Ultrasound-assisted diversion of nitrobenzene derivatives to their aniline equivalents through a heterogeneous magnetic Ag/Fe3O4-IT nanocomposite catalyst

Article abstract of DOI:10.1039/d0nj05147k

A heterogeneous magnetic catalytic system is fabricated and suitably applied for the fast and direct conversion of nitrobenzene (NB) derivatives to their aniline forms. For this purpose, different conditions and methods have been checked with numerous catalytic amounts of the nanocatalyst composite, which was constructed of iron oxide and silver nanoparticles and possessed an isothiazolone organic structure. Herein, the mechanistic aspect of the catalytic functioning of this highly efficient nanocatalyst is highlighted and discussed. Firstly, a convenient preparation route assisted by ultrasonication for this metal and metal oxide nanocomposite is presented. Further, a fast and direct reduction strategy for NBs is investigated using ultrasound irradiation (50 kHz, 200 W L-1). As two great advantages of this catalyst, high magnetic property and excellent reusability are also mentioned. This report well reveals that a really convenient conversion of NBs to anilines can be achieved with a high yield during the rapid reaction time in presence of mild reaction conditions. This journal is

Full text of DOI:10.1039/d0nj05147k

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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
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Ultrasound-Assisted Diversion of Nitrobenzene Derivatives to their Aniline
Equivalents through Heterogeneous Magnetic Ag/Fe3O4-IT Nanocomposite Catalyst
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Reza Taheri-Ledari1, Jamal Rahimi1, Ali Maleki1,* and Ahmed Esmail Shalan2,3,*
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1 Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of
Science and Technology (IUST), Tehran 16846-13114, Iran.
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2 Central Metallurgical Research and Development Institute (CMRDI), P.O. Box 87, Helwan, Cairo
11421, Egypt.
3 BCMaterials, Basque Center for Materials, Applications and Nanostructures, Martina Casiano,
UPV/EHU Science Park, Barrio Sarriena s/n, Leioa 48940, Spain.
*Corresponding authors. (A. M) Tel.: +98 21 77240640-50; fax: +98 21 73021584. E-mail address:
maleki@iust.ac.ir; (A. E. S.) E-mail: a.shalan133@gmail.com
Author’s ORCIDs:
Reza Taheri-Ledari: https://orcid.org/0000-0002-6511-9411
Ali Maleki: https://orcid.org/0000-0001-5490-3350
Ahmed Esmail Shalan: https://orcid.org/0000-0002-3424-1609
Abstract
A heterogeneous magnetic catalytic system is fabricated and suitably applied for execution of the fast and
direct conversion of nitrobenzene (NB) derivatives to their aniline forms. For this purpose, different
conditions and methods have been indeed checked with existence of numerous catalytic amounts of the
nanocatalyst composite, which is constructed of iron oxide and silver nanoparticles, and isothiazolone
organic structure. Herein, the mechanistic aspect of the catalytic function of this highly efficient
nanocatalyst is highlighted and more discussed. Firstly, a convenient preparation route assisted by
ultrasonication is presented for this metal and metal oxide nanocomposite. Further, a fast and direct
reduction strategy for NBs is investigated using ultrasound wave irradiation (50 KHz, 200 W L-1). As two
great advantages for this catalyst, high magnetic property and excellent reusability could also be mentioned.
However, this report well reveals that really convenient conversion of NBs to anilines could be achieved
with high yield during a rapid reaction time, in presence of mild reaction conditions.
Keywords: Heterogeneity; Magnetism; Nanocatalyst; Nitrobenzene degradation; Ultrasonication
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1. Introduction
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Proportional to increase the application of the nanomaterials in different industries, attentions to
heterogeneous catalytic arrangements in micro and nano scales have been increased.1 In this respect, many
catalytic structures have been considered for different aims.2-5 Various catalysts with different properties,
specified for a particular application, have been fabricated.6-8 According to the most recent reports, it was
mentioned that the capability of the heterogeneous catalytic systems in facilitating the chemical reactions
would be enhanced through involving other effective agents like irradiations (different lights, ultrasound,
and etc.).9-12 For instance, we have recently investigated the synergistic catalytic influence between the
heterogeneous nanoscale catalytic arrangements and the ultrasound waves, and clearly disclosed that the
catalytic performance of the nanoparticles are greatly enhanced via this strategy.13-15 Moreover, Zhang et
al. have fabricated carbon quantum dots and investigated its photocatalytic capability for water splitting.16
Also, Shi et al. have reported a synergistic catalytic effect between iron(III) ion and iron oxide nanoparticles
as a heterogeneous catalyst for reduction of the nitro derivatives.17 However, the main question is to know:
how we can improve the catalytic action of the known individual catalysts and to what extent this catalytic
performance could be enhanced?
