Simple hydrothermal synthesis of sphere-like TiO2 nanoparticles and their functionalization with 1,4-butane sultone as a new heterogeneous catalyst

Article abstract of DOI:10.1007/s13738-017-1118-9

Abstract: For the first time, anatase TiO₂ nanoparticles with high specific surface area have been synthesized by hydrothermal method using titanium (IV) ethoxide solution. Nanocrystalline titania-based sulfonic acid (nano-TiO₂–Bu–SO

Full text of DOI:10.1007/s13738-017-1118-9

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1118-9
ORIGINAL PAPER
Simple hydrothermal synthesis of sphere‑like TiO2 nanoparticles
and their functionalization with 1,4‑butane sultone as a new
heterogeneous catalyst
Maliheh M. Hosseini1 · Eskandar Kolvari1 · Somayeh Zolfagharinia1 · Mina Hamzeh1
Received: 26 September 2016 / Accepted: 12 April 2017
© Iranian Chemical Society 2017
Abstract For the frst time, anatase TiO2 nanoparticles
with high specifc surface area have been synthesized by
hydrothermal method using titanium (IV) ethoxide solu-
tion. Nanocrystalline titania-based sulfonic acid (nano-
TiO2–Bu–SO3H (n-TBSA)) was successfully prepared by
the reaction of nano-TiO2 and 1,4-butane sultone. The sam-
ples were characterized using FT-IR, XRD, TGA, EDX,
FESEM, TEM, BET and BJH analysis. The present cata-
lytic system can be applied in multicomponent reaction for
the synthesis of 1-amidoalkyl-2-naphthols and 1,8-dioxo-
octahydro-xanthenes. The simple preparation, chemical
stability, product selectivity and the recyclability of the
catalyst make it eco-friendly and economical worthwhile.
* Eskandar Kolvari
kolvari@semnan.ac.ir
1
Department of Chemistry, Semnan University, Semnan, Iran
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J IRAN CHEM SOC
Graphical Abstract
nanocrystalline metal oxides seem to be attractive nano-
catalysts in organic syntheses due to their broad reactive
surfaces with higher potential for selectivity, reusability
and benign character in the context of green chemistry [8–
10]. Recently, developing of novel strategies for obtaining
size- and shape-controllable nanomaterials is an important
topic in the science of the chemistry [11]. In nature, TiO2 is
known to exist in three different crystalline forms, brook-
ite, rutile and anatase. Anatase TiO2 has attracted particular
attention due to its promising applications in photovoltaic
cells, dye-sensitized solar cells, sensors and photocataly-
sis because of its superior activity compared to the other
phases [12–16]. Nanocrystalline titanium has emerged as
effcient and inexpensive support for the synthesis of het-
erogeneous catalyst owing to its unique properties [17].
However, further efforts are necessary in the design of new
heterogeneous catalysts using titanium dioxide as effcient
supports to achieve excellent catalytic activity and selectiv-
ity in multicomponent reaction.
Multicomponent reactions (MCRs) along with advan-
tages of effciency, atom economy and simplicity are argu-
ably one of the most important protocols in organic synthe-
sis that have attracted considerable attention for a long time
[18, 19]. Therefore, synthesis of heterocyclic compounds
through multicomponent reactions, environmentally benign
procedures and utilizing green reusable catalysts is a prom-
inent subject of interest.
Keywords Nano-TiO2–Bu–SO3H (n-TBSA) ·
Heterogeneous catalyst · Interphase catalyst ·
1-Amidoalkyl-2-naphthols · 1,8-Dioxo-octahydro-
xanthenes · Reusability
Introduction
Rising environmental pollution and global anxiety resulted
in the innovation of alternative methods for the production
of safe chemicals. Because of constant demand in renew-
able energy and sustainable environment, development
of novel heterogeneous catalyst instead of homogeneous
catalyst in various chemical transformations has attracted
increasing interest. Compared with homogeneous cata-
lysts, heterogeneous catalysis has emerged as a useful tool
to reduce waste production with regard to the simplicity of
the process, easy and safe handling, avoidance of the use
of toxic solvents, separation and recycling of the catalysts
and eliminating problems with corrosion, toxicity and envi-
ronmental harm [1–3]. An important strategy to transform
a homogeneous catalyst into a heterogeneous one is to
immobilize one or more components of the catalytic sys-
tems onto a broad solid surface area through an organic
entity (fexible spacer) to create new organic–inorganic
hybrid (interphase) catalysts. This interphase nanocatalyst
has advantages of both of homogeneous and heterogeneous
catalyst due to the mobility of reactive center, easy sepa-
ration and recovery [4–7]. Among heterogeneous catalysts,
Considering the above facts and in the course of our
interest to develop eco-friendly new heterogeneous
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J IRAN CHEM SOC
catalysts in organic synthesis [20–24], the synthesis of
TiO2 nanoparticles under hydrothermal conditions is pre-
sented in the frst part of the present work. Then, chemi-
cally bound adsorbed sulfonic acid on TiO2 (TiO2–Bu–
SO3H (n-TBSA)) was prepared as a new organic–inorganic
hybrid acid catalysts by the reaction of 1,4-butane sultone
and TiO2 (Scheme 1). Furthermore, the catalytic activity of
nanocatalyst was applied to effective synthesis of 1-ami-
doalkyl-2-naphthols and 1,8-dioxo-octahydro-xanthenes
under solvent-free conditions.
