1770
S. NISHIKAWA ET AL.
EXPERIMENTAL
Ketone N-phenylsemicarbazones were prepared in good yields (83–95%) via
typical condensation reactions between N-phenylsemicarbazide and a small excess
of the ketone by refluxing in EtOH for 1–5 h. Preparative-scale electrooxidations
were carried out in a tall 50-mL beaker equipped with a fine frit cup as the cathode
compartment with a nickel coil cathode, along with a cylindrical platinum net anode
(50 mesh).
A solution of acetophenone N-phenylsemicarbazone 1f (8 mmol) in MeOH
(40 mL) containing KI (7.5 mmol) and NaOMe (2.5 mmol) was electrooxidized under
a constant current (0.3 A). During the course of the electrooxidation, the anolyte was
magnetically stirred at ca. 20 ꢀC, and the composition of the reaction mixture was
monitored by GC (FFAP, 1.5 m) analysis. Passage of the electric current was contin-
ued until almost all of the substrate was dissolved. Upon electric current passage of
4.2 F molÀ1, the reaction mixture was concentrated in vacuo (ca. 10 mL) at approxi-
mately 50 ꢀC. The resulting oily residue was treated with water (ca. 30 mL), then
extracted with ethyl ether (3 Â 40 mL), and dried over sodium sulfate overnight.
After removal of the solvent in vacuo, the crude mixture of 2 and 3f were purified
by silica-gel column chromatography using ether=hexane (3:5) as the eluent. The
electrooxidation products were identified by comparison against authentic samples
using GC analysis, high-resolution mass, and=or IR spectroscopy.
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