Diethylaminosulfur trifluoride

Diethylaminosulfur trifluoride (DAST)[2] 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.

Diethylaminosulfur trifluoride[1]
Names
IUPAC name
N,N-Diethylaminosuflur trifluoride
Other names
diethyl(trifluorosulfido)amine
Identifiers
3D model (JSmol)
Abbreviations DAST
ChemSpider
ECHA InfoCard 100.048.866
EC Number
  • 253-771-2
UNII
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
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H226, H302, H312, H314, H332
P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P280, P301+312, P301+330+331, P302+352, P303+361+353, P304+312, P304+340, P305+351+338, P310, P312, P321, P322, P330, P363
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

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. A slightly thermally more stable compound is morpho-DAST.[3] 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:[4]

Et2NSiMe3 + SF4 → Et2NSF3 + Me3SiF

The original paper calls for trichlorofluoromethane (Freon-11) as a solvent, a compound that has been banned under the Montreal Protocol and is no longer available as a commodity chemical. diethyl ether is a green alternative that can be used with no decrease in yield.[5] 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[6] was one of the few suppliers of the chemical but a number of companies now sell DAST. Carbolabs was acquired by Sigma-Aldrich in 1998.

Safety and alternative reagents

Upon heating, DAST converts to the highly explosive (NEt2)2SF2 with expulsion of sulfur tetrafluoride. To minimize accidents, samples are maintained below 50 °C.[7] Bis-(2-methoxyethyl)aminosulfur trifluoride (trade name: Deoxo-Fluor) and difluoro(morpholino)sulfonium tetrafluoroborate (trade name: XtalFluor-M) are reagents derived from DAST with less explosive potential[8][9] XtalFluor-E has been jointly developed by OmegaChem Inc. and Manchester Organics Ltd. in 2009–2010.[8][9]

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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. Middleton, William J. (1975-03-01). "New fluorinating reagents. Dialkylaminosulfur fluorides". The Journal of Organic Chemistry. 40 (5): 574–578. doi:10.1021/jo00893a007. ISSN 0022-3263.
  3. Markovskii, LN; Pashinnik, VE; KIRSANOVA, NA (1975). "SULFUR BIS (DIALKYLAMINO) DIFLUORIDES". Zhurnal Organicheskoi Khimii. 11: 74–77 – via Web of Science.
  4. W. J. Middleton, E. M. Bingham "Diethylaminosulfur Trifluoride" Organic Syntheses, Coll. Vol. 6, p.440; Vol. 57, p.50. Online version
  5. L. N. Markovskij; V. E. Pashinnik; A. V. Kirsanov (1973). "Application of Dialkylaminosulfur Trifluorides in the Synthesis of Fluoroorganic Compounds". Synthesis. 1973 (12): 787–789. doi:10.1055/s-1973-22302.
  6. 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)
  7. Messina, P. A.; Mange, K. C.; Middleton, W. J. (1989). "Aminosulfur trifluorides: relative thermal stability". Journal of Fluorine Chemistry. 42 (1): 137–143. doi:10.1016/S0022-1139(00)83974-3.
  8. 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. PMC 2869536.
  9. 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. PMC 2770860. PMID 19799406.
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