publisher=Micronutrient Information Center, Linus Pauling Institute, Oregon State University |access-date=14 April 2019|date=1 April 2017}}</ref>

==Structure==
The {{chem2|N\dC}} and {{chem2|C\dS}} distances are 117 and 158 [[picometer|pm]].<ref>{{cite journal |doi=10.1016/j.chemphys.2008.10.024|title=Structure and polarized IR spectra of 4-isothiocyanatophenyl 4-heptylbenzoate (7TPB)|year=2008|last1=Majewska|first1=Paulina|last2=Rospenk|first2=Maria|last3=Czarnik-Matusewicz|first3=Bogusława|last4=Kochel|first4=Andrzej|last5=Sobczyk|first5=Lucjan|last6=Dąbrowski|first6=Roman|journal=Chemical Physics|volume=354|issue=1–3|pages=186–195|bibcode=2008CP....354..186M}}</ref>  By contrast, in [[methyl thiocyanate]], {{chem2|N\tC}} and {{chem2|C\sS}} distances are 116 and 176 pm.

Typical [[bond angle]]s for {{chem2|C\sN\dC}} in aryl isothiocyanates are near 165°. Again, the thiocyanate isomers are quite different with {{chem2|C\sS\sC}} angle near 100°.<ref name= Erian>{{cite journal |doi=10.1016/S0040-4020(99)00386-5 |title=The chemistry of thiocyanic esters |date=1999 |last1=Erian |first1=Ayman W. |last2=Sherif |first2=Sherif M. |journal=Tetrahedron |volume=55 |issue=26 |pages=7957–8024 }}</ref>  In both isomers the {{chem2|SCN}} angle approaches 180°.

==Synthesis==
Allyl thiocyanate isomerizes to the isothiocyanate:<ref name=JCE>{{cite journal |doi=10.1021/ed048p81 |title=The Preparation and Isomerization of Allyl Thiocyanate. An Organic Chemistry Experiment |date=1971 |last1=Emergon |first1=David W. |journal=Journal of Chemical Education |volume=48 |issue=1 |page=81 |bibcode=1971JChEd..48...81E }}</ref>
:{{chem2|CH2\dCHCH2SCN  ->  CH2\dCHCH2NCS}}

Isothiocyanates can be prepared by treating organic [[dithiocarbamate]] salts with [[lead nitrate]] or [[tosyl chloride]].<ref>{{OrgSynth | author = Dains FB | author2 = Brewster RQ | author3 = Olander CP | title = Phenyl Isothiocyanate | year = 1926 | volume = 6 | pages = 72  | doi = 10.15227/orgsyn.006.0072}}</ref><ref>{{cite journal | last1 = Wong | first1 = R | last2 = Dolman | first2 = SJ | title = Isothiocyanates from tosyl chloride mediated decomposition of in situ generated dithiocarbamic acid salts | journal = The Journal of Organic Chemistry | year = 2007 | volume = 72 | issue = 10 | pages = 3969–3971 | pmid = 17444687 | doi = 10.1021/jo070246n}}</ref>
:[[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.<ref>{{ cite journal | last1 = O'Reilly | first1 = RJ | last2 = Radom | first2 = L | title = Ab initio investigation of the fragmentation of 5,5-diamino-substituted 1,4,2-oxathiazoles | journal = Organic Letters | year = 2009 | volume = 11 | issue = 6 | pages = 1325–1328 | pmid = 19245242 | doi = 10.1021/ol900109b }}</ref> This methodology has been applied to a polymer-supported synthesis of isothiocyanates.<ref>{{ cite journal | last1 = Burkett | first1 = BA | last2 = Kane-Barber | first2 = JM | last3 = O'Reilly | first3 = RJ | last4 = Shi | first4 = L | title = Polymer-supported thiobenzophenone : a self-indicating traceless 'catch and release' linker for the synthesis of isothiocyanates | journal = Tetrahedron Letters | year = 2007 | volume = 48 | issue = 31 | pages = 5355–5358 | doi = 10.1016/j.tetlet.2007.06.025 }}</ref>

==Reactions==
Isothiocyanates are weak [[electrophile]]s, susceptible to hydrolysis.  In general, [[nucleophile]]s attack at carbon:
[[Image:ThiazolidineSynthesis.gif|center|The reaction of [[acetophenone]] [[enolate]] with phenyl isothiocyanate. In this [[one-pot synthesis]]<ref>{{cite journal | author1 = Ortega-Alfaro, M. C. | author2 = López-Cortés, J. G. | author3 = Sánchez, H. R. | author4 = Toscano, R. A. | author5 = Carrillo, G. P. | author6 = Álvarez-Toledano, C. | title = Improved approaches in the synthesis of new 2-(1, 3-thiazolidin-2Z-ylidene)acetophenones | journal = Arkivoc | year = 2005 | volume = 2005 | issue = 6 | pages = 356–365 | doi = 10.3998/ark.5550190.0006.631 | doi-access = free | hdl = 2027/spo.5550190.0006.631 | hdl-access = free }}</ref> the ultimate reaction product is a [[Thiazolidine]]. This reaction is [[stereoselective]] with the formation of the [[Z-alkene|Z-isomer]] only.]]

Electrochemical reduction gives [[thioformamides]].<ref>{{cite book|title=The Chemistry of Cyanates and Their Thio Derivatives|volume=Part&nbsp;1|editor-first=Saul|editor-last=Patai|year=1977|publisher=Wiley|location=Chichester|lccn=75-6913|isbn=0-471-99477-4|chapter=The electrochemistry of cyanates and related compounds|first1=Ole|last1=Hammerich|first2=Vernon&nbsp;D.|last2=Parke}}</ref>{{rp|340}}

==Flavor research==
Isothiocyanates occur widely in nature and are of interest in food science and [[medical research]].<ref name=lpi/>  Vegetable foods with characteristic flavors due to isothiocyanates include [[bok choy]], [[broccoli]], [[cabbage]], [[cauliflower]], [[kale]], [[wasabi]], [[horseradish]], [[Mustard (condiment)|mustard]], [[radish]], [[Brussels sprout]]s, [[watercress]], [[papaya]] seeds, [[tropaeolum|nasturtiums]], and [[caper]]s.<ref name=lpi/> 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 [[glucosinolate]]s, and of the enzyme [[myrosinase]], which acts on glucosinolates to release isothiocyanates.<ref name=lpi/>
* [[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]].

==See also==
* [[Methyl isothiocyanate]]

==References==
{{Reflist}}

{{Cyanides}}
{{Nitrogen compounds}}
{{Functional Groups}}
{{Cruciferous Biochemistry}}
{{Transient receptor potential channel modulators}}
{{Authority control}}

[[Category:Antioxidants]]
[[Category:Functional groups]]
[[Category:Isothiocyanates]]
[[Category:Phytochemicals]]