Reaction with hydrogen fluoride

In the same way as intramolecular displacement leads to particularly stable atomic groupings within a molecule, the disproportionation reactions between several molecules are attributable to the tendency for the more stable compound with the higher fluorine content to form. Reactions of this kind are sometimes used to obtain highly fluorinated compounds from products with lower fluorine contents, for example, the catalytic fluorination of chloroalkanes with hydrogen fluoride or with fluorination agents such as antimony(V) fluoride or antimony(III) fluoride. The chlorine compound formed as the second product of the disproportionation process is reused as the starting material for the preparation of the compound to be dispropor-tionated. 

Table 1 Fluoromethyl Ketones by Reaction of Hydrogen Fluoride/Pyridine with Diazomethyl Ketones1 44 1...

There are a limited number of examples of the reaction of nitro alcohols with sulfur tetrafluoride. In each case the reaction was performed with additional hydrogen fluoride present. With these modifications relatively drastic conditions must be used and yields are low to moderate, depending on the substrate (Table 1). 

Hydrogen fluoride is most often employed to prepare metal fluorides by reaction of oxides, hydroxides, carbonates, and chlorides with either pure HF or concentrated aqueous solutions. Obviously water-sensitive fluorides require pure HF and conditions that will not result in a mixture of fluorides and oxides. Hydrogen fluoride reacts with all metals below hydrogen in the electromotive series and numerous metal fluorides can be prepared at high temperatures by reaction of the powdered metal with HF(g). Authoritative reviews on metal fluorides can be consulted for details. ... 

Iodofluorination reactions of acetylenes can be carried out with iodine fluoride, prepared directly from the corresponding elements,553 with jV-iodosuccinimide in the presence of polymer-supported hydrogen fluoride,258 with (difluoroiodo)mcthane,554 or with bis(pyridine)iodonium tetrafluoroborate in the presence of fluoride.555 Some examples are summarized in Table 45. 

Simple aliphatic oxiranes can be converted to fluorohydrin with hydrogen fluoride only with great difficulty, but the reaction can be carried out in systems with rigid conformations (e.g., steroids, 9,10-epoxydecalin). Good yields can be attained from cyclopentene and cyclohexene oxides with 42% pyridine-polyhydrogen fluoride and in a series of terpene oxides with an amine-hydrogen fluoride complex. ... 

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