A green approach to the synthesis of a nano catalyst and the role of basicity, calcination, catalytic activity and aging in the green synthesis of 2-aryl bezimidazoles, benzothiazoles and benzoxazoles

Article abstract of DOI:10.1039/c6ra25293a

A green synthesis of hydrotalcite (a double layered catalyst) by a grinding method using Al/Mg molar ratios of 1.0-3.0 at room temperature is described. The prepared double layered catalyst (hydrotalcite) has been characterized by TG, FT-IR, SEM, XRD and Hammett titration methods. Different factors such as the effect of molar ratios, catalyst loading, reaction time, aging time, and basicity have been investigated for the facile, efficient and green synthesis of 2-arylbenzimidazoles, benzothiazoles and benzoxazoles under solvent free conditions. The influence of catalyst loading on reactivity was studied and a catalyst loading of 20 mg was found to be optimal, giving the best yield with minimum time as compared to other catalysts. The present methodology reports, herein, a rapid and cost effective synthesis of hydrotalcite and its versatile applications in the synthesis of 2-arylbenzimidazoles, benzothiazoles and benzoxazoles.

Full text of DOI:10.1039/c6ra25293a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
A green approach to the synthesis of a nano
catalyst and the role of basicity, calcination,
catalytic activity and aging in the green synthesis of
2-aryl bezimidazoles, benzothiazoles and
benzoxazoles
Cite this: RSC Adv., 2017, 7, 42000
*
Pramod K. Sahu
A green synthesis of hydrotalcite (a double layered catalyst) by a grinding method using Al/Mg molar ratios
of 1.0–3.0 at room temperature is described. The prepared double layered catalyst (hydrotalcite) has been
characterized by TG, FT-IR, SEM, XRD and Hammett titration methods. Different factors such as the effect of
molar ratios, catalyst loading, reaction time, aging time, and basicity have been investigated for the facile,
efficient and green synthesis of 2-arylbenzimidazoles, benzothiazoles and benzoxazoles under solvent
free conditions. The influence of catalyst loading on reactivity was studied and a catalyst loading of
20 mg was found to be optimal, giving the best yield with minimum time as compared to other catalysts.
The present methodology reports, herein, a rapid and cost effective synthesis of hydrotalcite and its
versatile applications in the synthesis of 2-arylbenzimidazoles, benzothiazoles and benzoxazoles.
Received 15th October 2016
Accepted 25th November 2016
DOI: 10.1039/c6ra25293a
rsc.li/rsc-advances
lamellar solids. The main property of hydrotalcites is their anion
exchange capacity, which makes them unique inorganic mate-
rials to intercalate organic or inorganic anion.8 Hydrotalcites are
Introduction
The benzimidazole, benzoxazole and benzothiazole skeletons
may be found in numerous pharmaceutical agents with
a diverse spectrum of biological activities.1 These are important
structural intermediates in the synthesis of a variety of phar-
maceutical, natural, and agrochemical compounds (Fig. 1).
However various methods have been reported for the synthesis
of benzimidazoles,2 benzoxazoles,3 and benzothiazoles,4 but
a real need exists for new and simple procedures that support
many kinds of structural diversity and various substitution
patterns in the target library. A variety of catalysts was used for
the synthesis of 1,2-disubstituted benzimidazoles.5,6 Similarly
the substituted benzothiazoles and benzoxazoles were also
synthesized by several methods.7 Unfortunately, many of these
reported methods suffer from one or other limitations such as
drastic reaction conditions, long reaction time with poor yield,
side product formation, strong oxidizing agents, use of toxic
reagents, hazardous solvents, use of expensive catalyst, more
catalyst loading, and tedious workup procedure. Most of the
reported catalysts are homogeneous having no recyclability
whereas the reactions carried out with heterogeneous catalysts
required non green solvents and higher temperatures.