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Reportedly, among all of the various species of the nanoscale heterogeneous catalysts, silver (Ag) and iron
oxide nanoparticles (Fe3O4 NPs) have been extensively used for catalyzing the different types of the
chemical reactions.18-24 In addition, other distinguished features such as nontoxicity, convenient separation,
surface functionalization capability, and well composition capability with other materials, led Fe3O4 NPs to
be widely applied for various applications such as drug delivery and catalytic applications.25,26 Recently,
we have reported a composition of Ag and Fe3O4 NPs, functionalized with isothiazolone (IT) organic
compound, and used that for facilitating the peptide coupling reactions.27 In fact, the activation of the
carboxyl groups of amino acids was done without any need to the conventional peptide coupling reagents
such as TBTU and HBTU. There, we referred that the Heck reaction approach was implemented for surface
functionalization of the vinyl-coated Fe3O4 NPs, further, Ag NPs were composited with them.
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Here, we try to produce IT-functionalized silver/iron oxide (Ag/Fe3O4-IT) NPs via a novel in situ process
assisted by ultrasonication pathway. From physical aspect, wide surface area is provided by NPs due to
their nano scales.28 So, only a small amount of NPs would be enough to obtain the desirable result. From
chemical aspect, execution of the reactions under mild conditions leads to obtain stable structures with
lower decompositions. In this study, this is well revealed that this novel fabrication process yields in the
NPs with excellent morphology and composition form, and high catalytic performance is achieved in
follows. We intend to suitably apply the produced Ag/Fe3O4-IT nanocatalyst for fast and direct reduction
of nitrobenzene (NB) derivatives, which are considered as hazardous agents for human health.29 From
industrial aspect, this is so important issue to introduce a convenient, fast, economic, and environmentally
benign strategy for catalyzing the chemical reaction, through which hazardous agents are converted to their
useful analogues.
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2. Experimental
2.1. Materials and equipment
All the used reagents and solvents, and also the employed equipment in this project have been recorded in
Table S1 (supporting information).
2.2. Procedural pathways
2.2.1. Sonochemical synthesis of Ag/Fe3O4-APS NPs
In a glass tube (the brand shown in Table S1), AgNO3 (5.0 mmol, 0.85 g) was dissolved in DI water (5.0
mL) through ultrasonication pathway. All steps of the preparation route were carried out in an ultrasound
bath (50 KHz, 200 W L-1). Furthermore, the reaction environment was then basic using NH3 aqueous
solution (25%) and pH was controlled with pH meter paper to be around 12. Next, 5.0 mL of a mixture of
hydrated iron chloride salts (Fe2+ and Fe3+) in DI water was prepared (1 M per Fe2+ and 2 M per Fe3+), and
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dropwise added into the tube during ultrasonication at 60 C. After completion of the addition,
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ultrasonication was continued at the same conditions for 30 min. At that moment, a solution of APTES in
EtOH (40% v/v, 4.0 mL) was added drop by drop during ultrasonication (at 60 oC), and after completion of
the addition the produced Ag/Fe3O4-APS NPs were magnetically separated, washed with DI water and
EtOH, and dried at 60 oC.
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2.2.2. Sonochemical synthesis of IT-functionalized Ag/Fe3O4 nanocatalyst
In the same glass tube, Ag/Fe3O4-APSNPs (0.1 g) were isolated in DI water/EtOH (1:1, 5.0 mL) and K2CO3
(0.5 mmol, 0.069 g) 5-chloro-2-methyl-4-isothiazolin-3-one (2.0 mL, 1 M in EtOH) was added. Then, the
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mixture was ultrasonicated for 1 h, at 60 C. Ultimately, the magnetic NPs were collected, washed for
several times with EtOH and acetone, and dried at 60 oC.
