Core–shell structured magnetic mesoporous silica-titania: A novel, powerful and recoverable nanocatalyst

Article abstract of DOI:10.1016/j.poly.2019.114326

In this research, a novel core–shell nanostructured magnetic Ti-silica (Mag?MCM-41/TiO₂) is synthesized, characterized and its catalytic application is investigated in the production of 1-(α-aminoalkyl)-2-naphthols. The Mag?MCM-41/TiO₂ was prepared via surfactant directed hydrolysis and co-condensation of tetramethoxysilane (TMOS) around Mag?SiO₂ NPs followed by treatment with tetrabutylorthotitanate (Ti(O^tBu)₄). The Mag?MCM-41/TiO₂ catalyst was characterized using VSM, FTIR, EDX, SEM, TEM and PXRD. The Mag?MCM-41/TiO₂ was applied as an efficient catalyst in the synthesis of 1-(α-aminoalkyl)-2-naphthols under ultrasonic conditions at 50 °C. This nanocatalyst was recovered and reused for several times under applied conditions.

Full text of DOI:10.1016/j.poly.2019.114326

Journal Pre-proofs
Core-shell structured magnetic mesoporous silica-titania: A novel, powerful and
recoverable nanocatalyst
Marziyeh Vahidian, Dawood Elhamifar, Masoumeh Shaker
PII:
S0277-5387(19)30771-5
DOI:
https://doi.org/10.1016/j.poly.2019.114326
POLY 114326
Reference:
Polyhedron
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Accepted Date:
6 August 2019
22 November 2019
19 December 2019
Please cite this article as: M. Vahidian, D. Elhamifar, M. Shaker, Core-shell structured magnetic mesoporous silica-
titania: A novel, powerful and recoverable nanocatalyst, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.
2019.114326
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Core-shell structured magnetic mesoporous silica-titania: A novel,
powerful and recoverable nanocatalyst
Marziyeh Vahidian, Dawood Elhamifar* and Masoumeh Shaker
Department of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran
E-mail: d.elhamifar@yu.ac.ir
Abstract: In this research, a novel core-shell nanostructured magnetic Ti-silica (Mag@MCM-
41/TiO2) is synthesized, characterized and its catalytic application is investigated in the
production of 1-(α-aminoalkyl)-2-naphthols. The Mag@MCM-41/TiO2 was prepared via
surfactant directed hydrolysis and co-condensation of tetramethoxysilane (TMOS) around
Mag@SiO2 NPs followed by treatment with tetrabutylorthotitanate (Ti(OtBu)4). The
Mag@MCM-41/TiO2 catalyst was characterized using VSM, FTIR, EDX, SEM, TEM and
PXRD. The Mag@MCM-41/TiO2 was applied as an efficient catalyst in the synthesis of 1-(α-
aminoalkyl)-2-naphthols under ultrasonic conditions at 50 °C. This nanocatalyst was recovered
and reused for several times under applied conditions.
Keywords: Core-shell nanostructure, Magnetic Ti-silica, 1-(α-aminoalkyl)-2-naphthols,
Ultrasonic conditions, Nanocatalyst
1

1. Introduction
Over the past few decades, the synthesis of magnetic nanoparticles has been the subject of
extensive research. Among the magnetic nanoparticles, iron oxides are highly regarded in
scientific and technological terms due to their optical, electrical, magnetic, and catalytic
properties [1]. These NPs and their nanocomposites are widely used in various fields such as gas
sensors [2], information storage devices [3], catalysis [4, 5], adsorbent materials [6], pigments
[7], water purification [8], magnetic resonance imaging (MRI) [9-11], hyperthermia treatment
[12], tissue repair [13], detoxification of biological fluids [14], labeling and separation of cells
[15, 16], drug delivery [17-19] and biological sensors [20]. Up to now, 16 pure phases of iron
oxides including oxides, hydroxides and oxyhydroxides, have been identified. Among these,
magnetite (Fe3O4) offers the most interesting magnetic and electron properties due to the
presence of iron cations in both capacities (Fe2+, Fe3+). In comparison with other materials,
magnetite NPs are of great interest to researchers due to their proper biocompatibility, non-
toxicity, strong superparamagnetic properties and easy preparation [13, 21-23]. However, Fe3O4
NPs tend to self-assembly due to their large surface area, high surface energy, magnetic
properties and hydrophilic surfaces [24]. To solve these problems many studies are focused on
the modification of Fe3O4 NPs surface with different organic and inorganic materials to form
magnetic core-shell structures [25]. Due to its unique properties, silica is the most common
mineral substance to modify the surface of the magnetic MNPs. Magnetic mesoporous silicas are
very attracted between chemists due to they have advantages of both MNPs and mesostructures
such as simple recoverability, high surface area and easy modification of their surface with
different catalysts [26-28]. To date several magnetic nanosilica supported catalysts have been
prepared and their applications have been studied in chemical processes [29-34]. Some of
2

