Silver Nanoparticle Catalyzed Selective Hydration of Nitriles to Amides
687
and 30 mL of ethylene glycol solution (1.5 M) with
poly(vinyl pyrrolidone) (PVP, Aldrich, Mw = 55,000)
were injected into 15 mL of ethylene glycol (anhydrous,
99.8%, Aldrich) at a rate of *0.3 mL/min using a syringe
pump (KDS-100, Kd Scientific Co., Wood Dale, IL, USA).
After injection, the reaction mixture was refluxed at 433 K
for 60 min. The ochre colloidal dispersion was cooled to
room temperature and precipitated with acetone, followed
by centrifugation at 8,000 rpm for 10 min. The precipitated
Ag NPs were washed with ethanol several times.
smaller than what we obtained from TEM topography for
the most of NPs that is about 66 nm.
3.2 Reaction Test
Research studies testing catalyst effectiveness have
employed benzonitrile as a benchmark substrate. As shown
in Table 1, the best results were obtained when water was
used as the solvent. Foremost, no reaction occurred without
a catalyst. When the Ag NPs (0.5 mol%) were used,
benzamide was obtained in 100% conversion at reflux
(373 K) within 3 h (Table 1, entry 2).
2.3 A Typical Procedure for the Hydration of Nitriles
In general, it was found that increasing the reaction
temperature and time were effective means of increasing
conversion (Table 1, entries 3, 4). Furthermore, when
0.3 mol% of the catalyst was used, 25% yield was achieved
under the same reaction times (Table 1, entry 6). When the
catalyst amount was decreased to 0.1 mol%, 25% conver-
sion was found. In entry 5,100% conversion was achieved
by employing only 0.3 mol% of Ag NPs. Finally, the
optimum reaction conditions were established: the nitrile
(0.3 mL, 3.0 mmol) with Ag NPs (16.0 mg, 0.3 mol%) in
H2O (7.0 mL) contained in a 25 mL stainless steel reactor
(Table 1. entry 5). The catalytic activity of other Ag par-
ticles was compared. The use of Ag/HAP (average particle
size = 7.6 nm) showed a relatively high conversion of
benzonitrile [12]. The hydration reaction did not proceed
when Ag0 powder (average particle size = 106 nm) was
used. The mixture was stirred at 423 K for 1 h.
Ag NPs catalyst (16.0 mg, 0.3 mol%), water (7.0 mL), and
the corresponding nitrile (0.3 mL, 3.0 mmol) were intro-
duced into a stainless steel reactor and the reaction mixture
stirred at 423 K for 1 h. After the reaction, the nanoparti-
cles were separated from the solution by centrifugation.
1
The reaction products were analyzed by H-NMR using
Varian Mercury Plus (300 MHz). The identity of the
resulting amides was assessed by comparison of their
1H-NMR spectroscopic data with those reported in the
1
literature. Afterwards, we conducted a H-NMR experi-
ment to gain information of the resultant product. The
mixture of benzonitrile and Ag NPs was separately heated
for 0.5 and 1 h in water. 1H-NMR spectrum of the resultant
product (Fig. 2c) revealed the disappearance of proton
peak in benzene ring (7.85, 7.73, 7.58 ppm.)
3 Results and Discussion
Table 1 The catalytic hydration of benzonitrile using the Ag NPs
O
3.1 Catalyst Characterization
CN
NH2
Ag NPs
The scanning electron microscope (SEM) image in Fig. 1a
and transmission electron microscopy (TEM) image in
Fig. 1b show the regular polyhedral shape of the silver
nanoparticles. The Ag NPs were well dispersed and iso-
lated with an approximate 100 nm average diameter. The
crystalline features of the polyhedral spheres are repre-
sented in the XRD data (Fig. 1c). The main peaks at 38.2°,
44.4°, 64.5°, 77.4 °, and 81.6° are assigned to the reflections
of the (111), (200), (220), (311), and (222) planes in the Ag
phase (JCPDS No. 04-07831). The powder X-ray diffrac-
tion pattern of these precipitates show the presence of
metallic silver. It is also useful to calculate the average
grain size (D) of the NPs from X-ray diffraction data using
Scherrer formula, D = 0.9k/(BcoshB), where k is the X-ray
wavelength used for the diffraction experiments (Cu-
Entry
Cat
Temp (K)
Time(h)
Conv(%)a
1
Blank
Reflux
Reflux
423
3
N.R.
100
100
69
2
0.5 mol%
3
3
0.5 mol%
0.5
0.5
1
4
0.5 mol%
373
5
0.3 mol%
423
100
25
6
0.3 mol%
423
0.5
0.5
1
7
0.1 mol%
423
25
8
Recovered form #5
Recovered form #8
Recovered form #9
Recovered form #10
0.3 mol%
423
100
100
100
100
8b
9
423
1
10
11
12
a
423
1
423
1
˚
423
1
Ka = 1.54 A), B is the full width of the half maximum of a
1
particular peak in the radian unit, and hB is the peak
position. For the (111) peak, we obtained the grain size
normal to the scattering plane is about 55 nm, which is
Determined by H-NMR. Yields are based on the amount of ben-
zonitrile used
b
Mixture solvent was used (water/toluene: 7/0.25 ml)
123