2.2.3. General procedure for ultrasound-assisted reduction of NB derivatives, catalyzed by IT-
functionalized Ag/Fe3O4 nanocatalyst
Generally, in a glass tube, NB compound (1.0 mmol), N2H4.H2O (5.0 mol%), and IT-functionalized
Ag/Fe3O4 NPs (0.01 g) were well mixed in EtOH (3.0 mL), and ultrasonicated for 15 min at room
temperature. After accomplishment of the desired reaction, the NPs were magnetically disconnected and
5.0 mL of DMF was added to the reaction mixture. Finally, desired aniline compound was decontaminated
via flash-column chromatography. Additionally, the NMR spectra data of all of the synthesized aniline
derivatives are founded in Figures S5-S12, in the supporting information (SI).
3. Results and discussion
3.1. Synthesis of IT-functionalized Ag/Fe3O4 nanocatalyst
Scheme 1 briefly presents a simple preparation route for Ag/Fe3O4-IT NPs. As can be seen, in this method,
an alkaline solution of silver nitrate was prepared and then a mixture of iron(II) and iron(III) in deionized
(DI) water was dropwise added during ultrasonication process. For this purpose, a cleaner ultrasound bath
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with 50 KHz frequency and 200 W L-1 has been used. Afterward, ultrasonication at 60 oC was continued
and a solution of 3-aminopropyl triethoxysilane (APTES) was added and well mixed. Then, the magnetic
NPs were collected, and well dispersed again via ultrasonication. Next, a solution of 5-chloro-2-methyl-4-
isothiazolin-3-one in ethanol was added. The presented preparation route is more discussed in mechanistic
study section in more details.
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Scheme 1. Preparation route of IT-functionalized Ag/Fe3O4 nanocatalyst.
3.2. Characterization of IT-functionalized Ag/Fe3O4 nanocatalyst
From microscopic images for the prepared materials, it is well revealed that spherical-shaped
nanocomposite has been fabricated via the presented technique. As perceived in Figure 1, high uniformity
for the NPs has been resulted with average size of about 48 nm diameter. In comparison with reflux method
and Heck approach (reported in our previous article),27 monodispersed spheres have been formed of Fe3O4
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and Ag NPs via this ultrasound-assisted method. From scanning-electron microscopy (SEM) image (Figure
1a), it is figured out that the particles are accumulated in the solid state that is most likely due to their high
magnetic property. In contrast, in the suspension state, formed by ultrasonication, the uniform particles are
well dispersed. This claim was well proven by transmission-electron microscopy (TEM) (Figure 1b, c).
This new composition form of Ag and Fe3O4 NPs has shown excellent catalytic performance, magnetic
behavior, and stability in recovering process. All of these featured features are further discussed with more
details, in continue. However, to highlight the uniformity of the NPs (as a great feature), dynamic light
scattering (DLS) analysis has also been investigated. For this purpose, an ultrasound probe was used for
dispersion of the NPs. It is mentioned in the DLS spectrum (Figure 1b, inset) that a single peak with
polydispersity index (PDI) of 0.62 was observed around 48 nm, which confirms the extracted information
from the microscopic images. Besides, HRTEM of the produced Ag/Fe3O4-IT nanocomposite were
illustrated in Figure 1d, e. the obtained results confirm the prepared materials are in fine and homogenous
structure and the Ag domain can confirmed as founded in the inset of Figure 1d. Moreover, to gain more
information related to the structure proposed in Scheme 1 of the produced Ag/Fe3O4-IT nanocomposite, the
mapping measurements of the different elements including in the prepared nanocomposite was checked as
founded in Figure 1f.