recently reported materials are Fe3O4@MCM-41-Im@MnPor [29], Fe3O4@MCM-41@Pd-
SPATB [30], Rd-MCM-41@Fe3O4 [31], Yb(OTf)2-SO3Na&Ph-MCMSS [32] and
Fe3O4@MCM-41-SH [33].
On the other hand, multi-component reactions have been considered and developed as an
effective and helpful way for the synthesis of fine organic compounds. One of these important
processes is Betti reaction producing amino-naphthol products (or Betti bases) that are very
attractive between chemists due to their pharmacological properties such as blood pressure
reducer, anti-cancer, heart beat, anti-bacterial, antipain and selective estrogen receptors. Also, the
non-racemic aminonaphthols are as valuable chiral ligands or chiral auxiliaries in asymmetric
synthesis. [35-38]. The starting materials used for Betti reaction are primary and secondary
aliphatic or aromatic amines, aliphatic and aromatic aldehydes, phenols and β-naphthols
(Scheme 1). This reaction has been performed under both homogeneous and heterogeneous
conditions in the presence of different catalysts such as nanocrystalline MgO [35],
Cu(OTf)2.SiO2 [36], spherical Fe3O4 MNPs [37], reverse ZnO nanomicelles [39], rMGO-Au NPs
composite [40], Triton X-100 [38], nano-SiO2–H3BO3 [41], ChPS TSIL [42], triflic acids [43],
[Et3N–SO3H]Cl [44], Sodium dodecyl sulfate (SDS) [45].
R1
R
N
OH
R2
OH
Catalyst,heat
O
H
R1
N
N
R1
R2
+
R
H
OH
R
R2
OH
R, R1, R2: H, aryl, alkyl
Catalyst, heat
Scheme 1. The Betti reaction
3

Herein, synthesis and characterization of a novel magnetic mesoporous Ti-silica (Mag@MCM-
41/TiO2) with core-shell structure are developed. Moreover, the catalytic application of
Mag@MCM-41/TiO2 is studied in the Betti reaction to produce 1-(α-aminoalkyl)-2-naphthols
(Scheme 2).
2. Experimental Section
2. 1. General
All chemicals and reagents such as iron (II) chloride tetrahydrate (99%), iron (III) chloride
hexahydrate (99%), cetyltrimethylammonium bromide (CTAB, 98%), ammonia (NH3, 25% wt),
tetramethoxysilane (TMOS, 99%), tetrabutylorthotitanate ([Ti(OtBu)4], 97%), 2–naphthol and all
applied aldehydes and amines were purchased from Sigma-Aldrich, Merck and Fluka companies.
The reaction progress was monitored using TLC. The morphology of the particles was evaluated
by Philips, XL30 emission scanning electron microscope (SEM). Fourier transform infrared (FT-
IR) spectroscopy was recorded on a Brucker-Vector 22 spectrometer. Powder X-ray diffraction
(PXRD) was obtained using a Panalytical X-Pert diffractometer. The magnetic properties of the
particles were investigated using vibrating sample magnetometer (VSM) of Meghnatis Daghigh
Kavir Company. Energy-dispersive X-ray spectroscopy (EDX) was obtained by TESCAN Vega
Model. Melting points were determined using a KSB1N, Kruss apparatus in open capillary tubes.
Ultrasonic model KMM1-120WE301 was used to disperse the particles and to perform the
organic reactions. 1HNMR and 13CNMR spectra were recorded in DMSO solvent using a Bruker
Advanced DMX-400 MHz spectrometer.
2.2. Synthesis of Mag@MCM-41/TiO2
4

