Trimethylsilyl isothiocyanate

Last updated
Trimethylsilyl isothiocyanate
Trimethylsilylisothiocyanat Strukturformel.svg
Ball and stick diagram of trimethylsilyl isothiocyanate.png
Names
IUPAC name
isothiocyanato(trimethyl)silane [1]
Other names
  • TMSNCS
  • Trimethylsilyl isothiocyanate
  • Isothiocyanatotrimethylsilane
  • Silane, isothiocyanatotrimethyl-
  • (Trimethylsilyl)isothiocyanate
  • TMS-isothiocyanate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.017.209 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 218-929-7
PubChem CID
  • InChI=1S/C4H9NSSi/c1-7(2,3)5-4-6/h1-3H3
    Key: XLTUPERVRFLGLJ-UHFFFAOYSA-N
  • C[Si](C)(C)N=C=S
Properties
C4H9NSSi
Molar mass 131.27 g·mol−1
Density 0.931 g·mL −1 [2]
Melting point −32.8 °C (−27.0 °F; 240.3 K) [2]
Boiling point 143 °C (289 °F; 416 K)
Reacts with water [3]
Vapor pressure 100 mmHg
Hazards
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg [4]
Danger [4]
H226, H301, H311, H315, H319, H331, H334, H335
NFPA 704 (fire diamond)
[5]
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
2
0
Flash point 29 °C (84 °F; 302 K) [2]
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Trimethylsilyl isothiocyanate (TMSNCS) is an organosilicon compound that contains an isothiocyanate whose nitrogen atom is covalently bonded to a trimethylsilyl group. The isothiocyanate group is an analog of the isocyanate group, but having a sulfur instead of oxygen.

Contents

Reactions

TMSNCS is useful reagent in organic chemistry. It is an ambident nucleophile, able to react with various alkyl halides, acetals, aldehydes, unsaturated compounds, aziridines, oxiranes, polycyclic aromatic hydrocarbons, and acetylated hexoses to form either thiocyanate or isothiocyanate structures. [6] As an electrophile, it can react with other nucleophiles to form thioamide types of structures, some of which can undergo subsequent reactions to form heterocycles.

Halide substitutions

As a sulfur nucleophile, TMSNCS substitutes for halides on a range of alkyl substrates, giving alkyl thiocyanates. These substitution reactions involve tetrabutylammonium fluoride used as phase-transfer catalyst and occur under particularly mild conditions. [7]

Benzylthiocyanat Synthese.svg

Reactions with aldehydes and acetals

As a nitrogen nucleophile, TMSNCS adds across the carbonyl group of aldehydes and substitutes isothiocyanate for one of the ether groups on acetals via acid-catalyzed processes. [8]

Aldehyde and TMSNCS reaction.svg
Acetal and TMSNCS Reaction.png

Mercapto-1,2,4-triazoles

A one-step method to prepare mercapto-1,2,4-tiazoles is favored on the industrial scale due to its high efficiency (88% yield) and non-constraining conditions: not requiring anhydrous solvent, inert gas temperature, or chromatographic purification. The method can be summarized as follows: after the equimolar mixture of benzohydrazide and TMSNCS reflux in the presence of EtOH for 5 hours, NaOH is added to the reaction mixture and the solution is refluxed for 4 h. Acetic acid is then used to cool and neutralize, ultimately yielding the pure white solid 3-phenyl-5-mercapto-4H-1,2,4-triazole at 88% yield. [6]

Reaction to produce produce benzoyl thiosemicarbazide.png

2-Amino-1,3,4-oxadiazoles

TMSNCS used for the synthesis of 2-amino-1,3,4-oxadiazoles. The TMSNCS reagent assists in the production of the thiosemicarbazide and the subsequent reaction (cyclodesulfurization of thiosemicarbazides under basic conditions in the presence of I2/KI) results in 2-amino-1,3,4-oxadiazoles in high yields (79–94%). [9] The 2-amino-1,3,4-oxadiazoles resulting from this reaction are: 2-Amino-5-phenyl-1,3,4-oxadiazole, 2-Amino-5-(p-methylphenyl)-1,3,4-oxadiazole, 2-Amino-5-(p-chlorophenyl)-1,3,4-oxadiazole, 2-Amino-5-(p-methoxyphenyl)- 1,3,4-oxadiazole, 2-Amino-5-(p-nitrophenyl) -1,3,4-oxadiazole, 2-Amino-5-(o-methylphenyl)-1,3,4-oxadiazole, 2-Amino-5-(o-chlorophenyl)-1,3,4-oxadiazole, ect. [10]

2-Amino-1,3,4-oxadiazole Synthese.svg

Notes

  1. ↑ "Trimethylsilyl isothiocyanate (Compound)". Pubchem. Retrieved April 9, 2020.
  2. 1 2 3 "(Trimethylsilyl)isothiocyanate". sigmaaldrich. Retrieved April 9, 2020.
  3. ↑ "Trimethylsilyl isothiocyanate, 94%". Alfa Aesar. Thermo Fisher Scientific. Retrieved April 9, 2020.
  4. 1 2 "Trimethylsilyl isothiocyanate". Summary of Classification and Labeling. European Chemicals Agency (ECHA). Retrieved April 9, 2020.
  5. ↑ "Safety Data Sheet". Alfa. Thermo Fisher Scientific. Retrieved April 10, 2020.
  6. 1 2 Guda, Dinneswara Reddy; Wang, Tengjiao; Cho, Hyeon Mo; Lee, Myong Euy (September 2012). "Trimethylsilyl isothiocyanate (TMSNCS): an efficient reagent for the one-pot synthesis of mercapto-1,2,4-triazoles" . Tetrahedron Letters. 53 (39): 5238. doi:10.1016/j.tetlet.2012.07.054.
  7. ↑ Renard, Pierre-Yves; Schwebel, Hervé; Vayron, Philippe; Leclerc, Eric; Dias, Sonia; Mioskowski, Charles (2001). "Optimized access to alkyl thiocyanates". Tetrahedron Lett. 42 (48): 8479–8481. doi:10.1016/S0040-4039(01)01846-9.
  8. ↑ Nishiyama, Kozaburo; Oba, Makoto (June 1987). "Reactions of Trimethylsilyl Isothiocyanate with Aldehydes and Acetals. Synthesis of Symmetrically and Unsymmetrically Isothiocyanato-Substituted Ethers". Bulletin of the Chemical Society of Japan. 60 (6): 2289–2291. doi: 10.1246/bcsj.60.2289 .
  9. ↑ Guda, Dinneswara Reddy; Cho, Hyeon Mo; Lee, Myong Euy (2013). "Mild and convenient one-pot synthesis of 2-amino-1,3,4-oxadiazoles promoted by trimethylsilyl isothiocyanate (TMSNCS)" . RSC Advances. 3 (21): 7684. Bibcode:2013RSCAd...3.7684G. doi:10.1039/C3RA41044G . Retrieved 10 April 2020.
  10. ↑ Guda, Dinneswara Reddy; Cho, Hyeon Mo; Lee, Myong Euy (2013). "Electronic Supplementary Information (ESI)" (PDF). RSC Advances: S1 –S8. Retrieved 10 April 2020.
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