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Figure 1. (a) SEM image for Ag/Fe3O4-IT nanocomposite in solid state (powder), (b, c) TEM images of Ag/Fe3O4-
IT nanocomposite (suspension and sampling on lam), and (inset) intensity-based DLS spectrum of the produced
Ag/Fe3O4-IT nanocomposite, (d, e) HRTEM images of Ag/Fe3O4-IT nanocomposite, (f) The mapping of the different
elements including in the produced Ag/Fe3O4-IT nanocomposite.
Moreover, to provide more evidences for the formation of the IT-functionalized Ag/Fe3O4 nanocatalyst,
energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared
(FT-IR) spectroscopic methods were employed (Figure 2). As shown in the EDX spectra (Figure 2a,b), all
the necessary elements are exist in the final structures. Furthermore, this is observed that the peaks intensity
related to carbon atom has been increased after functionalization process of IT. In addition, the appearance
of the sulfur atom around 2.6 keV, proves successfully functionalization of the Ag/Fe3O4 NPs with IT
organic compound (Figure 2b). To obtain more confirmation on the preparation process, XPS spectrum of
the IT-functionalized Ag/Fe3O4 nanocatalyst was detected. As exhibited, the existence of all the essential
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elements was well confirmed (Figure 2c). Besides, the high-resolution XPS spectra of the different elements
including Ag and Fe elements are founded in Figure 2d, e. the high-resolution XPS spectra detected to
further valid the presence of constituent of Ag/Fe3O4-IT nanocomposite and help to analyze the valence
state of the different elements. Figure 2d shows the XPS spectra of Ag 3d state at 373.13 and 368.13 eV,
which can be fitted with two spin-orbit splitting doublets of Ag to 3d5/2 and 3d3/2, while Figure 2e shows
the XPS spectra of Fe 2p state at 712.52 and 725.12 eV, which can be fitted with two spin-orbit splitting
doublets of Fe to 2p3/2 and 2p1/2. The results are reliable with the reported values of both Ag and Fe3O4.30,
31Finally, the FT-IR spectra was needed to investigate the functional groups of the products. As can be seen
in Figure 2f, a sharp peak has been appeared in both spectra around 3450 cm-1 that is related to Ag NPs.32
In spectrum (I), which belongs to Ag/Fe3O4-APS NPs, the existence of N─H, C─H (sp3), Si─O, SiO─H,
and Fe─O bonds have been confirmed by the appeared peaks at 3350, 2920, 950, 870, and 590 cm-1,
respectively.33 In spectrum (II), it is plainly seen that the peak intensity of the C─H (sp3) band has been
increased. Most likely, this is because of the addition of a methyl group through functionalization with IT
organic compound. Also, the peak related to the N─H band has been almost disappeared. It could be due to
well attachment of the amine group to the IT. Obviously, there is a strong resonance between the amine
group and the IT organic compound. That is maybe the reason beyond why the related peak to N─H band
is almost disappeared. However, the main criterion of the IT-functionalization is a peak performed at ~1730
cm-1 that approaching from C=O group of the loaded IT onto the surfaces. Furthermore, to reveal the crystal
structure of the produced Ag/Fe3O4-IT nanocomposite catalyst, XRD measurements were noticed (Figure
3). The obtained patterns indicate the presence of Ag as well as F3O4 nanoparticles. The as-prepared Ag-
Fe3O4 were approved using XRD data and composed of identical crystalline particles that corresponded to
JCPDS cards of silver (#04–0783) and magnetite (#16–0629), respectively.34, 35 For Ag nanoparticles,
different planes including (111), (200) and (220) that crossponding to XRD peaks at 2θ of 38.18°, 44.25°
and 64.72°, respectively were founded and indicated that the structure of Ag-NPs crystals is face-centered
cubic,36, 37 while different diffraction peaks that crossponding to the planes including (220), (311), (400),
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(422) and (440) were detected for Fe3O4 with inverse spinel structure (JCPDS No. 19-0629, a = 8.396 Å).38
Besides, new peak were founded at around 52o, which may refer to the IT crystalline network, which has
been formed onto the surfaces. Besides, there are other new peaks too, which have not been referred due to
their low intensity such as around 36o, 44o, 58o, and 62o. All of these new peaks can be attributed to the
formed layer by the IT compound onto the nanoparticles surfaces.