For the synthesis of Mag@MCM-41/TiO2, firstly the Fe3O4 and Mag@SiO2 nanoparticles were
prepared according to reported procedures [46, 47]. To prepare the Mag@MCM-41
nanoparticles, Mag@SiO2 nanospheres (0.6 g) were first ultrasonically dispersed in
deoxygenated water (60 mL) for 0.5 h under argon atmosphere. Then, cetyltrimethylammonium
bromide (CTAB, 1 g) and NH3 (25% wt, 3 mL) were added and the mixture was stirred
mechanically at 25 ºC. After that, 0.7 mL of TMOS was drop-wise added and stirring was
continued at same temperature for 2 h under argon atmosphere. Next, the obtained combination
was statically heated during 48 h at 100 °C. The product was collected using an external magnet,
washed completely with EtOH and dried for 6 h at 70 °C. The cetyltrimethylammonium bromide
(CTAB) surfactant was eliminated by calcination at 500 °C for 6 h and the obtained powder was
called Mag@MCM-41. Finally, the Mag@MCM-41 (0.5 g) was stirred in 40 mL of
deoxygenated DMSO and concurrently 1 mL of tetrabutylorthotitanate [Ti(OtBu)4] was added
drop-wise at room temperature under argon atmosphere. After 2 h stirring, the final product was
isolated, washed with EtOH, dried at 80 ºC for 10 h and called Mag@MCM-41/TiO2
nanocatalyst. The loading of titanium onto/into material framework was calculated based on ICP
and EDX results (4.56 mmol Ti/gram of material).
2.3. Synthesis of 1-(α-aminoalkyl)-2-naphthols using Mag@MCM-41/TiO2 catalyst
For this, 1 mmol of 2–naphthol, 1 mmol of aldehyde, 1 mmol of amine and catalyst
Mag@MCM-41/TiO2 (2.3 mol%) were added in a reaction flask and this mixture was heated at
50 °C under ultrasonic irradiations. After completion of the process, monitored by TLC, 10 mL
of ethyl acetate was added and the Mag@MCM-41/TiO2 was removed via a magnetic field.
Finally, the solvent was evaporated and pure products were obtained after recrystallization in
5

ethanol. The products were characterized using NMR and IR spectroscopies. It is important to
note that in this process, the 2–naphthol was limiting reagent. For performing reaction in an oil
bath, the above mentioned amounts of starting materials and catalyst were added in a flask while
stirring at 50 °C in an oil bath. After completing of the process, the pure product was obtained as
above.
2.4. Procedure for the recovery of Fe3O4@MCM-41/TiO2 nanocatalyst
For this, the reaction between benzaldehyde, 2–naphthol and pipiridine in the presence of
designed catalyst was selected as a reaction model under optimized reaction. The reaction
progress was monitored by TLC. After finishing of the reaction, ethyl acetate (10 mL) was added
in reaction vessel and catalyst was removed using an external magnet. The catalyst was washed
with ethanol and dried at 80 ºC. The recovered catalyst was reused in the next run under
conditions as the first run. These steps were repeated several times and the yield of each run was
calculated and reported.
2.5. The IR and NMR data of some Betti products are as following
2.5.1. 1-((4-Bromophenyl)(piperidin-1-yl)methyl)naphthalen-2-ol
White solid; yield: 0.371g, 94 %; mp: 159-161 ºC [48]; IR (KBr, cm-1): 3328 (O-H), 3080 (=C-
H, stretching vibration, sp2), 2939 (C-H stretching vibration, sp3), 1508-1624 (C=C, Ar), 1234
(C-N), 749 (C-Br). 1H NMR (DMSO, 400 MHz)  (ppm):1.47 (s, 2H), 1.58 (s, 4H), 2.37(s,
4H), 5.34 (s, 1H), 7.09 (d, J= 8.8 Hz, 1H,), 7.25 (t, J= 7.6, 1H), 7.40 (t, J 7.6 Hz,1H), 7.51 (d,
J= 8 Hz, 2H), 7.58 (d, J= 7.6 Hz, 2H), 7.72 (d, J= 6.4 Hz,1H), 7.76 (d, J= 8.4 Hz, 1H), 8.01 (d,
6

