Diethylaminosulfur trifluoride (DAST) is the

organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...

with the formula Et₂NSF₃. This liquid is a fluorinating

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

used for the synthesis of

organofluorine compound Organofluorine chemistry describes the chemistry of the organofluorines, organic compounds that contain the carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, refri ...

s. The compound is colourless; older samples assume an orange colour.

Use in organic synthesis

DAST converts

alcohols In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...

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 Sulfur tetrafluoride is the chemical compound with the formula S F4. It is a colorless corrosive gas that releases dangerous HF upon exposure to water or moisture. Despite these unwelcome characteristics, this compound is a useful reagent for t ...

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. 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

: :Et₂NSiMe₃ + SF₄ → Et₂NSF₃ + Me₃SiF The original paper calls for

trichlorofluoromethane Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance ...

(''Freon-11'') as a solvent, a compound that has been banned under the

Montreal Protocol The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion Ozone depletion consists of two related events observed sinc ...

and is no longer available as a commodity chemical.

Diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...

is a green alternative that can be used with no decrease in yield. 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 CarbolabsREACTION 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) 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

. To minimize accidents, samples are maintained below 50 °C. ''Bis''-(2-methoxyethyl)aminosulfur trifluoride (trade name: Deoxo-Fluor) and difluoro(morpholino)sulfonium

tetrafluoroborate Tetrafluoroborate is the anion . This tetrahedral species is isoelectronic with tetrafluoroberyllate (), tetrafluoromethane (CF4), and tetrafluoroammonium () and is valence isoelectronic with many stable and important species including the perchl ...

(trade name: XtalFluor-M) are reagents derived from DAST with less explosive potential XtalFluor-E has been jointly developed by OmegaChem Inc. and Manchester Organics Ltd. in 2009–2010.

References

{{reflist Organofluorides Reagents for organic chemistry Fluorinating agents Diethylamino compounds Organosulfur compounds

Use in organic synthesis

Synthesis

Safety and alternative reagents

See also

References