Green synthesis, optical properties and catalytic activity of silver nanoparticles in the synthesis of N-monosubstituted ureas in water

Article abstract of DOI:10.1016/j.saa.2014.04.186

We report the green synthesis of silver nanoparticles by using Euphorbia condylocarpa M. bieb root extract for the synthesis of N-monosubstituted ureas in water. UV-visible studies show the absorption band at 420 nm due to surface plasmon resonance (SPR) of the silver nanoparticles. This reveals the reduction of silver ions (Ag⁺) to silver (Ag^o) which indicates the formation of silver nanoparticles (Ag NPs). This method has the advantages of high yields, simple methodology and easy work up.

Full text of DOI:10.1016/j.saa.2014.04.186

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Green synthesis, optical properties and catalytic activity of silver
nanoparticles in the synthesis of N-monosubstituted ureas in water
Mahmoud Nasrollahzadeh a, , Ferydon Babaei , S. Mohammad Sajadi , Ali Ehsani
⇑
b
c
a
a
Department of Chemistry, Faculty of Science, University of Qom, P.O. Box 37185-359, Qom, Iran
b
Department of Physics, Faculty of Science, University of Qom, Qom, Iran
c
Department of Petroleum Geoscience, Faculty of Science, Soran University, P.O. Box 624, Soran, Kurdistan Regional Government, Iraq
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
Green synthesis of silver
nanoparticles using Euphorbia
condylocarpa M. bieb root extract.
Silver nanoparticles were
investigated by FT-IR, TEM and
UV–vis spectrum.
Synthesized silver solutions were
found to be stable for a very long
period.
ꢀ
ꢀ
The optical properties were
investigated by UV–vis spectrum.
Hydration of cyanamides with silver
nanoparticles in water.
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the green synthesis of silver nanoparticles by using Euphorbia condylocarpa M. bieb root extract
for the synthesis of N-monosubstituted ureas in water. UV–visible studies show the absorption band at
Received 5 January 2014
Received in revised form 26 April 2014
Accepted 30 April 2014
4
20 nm due to surface plasmon resonance (SPR) of the silver nanoparticles. This reveals the reduction of
+
o
silver ions (Ag ) to silver (Ag ) which indicates the formation of silver nanoparticles (Ag NPs). This
method has the advantages of high yields, simple methodology and easy work up.
Ó 2014 Elsevier B.V. All rights reserved.
Available online 17 May 2014
Keywords:
UV–visible
N-Monosubstituted urea
Surface plasmon resonance
Ag nanoparticles
Euphorbia condylocarpa M. bieb
Introduction
isocyanates [3,4], toxic phosgene or its derivatives [5,6], insertion
2
of CO or CO into amino compounds in the presence of different cat-
N-Monosubstituted ureas have potential medical and agricul-
tural applications [1,2]. Several methods for their preparation have
been reported, but synthetic approaches for these compounds are
needed. Classical methods for the synthesis of N-monosubstituted
ureas have involved reaction of primary or secondary amines with
alysts in organic solvents at high temperature and pressure [7–10],
reaction of amines with sodium or potassium cyanate in aqueous
solution in the presence of one equivalent of HCl [11], acid or
base-catalyzed hydration of cyanamides [12–15], and reaction of
S,S-dimethyl dithiocarbonate with ammonia in water–dioxane [16].
Earlier reported methods for the preparation of N-monosubsti-
tuted ureas suffer from drawbacks such as the use of expensive and
toxic reagents and catalysts, the environmental pollution caused
⇑
Corresponding author. Tel.: +98 25 32850953; fax: +98 25 32103595.
E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh).
http://dx.doi.org/10.1016/j.saa.2014.04.186
386-1425/Ó 2014 Elsevier B.V. All rights reserved.
1

4
24
M. Nasrollahzadeh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
by utilization of organic solvents and use of corrosive base or acids
such as HF-pyridine complex, H SO , H /NaOH and HCl, low
O
C
2
4
2 2
O
H
Ag Nanoparticles
Ar
yields, high temperatures, long reaction times, harsh reaction con-
ditions, difficulty in availability or preparing the starting materials
or catalysts, tedious work-up, waste control and formation of side
products. Therefore, the need for ‘greener’ methods or chemical
products that reduce or eliminate the use and generation of haz-
ardous compounds is essential.