13
J= 8 Hz,1H), 13.73(s, 1H, OH). C NMR (CDCl3, 100 MHz) δ (ppm): 24.0, 26.0, 52.7, 69.6,
116.5, 120.1, 121.3, 121.7, 122.9, 127.0, 128.49, 128.59, 128.5, 129.1, 129.7, 131.2, 132.1,
132.3, 141.1, 155.5.
2.5.2. 1-((2-Chlorophenyl)(piperidin-1-yl)methyl)naphthalen-2-ol
White solid; yield: 0.309g, 88 %; mp: 136-138 ºC [48]; IR (KBr, cm-1): 3331 (O-H), 3065 (=C-
H, stretching vibration, sp2), 2977 (C-H stretching vibration, sp3), 1510-1657 (C=C, Ar), 1230
(C-N), 753 (C-Cl).
2.5.3. 1-(Phenyl(piperidin-1-yl)methyl)naphthalen-2-ol
White solid; yield: 0.301g, 95 %; mp: 195-196 ºC [49]; IR (KBr, cm-1): 3311 (O-H), 3073 (=C-
H, stretching vibration, sp2), 2947 (C-H stretching vibration, sp3), 1503-1641 (C=C, Ar), 1238
(C-N).
2.5.4. 1-(Piperidin-1-yl(p-tolyl)methyl)naphthalen-2-ol
White solid; yield: 0.278g, 84 %; mp: 144-146 ºC [49]; IR (KBr, cm-1): 3396 (O-H), 3064 (=C-
H, stretching vibration, sp2), 2963 (C-H stretching vibration, sp3), 1508-1657(C=C, Ar), 1231
(C-N).
2.5.5. 1-((2-Nitrophenyl)(piperidin-1-yl)methyl)naphthalen-2-ol
Yellow solid; yield: 0.347g, 96 %; mp: 196-198 ºC [49]; IR (KBr, cm-1): 3354 (O-H), 3024 (=C-
H, stretching vibration, sp2), 2931 (C-H stretching vibration, sp3), 1508-1657(C=C, Ar), 1564
and 1342 (NO2), 1240 (C-N).
7

2.5.6. 1-((2-Nitrophenyl)(phenylamino)methyl)naphthalen)-2-ol
Yellow solid; yield: 0.333g, 90 %; mp: 132-134 ºC [39]; IR (KBr, cm-1): 3412 (N-H), 3363 (O-
H), 3008 (=C-H, stretching vibration, sp2), 2947 (C-H stretching vibration, sp3), 1510-
1642(C=C, Ar), 1584 and 1372 (NO2), 1235 (C-N).
2.5.7. 1-((Phenyl)(butylamino)methyl)naphthalen-2-ol
White solid; yield: 0.286g, 94 %; mp: 130-132 ºC [40]; IR (KBr, cm-1): 3442 (N-H), 3300 (O-H),
3014 (=C-H, stretching vibration, sp2), 2937 (C-H stretching vibration, sp3), 1503-1641 (C=C,
Ar), 1238 (C-N).
3. Results and discussion
To prepare Mag@MCM-41/TiO2, the Fe3O4@SiO2 core-shell nanoparticles were firstly prepared
according to a well-known procedure [46, 47]. Secondly, the magnetic mesoporous
Mag@MCM-41 nanocomposite was prepared through hydrolysis and condensation of TMOS
around Mag@SiO2 nanoparticles in the presence of CTAB surfactant under alkaline conditions.
After calcination to remove CTAB, the Mag@MCM-41 was treated with tetrabutylorthotitanate
[Ti(OtBu)4] to deliver desired Mag@MCM-41/TiO2 catalyst (Scheme 2). The structural and
chemical properties of the Mag@MCM-41/TiO2 nanocatalyst were investigated using FT-IR,
SEM, TEM, EDX, PXRD and VSM.
8

