Diethylaminosulfur trifluoride

Diethylaminosulfur trifluoride[1]
Names
IUPAC name
N,N-Diethylaminosuflur trifluoride
Other names
diethyl(trifluorosulfido)amine
Identifiers
38078-09-0 YesY
3D model (Jmol) Interactive image
Interactive image
Abbreviations DAST
ChemSpider 110068 N
ECHA InfoCard 100.048.866
Properties
C4H10F3NS
Molar mass 161.19 g·mol−1
Appearance colourless oil
Density 1.220 g/cm3
Boiling point 30 to 32 °C (86 to 90 °F; 303 to 305 K) at 3 mmHg
Reacts with water
Solubility reacts with ethanol
soluble in acetonitrile
Hazards
Main hazards corrosive, flammable, can be explosive
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Diethylaminosulfur trifluoride (DAST) is the organosulfur compound with the formula Et2NSF3. This liquid is a fluorinating reagent used for the synthesis of organofluorine compounds. The compound is colourless; older samples assume an orange colour.

Use in organic synthesis

DAST converts alcohols to the corresponding alkyl fluorides as well as aldehydes and unhindered ketones to geminal difluorides. Carboxylic acids react no further than the acyl fluoride (sulfur tetrafluoride effects the transformation —CO2H → —CF3). DAST is used in preference to the more classical gaseous SF4, since as a liquid it is more easily handled. Acid-labile substrates are less likely to undergo rearrangement and elimination since DAST is less prone to contamination with acids. Reaction temperatures are milder as well - alcohols typically react at -78 °C and ketones around 0 °C.

Synthesis

DAST is prepared by the reaction of diethylaminotrimethylsilane and sulfur tetrafluoride:[2]

Et2NSiMe3 + SF4 → Et2NSF3 + Me3SiF

The Organic Syntheses protocol calls for trichlorofluoromethane as a solvent, a compound that has been banned under the Montreal Protocol and is no longer available as a commodity chemical. Diethyl ether may be used instead with no decrease in yield.[3] Because of the dangers involved in the preparation of DAST (glass etching, possibility of exothermic events), it is often purchased from a commercial source. At one time Carbolabs[4] was one of the few suppliers of the chemical but a number of companies now sell DAST.

Safety and alternative reagents

Upon heating, DAST converts to SF4 and (NEt2)2SF2, a high-boiling and explosive compound. To minimize accidents, samples are maintained below 50 °C. Bis-(2-methoxyethyl)aminosulfur trifluoride (Deoxo-Fluor) and morpholinosulfur trifluoride (morpho-DAST or MOST) are related reagents which are more thermally stable.

Recent alternatives[5][6] have been manufactured by OmegaChem based on DAST but crystalline and with better handling properties. The XtalFluor range[7] offers XtalFluor-E (diethylamine) and XtalFluor-M (morpholine) difluorosulfonium salts (tetrafluoroborates).

See also

References

  1. ↑ A. H. Fauq, "N,N-Diethylaminosulfur Trifluoride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York.
  2. ↑ W. J. Middleton, E. M. Bingham "Diethylaminosulfur Trifluoride" Organic Syntheses, Coll. Vol. 6, p.440; Vol. 57, p.50. Online version
  3. ↑ L. N. Markovskij; V. E. Pashinnik; A. V. Kirsanov (1973). "Application of Dialkylaminosulfur Trifluorides in the Synthesis of Fluoroorganic Compounds". Synthesis. 1973: 787–789. doi:10.1055/s-1973-22302.
  4. ↑ REACTION OF SULFOXIDES WITH DIETHYLAMINOSULFUR TRIFLUORIDE: FLUOROMETHYL PHENYL SULFONE, A REAGENT FOR THE SYNTHESIS OF FLUOROALKENES, Organic Syntheses, Coll. Vol. 9, p.446 (1998); Vol. 72, p.209 (1995)
  5. ↑ l’Heureux, A.; Beaulieu, F.; Bennett, C.; Bill, D. R.; Clayton, S.; Laflamme, F. O.; Mirmehrabi, M.; Tadayon, S.; Tovell, D.; Couturier, M. (2010). "Aminodifluorosulfinium Salts: Selective Fluorination Reagents with Enhanced Thermal Stability and Ease of Handling†,‡". The Journal of Organic Chemistry. 75 (10): 3401–3411. doi:10.1021/jo100504x.
  6. ↑ Beaulieu, F.; Beauregard, L. P.; Courchesne, G.; Couturier, M.; Laflamme, F. O.; l’Heureux, A. (2009). "Aminodifluorosulfinium Tetrafluoroborate Salts as Stable and Crystalline Deoxofluorinating Reagents". Organic Letters. 11 (21): 5050–5053. doi:10.1021/ol902039q.
  7. ↑ http://www.omegachem.com/index.php?option=com_content&view=article&id=53
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