Prior to the introduction of diethylaminosulfur trifluoride (DAST) in 1970 for the replacement of hydroxyl groups with fluoride, sulfur tetrafluoride was the reagent most commonly used to accomplish this transformation. However, sulfur tetrafluoride only reacts with the most acidic hydroxyl groups (its substrate scope is limited), and is difficult to handle, toxic, and capable of generating hydrogen fluoride upon hydrolysis. Thus, aminosulfurane reagents such as diethylaminosulfur trifluoride have largely replaced SF as the reagents of choice for replacement of hydroxyl groups with fluoride.
Aminosulfuranes are usually prepared by reaction of the corresponding dialkylamino(trialkyl)silanes with SF. When the aminosulfurane is exposed to a second equivalent of aminosilane, bis(dialkylamino)sulfur difluorides result. Tris(dialkylamino)sulfonium difluorotrimethylsilicates such as tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) have achieved synthetic utility as reagents for the fluorination of halides. These form when three equivalents of aminosilane are exposed to sulfur tetrafluoride.