1. H2O, 25 °C, Ar, 30 min
2. NH3 (25%), CTAB, 25 °C
DMSO, Ti(OtBu)4, r.t., Ar, 2 h
3. TMOS, 25 °C, Ar, 2 h
4. Static condition, 100 °C, 48 h
5. Calcination
Mag@MCM-41/TiO2
Mag@MCM-41
Mag@SiO2
: TiO2
R1
Ar
N
R2
OH
O
H
OH
Mag@MCM-41/TiO2 (2.3 mol %)
50 °C, solvent free, )))
+
N
+
Ar
H
R1
R2
Scheme 2. Synthesis of Mag@MCM-41/TiO2 and its catalytic application in Betti reaction
The FT-IR of Fe3O4 (Fig. 1 a) showed two peaks at 559 and 3419 cm-1 corresponding to the Fe-
O and O-H bonds, respectively. For Mag@MCM-41 (Fig. 1 b) and Mag@MCM-41/TiO2 (Fig. 1
c), the signals of Si-O-Si bonds were appeared at 1050 and 955 cm-1. Also for the latter samples,
the peak observed at 3419 cm-1 is related to stretching vibration of O-H bond. Moreover, the
band cleared at 1632 cm-1 is due to bending vibration of O–H bonds. The broad signals in the
absorption range of 500-900 and 940–960 cm-1 are assigned to Ti-O-Ti and Ti-O-Si bonds,
respectively (Fig. 1) [50]. In fact, the successful immobilization of titanium oxide particles on
the surface of Mag@MCM-41 is confirmed by this analysis.
9

Fig. 1. FT-IR spectra of a) Fe3O4, b) Mag@MCM-41 and c) Mag@MCM-41/TiO2 materials
The PXRD analysis of the Fe3O4 and Mag@MCM-41/TiO2 (Fig. 2) showed the same pattern
with six reflection peaks at 2θ of 63.41, 57.56, 54.10, 43.92, 36.01 and 30.38 degrees,
corresponding to the Miller indices values (hkl) of 440, 511, 422, 400, 311 and 220, respectively,
proving that the crystalline structure of the magnetite NPs is maintained during the catalyst
preparation steps [2, 6].
10

Fig. 2. PXRD pattern of the a) Fe3O4 and b) Mag@MCM-41/TiO2 nanomaterials
The expected composition of Mag@MCM-41/TiO2 was studied by EDX spectroscopy. As
shown, the peaks of titanium, iron, silicon and oxygen are observed in the EDX spectrum
confirming successful coating of silica-titania species onto iron oxide particles (Fig. 3). Worth
noting that quantitative determination of the elements was also performed using EDX analysis
that for Ti, Fe, Si and O this was 21.84 %, 58.70 %, 7.11 % and 12.36 %, respectively.
11

Fig. 3. EDX analysis of the Mag@MCM-41/TiO2 nanocatalyst
The SEM analysis showed the presence of particles with spherical morphology and average size
of 70 nm for the Mag@MCM-41/TiO2 nanocatalyst (Fig. 4). The TEM image (Fig. 5) also
showed a core-shell stricture for the material with black core (magnetite NPs) and gray shell
(MCM-41/TiO2 layer).
12

Fig. 4. SEM analysis of Mag@MCM-41/TiO2
Fig. 5. TEM analysis of Mag@MCM-41/TiO2
13