increasingly regarded as a good alternative to the traditional
homogenous base catalysts such as NaOH and KOH for several
base-catalyzed reactions that are important for the pharmaceu-
tical and fragrance industries,9 electrode modiers and catalyst
supports.10 A well-documented example is the isomerization of
eugenol and safrole.11 The structure consists of positively charged
brucite (magnesium hydroxide)-like layers with interlayer space
containing charge compensating anions and water molecules.12
As far as green chemistry is concerned, hydrotalcites offer several
advantages over corrosive and dissolved catalysts; easy separation
from the reaction mixture, recycling possibilities, decreased
corrosion of the reactor.13 Hydrotalcites can be implicated in the
preparation of catalysts dedicated to the production of H2,14 wide
range of organic compounds,15 and production of biodiesel by
trans-esterication of triglycerides with methanol.16 In addition
to the above numerous experimental investigations have been
published on the use of hydrotalcites for catalytic applications.17
Considering all above issues, there is a need to develop
environmental benign green route and search new catalyst for
the synthesis of benzimidazoles, benzothiazoles, and benzox-
azoles. Hydrotalcite have higher catalytic activity due to high
surface area than their bulk counterparts and due to this they
have attracted considerable attention in organic synthesis.
Therefore, as a part of our ongoing research aimed at the
development of new catalysts and their application in synthesis
of hetrocycles,18 we report herein, a rapid and cost effective
Layered double hydroxides (LDHs), which are referred to
anionic clays in comparison with cationic clays and also as
hydrotalcite like compounds (HT) are an important class of ionic
School of Studies in Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh,
India. E-mail: sahu.chemistry@gmail.com; researchdata6@gmail.com
42000 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 1 Some benzimidazoles, benzothiazoles, and benzoxazoles.
Fig. 2 Reaction of 1,2-phenylenediamine, 2-aminothiophenol, and 2-aminophenol with aldehyde respectively using hydrotalcite.
method (grinding method) for synthesis of hydrotalcite and within the hydrotalcite layers.19 The weak bands at 2930 cmꢀ1
used in synthesis of benzimidazoles, benzothiazoles, and ben- and 2880 cmꢀ1 are suggested to the strongly hydrogen bonded
zoxazoles under solvent free conditions (Fig. 2).
water molecules to interlayer anions such as carbonate.20 Strong
water deformation modes at 1631 cmꢀ1 found due to hydro-
talcites containing physically adsorbed water.19 Carbonate
which is bonded to hydroxyl surface of hydrotalcite shown
Results and discussion
Characterization of hydrotalcite
a band at 1364 cmꢀ1 20 The IR absorption band at 1024 cmꢀ1 has
.
been assigned to symmetric stretch of free carbonate canions.19
Bending vibration of free carbonate anions give a band at
777 cmꢀ1. The IR absorption band at 443 cmꢀ1 has been
assigned to Al–O bonds.21
Absorption band at higher wave numbers 3695 and 3471 cmꢀ1
in IR spectra (Fig. 3) assigned to the O–H stretching vibrations
of water bonded to M3OH units. The shorter O–H bonds existing
in hydrotalcite causes an increase in electrostatic attraction
Mg : Al atomic ratio was measured using X-ray microanalysis
and found 3.16, which is in good agreement with the metallic
ratio (3.0) taken in solution. The value of x [x ¼ MIII/MII + MIII]
was found to 0.24, which suggest the purity of hydrotalcite.22
Powder X-ray diffraction (P-XRD) pattern for sample Mg–Al–CO3
is shown in Fig. 4. The presence of CO32ꢀ anion in the interlayer
gallery of the hydrotalcite is conrmed by the characteristic
ꢀ
basal spacing d003 ¼ 7.76 A. This indicates a gallery height of
ꢀ
ꢀ
2.96 A (assuming a thickness of 4.8 A for the cationic sheets).
The material is reasonably crystalline and suggests a relatively
well-ordered sheet arrangement.23 The crystallite size of this
sample was found 24.87 nm as calculated using Scherrer
formula.24 More intensive and sharper reections of the (003)
and (006) planes has found at low 2q values (11–23ꢁ). A typical
SEM image of Mg–Al–CO3 hydrotalcite is shown in Fig. 4. This
gure indicates the existence of lamellar particles looks like
rounded hexagonal shape and typical of hydrotalcite like
Fig. 3 FT-IR spectra of the hydrotalcite (Mg–Al–CO3).
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42001

View Article Online
RSC Advances
Paper
Fig. 4 XRD pattern and SEM image of hydrotalcite (Mg–Al, 3 : 1).
material. The material was found mesoporous with the surface up to 330 ꢁC. Finally third mass loss has been assigned to
area 90 m2 gꢀ1
progressive elimination of hydroxyl ions and produce metal
.
