The uses of Diethylaminosulfur trifluoride

Diethylaminosulfur trifluoride is a useful and convenient reagent for replacing primary, secondary, and tertiary hydroxyl and aldehyde and ketone carbonyl oxygen with fluorine, even in the presence of other halogens and other functional groups, such as carboxylic esters.

Uses

In contrast to sulfur tetrafluoride, Diethylaminosulfur trifluoride is a liquid easily measured and used in standard glass equipment at moderate temperatures and atmospheric pressure, and can be used on acid-sensitive compounds (such as pivaldehyde) to convert them into the fluorinated derivative. In contrast to other reagents such as SF₄, SeF₄ pyridine HF, HF.pyridine, and (C₂H₅)₂NCF₂CFHCl, this reagent can replace hydroxyl groups with fluorine in primary alcohols such as 2-methyl-1-propanol without causing extensive rearrangement or dehydration.

Use in organic synthesis

Diethylaminosulfur trifluoride 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.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.

Preparation

This preparation of diethylaminosulfur trifluoride is an adaptation of a procedure first described by von Halasz and Glemser.The same procedure can also be used to prepare other dialkylaminosulfur trifluorides by the substitution of the diethylaminotrimethylsilane with other dialkylaminotrimethylsilanes.

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