The VSM curve of Mag@MCM-41/TiO2 nanocatalyst is presented in Fig. 6. As shown, the
saturation magnetization for the material is 25 emu/g confirming good magnetic properties of
this sample.
Fig. 6. VSM diagram of the Mag@MCM-41/TiO2 nanocatalyst
After characterization of Mag@MCM-41/TiO2 nanocatalyst, its catalytic application was
investigated in the production of 1-(α-aminoalkyl)-2-naphthols (Scheme 2) under different
conditions (Table 1). For this, the reaction between 2–naphthol, benzaldehyde and piperidine in
14

the presence of Mag@MCM-41/TiO2 in an ultrasonic bath was chosen as a test experiment.
Firstly, the effect of catalyst loading in the reaction progress was studied. It was found that the
existence of catalyst is essential for performing the reaction (Table 1, entry 1). The study of
effect of catalyst loading showed that the best result is obtained in the presence of 2.3 mol% of
Mag@MCM-41/TiO2 (Table 1, entries 2-4). The temperature effect was also studied in the
reaction progress that 50 °C was introduced as optimum (Table 1, entry 3 versus entries 5, 6).
The solvent study showed that under solvent-free media the better result is obtained compared to
water and ethanol solvents (Table 1, entry 3 versus entries 7, 8). In the next, the reaction progress
was studied in an oil bath and the result was compared with that of ultrasonic bath (Table 1,
entry 3 versus entry 9). Interestingly, both catalytic activity and product yield were better for
ultrasonic media confirming the important role of ultrasonic waves in the progress of reaction
that may be attributed to better dispersion of isolated catalytic nanoparticles under ultrasonic
conditions. In another study, the catalytic activity of Ti-free Fe3O4 and Mag@MCM-41 materials
in the model reaction was studied and the results were compared with those of present catalyst.
Interestingly, under the same conditions as Mag@MCM-41/TiO2, the Fe3O4 and Mag@MCM-41
delivered only 22 and 9% of desired product, respectively, confirming that the process is mainly
catalyzed by supported Ti-species (Table 1, entry 3 versus entries 10, 11). According to these
studies, 2.3 mol% of Mag@MCM-41/TiO2 catalyst, 50 °C, solvent free conditions and ultrasonic
irradiations were introduced as optimum conditions.
15

Table 1. Screening different parameters to prepare 1-(α-aminoalkyl)-2-naphthols
O
H
N
N
OH
Mag@MCM-41/TiO2
)))
H
+
+
OH
Entry
1
Solvent
---
Cat. (mol %)
T (°C) Time (min)
Yield (%)a
---
1.36
2.3
50
50
50
50
r.t.
60
50
50
50
50
50
60
60
60
60
60
60
60
60
60
60
60
---
90
95
95
75
96
70
85
73
22
9
2
---
3
---
4
---
3.19
2.3
5
---
6
---
2.3
7
H2O
EtOH
---
2.3
8
2.3
9b
10
11
2.3
c
---
Fe3O4
---
Mag@MCM-41 d
a Isolated yields. b The reaction was performed in an oil bath. c 0.005 g of Fe3O4 was used. d
0.005 g of Mag@MCM-41 was used.
After optimization of reaction conditions, various aldehydes were applied to prepare different 1-
(α-aminoalkyl)-2-naphthols (Table 2). The results showed that both electron donating and
electron withdrawing containing substituents afford their corresponding products in high yield
16

and selectivity confirming high efficacy of this catalyst to prepare desired products. The other
aromatic and aliphatic primary amines such as aniline and butanamine were also used as
substrate delivering high yield of corresponding 1-(α-aminoalkyl)-2-naphthols. These data
confirm high efficiency of designed catalyst in the synthesis different derivatives of Betti
products.
Table 2. Production of 1-(α-aminoalkyl)-2-naphthols in the presence of Mag@MCM-41/TiO2
R1
Ar
N
R2
OH
O
H
OH
Mag@MCM-41/TiO2 (2.3 mol %)
50 °C, solvent free, )))
+
N
+
Ar
H
R1
R2
Entry
1
Ar
Amine
t (min) Yield (%)a Found M. P. (ºC) Reported M. P. (°C)
H
N
65
75
60
75
94
88
95
84
159-161
136-138
195-196
144-146
158-160 [48]
136-138 [48]
194-195 [49]
145-147 [49]
Br
H
N
2
3
4
Cl
H
N
H
N
Me
17