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Figure 2. EDX spectra of (a) Ag/Fe3O4-APS, and (b) Ag/Fe3O4-IT nanocomposite, (c) XPS spectrum of the produced
Ag/Fe3O4-IT nanocomposite, (d,e) high-resolution XPS spectrum of Ag and Fe elements, and (f) FT-IR spectra of
Ag/Fe3O4-APS (I) and Ag/Fe3O4-IT nanocomposite (II).
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Figure 3. XRD patterns of Ag/Fe3O4-IT nanocomposite
3.4. Application of Ag/Fe3O4-IT nanocatalyst in direct reduction of NB derivatives
3.4.1. Optimization
Obviously, the first step for performing the catalytic process is to check and determine the optimal
conditions. For this purpose, a model reaction was chosen and different conditions were applied for that
purpose. Table 1 briefly reports the applied conditions including various catalytic amounts of Ag/Fe3O4-IT
nanocomposite, different frequencies of the ultrasound bath, temperature, and etc. that intended for the
reduction process of nitrobenzene (NB). In this way, thin-layer chromatography was used for controlling
the reaction progress, and melting point measurement, FT-IR and NMR spectroscopy were applied to detect
the final aniline products. Applying several catalysis systems with different amount of Ag/Fe3O4-IT
nanocomposite catalysts at different ultrasound-assisted reduction reaction conditions were yield different
quantities of NB derivatives. For instance, the lowest amount of yield for NB derivatives was obtained at
temperature of 25o C and time of 15 min, while the highest amount of yield for NB derivatives was obtained
at temperature of 50o C and time of 15 min. Accordingly, the optimal parameters for the ultrasound-assisted
reduction of the NBs was obtained when only 0.01 g of Ag/Fe3O4-IT nanocomposite was used, during 15
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min of ultrasonication with 50 KHz frequency as well as 200 W L-1 power density, at room temperature.
As discussed in the introduction section, the efficiency of the nanoscale catalytic systems is substantially
enhanced through applying various effective agents. Today, different irradiations are being used for this
aim. For instance, gold NPs are converted to hot spots in the body’s internal environment, through applying
near-IR irradiation and surface plasmon resonance (SPR) effect for cancer therapy.39 Here, the main driving
force for catalyzing the reduction reactions of NB derivatives, is provided through irradiation of the
ultrasound waves (with particular frequency besides the power density) to Ag NPs. In fact, it seems that the
ultrasound waves enhance the surface resonance of the Ag NPs (due to electron excitation), and the prepared
hot surfaces provide the required driving force for chemical reactions.40,41 On the other hand, the ultrasound
irradiation causes NPs to be well dispersed and accordingly an extreme surface area is delivered in the
suspension state. Moreover, it should be noted that the required driving force is only provided at the main
and essential sites of chemical structure and other area remain unstimulated. In other words, the desired
chemical reaction is generally carried out under mild conditions via this method (Figure 4).
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According as our previous experiences42,43 and also the new experimented reaction (Table 1, entry 14), a
catalytic saturation is occurred in a specified and known ratio. In this work, it has been observed that
increasing the amount of the catalyst from 0.01 g to 0.03 g has no significant effect on the obtained yield
(Table 1, entries 5 and 7). While, decreasing that to ~0.005 g has dramatically affected the reaction yield
(entry 14). Accordingly, it can be supposed that a catalytic saturation is occurred around 0.01 g.
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Table 1. Different reaction conditions optimized for ultrasound-assisted reduction of the NB derivatives, catalyzed
2
3
4
via Ag/Fe3O4-IT nanocomposite.
