Organic Electrosynthesis - Fundamentals and Applications of Organic Electrochemistry - page 239

conductivity because of their low viscosity
[49,50]. They become more anodically stable
with increasing HF content (increasing n ). As
described in Chapter 5 , conventional
electrochemical fluorination has been carried
out in organic solvents containing fluoride salts,
such as Et 3 N-3HF and Et 4 NF-3HF [49-51].
However, anodic passivation (the formation of
a non-conducting polymer film on the electrode
surface that suppresses Faradaic current) takes
place often, resulting in poor yield and low
current efficiency. Moreover, acetoamidation
also occurs preferentially when MeCN is used
as an electrolytic solvent. In order to overcome
such problems, solvent-free electrochemical
fluorination is an alternative method of
preventing anode passivation and
acetoamidation. Solvent-free selective
electrochemical fluorination of benzenes,
naphthalene, olefins, furan, benzofuran and
phenanthroline was first achieved in less than
50% yield using the ionic liquid Et 3 N-3HF as
the reaction medium, supporting electrolyte
and a fluorine source [52].
Although Et 3 N-3HF and Et 4 NF-3HF are easily
oxidized (lower or around 2 V vs. Ag/Ag + ),
anodically very stable poly(hydrogen fluoride)
salts, Et 4 NF- m HF ( m > 3.5) and Et 3 N-5HF (3 V
vs. Ag/Ag + ) have also been developed [50].
Using ionic liquid Et 4 NF- m HF ( m > 3.5),
solvent-free anodic partial fluorination of