Diethylaminosulfur trifluoride

Diethylaminosulfur trifluoride[1]
IUPAC name N,N-Diethylaminosuflur trifluoride
Identifiers
CAS number	38078-09-0 Y
ChemSpider	110068 N
Jmol-3D images	Image 1 Image 2
SMILES FS(F)(F)N(CC)CC [F-].[F-].[F-].N[S+](CC)CC.CC[S+](N)CC.CC[S+](N)CC
InChI InChI=1S/3C4H12NS.3FH/c3*1-3-6(5)4-2;;;/h3*3-5H2,1-2H3;3*1H/q3*+1;;;/p-3 Y Key: OJRFYRBETDFODT-UHFFFAOYSA-K Y InChI=1/3C4H12NS.3FH/c3*1-3-6(5)4-2;;;/h3*3-5H2,1-2H3;3*1H/q3*+1;;;/p-3 Key: OJRFYRBETDFODT-DFZHHIFOAR
Properties
Molecular formula	C4H10F3NS
Molar mass	161.18
Appearance	colourless oil
Density	1.220 g/cm3
Boiling point	30-32 °C at 3 mmHg
Solubility in water	Reacts violently
Hazards
Main hazards	Very hazardous, can be explosive
N trifluoride (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 is more thermally robust.

See also

• Ishikawa reagent

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, and A. V. Kirsanov (1973). Synthesis (787). 
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)