Among currently available synthetic routes to N-monosubsti-
tuted ureas, the most widely used one is based upon hydration
of cyanamides [12–15], which involves the treatment of cyana-
mides with corrosive acids or bases. To resolve this problem,
recently Kim et al. described the hydration of cyanamides into
Ar
N
C
N
N
NH2
H O, reflux
2
H
Scheme 1.
UV–visible spectrophotometer and observed the absorption peak
in 440 nm region due to surface plasmon resonance (SPR) of the
silver nanoparticles.
In addition, we hereby report a new protocol for the hydration
of cyanamides in water using silver nanoparticles as a stable heter-
ogeneous catalyst (Scheme 1).
3
ureas using InCl and acetaldoxime as a water surrogate in toluene
as the toxic organic solvent [17]. However, the development of an
efficient and versatile method for the hydration of cyanamides is
an active ongoing research area, and there is a potential for further
improvement toward green chemistry.
From the standpoint of ‘green chemistry’ and for reasons of
economy and pollution, organic reactions in water are of great
interest to make the classical procedures more clean, safe and easy
to perform [18,19]. Water is cheap, non-toxic, non-combustible,
non-explosive, and environmentally acceptable [18,19].
Nanotechnology is emerging as a cutting edge technology inter-
disciplinary with biology, chemistry and material science. In recent
years, noble metal nanoparticles have been the subjects of focused
researches due to their unique electronic, optical, mechanical,
magnetic and chemical properties that are significantly different
from those of bulk materials [20]. For these reasons, metallic nano-
particles have found uses in many applications in different fields,
such as catalysis, photonics, and electronics.
In nanotechnology, silver nanoparticles are the most promising
one. Silver nanoparticles (Ag NPs) have been widely used during
the past few years in various applications, such as biomedicine,
biosensors, catalysis, pharmaceuticals, electrical conductivity, pho-
tonics and as the substrates for surface-enhanced Raman spectros-
copy (SERS) due to the existence of surface plasmons [21–26]. The
silver nanoparticles provide high surface energy, which promotes
surface reactivity (e.g., adsorption, catalysis). One unique property
of silver nanoparticles includes their utilization in fluorescence and
surface plasmon resonance (SPR) [23,24,27]. The frequency and
intensity of plasmon resonance are dependent on the distribution
of charge across the nanostructure, which in turn is determined
by the shape [28].
Experimental and modeling
All reagents were purchased from the Merck and Aldrich chem-
ical companies and used without further purification. Products
were characterized by different spectroscopic methods (FT-IR and
NMR spectra), elemental analysis (CHN) and melting points. The
1
NMR spectra were recorded in acetone and DMSO. H NMR spectra
were recorded on a Bruker Avance DRX 250, 300 and 400 MHz
instrument. The chemical shifts (d) are reported in ppm relative
to the TMS as internal standard. J values are given in Hz. IR (KBr)
spectra were recorded on a Perkin-Elmer 781 spectrophotometer.
Melting points were taken in open capillary tubes with a BUCHI
5
10 melting point apparatus and were uncorrected. The elemental
analysis was performed using Heraeus CHN-O-Rapid analyzer. TLC
was performed on silica gel polygram SIL G/UV 254 plates.
UV–visible spectral analysis was recorded on a double-beam
spectrophotometer (Hitachi, U-2900) to ensure the formation of
nanoparticles.
General procedure for the synthesis of cyanamides
Cyanamides were prepared according to the literature [41].
Preparation of E. condylocarpa M. bieb root extract
1
0 G of dried plant powder was extracted using boiling in
1
00 mL double distillated water for 10 min and aqueous extract
was filtered.
Hence in recent years the green synthesis approach has
emerged as one of the active areas of research. The green synthesis
techniques are generally synthetic routes that utilize relatively
nontoxic solvents such as water, biological extracts, biological sys-
tems and microwave assisted synthesis [29–35]. Green synthesis of
NPs has several advantages over chemical synthesis, such as sim-
plicity, cost effectiveness as well as compatibility for biomedical
and pharmaceutical applications.
The plants of the Euphorbiaceae contain acrid, milky, or colorless
juice. Chemical data are available for several genera, especially
Euphorbia, where more than 120 species have been investigated.
