Solvent-Free Microwave-Assisted Peroxidative Oxidation of Alcohols Catalyzed by Iron(III)…
added dropwise an ethanol solution (5 mL) of FeCl .6H O
3
personal computer through a GPIB interface. Cyclic
2
(
0.27 g, 1 mmol) to produce a dark red solution which was
voltammetry (CV) studies were undertaken in 0.2 M
n
[ Bu N][BF ]/MeCN, at a platinum disc working electrode
kept for slow evaporation. After 2 days, the red crystalline
compound containing diffractable crystals that deposited
was collected by filtration and washed with ethanol. Yield:
4
4
(d = 0.5 mm) and at room temperature. Controlled-po-
tential electrolyses (CPE) were carried out in electrolyte
solutions with the above-mentioned composition, in a
three-electrode H-type cell. The compartments were sepa-
rated by a sintered glass frit and equipped with platinum
gauze working and counter electrodes. For both CV and
CPE experiments, a Luggin capillary connected to a silver
wire pseudo-reference electrode was used to control the
working electrode potential. A Pt wire was employed as the
counter-electrode for the CV cell. The CPE experiments
were monitored regularly by CV, thus assuring no signifi-
cant potential drift occurred along the electrolysis. The
solutions were saturated with N2 by bubbling this gas
before each run, the redox potentials of the complexes were
measured by CV in the presence of ferrocene as the internal
standard, and their values are quoted relative to the SCE by
7
8 % (0.35 g) based on Fe. Anal. Calcd. for C H Cl
12 15 2
FeN O (M = 450.05): C, 32.03; H, 3.36; N, 18.67; Found:
6
5
-
1
C, 32.13; H, 3.21; N, 18.18. FT-IR (KBr, cm ): 3421(bs),
301 (bs), 1631 (s), 1542 (m), 1501 (m), 1432 (m), 1381
s), 1330 (m), 1234 (s), 1208 (s), 1109 (m), 925 (m), 841
3
(
(
(
1
6
m), 816 (m), 724 (s), 625 (m); H-NMR (DMSO-d ): 8.24
1H, s, Ar–H), 7.88 (1H, s, Ar–H), 7.37 (2H, bs, –NH2).
2
.2 Synthesis of 2
The mixture of FeCl .6H O (0.27 g, 1 mmol), 3-amino-2-
3
2
0
pyrazinecarboxylic acid (0.28 g, 2 mmol) and 4, 4 -bipyr-
idine (0.15 g. 1 mmol) was dissolved in 4 mL of DMF and
MeOH (1:1) mixture. The resulting solution was sealed in a
vessel and heated at 75 °C for 48 h. It was subsequently
cooled to room temperature (0.2 °C min ), affording
block-type reddish crystals. Yield: 74 % (0.41 g) based on
Fe. Anal. Calcd. for C H Cl FeN O (M = 555.15): C,
5
0/?
using the [Fe(g -C H ) ] redox couple (E = 0.42 V vs.
5
5 2
-
1
SCE) [34–36].
2.5 General Procedure for the Peroxidative
Oxidation of 1-Phenylethanol
1
8
20
2
8 5
3
2
1
8.94; H, 3.63; N, 20.18; Found: C, 38.65; H, 3.41; N,
1
-
0.08. FT-IR (KBr, cm ): 3411 (bs), 3304 (bs), 1621 (s),
554 (m), 1491 (m), 1442 (m), 1383 (s), 1327 (m), 1232
The catalytic tests under MW irradiation (MW) were per-
formed in a focused Anton Paar Monowave 300 MW
reactor using a 5 mL capacity reaction tube with a 10 mm
internal diameter, fitted with a rotational system and an IR
temperature detector.
(
s), 1204 (s), 923 (m), 840 (s), 821 (s), 556 (m), 451 (m);
6
1
H-NMR (DMSO-d ): 8.78 (2H, s, Ar–H), 8.23 (1H, s, Ar–
H), 7.94 (2H, s, Ar–H), 7.87 (1H, s, Ar–H), 7.36 (2H, bs,
–
NH2).
Chromatographic analyses were undertaken by using a
Fisons Instruments GC 8000 series gas chromatograph with
a DB-624 (J&W) capillary column (DB-WAX, column
length: 30 m; internal diameter: 0.32 mm), FID detector,
and the Jasco-Borwin v.1.50 software. The temperature of
injection was 240 °C. The initial temperature was main-
tained at 140 °C for 1 min, then raised 10 °C min to
220 °C and held at this temperature for 1 min. Helium was
used as the carrier gas. The internal standard method was
used to quantify the organic products.
2
.3 Synthesis of 3
The mixture of FeCl .6H O (0.27 g, 1 mmol), 3-amino-2-
3
2
0
pyrazinecarboxylic acid (0.14 g, 1 mmol) and 2,2 -bipyr-
idine (0.15 g. 1 mmol) was dissolved in 4 mL of methanol.
The resulting solution was sealed in a vessel and heated at
-
1
7
5 °C for 48 h. It was subsequently cooled to room tem-
-1
perature (0.2 °C min ), affording reddish crystals. Yield:
1 % (0.34 g) based on Fe. Anal. Calcd. For C H Cl
2
8
1
5
12
FeN O (M = 421.05): C, 42.79; H, 2.87; N, 16.63; Found:
5
Oxidation reactions of the alcohols were carried out in
sealed cylindrical Pyrex tubes under focused MW irradia-
tion as follows: the alcohol (2.5 mmol), TBHP (70 %
aqueous solution, 5.0 mmol) and catalyst precursor 1–3
(1–10 lmol, 0.04–0.4 mol% vs. substrate) were introduced
in the tube which was then placed in the MW reactor. In the
experiments with radical traps, CBrCl3 (2.5 mmol) or
2
-
C, 42.83; H, 2.21; N, 16.18. FT-IR (KBr, cm ): 3422 (s),
1
3
1
8
8
7
7
308 (s), 1639 (s), 1603 (s), 1555 (m), 1497 (w), 1443 (m),
368 (s), 1328 (m), 1235 (m), 1150 (m), 1026 (w), 918 (m),
1
6
38 (m), 821 (m), 772 (s), 731 (m); H-NMR (DMSO-d ):
.63 (1H, s, Ar–H), 8.33 (1H, s, Ar–H), 8.22 (1H, s, Ar–H),
.89 (1H, s, Ar–H), 7.88 (1H, s, Ar–H), 7.40 (1H, s, Ar–H),
.35 (2H, bs, –NH2).
NHPh (2.5 mmol) was added to the reaction mixture. In
2
the experiments with other additives (TEMPO, nitric acid
1 M solution, or potassium carbonate 1 M solution), a
2
.4 Electrochemical Studies
2.5 % additive/substrate molar ratio was used. The system
The electrochemical experiments were performed on an
EG&G PAR 273A potentiostat/galvanostat connected to a
was stirred and irradiated (10 W) for 0.5–2 h at 50–150 °C.
After the reaction, the mixture was allowed to cool down to
123