ꢁ
A total mass 38.26% at 330–570 C in TG graph (Fig. 5)ꢁ of oxides and spinel structure.
hydrotalcite (Al : Mg : CO3) and other mass loss at 60–230 C,
The Ca : Al metal ratio was found in good agreement with the
ꢁ
ꢁ
230–330 C, and 570–670 C respectively. The TG results point initially taken metallic ratio. The observed value for Ca–Al–CO3
out that the hydrotalcite (Al : Mg : CO3) is thermally stable up to was 3 : 2 : 1. The P-XRD patterns for the LDHs Ca–Al–CO3
230 ꢁC.25 The second mass loss between 223 and 330 ꢁC has exhibits features commonly shown by layered materials. There
been ascribed to the dehydroxylation of the brucite like layers are narrow, symmetric, strong lines at low 2q values and weaker,
2ꢀ
along with anion decomposition leaving a Mg, Al oxo-hydroxide less symmetric lines at high 2q value (Fig. 6).26 Presence of CO3
42002 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
CO3 hydrotalcite (Table 2, entry 6) as compared to Mg–Al–CO3
hydrotalcite. Other metal oxide, hydroxide and chlorides give
moderate yield of nal product (Table 2, entries 7–13).
Recyclability of the catalyst is an important task in industrial
applications. Therefore reusability of hydrotalcite (Mg–Al–CO3)
was investigated for eight runs (Table 3, entries 2–9) in a model
reaction of benzaldehyde and o-phenylenediamine by incorpo-
rating 20 mg of hydrotalcite as catalyst (Fig. 7). Aer completion
of reaction, the contents were ltered to recycle the hydrotalcite
catalyst. Recycled hydrotalcite washed with methanol to remove
organic impurities. MgII hydrotalcite catalyst can be readily
recovered and reused for eight runs. It was found that the
reactivity of the catalyst decreases marginally (approx. 9–10%)
for the eight runs.
To generalize the applicability and scope of this protocol in
the formation of functionalized heterocycles were investigated by
using various substituted aldehydes. Different electron donating
and electron withdrawing aldehydes were used and as expected it
give good yield of target products, it can be seen that electron
donating and electron withdrawing groups does not show any
signicant difference on the reaction yields (Tables 4–6). This
indicated that present catalytic system efficiently makes the
condensation reaction much faster with increased yields.
Fig. 5 DTG curve of hydrotalcite (Mg–Al; 3 : 1).
anion in the interlayer gallery of the hydrotalcite is conrmed by
ꢀ
the characteristic basal spacing d003 ¼ 3.38 A. Sharp intense
peaks at low diffraction angles (peaks close to 2q ¼ 11ꢁ, 24ꢁ, and
35ꢁ; ascribed to diffraction by basal planes (003), (006), and (009),
respectively) and broad, less intense peaks at higher angles
(peaks close to 2q ¼ 38ꢁ, 46ꢁ, and 60ꢁ) ascribed to diffraction by
(105), (108) and (110) planes conrm the presence of hydrotalcite.
The crystallite size of this sample was found 47.025 nm. SEM
(Fig. 6) of the material shows high crystallinity. The particles of
hydrotalcite Ca–Al–CO3 clearly exhibit the hexagonal shape;
however, big needle shape particles are also visible.
Leaching test
Filtrate was analyzed for leached metal content by ICP emission
spectroscopy. No metal was detected. These results conrmed
that the metal leaching did not occur. However, Mg–Al mixed
oxide was found to be thermally and mechanically stable and no
signicant difference was observed in particle size and
morphology of the used catalyst as evidenced by SEM.27 To
ensue the sustainability of structure of recovered hydrotalcite,
XRD has been carried out which showed the similar prole as
fresh catalyst which conrmed that layered structure of hydro-
talcite was maintained aer the reaction.
