Ag Catalyzed Bromination of Aromatics
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Scheme 1 Ag/HMB catalyzed
bromination of aromatics with
NBS in DCE
O
O
Ag/HMB
DCE
N Br
O
Ar H
Ar Br
+
+
N H
O
column. 1H-NMR spectra were recorded on a Bruker
500 MHz instrument with chemical shifts reported in ppm
relative to the residual deuterated solvent or the internal
standard tetramethylsilane. The inductively coupled plasma
optical emission spectroscopy (ICP-OES) analysis was
performed with a Perkin Elmer OPTIMA 2000DV. Trans-
mission electron microscopy (TEM) images were obtained
on a JEM-2010URH with an accelerating voltage of 200 kV.
The specific surface areas and the average pore sizes of the
materials were measured on a Belsorp II physical adsorption
apparatus by BET and BJH methods, and scanning electron
microscope (SEM) images were taken using a HITACHI
S4800 operated at an accelerating voltage of 10–20 kV.
X-ray powder diffraction (XRD) analysis was carried out
using a D8 Diffractometer (advance superspeed, Bruker-
AXS Company).
580 °C. And then the solid was treated with NH4Cl solu-
tion and calcined again to give the molecular sieve beta
(the H? form).
2.4 Synthesis of the Supported Metal Catalysts
Ag/HMB and Ag/Beta were prepared by cation-exchange/
reduction method, and the procedure was as following: The
HMB (0.5 g) was added into 20 mL AgNO3 (0.02 g)
aqueous solution in a round bottom flask. After stirring for
10 h at room temperature, the solid was filtered off, washed
with water, dried under vacuum, and then reduced with H2
at 180 °C for 5 h to afford brown powder Ag/HMB catalyst
(0.5 g, Ag 2.15 wt%). Ag/Beta (Ag supported on molecu-
lar sieve beta) was prepared in the similar way (Ag
2.09 wt%). Au/HMB was prepared as follows: the HMB
(0.5 g) was added into 20 mL HAuCl4 (0.025 g) aqueous
solution in a round bottom flask with vigorously stirring at
room temperature. After stirring for 10 h at room temper-
ature, the solid was filtered off, washed with water, dried
under vacuum, and then reduced with H2 at 180 °C for 5 h
to afford violet powder Au/HMB catalyst (Au 2.10 wt%).
Other Ag catalysts were prepared as follows: the support
(0.5 g) was added into 20 mL AgNO3 (0.016 g) solution in
a round bottom flask. After stirring for 10 h at room tem-
perature, the solid was dried under vacuum, and then
reduced with H2 at 180 °C for 5 h to afford Ag/TiO2
(Ag/anatase, Ag 2.05 wt%), Ag/CeO2 (Ag/ceria, Ag
2.09 wt%), Ag/C (Ag 2.07 wt%), Ag/HT (Ag/hydrotalcite,
Ag 2.07 wt%), Ag/HAP (Ag/hydroxyapatite, Ag 2.03 wt%)
respectively. The content of Ag/Au was determined by ICP-
OES.
2.3 General Procedure for Synthesis of HMB
Tetraethyl ammonium hydroxide (20% aqueous solution,
5 mL, 6.7 mmol), sodium aluminate (0.1255 g, 1.0 mmol),
and silicon dioxide (2 g, 33.3 mmol) were added in
22.87 mL water at 40 °C. The mixture was stirred at 40 °C
for 2 h, and then aged at 100 °C for 18 h. After the mixture
was cooled to room temperature, cetyltrimethyl ammonium
bromide (1.58 g, 4.33 mmol) was added with stirring, and
the mixture was aged again at 150 °C for 2 days. When the
mixture was cooled, the solid was filtered and washed with
water until the filtrate was neutral (pH = 7). The solid was
dried under vacuum and then heated to 580 °C (with a
heating rate of 1 °C min-1) and calcined at 580 °C for 5 h
to give NaMB (the Na? form). The NaMB (1.0 g) was
treated with NH4Cl solution (3.75 g NH4Cl contained) at
?
60 °C for 12 h to form the NH4MB (the NH4 form), and
2.5 Typical Procedure for the Bromination
of Aromatics with NBS
then the NH4MB was calcined at 500 °C for 4 h to afford
HMB (the H? form).
Molecular sieve beta was synthesized as following:
Tetraethyl ammonium hydroxide (20% aqueous solution,
5 mL, 6.7 mmol), sodium aluminate (0.1255 g, 1.0 mmol),
and silicon dioxide (2 g, 33.3 mmol) were added in
22.87 mL water at 40 °C. The mixture was stirred at 40 °C
for 2 h, and then aged at 100 °C for 18 h. After the mixture
was cooled to room temperature, the solid was filtered,
washed with water until the filtrate was neutral (pH = 7).
The solid was dried under vacuum and then calcined at
An aromatic compound (1.0 mmol), Ag/HMB (Ag:
2–4 mol%), NBS (1.1 mmol), and dichloroethane (DCE)
(2.0 mL) were added in a pressure tube with a magnetic stir
bar, and the tube was kept at 25–100 °C for 16 h (see
Table 2 for the detailed reaction conditions). After the
reaction was completed, the reaction mixture was added
100 lL hexadecane (internal standard), and the Ag/HMB
was separated by filtration. The conversions and yields
were determined by GC with an internal standard (C16H34).
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