Organic thiocyanates

Several synthesis routes exist,{{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 }} the most common being the reaction between alkyl halides and alkali thiocyanate in aqueous media.{{cite web | title = Synthesis of thiocyanates | url = https://www.organic-chemistry.org/synthesis/C1S/thiocyanates.shtm}} Illustrative is the preparation of isopropyl thiocyanate by treatment of isopropyl bromide with sodium thiocyanate in boiling ethanol.{{cite journal |doi=10.15227/orgsyn.011.0092|title=Isopropyl Thiocyanate|journal=Organic Syntheses|year=1931|volume=11|page=92|author=R. L. Shriner}} 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:{{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 }}

:{{chem2|CH2\dCHCH2Cl + Na2S2O3 -> CH2\dCHCH2S2O3Na + NaCl}}

:{{chem2|CH2\dCHCH2S2O3Na + NaCN -> CH2\dCHCH2SCN + Na2SO3}}

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:

:{{chem2|[ArN2]BF4 + CuSCN -> ArSCN + CuBF4 + N2}}

Some arylthiocyanates can also often be obtained by thiocyanogenation, i.e. the reaction of thiocyanogen. This reaction is favored for electron-rich aromatic substrates.

In methyl thiocyanate, {{chem2|N\tC}} and {{chem2|C\sS}} distances are 116 and 176 pm. By contrast, {{chem2|N\dC}} and {{chem2|C\dS}} distances are 117 and 158 pm in isothiocyanates.{{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}}

Typical bond angles for {{chem2|C\sS\sC}} are 100°. By contrast {{chem2|C\sN\dC}} in aryl isothiocyanates is 165°. Again, the thiocyanate isomers are quite different with {{chem2|C\sS\sC}} angle near 100°.

In both organic thiocyanate and isothiocyanate isomers the {{chem2|SCN}} 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.{{cite book|title=The Chemistry of Cyanates and Their Thio Derivatives|volume=1|editor-first=Saul|editor-last=Patai|year=1977|publisher=Wiley|location=Chichester|lccn=75-6913|isbn=0-471-99477-4|pages=331–335|series=The Chemistry of Functional Groups}}

Some thiocyanates isomerize to the isothiocyanates. This reaction is especially rapid for the allyl isothiocyanate:

:{{chem2|CH2\dCHCH2SCN -> CH2\dCHCH2NCS}}

Likewise, acyl thiocyanates are difficult to synthesize because any excess thiocyanate ion catalyzes isomerization to the acyl isothiocyanate.{{sfn|Patai|1977|pp=451-453}}

• Isothiocyanate, isomers of organic thiocyanates with the formula R−N=C=S
• Methyl thiocyanate, the simplest organic thiocyanate

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Category:Functional groups