H
N
5
6
50
96
196-198
194-195 [49]
NO2
NO2
NH2
52
50
90
94
132-134
130-132
131.7-133.9 [39]
133-135 [40]
NH2
7
a Isolated yields.
Since the use of efficient heterogeneous catalysts in chemical industries has become increasingly
important to reduce environmental pollution and production costs, in the next some experiments
were carried out to study the recoverability and reusability of the Mag@MCM-41/TiO2 catalyst.
With this aim, after completion of the reaction, the Mag@MCM-41/TiO2 was recovered and then
reused under the same conditions as the first run. The procedure was repeated and the result
demonstrated that the catalyst can be recovered and reapplied for at least seven times with no
noticeable reduction in its activity (Fig. 7).
18

Fig. 7. Reusability of the Mag@MCM-41/TiO2 nanocatalyst
In the next step, the leaching test was performed to prove heterogeneity behavior of catalyst. For
this purpose, the reaction between 2–naphthol, benzaldehyde and piperidine in the presence of
Mag@MCM-41/TiO2 was selected as model reaction under the optimal conditions. After about
50 % progress of the reaction, the Mag@MCM-41/TiO2 was removed by a magnet. Then, the
reaction of residue was screened under optimal conditions. Interestingly, after 2 h, no significant
conversion was observed confirming that the Mag@MCM-41/TiO2 catalyst heterogeneously
works under applied conditions.
Finally, the efficiency of Mag@MCM-41/TiO2 catalyst was compared with the recently catalysts
used in the synthesis of 1-(α-aminoalkyl)-2-naphthols (Table 3). The results showed that the
19

present catalyst is more favorable than other catalysts, especially in terms of catalyst loading,
yield and the number of recycling times.
Table 3. Comparative study of the efficiency of the present catalyst with that of previously
reported catalytic systems
O
H
N
N
OH
H
+
+
OH
Recovery
times
Catalyst
Conditions
Time Yield (%)
Ref.
[38]
Non-ionic surfactants
(Triton X-100)
Cat. 5 mol %, 25 ºC, H2O
150
90
---
Cu(OTf)2.SiO2
Cat. 10 mol %, 40 ºC, neat
Cat. 50 mg, 25 ºC, H2O
Cat. 0.1 g, 80 ºC, solvent-
free, )))
45
92
90
---
---
[36]
[35]
Nanocrystalline MgO
180
Fe3O4 MNPs
25
60
90
95
6
7
[37]
Cat. 2.3 mol %, 50 ºC,
solvent-free, )))
This
Mag@MCM-41/TiO2
work
20

4. Conclusion
In this paper, a novel Ti-containing core-shell material with magnetite core and nanoporous
MCM-41 shell (Mag@MCM-41/TiO2) was prepared, characterized and its catalytic application
was studied in the synthesis of 1-(α-aminoalkyl)-2-naphthols. The VSM analysis showed
magnetic good properties for Mag@MCM-41/TiO2 nanocatalyst. The spherical morphology of
this nanocatalyst was confirmed by using SEM and TEM analyses. The PXRD analysis proved
high stability of crystalline Fe3O4 NPs during catalyst preparation. The Mag@MCM-41/TiO2
was applied as an effective and powerful catalyst in the synthesis of 1-(α-aminoalkyl)-2-
naphthols. The Mag@MCM-41/TiO2 nanocatalyst was successfully recovered for seven times
with no remarkable reduction in its activity. Other outstanding properties of this work were
solvent free conditions, high reaction rate and no leaching of catalytic TiO2 centers during
reaction. According to the results obtained in this study, some applications of the present catalyst
in other organic processes are underway in our laboratories.
Acknowledgments
The authors thank the Yasouj University and the Iran National Science Foundation (INSF) for
supporting this work.
21

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Graphical abstract:
24

A novel magnetic ordered mesoporous silica-titania (Mag@MCM-41/TiO2) material with
core-shell structure was synthesized, characterized and its catalytic application was
investigated in Betti reaction.
Marziyeh Vahidian, Dawood Elhamifar* and Masoumeh Shaker
Department of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran
E-mail: d.elhamifar@yu.ac.ir
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