5
6
Entry
Cat. system
Cat. (g)
Conditions
Temp. Time Yield a
7
8
9
(oC)
25
50
50
25
25
50
25
25
25
25
25
25
25
25
(min)
15
15
15
15
15
15
15
30
15
15
15
15
15
15
(%)
Trace
Trace
55
1
-
-
Stirring
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
-
-
Stirring
3
Ag/Fe3O4-IT
-
0.01
-
Stirring
4
Ultrasonication (F: 50, P: 200)b
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 100)
Ultrasonication (F: 50, P: 150)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
Ultrasonication (F: 50, P: 200)
31
5
Ag/Fe3O4-IT
Ag/Fe3O4-IT
Ag/Fe3O4-IT
Ag/Fe3O4-IT
Ag/Fe3O4-IT
Ag/Fe3O4-IT
Ag NPs
0.01
0.01
0.03
0.01
0.01
0.01
0.01
0.01
0.01
0.005
97*
97
6
7
97
8
97
9
94
10
11
12
13
14
96
38
Fe3O4 NPs
Fe3O4-IT
Ag/Fe3O4-IT
36
50
69
a Isolated yield for reduction reaction of nitrobenzene using 1.0 mmol of nitrobenzene, 5.0 mol% of N2H4.H2O, 3.0
mL of ethanol; F: frequency, P: power density (ultrasonication was supported in an ultrasound cleaner bath);
b
*optimal conditions.
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Figure 4. Schematic of the catalytic process of ultrasound-assisted conversion of the NB derivatives to their aniline
analogues by metallic NPs.
3.4.2. Reduced NB derivatives
To monitor the catalytic activity of the presented IT-functionalized Ag/Fe3O4 nanocatalyst in the presence
of the ultrasound waves, different derivatives of NB were used. All the reactions have been supported with
the optimized parameters (Table 1). Furthermore, Table 2 presents the structure and reaction yields of the
resulted aniline products. Different NB derivatives were obtained via the ultrasound-assisted reduction reaction,
catalyzed by IT-functionalized Ag/Fe3O4 nanocatalyst. The obtained NB derivatives display isolated yield of
97, 96, 96, 97, 96, 94, 96, 95, 94 and 97% for Nitrobenzene, 1,4-Dinitrobenzene, 1,3-Dinitrobenzene, 3-
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Nitrobenzaldehyde, 4-Nitrobenzoic acid, 4-Nitrophenol, 4-Nitrobenzaldehyde, 1-(4-Nitrophenyl)ethan-1-
2
3
4
one, 3,4-Dinitrobenzoic acid and 1-Chloro-4-nitrobenzene, respectively.
5
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7
8
9
Table 2. Different nitrobenzene derivatives reduced to their aniline analogues via the ultrasound-assisted reduction
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reaction, catalyzed by IT-functionalized Ag/Fe3O4 nanocatalyst.
Entry
NB derivative
Yield a (%)
Melting point (oC)
Ref.
Found
-
Reported
-
1
Nitrobenzene
1,4-Dinitrobenzene
97
96
96
97
96
94
96
95
94
97
[44]
[45]
[46]
[44]
[44]
[47]
[47]
[44]
[48]
[45]
2
144
65
145
65
3
1,3-Dinitrobenzene
4
3-Nitrobenzaldehyde
4-Nitrobenzoic acid
4-Nitrophenol
31
30
5
188
187
79
187
186
78
6
7
4-Nitrobenzaldehyde
1-(4-Nitrophenyl)ethan-1-one
3,4-Dinitrobenzoic acid
1-Chloro-4-nitrobenzene
8
105
209
71
105
208
70
9
10
a Isolated yield.
3.4.3. Recyclability
One of the most important properties of each heterogeneous catalytic system is related to its capability to
be used for several times deprived of significant decay in the catalytic activity. Here, we have fabricated a
magnetic system that is conveniently collected by using a magnet, then washed, dried, and reused again.
Magnetic behavior of the produced IT-functionalized Ag/Fe3O4 nanocatalyst has been considered through
vibrating-sample magnetometer (VSM) technique (Figure S1, in supporting information section).
Accordingly, our catalytic system was magnetically separated from the reaction mixture (reduction reaction
of nitrobenzene), and reused for additional 10 times. As can be seen in Figure 5, the catalytic activity of the
fabricated IT-functionalized Ag/Fe3O4 nanocatalyst has been almost maintained after 10 times recycling.
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5
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7
8
Moreover, the structure of the catalyst was checked after the recycling process by FT-IR, EDX, and SEM
analyses (Figures S2-S4, in supporting information section). From these analyses, it was clearly disclosed
that the structure of the IT-functionalized Ag/Fe3O4 nanocatalyst is stable under the reduction reaction
conditions.