X‑ray diffraction (XRD) analysis
Figure 2a shows the XRD pattern of TiO2 nanoparticle
before modifcation process, presenting the character-
istic peaks of anatase structure. The pattern indicates a
crystallized structure with the peak positions of 2θ: 25.3°,
36.3°, 37.6°, 39.3°, 48.0°, 54.2°, 55.0°, 62.5°, 68.8°,
75.5° and 82.7°, which are assigned to the (101), (103),
(004), (112), (200), (105), (211), (204), (220), (215) and
(303) crystallographic faces of anatase TiO2 (ICCD no.
21-1272) [27]. The crystal size of the TiO2 nanoparticles
was also determined from X-ray pattern using the Scher-
rer formula given as t = 0.9λ/B1/2cosθ, that t is the aver-
age crystal size, λ the X-ray wavelength used (1.54 Å),
B1/2 the angular line width at half maximum intensity and
θ the Bragg’s angle. The average crystal size of the TiO2
Results and discussion
Catalyst characterization
FT‑IR spectroscopy
FT-IR spectra for the pure nano-TiO2 and nano-TiO2–
Bu–SO3H samples are presented in Fig. 1. In the case of
nano-TiO2, the peaks positioned at 3426 and 1645 cm−1
are related to the –OH stretching and bending vibrations
of the adsorbed water, respectively. The presence of a well-
defned band positioned at 611 cm−1 is related to the Ti–O
stretching and Ti–O–Ti bending which characterizes the
formation of the anatase structure of TiO2 [25]. This result
is in accordance with that obtained from the XRD studies.
The spectrum of functionalized nano-TiO2 by sulfonic acid
displays almost the same pattern as that of pristine nano-
TiO2, but the band at 3427 cm−1 is fattened in sulfonated
nano-TiO2 which can be attributed to the modifcation of
nano-TiO2. Also, CH stretching vibrations were observed
at 2945 and 2918 cm−1 and the peaks positioned at 1228,
1151 and 1041 cm−1 are related to the stretching frequency
of S–O and S=O in SO3H [26]. This result shows modif-
cation of nano-TiO2 using 1,4-butane sultone.
Fig. 1 FT-IR spectra of a nano-TiO2 and b nano-TiO2–Bu–SO3H
Scheme 1 Synthesis of nano-TiO2–Bu–SO3H
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J IRAN CHEM SOC
Fig. 2 X-ray diffraction patterns of a nano-TiO2 and b nano-TiO2–
Bu–SO3H
Fig. 3 TGA curve of a nano-TiO2 and b nano-TiO2–Bu–SO3H
nanoparticles for 2θ = 26.06° is calculated to be around
14.9 nm. This was coincident with the results obtained
from the TEM analysis. In Fig. 2b, it can be seen that the
diffraction peaks of nano-TiO2–Bu–SO3H are similar to
those of the parent TiO2 nanoparticles, which suggest that
the phase structure of the synthesized nanoparticle is well
retained after modifcation.
with organic group resulted in the formation of larger clus-
ters of the obtained TiO2 nanoparticle.
TEM analysis
Figure 5 shows the TEM images of the TiO2 nanoparti-
cle. It was found that the as-synthesized nanomaterial has
spherical morphology. According to the TEM images, it
is also clear that the morphology, size and distribution
of the nanoparticles are almost homogeneous. This fg-
ure also indicates the average particle size distribution of
nano-TiO2 was in the range of 10–15 nm.