Chemistry
To optimize the reaction conditions, a model reaction of 4-
hydroxy coumarin, benzaldehyde and 2-aminobenzothiazole
was carried under solvent free conditions. Under room
temperature (Table 1, entry 1), reaction was slow and yield of
target product was too low, even reaction has performed at 90
and 120 ꢁC (Table 1, entries 4 and 5). Best yield was obtained at
Effect of aging time and SEM analysis
To observe the effect of aging time on the morphology of the
material, SEM images of hydrotalcite samples at Mg/Al molar
ratio of 3.0 were recorded. The micrographs at different aging
times are shown in Fig. 8. Micrographs of hydrotalcite show
a well-developed layered and platelet structure of the hydro-
talcite. However, a spongy type structure is exhibited due to
overlapping of such platelets. The SEM images of the hydro-
talcite showed a gradual crystallization during the hydro-
thermal treatment conditions. At the temperature 110 ꢁC
(hydrothermal treatment temperature) and 0 h aging time,
crystallinity of the hydrotalcite was observed to be very poor;
however, as aging time increases from 0 to 10 h, the crystallinity
of the hydrotalcite also increased. These results conrmed an
increase in the crystallinity of the hydrotalcite samples at Mg/Al
under hydrothermal treatment conditions.
ꢁ
ꢁ
70 C with minimum time (3.0 h). So, 70 C temperature was
choose for further study. As shown in Fig. 2, the reactions of 1,2-
phenylenediamine with benzaldehyde (Scheme 1), 2-amino-
thiophenol with benzaldehyde (Scheme 2), and 2-aminophenol
with benzaldehyde (Scheme 3) were selected as model reactions
to investigate catalytic activity of hydrotalcite under solvent free
conditions. To optimize the reaction conditions, variety of
catalysts were screened in a model reaction of o-phenylenedi-
amine and benzaldehyde and results are summarized in Table
2. This clearly indicates that in the absence of catalyst, reaction
did not work benecially (Table 2, entry 1). From Table 2, it has
been found that best yield was obtained with hydrotalcite (HT,
Mg–Al–CO3) with lower time as compared to other catalysts.
Further to identify the catalyst loading, different amount of
loading (Table 2, entries 2–5) was used and 20 mg of catalyst
(HT) was suitable to promote the reaction efficiently (Table 2,
entry 4). An increment in catalyst concentration more than
Basicity of hydrotalcite
20 mg did not show effective improvement in product yield Basicity of the catalyst was determined using Hammett indi-
(Table 2, entry 5). Slightly lower yield was obtained with Ca–Al– cator and benzoic acid titration method.28 All samples prepared
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42003

View Article Online
RSC Advances
Paper
Fig. 6 P-XRD and pattern and SEM image of hydrotalcite (Ca–Al, 3 : 1).
Table 1 Optimization of reaction temperaturea
in our study had the basic strength in the range of 9.3–15.0. The
basicity of the catalysts with different Mg/Al molar ratios was
Entry
Time (h)
Temperature (ꢁC)
Yield% of 3ab
shown in Fig. 9. The main basic sites with H in the range of
ꢀ
7.2–9.8 and the other sites with H in the range of 9.8–15.0 were
ꢀ
1
2
3
4
5
5.0
5.0
3.0
3.0
3.0
RTc
50
70
90
120
20
60
95
95
93
observed, thus suggesting the calcined hydrotalcites contain
different types of surface basic sites. Di Cosimo et al.29 sug-
gested that pure MgO possesses strong basic sites consisting
predominantly of O2ꢀ and calcined hydrotalcites contain
surface basic sites. Our experimental results on the Hammett
titration method conform to this viewpoint. It indicates a wide
basic site distribution as far as the basicity is concerned.
a
Reaction conditions: benzaldehyde (1.0 mmol), o-phenylenediamine
b
c
(1.0 mmol), hydrotalcite (20 mg), at 70 ꢁC. Isolated yield. RT ¼
room temperature.
42004 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Table 2 Optimization of reaction conditionsa
Entry
Catalyst (in grams)
Time (h)
Yield% of 3ab
1
2
3
4
5
6
7
8
No catalyst
6.0
6.0
4.0
3.0
3.0
2.0
5.0
4.0
4.0
4.5
4.0
4.5
4.5
25
75
88
95
95
89
59
72
61
50
51
60
42
Mg–Al–CO3, HT (0.005)
Mg–Al–CO3, HT (0.01)
Mg–Al–CO3, HT (0.02)
Mg–Al–CO3, HT (0.05)
Ca–Al–CO3, HT (0.02)
AlCl3 (0.02)
SiO2 (0.02)
MnO2 (0.02)
Al(OH)3 (0.02)
Ca(OH)2 (0.02)
Fig. 7 Recyclability and reusability of hydrotalcite catalyst.
were obtained with 3.0 HT, therefore basicity of 3.0 HT calcined
at different temperatures was measured with the same method;
the results are illustrated in Fig. 10. From this gure, it can be
seen that the maximum basicity (reaching 3.6 mmol gꢀ1) is
found at a calcinations temperature of 750 K and a low level of
basicity is observed below 573 K and above 750 K. The increased
basicity could be expected to correlate with an increase of the
catalyst activity.
