Chemistry of Heterocyclic Compounds 2017, 53(8), 861–866
The course of the reaction was monitored by UV-Vis spectro-
reaction mixture was heated to 75°C for 7 h with stirring in
an oil bath or ultrasonic bath. For the analysis, the reaction
mixture sample (0.1 ml) was diluted to 1 ml and 0.05 ml
was taken in a GC-MS sequential injection flask and
completed to a volume of 2 ml with ethyl acetate or
acetonitrile.
Catalytic experiment of trans-stilbene oxidation. The
appropriate catalyst 1–3 (1.32 µmol (0.6 mol %) or
2.2 µmol (1 mol %)) was added to a solution of trans-
stilbene (40 mg, 0.22 mmol) and TBHP (56.4 mg,
0.44 mmol) in ethyl acetate (4 ml). The reaction mixture
was heated to 75°C for 7 h with stirring in an oil bath or
ultrasonic bath. The reaction mixture of ethyl acetate was
left cooling to room temperature. The catalyst precipitated
upon the evaporation of the solvent and filtered off. The
solid was rinsed with an appropriate cold solvent (2×3 ml). For
the analysis, the sample of the liquid layer (0.1 ml) was
diluted to 1 ml and 0.05 ml was taken in a GC-MS
sequential injection flask and completed to a volume of
2 ml with ethyl acetate or acetonitrile.
Catalytic experiment of trans-stilbene oxidation with
different solvents (chloroform, tetrahydrofuran, N,N-di-
methylformamide, and dioxane). Catalyst 3 (1.1 mg,
1.32 µmol, 0.6 mol %) was added to a solution of trans-
stilbene (40 mg, 0.22 mmol) and TBHP (56.4 mg,
0.44 mmol) in solvent (4 ml), and the reaction mixture was
heated to 75°C for 7 h with stirring in an oil bath. For the
analysis, the reaction mixture sample (0.1 ml) was diluted
to 1 ml and 0.05 ml was taken in a GC-MS sequential
injection flask and completed to a volume of 2 ml with
ethyl acetate or acetonitrile.
Catalytic oxidation of cis-stilbene and styrene.
Catalyst 3 (1.84 mg, 2.2 µmol, 1.0 mol %) was added to a
solution of cis-stilbene (40 mg, 0.22 mmol) or styrene
(22.88 mg, 0.22 mmol) and TBHP (56.4 mg, 0.44 mmol) in
ethyl acetate (4 ml). The reaction mixture was heated to
75°C for 7 h in an ultrasonic bath. The reaction mixture
was filtered and, for the analysis, 0.1 ml of the filtrate was
diluted to 1 ml and 0.05 ml was taken in a GC-MS
sequential injection flask and completed to a volume of
2 ml with ethyl acetate or acetonitrile.
scopy (Fig. 2). Ethyl acetate solution of TBHP (1.2 ml,
187.5 mM) was added in portions (0.2 ml, 37.5 µmol) and
a spectrum of a sample (0.2 ml) of the reaction mixture was
recorded after every addition and waiting for 15 min. The
first addition was resulted in a bathochromic shift for the
n–π* and ligand-to-metal (L–M) transition bands (to 373
and 474 nm, respectively) with coordinating oxygen, and
after the subsequent additions all the transitions (π–π*, L–M,
and n–π*; at 262, 367, and 464 nm, respectively in
ethyl acetate) slowly became weaker and disappeared as
expected. These results are in accord with previous
reports34,35 and the formation of the peroxo copper(III)
intermediate species in the suggested mechanism.
In summary, it was found that three different azo- and
bisazopyrazol-5-one-based copper(II) catalysts are all
active in the catalytic oxidation of trans-stilbene. All
catalysts are soluble in ethyl acetate under heating, but easy
recovery of the catalyst is available from the reaction
mixture. The catalysts can be used without further
decomposition at 75°C. The catalysts are all active
under heating with and without simultaneous ultrasonic
treatment, but ultrasonic irradiation gives rise to higher
yields of trans-stilbene oxide. These results, once more,
show the importance of sonochemistry in organic
synthesis, especially for catalytic reactions. The catalytic
potential in ethyl acetate of these complexes is high
in terms of selectivity and conversion compared with
the other solvents used: chloroform, tetrahydrofuran,
N,N-dimethylformamide, and dioxane. The catalytic
oxidation of trans-stilbene is found to range between
42.0–69.3% conversion, where the major oxidation product
is trans-stilbene oxide. Two of the catalysts are
water soluble, therefore, work to extend their applicability
toward catalytic oxidations under green conditions is in
progress.
Experimental
Electronic spectra in the 200–400 nm range (200–
800 nm for the mechanism determination work) were
obtained on a Shimadzu UV 1800 spectrophotometer. Gas
chromato-mass spectrometry (GC-MS) analysis was performed
on a Shimadzu QP2010 instrument operating in the split
mode (ratio 10:1) using Restek/Rtx®-5 30 m × 0.25 mm
column and chromatographic grade helium as the carrier
gas. In GC calculations, all peaks amounting to at least
0.5% of the total products were taken into account. All
reactions were carried out in a two-necked glass flask fitted
with a water condenser. The ultrasonic reactions were
performed in a Bandelin-Sonorex Super RK 100(H)
ultrasonic cleaner with a frequency of 35 kHz and a total
power of 320 W. The reaction flask was located in the
water bath of the equipment. All reagents and solvents
were supplied from Sigma-Aldrich or Merck in the highest
purity grade available and used without further purification.
70% TBHP in water was used as the oxidant.
Supplementary information file, containing GC
chromatograms and mass spectra of the reaction mixture in
experiments and UV-Vis spectra according to the reaction
time determination, is available at the journal website at
The author is thankful to ODU/BAP, Ordu University,
Scientific Research Projects Coordination Department
(Project number AR-1235) and TUBITAK, the Scientific
and Technological Research Council of Turkey (Project
number 110T549) for financial support, and to the Central
Research Laboratory of Ordu University for GC-MS
analysis.
A part of this work was presented by E. Bagdatli at the
conference ''Trans Mediterranean Colloquium on Hetero-
cyclic Chemistry (TRAMECH-VIII)'', November 11–15,
2015, Antalya, Turkey.
Blank experiment of trans-stilbene oxidation. trans-
Stilbene (40 mg, 0.22 mmol) and TBHP (56.4 mg,
0.44 mmol) were dissolved in ethyl acetate (4 ml), and the
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