Figure 6 shows TEM images of the modifed TiO2 nano-
material. It was found that the morphology of the obtained
material was still spherical. However, Fig. 6c shows that
the size of the as-synthesized nanomaterial is not homoge-
neous and there are different kinds of the nanomaterial in
view of their sizes. It also indicated that the average parti-
cle size distribution was in the range of 15–20 nm.
Thermogravimetric analysis (TGA)
Thermogravimetric analysis (TGA) of nano-TiO2–Bu–
SO3H in comparison with nano-TiO2 is displayed in Fig. 3.
The TGA curve of nano-TiO2 (Fig. 3a) exhibits a weight
loss below 100 °C which corresponds to the loss of the
physically adsorbed water and then a steady weight loss in
the range of 150–700 °C, which possibly corresponds the
to the dehydroxylation of nano-TiO2. For the n-TBSA, the
TGA curve (Fig. 3b) seems to indicate two-stage decom-
position. One initial weight loss assigned to the loss of
the physically adsorbed water below 120 °C and the other
that started at approximately 216 up to 700 °C assigned to
the decomposition of the covalently bound organic group.
Also from the TGA, it was found that catalyst has a great
thermal stability (until 150 °C) confrming that it could
be safely used in organic reactions at temperatures up to
140 °C [17].
BET and BJH analysis
The surface area, pore volume and pore size of the syn-
thesized powders were calculated using the Brunauer–
Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH)
equations, respectively. Prior to N2-physical adsorption
measurements, the samples were degassed at 150 °C for
120 min in the nitrogen atmosphere. The specifc surface
area (SBET) of the obtained materials was determined with
adsorption–desorption isotherms of N2 at 77 K. The sur-
face area, pore volumes and pore diameters of the synthe-
sized materials are summarized in Table 1. Besides, Table 2
shows the textural properties of the as-prepared materials.
SEM analysis
According to the FESEM analysis (Fig. 4), it was observed
the synthesized nano-TiO2 (Fig. 4a–c) and n-TBSA
(Fig. 4d–f) were homogeneous spherical-shaped particles.
It is clear that the primary surface morphology of the as-
synthesized TiO2 has been changed after functionalization
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J IRAN CHEM SOC
Fig. 4 SEM images of a–c nano-TiO2 and d–f nano-TiO2–Bu–SO3H
XRD energy‑dispersive X‑ray spectroscopy (EDX) analysis
Synthesis of 1‑amidoalkyl‑2‑naphthol derivatives
The elemental composition of nano-TiO2–Bu–SO3H from
EDX analysis also indicated the presence of Ti, O, S and C
elements (Fig. 7), and the percent of elements is shown in
Table 3.
The catalytic activity of n-TBSA was assessed in the synthe-
sis of 1-amidoalkyl-2-naphthols 4. Initially, the reaction of
benzaldehyde 1, β-naphthol 3 and benzamide 2 (mole ratio
1:1:1.2) was considered as the model reaction (Scheme 2).
To select an appropriate amount of catalyst on the cat-
alytic performance, the model reaction was also carried
out in the presence of various molar ratios of n-TBSA and
the best yield was observed when the reactions were per-
formed by using of 3 mol% of n-TBSA (Table 4, entry 5).
Through examination, it was found that the reaction did
not proceed in the absence of the catalyst in any tempera-
ture (Table 4, entries 1–3). To fnd out the best operative
reaction temperature, the reaction was carried out under
varying reaction temperature with 3 mol% of n-TBSA
under solvent-free conditions (Table 4, entries 5, 7–8).
Thus, 100 °C was selected as the optimum temperature.
To investigate the effect of the solvent on the catalytic
reaction, the model reaction in the presence of 3 mol% of
n-TBSA was carried out in several solvents such as etha-
nol, methanol, water, THF and toluene and in a solvent-
free condition (Table 4, entries 5, 9–13).
PH analysis of catalyst
The optimum concentration of H+ of nano-TiO2–Bu–SO3H
was determined by acid–base potentiometric titration of the
aqueous suspension of the weighed amount of thoroughly
washed catalyst with standard NaOH solution. At frst,
100 mg nano-TiO2–Bu–SO3H was dispersed in 20 ml H2O
by ultrasonic bath for 60 min at room temperature after
which the pH of solution was 3.36. The amount of the acid
was neutralized by addition of standard NaOH solution
(0.088 N) to the equivalence point of titration. The required
volume of NaOH to this point was 0.5 ml. This is equal to a
loading of 0.44 mmol H+/g.