9
10
11
12
13
Al2O3 (0.02)
Mg(OH)2 (0.02)
a
Reaction conditions: benzaldehyde (1 mmol), o-phenylenediamine (1
mmol), hydrotalcite (20 mg), at 70 ꢁC. b Isolated yield.
Conclusion
Table 3 Recyclability of hydrotalcite (Mg–Al–CO3) in model reaction
In conclusion, we have developed green methodology for
synthesis of hydrotalcite by grinding method. Prepared hydro-
talcite could be used efficiently in selective, eco-friendly and
green synthesis for variety of substituted benzimidazoles, ben-
zothiazoles and benzoxazoles from 1,2-phenylenediamine, 2-
aminothiophenol, and 2-aminophenol with substituted
aromatic aldehydes under solvent free conditions. The catalytic
activities of the calcined hydrotalcite show a striking correlation
with their corresponding basic properties. The prepared catalyst
were characterized with Hammett titration method, SEM, TG,
IR and XRD showing the strong basic sites in double layers and
coordinatively unsaturated O2ꢀ ion acting as basic sites in the
calcined hydrotalcite may be responsible for their catalytic
activity. The crystallization of hydrotalcite was signicantly
affected by hydrothermal treatment temperature and time.
This is rst attempt to synthesize substituted benzimid-
azoles, benzothiazoles and benzoxazoles using hydrotalcite as
heterogeneous catalyst which is easily separable and recyclable
up to eight runs. Compared to previously reported methods,
moreover, the mild reaction conditions, easy work-up, clean
reaction proles, lower catalyst loading and cost efficiency
render this approach as an interesting alternative to the existing
methods.
Entry
No. of runs
Yield% of 3aa
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
95
93
91
89
88
88
86
86
85
a
Isolated yield.
As molar ratio of Mg/Al reach up to the maximum value 3.0,
the total basicity of the hydrotalcite (catalyst) was increased
gradually. But basicity was decreased when further increase the
molar ratio of Mg/Al, which resulted in a loss of the catalytic
activity. Qualitatively similar trends were also reported by other
researchers.30 Nakatsuka et al.30a found that the basicity
measured by titration with benzoic acid reached a maximum for
Mg/Al ratio of about 2.6. Also, Fishel and Davis30b measured the
number of basic sites by TPD of CO2 and a maximum of the
basic site density was observed at Mg/Al ratio of 3.0. Best results
Materials and methods
Experimental
The 1H NMR spectra were measured using BRUKER AVANCE II
400 NMR spectrometer with tetramethylsilane as an internal
standard at 20–25 ꢁC; data for 1H NMR are reported as follows:
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42005

View Article Online
RSC Advances
Paper
Table 4 Hydrotalcite catalyzed synthesis of benzimidazole derivativesa
MP (ꢁC)
Found
R
Product
Yield (%)
95
Time (h)
3.0
Reported
Ref.
7f
H
290–291
321–323
290–293
322–323
4-NO2
4-OH
91
90
2.5
2.0
7f
277–279
222–224
265–267
236–237
7h
2-OH
93
2.5
7n
4-Cl
92
96
2.0
2.0
288–291
221–223
288–291
180–182
7g
7i
4-OCH3
4-CH3
95
2.0
260–262
264–265
7f
a
Reaction conditions: aldehydes (1 mmol), o-phenylenediamine (1 mmol), hydrotalcite (20 mg), at 70 ꢁC temp.
chemical shi (ppm), integration, multiplicity (s, singlet; d, Merck pre-coated TLC plates and RANKEM silica gel G were
doublet; t, triplet; q, quartet; m, multiplet, and br, broad), used for preparative thin-layer chromatography. Melting points
coupling constant (Hz). IR spectra were recorded by SHI- were determined in open capillaries and are uncorrected. AR
MADZU; IR spectrometer of sample dispersed in KBr pellet or grade of o-phenylenediamine, 2-aminothiophenol, 2-amino-
Nujol is reported in terms of frequency of absorption (cmꢀ1). E- phenol, aldehydes and other catalysts were purchased from
42006 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Table 5 Hydrotalcite catalyzed synthesis of benzothiazole derivativesa
MP (ꢁC)
Found
R
Product
Yield (%)
96
Time (h)
2.0
Reported
Ref.
