[1] 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.
Attack of the hydroxyl group of the substrate on sulfur and elimination of hydrogen fluoride lead to an alkoxyaminosulfur difluoride intermediate.
An important side product in fluorinations of enolizable ketones is the corresponding vinyl fluoride, which results from deprotonation of intermediate fluoro carbocations.
[8] However, unlike sulfur tetrafluoride, aminosulfuranes do not convert carboxylic acids into trifluoromethyl groups; the reaction halts at the acyl fluoride stage.
Perfluorinated alkylamines, such as Ishikawa's reagent (N,N-diethyl-1,1,2,3,3,3-hexafluoropropylamine WRONG MOLECULE IN SCHEME BELOW),[16] are highly selective for hydroxyl groups and do not react with aldehydes and ketones.
Alkali and tetraalkylammonium fluorides can be used to displace sulfonate esters; however, these reactions require higher temperatures than aminosulfurane fluorination of the corresponding free alcohols.
Workup usually involves pouring the reaction mixture over water or ice, followed by neutralization of acidic byproducts with sodium bicarbonate.
The reaction mixture was warmed to 25°, 50 mL of water was added, and the lower organic layer was separated and dried with anhydrous magnesium sulfate and distilled to give 12.0 g (90%) of 1-fluorooctane as a colorless liquid, bp 42–43° (20 mm).