Catalytic activity of nano‑TiO2–Bu–SO3H in one‑pot
multicomponent reactions
It was found that ethanol is better than other solvents
for this reaction but the best yield obtained under solvent-
free conditions (Table 4, entry 5).
On the basis of the information obtained from the above
mentioned studies, catalytic activity of n-TBSA was exam-
ined in multicomponent reactions for the synthesis of het-
erocyclic compounds such as 1-amidoalkyl-2-naphthol and
1,8-dioxo-octahydro-xanthene derivatives. All products
were characterized by spectral data and compared with
their physical data with the literature.
Having established effcient optimized conditions for
the synthesis of 1-amidoalky-2-naphthols, a range of
aryl aldehydes were subjected to react with 2 and 3 to
generate 4a–n in high to moderate yields. The results are
summarized in Table 5. The products were characterized
1
by IR, H NMR and 13C NMR spectroscopy, and also by
comparison with authentic samples.
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J IRAN CHEM SOC
Fig. 5 TEM images of nano-
TiO2 and particle size distribu-
tion
Synthesis of 1,8‑dioxo‑octahydro‑xanthene derivatives
A possible mechanism for the formation of 1,8-dioxo-
octahydro-xanthenes and 1-amidoalkyl-2-naphthols is
shown in Scheme 4.
The effciency of n-TBSA was compared with some
other published works in the literature for the synthesis of
1-amidoalkyl-2-naphthols (Table 7). Each of these methods
has their own advantages, but they often suffer from some
troubles including reaction conditions, time and product
yields. As can be seen in this table, the present catalyst was
The effciency of the obtained n-TBSA has been tested
by the synthesis of 1,8-dioxo-octahydro-xanthene deriva-
tives 6a–m under optimal conditions (3 mol% of n-TBSA
in 120 °C and solvent-free condition) by condensation
between aromatic aldehyde 1 (1 mmol) and dimedone
5 (2 mmol) (Scheme 3). The results are summarized in
Table 6.
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Fig. 6 TEM images of nano-
TiO2–Bu–SO3H and particle
size distribution
Table 1 BET data showing the textural properties of the obtained
Table 2 BJH data showing the textural properties of the obtained
materials
materials
Sample
BET surface area
Pore volume
Pore diameter
(nm)
Property
n-TiO2
n-TBSA
(m2g−1
)
(cm3g−1
)
Desorption surface area (m2g−1
Cumulative desorption pore volume (cm3g−1
)
131.4
0.26
5.29
126.7
0.24
3.53
n-TiO2
91.4
84.8
0.24
0.21
10.63
10.36
)
n-TBSA
Desorption pore diameter (nm)
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J IRAN CHEM SOC
Fig. 7 EDX spectra of nano-
TiO2–Bu–SO3H
activity. Moreover, the stability of catalyst was checked
by XRD pattern of recycled catalyst and indicated that
the catalyst was not changed after fve runs (Fig. 8).
Table 3 The percent of elements in EDX analysis
Element
Atom. C (at%)
Carbon
Oxygen
Sulfur
1.76
60.07
8.54
Experimental
Titanium
29.63
Materials and instrumentation
found to be the most effcient catalyst for the synthesis of
1-amidoalkyl-2-naphthols.
All reagents and starting materials were obtained commer-
cially from Sigma–Aldrich and Merck and were used as
received without any further purifcation. Thermal analy-
sis was done by using a thermogravimetric analyzer on a
Du Pont 2000 thermal analysis apparatus at a heating rate
of 5 °C min−1 under air atmosphere. X-ray powder diffrac-
tion (XRD) patterns were recorded using a Cu Kα radiation
source on a Siemens D5000 (Siemens AG, Munich, Ger-
many) X-ray diffractometer. Field emission scanning electron
microscope (FESEM) images were acquired with a Philips
XL30 feld emission scanning electron microscope (Philips,
Amsterdam, Netherlands). TiO2 nanoparticles were dispersed
in water and cast onto a copper grid to study the sizes and
morphology of the particles by TEM (transmission electron
microscopy) using a Philips—CM300—150 kV microscope.
The average particle size distribution was carried out using
Reusability of the catalyst
The possibility of reusing the catalyst without loss of
activity is one of the most important advantages of het-
erogeneous catalyst from the viewpoint of green chem-
istry. The recovery and reusability of the catalyst was
investigated in the synthesis of 1-amidoalkyl-2-naphthol.
In each cycle, the n-TBSA was separated by centrifug-
ing and washed with hot ethanol and water to ensure the
organic reagents do not remain on the surface of catalyst.