The family Euphorbiaceae is rich in flavonoids, particularly flavones
and flavonols, which have been identified from several genera. Fur-
thermore, the previous studies in 1970 on Euphorbia condylocarpa
demonstrated the presence of phytochemicals such as flavonoids,
tetracyclic triterpenoids, and trifolin in different parts of the plant
Green synthesis of silver nanoparticles using E. condylocarpa M. bieb
root extract
In a typical synthesis of Ag NPs, 5 mL of aqueous extract was
added dropwise to 50 mL of 0.003 M aqueous solution of AgNO
0.003 M) with constant stirring at 50 °C. After 30 min the color
3
(
of the solution changed from yellow to reddish brown during the
heating process due to excitation of surface plasmon resonance
which indicates the formation of Ag nanoparticles. Reduction of sil-
+
o
ver ions (Ag ) to silver (Ag ) was completed around 1 h (as moni-
tored by UV–vis and FT-IR spectra of the solution). Then the
colored solution of silver nanoparticles was centrifuged at
6
000 rpm for 30 min to completely dispersing. The nanoparticles
solution was diluted 10 times with distilled water to avoid the
errors due to high optical density of the solution.
[
33–36].
In continuation of our recent works on the green chemistry [36–
0], we wish to report a new and rapid protocol for the preparation
General procedure for the hydration of cyanamides to
N-monosubstituted ureas using silver nanoparticles
4
of silver nanoparticles by using Euphorbia condylocarpa M. bieb root
extract (Fig. S1, Supporting Information) as a reducing and stabiliz-
ing agent. Also, the optical absorption properties was measured by
A mixture of the appropriate cyanamide (1.0 mmol), water
(10 mL) and Ag NPs (5.0 mg) was stirred under reflux conditions
for 1 h. After completion of reaction (as monitored by TLC), Ag

M. Nasrollahzadeh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
425
NPs were separated from the reaction mixture by centrifugation.
Table 2
The desired pure products were characterized by 1H NMR,
13
Hydration of different cyanamides by the silver nanoparticles.
C
NMR, FT-IR, elemental analysis (CHN), and melting points. The
physical data (mp, IR, NMR) of known compounds were found to
be identical with those reported in the literature [15,17].
Entry
1
Cyanamide
Product
Yield (%)a
93
MeO
NH
CN
2
3
4
92
Spectral data of unknown products
95 (95,94,93)b
93
N-(2,5-Dichlorophenyl)urea (Table 2, entry 7): M.p. 232–
ꢁ
1
2
2
1
34 °C; FT-IR (KBr, cm ) 3495, 3417, 3364, 3340, 3308, 3206,
826, 1676, 1610, 1586, 1535, 1466, 1410, 1385, 1351, 1263,
089, 1056, 873, 805, 792, 764, 583, 557, 475, 440, 418; H NMR
1
5
6
7
95
90
93
(
6
d
300 MHz, DMSO-d
6
) d
.96 (d, J = 8.1 Hz, 1H), 6.55 (s, 2H); C NMR (75 MHz, DMSO-d
= 154.7, 137.7, 131.7, 129.9, 121.5, 119.5, 118.8; Anal. Calcd
for C OCl : C, 41.00; H, 2.95; N, 13.66. Found: C, 39.84; H,
.89; N, 13.80.
N-(3-Bromophenyl)urea (Table 2, entry 8): M.p. 141–143 °C;
H
= 8.24 (s, 2H), 7.38 (d, J = 8.1 Hz, 1H),
13
6
)
C
7
H
N
6 2
2
2
8
95
ꢁ1
FT-IR (KBr, cm ) 3375, 3333, 3189, 1679, 1578, 1476, 1410,
091, 861, 777, 674, 599; 1H NMR (400 MHz, DMSO-d
) d = 8.74
s, 1H), 7.83 (s, 1H), 7.23–7.15 (m, 2H), 7.07 (d, J = 8.1 Hz, 1H),
1
(
5
1
3
6
H
9
94
94
1
3
.97 (s, 2H); C NMR (100 MHz, DMSO-d
6
) d
C
= 156.2, 142.7,
OBr: C,
10
31.0, 123.0, 120.4, 120.2, 116.8; Anal. Calcd for C
9.10; H, 3.28; N, 37.16. Found: C, 39.20; H, 3.34; N, 37.26.
7
7 2
H N
N-(4-Acethylphenyl)urea (Table 2, entry 9): M.p. 297–298 °C;
FT-IR (KBr, cm ) 3407, 3307, 3215, 1672, 1613, 1584, 1536,
a
Yields are after work-up.
Yield after the fourth cycle.