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Figure 5. Recycling diagram of IT-functionalized Ag/Fe3O4 nanocatalyst applied in ultrasound-assisted reduction
reaction of nitrobenzene.
3.5. Mechanistic study
To prepare the catalyst, from the mechanistic aspect, chlorine is in a suitable situation for leaving the
structure of 5-chloro-2-methyl-4-isothiazolin-3-one after amine attack. For this purpose, basic conditions
activates the amine group, present in the structure of aminopropyl silane (APS) for attack. The electronic
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resonance in the structure of 5-chloro-2-methyl-4-isothiazolin-3-one provides an appropriate substrate
(carbocation) to be attacked by activated amine group. Here, one of the advantages for enhancing this
mechanism is Ag NPs that assist this electronic resonance through effective electronic interactions with
oxygen atom of carbonyl (Scheme 2a). These electronic interactions are positively enhanced by ultrasound
waves and heating the surfaces. In reduction process of the NB derivatives, again, Ag NPs create positive
electronic interactions with oxygen atoms of NBs.49 At this stage; ultrasonication provides well dispersed
NPs with hot surfaces, created through the enhanced SPR. Another oxygen atom is grafted by sulfur atom
present in the structure of the leaded IT onto the Fe3O4 NPs. Finally, reduction is occurred by hydrazine
hydrate during some successive stages (Scheme 2b).
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Scheme 2. Plausible mechanism for: (a) functionalization of the Ag/Fe3O4 NPs with IT organic compound, and (b)
reduction of the NB derivatives.
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4. Conclusions
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3
4
5
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8
9
In this report, we introduced an innovative process for expedient preparation of isothiazolone-functionalized
silver/iron oxide nanocomposite assisted by ultrasound wave irradiation. Then, it has been shown that a fast
and direct reduction of nitrobenzene derivatives is performed through synergistic effect between the
fabricated heterogeneous organic-functionalized Ag/Fe3O4 nanocomposite and ultrasound waves. Here, we
have easily converted the nitrobenzene derivatives to their aniline analogues with high yield (97%) in 15
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o
min ultrasonication, under mild reaction conditions (25 C). However, from microscopic images it was
revealed that a special morphology has been obtained via the presented preparation method. In the
microscopic images, it has been observed that highly uniform nanoparticles with spherical morphology,
which are formed by silver and iron oxide nanoparticles, are obtained. Also, surface functionalization of
the particles with isothiazolone organic compound has been investigated by various analytical methods.
Moreover, a mechanistic study for the synthesis of the catalytic structure and the reduction process of the
nitrobenzene derivatives has been suggested and discussed in the current paper. For all of the practical
stages, an ultrasound cleaner bath with 50 KHz frequency and 200 W L-1 power density has been used.
Overall, the presented strategy for direct conversion of the nitrobenzene derivatives to their useful aniline
analogues is strongly suggested for industrial applications due to its high convenience, great reusability of
the catalytic system, low cost, excellent time saving and etc.
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1
2
Abbreviations
3
4
NB: Nitrobenzene
5
6
NPs: Nanoparticles
7
8
IT: Isothiazolone
9
APS: Aminopropyl silane
APTES: 3-aminopropyl triethoxysilane
DI: Deionized
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60
DMF: Dimethyl formamide
TBTU: N,N,N′,N′-Tetramethyl-O-(benzotriazol-1-yl)uronium tetrafluoroborate
HBTU: N,N,N′,N′-Tetramethyl-O-(1H-benzotriazol-1-yl)uronium hexafluorophosphate
Acknowledgements
The authors gratefully acknowledge the partial support from the Research Council of the Iran University of
Science and Technology (IUST). Furthermore, AES thanks the National Research grants from MINECO
“Juan de la Cierva” [FJCI-2018-037717].
Conflict of Interest
The authors affirm no conflict of interest.
Supporting Information
The SI section includes NMR spectra (and spectral data) of the produced aniline derivatives, VSM analysis
of nanocatalyst, FT-IR, EDX, and SEM analyses of recovered nanocatalyst, and Table related to the applied
materials and equipment.
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