Then, the recovered catalyst was used in the next run. The
results of fve consecutive runs showed that the catalyst
can be reused four times without signifcant loss of its
Scheme 2 Synthesis of
1-amidoalkyl-2-naphthol using
of nano-TiO2–Bu–SO3H
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Table 4 Optimization of
synthesis of 1-amidoalkyl-2-
naphthols
Entry
Solvent
Condition
Nano-TiO2–Bu–SO3H
Amount of catalysts (mol%)
Time (min)
Yield (%)a
1
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Ethanol
r.t
–
–
–
1
3
5
3
5
3
3
3
3
3
120
120
120
20
NRb
NR
Trace
82
2
50 °C
100 °C
100 °C
100 °C
100 °C
80 °C
120 °C
Refux
Refux
Refux
Refux
100 °C
3
4
5
15
95
6
20
90
7
20
60
8
20
92
9
120
120
120
120
120
86
10
11
12
13
Methanol
Water
75
52
THF
40
Toluene
Trace
Reaction condition: benzaldehyde (1 mmol), β-naphthol (1 mmol), benzamide (1 mmol)
a
Isolated yields
b
No reaction was observed
Table 5 n-TBSA-catalyzed
one-pot synthesis of
Entry
Ar
Product
Time (min)
Yield (%)a
MP
MP (Refs.)
1-amidoalkyl-2-naphthols
1
C6H5
4a
4b
4c
4d
4e
4f
10
35
60
28
25
35
60
40
45
20
50
40
60
50
97
85
80
90
82
95
70
85
80
98
95
92
95
82
235–237
233–236
265–267
221–223
285
235–237 [28]
234–236 [28]
265–267 [28]
220–223 [28]
284–285 [28]
178 [29]
2
2-HO–C6H4
3-HO–C6H4
4-HO–C6H4
2-Cl–C6H4
4-Cl–C6H4
(CH3)2NC6H4
2-MeO–C6H4
4-MeO–C6H4
4-Br–C6H4
4-Me–C6H4
4-NO2–C6H4
3-NO2–C6H4
4-Fl–C6H4
3
4
5
6
177–179
220–222
266–268
209–211
182–184
226–228
228–229
239–241
193–194
7
4g
4h
4i
220–221 [28]
266–267 [28]
209 [29]
8
9
10
11
12
13
14
4j
182–184 [30]
228 [31]
4k
4l
228–229 [32]
240–242 [28]
193–194 [28]
4m
4n
Reaction condition aromatic aldehyde (1 mmol), β-naphthol (1 mmol), benzamide (1.2 mmol), n-TBSA
(3 mol%), solvent-free, 100 °C
a
Isolated yields
Scheme 3 Synthesis of
1,8-dioxo-octahydro-xanthene
using of n-TBSA
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J IRAN CHEM SOC
Table 6 n-TBSA—catalyzed one-pot synthesis of 1,8-dioxo-octahy-
dro-xanthene
autoclave was sealed and heated at 180 °C for 24 h and
then cooled to room temperature by water immediately.
When the reaction was completed, a white powder was
collected from the solution and washed with distilled
water. The prepared powder was dried at 110 °C under
normal atmospheric conditions and then calcined at
500 °C for 2 h.
Entry Ar
Product Time (min) Yield (%)a MP
1
2
C6H5
4-OH–
3-OMe–
6a
6b
18
30
90
75
205–206 [33]
225–227 [34]
C6H3
3
4-HO–
C6H4
6c
25
92
180–183 [35]
Preparation of nano‑TiO2–Bu–SO3H
4
5
4-Br–C6H4 6d
19
50
94
93
244–246 [35]
219–221 [35]
Nano-TiO2 was treated with 1 N HCl at 300 K to convert
into hydrogen titanate. The surface functionalization of
H+-titanate was performed using the surface hydroxyl
groups of titanate by dehydration with 1,4-butane sultone
(1,4-BS) as sulfonic acid precursors. The reactions were
carried out at the refuxing temperature of toluene (383 K)
for 24 h with the molar ratio of H+-titanate, sulfonic acid
precursor and toluene of 1:0.5:15. The prepared samples
were separated by centrifugation and washed with toluene.
Then, the sample was dried at 383 K in vacuum oven over-
night. The nanocatalyst was treated by 0.5 M H2SO4 before
being used.
