Diethylaminosulfur

Diethylaminosulfur trifluoride, commonly abbreviated as DAST, is a sulfur(VI) fluorinating reagent used in organic synthesis. It is employed to fluorinate alcohols to give alkyl fluorides and, under appropriate conditions, to convert carbonyl compounds to gem-difluorides. The reagent is typically used in dry, inert conditions and is often supplied as a colorless liquid that is moisture sensitive.

The chemical structure of DAST features a pentavalent sulfur center bonded to three fluoride ligands and an N,N-diethylamino substituent, giving the formula (Et2N)SF3. It is reactive toward protic media and water, where it can decompose to release hydrogen fluoride and other fluorinating byproducts. Because of its reactivity, DAST is usually handled under inert atmosphere in dry solvents.

DAST is commercially available from specialty chemical suppliers and is also described in some literature as being prepared in situ or via routes from diethylamine and sulfur-fluorinating reagents. In practice, many laboratories use commercially available DAST rather than attempting in-house preparation due to its handling hazards and the need for strictly anhydrous conditions.

In terms of scope, primary and secondary alcohols generally undergo smooth conversion to the corresponding alkyl fluorides. Aldehydes and ketones can be transformed to gem-difluorides. Substrate limitations include sensitivity to elimination, competing rearrangements, and reduced reactivity for certain hindered or highly functionalized systems. For difficult substrates, alternative fluorinating agents such as Deoxo-Fluor may be considered.

Safety and handling: DAST is corrosive, moisture sensitive, and can release HF on decomposition. It should be used in a well‑ventilated fume hood with appropriate personal protective equipment. Dry glassware and solvents are essential, and waste should be managed according to applicable regulations.

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