Diethylaminosulfur trifluoride CAS 38078-09-0 DAST

DAST converts alcohols to corresponding alkyl fluorides and aldehydes and unimpeded ketones to acyclic difluorides. Carboxylic acid only reacts with acyl fluoride (sulfur tetrafluoride affects the conversion of -co2 h → -cf 3). DAST is preferred over the more classical gaseous SF 4 because it is easier to handle as a liquid. A slightly thermally stable compound is morpho DAST. Acid unstable substrates are less likely to be rearranged and eliminated because DAST is less susceptible to acid contamination. The reaction temperature is also mild – alcohols usually react at -78 ° C and ketones at about 0 ° C.

DAST is prepared by the reaction of diethylaminotrimethylsilane and sulfur tetrafluoride:
Et 2 NSiMe 3 + SF 4 → Et 2 NSF 3 + Me 3 SiF
The initial paper required using trichlorofluoromethane (Freon-11) as a solvent, which has been outlawed by the Montreal Method and also is no more available as a commercial chemical. Ether is an eco-friendly substitute that can be made use of without minimizing manufacturing. As a result of the dangers associated with the prep work of DAST (glass etching, possibility of exothermic events), it is generally bought from commercial sources.