(CH3)2N– 6e
C6H4
6
7
8
2-Cl–C6H4 6f
4-Cl–C6H4 6g
20
15
30
91
93
95
226–228 [33]
233–235 [35]
210–212 [33]
4-Me–
C6H4
6i
6j
6k
9
4-NO2–
C6H4
15
30
88
87
227–228 [33]
170–172 [33]
10
3-NO2–
C6H4
11
12
4-Fl–C6H4 6l
30
40
93
85
234–235 [33]
252–254 [33]
4-OMe–
C6H4
6m
Reaction condition aromatic aldehyde (1 mmol), dimedone (2 mmol),
n-TBSA (3 mol%), solvent-free, 120 °C
Typical procedure for the synthesis
of 1‑amidoalkyl‑2‑naphthols
a
Isolated yields
The mixture of the aromatic aldehyde 1 (1 mmol), ben-
zamide 2 (1 mmol), 2-naphthol 3 (1 mmol) and n-TBSA
(0.075 g, 3 mol%) was stirred at 120 °C for the appropriate
time (monitored by TLC). Then, hot ethanol (10 mL) was
added and the reaction mixture was fltered. The solid cata-
lyst was washed with ethanol and acetone (2 × 10 mL) and
dried under vacuum. Pure 1-amidoalkyl-2-naphthols were
afforded by evaporation of the solvent followed by recrys-
tallization from ethanol. All products were characterized by
spectral data and compared with their physical data with
the literature.
Image software. Fourier transform infrared (FT-IR) spec-
tra were obtained on a Shimadzu 8400 s spectrometer using
KBr pressed powder disks. BET surface areas were acquired
on a Beckman Coulter SA3100 surface area analyzer. The
EDX characterization of the catalyst was performed using a
Mira 3-XMU scanning electron microscope equipped with an
energy-dispersive X-ray spectrometer operating.
1H-NMR spectra were recorded in chloroform and dime-
thyl sulfoxide with TMS as an internal standard at ambient
temperature on Bruker Avance 300 MHz instruments. The
purity of products was checked by thin layer chromatog-
raphy (TLC) on glass plates coated with silica gel 60 F254
using n-hexane/ethyl acetate mixture as mobile phase.
Typical procedure for the synthesis
of 1,8‑dioxo‑octahydro‑xanthenes
Catalyst preparation
In a round bottom fask, n-TBSA (0.075 g, 3 mol%) was
added to the mixture of aromatic aldehyde 1 (1 mmol),
dimedone 5 (2 mmol), at 120 °C for the appropriate time
(monitored by TLC). After the completion of the reaction,
hot ethanol was added to the reaction fask. The catalyst
was isolated by centrifugation. Pure 1,8-dioxo-octahydro-
xanthenes were afforded by evaporation of the solvent fol-
lowed by recrystallization from ethanol.
Preparation of nano‑TiO2
In a typical synthetic experiment, titanium (IV) ethox-
ide (TEOT) (0.0047 mmol, 1.088 g) was added to 50 mL
of water, and the resultant solution was transferred into
a 100-mL Tefon-lined stainless steel autoclave. The
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J IRAN CHEM SOC
Scheme 4 Proposed reaction pathway for the preparation of 1,8-dioxo-octahydro-xanthenes and 1-amidoalkyl-2-naphthols catalyzed by
n-TBSA
Table 7 Comparison study of the effciency of the n-TBSA with
some different reported catalysts for the synthesis of 1-amidoalkyl-
2-naphthols
Entry Catalyst
Condition
Yield (%) Time
Refs.
1
2
3
4
5
6
n-TBSA
100 °C/
solvent-free
97
86
95
82
92
92
10 min This work
75 min [36]
15 min [37]
10 min [38]
30 min [28]
Nano-
Ba3(PO4)2
n-FZSAa
100 °C/
solvent-free
100 °C/
solvent-free
MNPs-
SO3Hb
100 °C/
solvent-free
HPA/TPI-
Fe3Oc4
HPMOd
100 °C/
solvent-free
65 °C/ethyl
acetate
3.5 h
[39]
a
b
c
d
Nano-Fe3O4@ZrO2–SO3H
Magnetic nanoparticle-supported sulfuric acid
H6P2W18O62/pyridino-Fe3O4
Molybdophosphoric acid (H3[P(Mo3O10)4])
Conclusion
To sum up, the synthesis of anatase TiO2 nanoparticles was
performed by the hydrothermal method using titanium (IV)
ethoxide solution for the frst time. Supported 1,4-BS on
Fig. 8 Recyclability nano-TiO2–Bu–SO3H after four runs
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Acknowledgements The authors are thankful to the Semnan Univer-
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