ꢁ1
b
1
7
508, 1410, 1357,1310, 1273, 1117, 1013, 963, 874, 835, 766,
47, 718, 632, 655, 594, 494, 410; 1H NMR (300 MHz, DMSO-d
= 8.93 (s, 1H), 7.80 (d, J = 8.4 Hz, 2H), 7.50 (d, J = 8.4 Hz, 2H),
.02 (s, 2H), 2.47 (s, 3H); 13C NMR (75 MHz, DMSO-d
) d = 196.6,
56.0, 145.7, 130.2, 130.0, 117.0, 26.7; Anal. Calcd for C
6
)
d
H
6
1
6
C
9
10 2 2
H N O :
C, 60.66; H, 5.66; N, 15.72. Found: C, 60.47; H, 5.45; N, 15.59.
Results and discussion
In this study, E. condylocarpa M. bieb root extract has been used
as a reducing and stabilizing agent for the synthesis of silver nano-
particles. Figs. 1 and 2 show the UV–vis and FT-IR spectra of E.
condylocarpa M. bieb root extract, respectively.
nm
The UV spectrum with bonds at kmax 387 (bond 1) which is due
to the transition localized within the B ring of cinnamoyl system;
whereas the one depicted at 283 (bond 2) is consistent with absor-
bance of ring A of benzoyl system (Scheme 2). They are related to
Fig. 1. UV–vis spectrum of Euphorbia condylocarpa M. bieb root extract.
the
p ? p transitions and these absorbent bonds demonstrated the
root extract was mixed in the aqueous solution of the silver nitrate,
it started to change the color from watery to reddish brown
(Fig. S2, Supporting Information) due to the surface Plasmon reso-
nance phenomenon which indicated formation of silver nanoparti-
cles. The intensity of the color was increased during the process.
Fig. 3 shows the UV–vis spectra of Ag NPs formation. The pro-
gression of the reaction, formation and stability of silver nanopar-
ticles were controlled by UV–vis spectroscopy. The best time was
presence of flavon nuclei.
The FT-IR spectrum depicted some peaks at 3436 to 3000, 1643,
ꢁ1
1
561, 1413 and 1277 cm which represent free OH in molecule
and OH group forming hydrogen bonds, carbonyl group (C@O),
stretching C@C aromatic ring and CAOH stretching vibrations,
respectively.
Reduction of silver ion to silver nanoparticles during exposure
to the plant extracts could be followed by color change and spec-
troscopic techniques such as UV–vis. As the E. condylocarpa M. bieb
1
h and the best concentration of AgNO
3
was 0.003 M. Also the
ratio of plant extract to AgNO solution was 1/10. No significant
3
increase in absorbance was observed after 1 h of reaction time,
which indicates the completion of reaction. The appearance of a
single, bell shaped, surface plasmon band at the wavelength of
maximum absorbance at 420 nm, indicated the formation of Ag
NPs. The synthesized silver nanoparticles by the this method are
quite stable and no obvious variance in the shape, position and
symmetry of the absorption peak is observed even after two
months which indicates that the as-prepared silver nanoparticles
can remain stable.
Table 1
a
Hydration of 4-methylphenylcyanamide promoted by silver nanoparticles .
Entry
Ag NPs (mg)
Solvent
Time (h)
Yield (%)b
1
2
3
4
5
6
2
4
6
8
6
0
H
H
H
H
H
H
2
2
2
2
2
2
O
O
O
O
4
1
1
1
1
4
60
80
95
95
63
0
O:Toluene (8:2 mL)
O
a
Fig. 4 represents the FT-IR spectrum of biosynthesized silver
nanoparticles by the E. condylocarpa M. bieb root extract and shows
bands at 3387, 2920, 2851, 1714, 1462, 1381, 1273 and 1074. The
Reaction conditions: cyanamide (1.0 mmol), water (10 mL), Ag NPs (5.0 mg),
reflux, 1 h.
b
Isolated yield.

4
26
M. Nasrollahzadeh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
Fig. 2. FT-IR spectrum of Euphorbia condylocarpa M. bieb root extract.
3
'
In Fig. 5, the TEM micrograph of the green silver nanoparticles
indicates the nanoparticles are spherical in shape with a narrow
size.
