Onium-poly hydrogen fluorides, the amine or ether complexes of
hydrogen fluoride, have been widely used as fluorinating agents in organic
synthesis. A variety of fluorination reactions involving electrophilic additions to
unsaturated compounds, nucleophilic substitutions, desulfurative fluorinations,
strained ring-opening fluorinations, and deprotection of acetal, ketal and O-silyl
ethers could be achieved with these onium-poly hydrogen fluorides. Fluorination
of alcohols could be achieved under either SN1 or SN2 conditions, depending on
the reagent choice and reaction conditions. Deaminative fluorinations using these
reagents provide convenient access to chiral α-fluoro acids. As strong Bronsted
acids they can be used to catalyze the electrophilic alkylation of alkanes with
alkenes to give high-octane gasoline-range hydrocarbons. They also serve as high
dielectric constant ionic liquid media. In addition, polymer-supported onium
polyhydrogen fluorides such as polyvinylpyridinium polyhydrogen fluoride
(PVPHF) have been developed as convenient alternative reagents, which could be
recovered and recycled for further use.
