Organic Electrosynthesis - Fundamentals and Applications of Organic Electrochemistry - page 242

amount of Et 4 NF-4HF (only 1.5-1.7 equiv. of
F − to the substrate) at a high current density
(150 mA cm −2 ) ( Eqs. 6.20 and 6.21 ) [60]. In
this method, the substrate was selectively
oxidized to provide the corresponding
monofluorinated product in good yield and with
good current efficiency. In sharp contrast, the
use of organic solvents or a large amount of
Et 4 NF-4HF resulted in no formation or low
yield (about 10%) of the desired fluorinated
product. Isolation of the fluorinated products is
easy: fluorinated lactone and carbonates can be
isolated by extraction with solvent, while
fluorinated tetrahydrofuran can be easily
isolated by distillation of the reaction mixture
after electrolysis. In these cases, the substrates
are predominantly oxidized to result in efficient
fluorination because only a small amount of
supporting fluoride salt is used. Since platinum
with a low hydrogen overpotential is used as a
cathode, the acidic protons of the ionic fluoride
salt are predominantly reduced at the cathode
to generate hydrogen gas, hence a separator for
the electrolysis is not necessary. As explained, a
small amount of fluoride salt is enough for the
fluorination, therefore this fluorination method
is desirable from an atom economical
perspective.