The mechanism of fluorination by DAST parallels that of sulfur tetrafluoride. Attack of the hydroxyl group of the substrate on sulfur and elimination of hydrogen fluoride lead to an alkoxyaminosulfur difluoride intermediate. Nucleophilic attack by fluoride, either by an S1 or S2 pathway, leads to the product. Although clean configurational inversion has been observed in a number of chiral alcohols, carbocationic rearrangements have also been observed in some cases. The operative pathway depends on the structure of the substrate.
Conversion of aldehydes and ketones to the corresponding geminal difluorides proceeds by a similar mechanism, with addition of hydrogen fluoride preceding the hydroxyl replacement mechanism described above. An important side product in fluorinations of enolizable ketones is the corresponding vinyl fluoride, which results from deprotonation of intermediate fluoro carbocations.
Halides react by an essentially metathetical exchange of the halide for fluoride. Byproducts containing the exchanged halide have been isolated.