2
'
4'
5'
B
1
8
A
5
1'
O
9
2
7
6
Optical modeling
6
'
C
3
Let us consider a region 0 6 z 6 d occupied by silver nanoparti-
cles dispersed in water (Fig. S3, Supporting Information) while the
regions z 6 0 and z P d are vacuous. Suppose an arbitrarily
polarized plane wave is normally incident (axial excitation) on
the chosen structure from the z 6 0. The phasors of incident,
reflected and transmitted electric fields are given as [42]:
1
0
4
O
Scheme 2.
8
ꢂeiK0z;
z ꢃ 0
>
<
E
E
E
incðrÞ ¼ ½a
s
u
u
y
ꢁ a
þ r
p
u
x
ꢁ
ref ðrÞ ¼ ½r
s
y
p
u
x
ꢂe iK0z; z ꢃ 0
ð1Þ
>
:
iK
0
ðzꢁdÞ
trðrÞ ¼ ½t
, a
s
u
y
ꢁ t
p
u
x
ꢂe
;
z ꢄ d
where (a
s
p
),(r
s
p
, r )and (t
s p
, t ) are the amplitudes of incident plane
wave, and reflected and transmitted waves with S- or P-polariza-
pffiffiffiffiffiffiffiffiffiffi
tions,
K
0
¼
x
l
e
0
¼ 2
p
=k
0
is the free space wave number,
0
ꢁ12
ꢁ1
k
0
is the free space wavelength,
e
0
= 8.854 ꢅ 10 Fm
, and
ꢁ7
ꢁ1
l
0
= 4
p
ꢅ 10 Hm are the permittivity and permeability of free
space (vacuum), respectively, and ux;y;z are the unit vectors in
Cartesian coordinates system.
The reflectance and transmittance amplitudes can be obtained,
using the continuity of the tangential components of electrical and
magnetic fields at interfaces and solving the algebraic matrix equa-
tion [43–45]:
2
3
2
3
Fig. 3. UV–vis spectrum of green synthesized Ag NPs at different times.
t
s
a
s
6
6
6
4
7
7
6
6
7
7
7
ꢁ1
tp
0
ap
band at 3387 cm corresponds to free OAH or stretching vibra-
7¼ ½Kꢂꢁ1:½MAgꢁWaterꢂ ꢆ ½Kꢂ ꢆ 6
ð2Þ
5
4r 5
tions of hydroxyl group of alcohols or phenols in bonding. Signals
s
ꢁ1
ranging under 3000–2900 cm identify the methylene stretching
bonds. As shown in Fig. 4, a prominent shift in the wave numbers
0
r
p
ꢁ1
The different terms and parameters of this equation are given in
was observed from 1381 to 1000 cm
characterize the CAC
detail by Lakhtakia and Messier [42]. In our work the absorption
for natural light is considered as A ¼
stretching bond of hydrocarbon skeletal vibrations. From the anal-
ysis of FT-IR bands of silver nanoparticles studies we grasp that the
antioxidant polyphenolics have the stronger ability to bind metal
indicating that could possibly from the metal nanoparticles
A
S
þA
P
, where
2
!
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
2
X
r
a
i
t
i
A
i
¼ 1:0 ꢁ
R
ji þ Tji
;
R
i;j
¼
;
T
i;j
¼
; i; j ¼ s; p:
j
a
j
(
capping of silver nanoparticles) to form biometallic complex (bio
j¼s;p
chelating) and thereby remove the oxidant agent and stabilize
the medium. This suggests that the E. condylocarpa aqueous extract
could possibly perform dual functions of formation and stabiliza-
tion of Ag NPs in the aqueous medium.
In optical modeling, the effective dielectric constant
ꢁ
ꢂ
3
þ
fð
e
W
ꢁ
e
e
Ag
Þ
e
eff
¼
e
W
1 ꢁ 2
of silver nanoparticles in water was
and
e
W
e
Ag þfð
W
ꢁ
e
Ag
Þ
calculated using Maxwell–Garnett theory (MGT), where e
W

M. Nasrollahzadeh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
427
Fig. 4. FT-IR spectrum of Ag NPs produced from the root of the Euphorbia condylocarpa M. bieb extract.
Fig. 5. TEM image of green synthesized Ag NPs.
Fig. 6. Calculated absorption as a function of wavelength at different volume
fractions silver nanoparticles.
e
Ag are dielectric constants of water and silver, while f is the volume
fraction of dispersed material [46]. We have used the bulk experi-
mental refractive indexes silver and water for homogenization
the hydration of 4-methylphenylcyanamide in the presence of
the silver nanoparticles (Table 1). Control experiments show that
there is no reaction in the absence of catalyst (Table 1, entry 6).
However, addition of the catalyst to the mixture has rapidly
increased the synthesis of N-monosubstituted ureas in high yields.
The best result was obtained with 1.0 mmol of cyanamide, 5.0 mg
of Ag NPs and 10 mL of water under reflux conditions, which gave
the product in an excellent yield.
Next we examined the utility of the Ag NPs catalyst with other
cyanamides (Table 2). Cyanamides contain both electron-releasing
and electron-withdrawing groups underwent the conversion in
excellent yields. Significantly, the reactions between 1-naphthylc-
yanamide and water in the presence of Ag NPs afforded corre-
sponding N-(1-naphthyl)urea product in excellent yield (Table 2,
entry 10).
The first principle of green chemistry states that it is better to
prevent waste production than to treat waste or clean it up after
it has been created [49]. In all of reported methods in the literature,
by-product as waste or pollution is produced. It is not in compli-
ance with the first principle of green chemistry. In our methods,
after completion of the reaction, there is no cyanamide residue in
the reaction mixture. Also, no organic solvents were used for the
extraction of the product in the work-up step and the method
did not require any further purification. Compared to the reported
methods, our method is convenient, fast, safe and easy to work-up.
[
47]. The calculated optical absorption of structure as a function
of wavelength for natural light plane wave at different volume
fractions of silver nanoparticles is plotted in Fig. 6. The existence
of peak in optical absorption of structure at about 400 nm is due
to excitation surface plasmon wave [48]. It can be observed that
as the volume fraction of nanoparticles increases the width of sur-
face plasmon peak broadens that is consistent with experiment
result. By comparison the results of optical modeling and experi-
ment it is seen that there are qualitative agreement between
experimental data and results of our applied optical modeling. This
slight difference between our optical modeling and experimental
result can be related to the structural difference between the ide-
alized theoretical model for structure and that obtained in experi-
mental result. On the other hand, the experimental composite
films exhibit a large amount of scattering due to the highly com-
plex and non-ideal structure that the individual nanoparticles
exhibit.
Activity of Ag NPs catalyst for the preparation of N-monosubstituted
ureas
In the next step, we tested the catalytic activity of the Ag nano-
particles for the hydration of cyanamides in water. Initial studies
were performed in order to optimize the reaction conditions for

4
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M. Nasrollahzadeh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 132 (2014) 423–429
Nevertheless some disadvantages of the literature works are as
below:
ꢀ The reaction system is simple.
ꢀ Organic solvents are not needed.
ꢀ
Brønsted acids and organic reagents such as acetaldoxime are
not needed.
ꢀ
The use of organic solvent and toxic and volatile reagents such
as phosgene and isocyanates.
ꢀ The use of water as a green solvent.
ꢀ
ꢀ
Long reaction times, low yield and harsh reaction conditions.
The use of Flash chromatography or recrystallization for purifi-
cation of the products.
ꢀ The yields of the products are very high.
ꢀ The use of plant extract as an economic and effective alternative
represents an interesting, fast and clean synthetic route for the
large scale synthesis of silver nanoparticles.
ꢀ
ꢀ
ꢀ
The use of corrosive acids or bases.
The use of homogeneous catalysts.
Several-step methods.
ꢀ The Ag NPs catalyst can be easily recovered.
ꢀ High reaction pressure are avoided; and;
ꢀ
No side product was observed under the reaction conditions,
thus this method did not require any further purification.
All above items are wasting money and time consuming, so
our proposed method can be considered as a green protocol
which the reaction will take place at room temperature with high
atom economy, high yields and easy operations without applica-
tion of toxic organic solvents, bases, acids and expensive reagents
or catalysts. Compared with the other literature works on the
synthesis of N-monosubstituted ureas, the notable features of
our method are:
The second principle of green chemistry states that the syn-
thetic systems should be focused to improve the atom economy
or atom efficiency [49]. Atom economy (AE) is a useful concept
for estimating the environmental impacts of starting materials in
a reaction to reach a desired product [50]. In comparison with of
the literature works, atom economy of our work is very excellent.
Fig. 7. FT-IR spectrum of N-(3-bromophenyl)urea.
Fig. 8. 1H NMR spectrum (400 MHz, DMSO-d
) of 5-(3-bromophenyl)urea.
6

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429
To the best of our knowledge, Ag NPs catalyst is one of the most
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.04.186.