7k
H
112–114
104–106
112–114
103–104
4-Cl
93
92
94
91
92
2.5
2.0
2.0
3.0
2.0
7l
4-Br
106–108
226–228
220–222
84–86
102–104
230–231
227
7p
4-NO2
4-OH
4-CH3
7m
7m
7m
85
4-OCH3
93
0.5
120–122
120–121
7k
a
Reaction conditions: aldehyde (1 mmol), 2-aminothiophenol (1 mmol), hydrotalcite (20 mg), at 70 ꢁC temp.
Himedia Laboratory Ltd., Mumbai, India and used without ltered and repeatedly washed with distilled water and dried at
ꢁ
further purication.
100 C.
Typical procedure for synthesis of benzimidazoles, benzo-
thiazoles and benzoxazoles. A mixture of aldehydes (1 mmol)
and o-phenylenediamine, 2-aminothiophenol, or 2-amino-
phenol (1 mmol) was heated at 70 ꢁC under solvent free
conditions using hydrotalcite (20 mg) as a catalyst. Aer
completion of the reaction (by TLC analysis), the reaction
mixture was cooled to room temperature and poured in cold
water. Then the solid mass obtained was dissolved in ethanol
and ltered. The solid hydrotalcite got separated as solid.
Preparation of hydrotalcite (HT)
Typical procedure. Al2O3 (1.02 g) was suspended in distilled
water (2 ml) and magnesium hydroxide (3.5 g) was added to the
mixture and the contents were stirred giving the pH of 8. Then
sodium bicarbonate (2.4 g) was added to bring the pH of the
mixture at 10. The mixture was ground in mortar–pestle for
5 min at room temperature and the resulting white product was
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42007

View Article Online
RSC Advances
Paper
Table 6 Hydrotalcite catalyzed synthesis of benzoxazole derivativesa
MP (ꢁC)
Found
R
Product
Yield (%)
93
Time (h)
3.0
Reported
Ref.
7f
H
98–100
102–103
149–150
4-Cl
95
92
2.0
2.5
142–144
7f
3,4-OCH3
109–112
4-NO2
4-OH
4-CH3
90
94
95
3.0
2.0
2.5
262–264
284–286
122–124
266–267
287–298
115–116
7f
7j
7o
4-OCH3
94
2.0
98–100
100–101
7f
a
Reaction conditions: aldehyde (1 mmol), 2-aminophenol (1 mmol), hydrotalcite (20 mg), at 70 ꢁC temp.
2-(4-Nitrophenyl)-1H-benzimidazole 3b. Mp 321–323 ꢁC; Rf ¼
0.45; ESI-MS (m/z) ¼ 240 (M + 1); 1H-NMR (400 MHz, DMSO-d6),
13.07 (s, 1H, NH), 8.45 (d, 2H, ArH-3, 4, J ¼ 8.96 Hz), 8.37 (d, 2H,
ArH-8, 9, J ¼ 8.88 Hz), 7.64 (s, 2H, ArH-4, 5), 7.27 (d, 2H, ArH-1,
2, J ¼ 7.76 Hz); 13C-NMR (75.45 MHz, DMSO) 111.7, 119.4, 122.3,
123.5, 124.1, 127.3, 135.2, 135.9, 143.8, 147.6, 148.9.
2-(4-Hydroxyphenyl)-1H-benzimidazole 3c. Mp 277–280 ꢁC;
Rf ¼ 0.55; ESI-MS (m/z) ¼ 209 (M ꢀ 1); 1H-NMR (400 MHz,
DMSO-d6), 9.78 (s, 1H, NH), 8.01 (t, 2H, ArH-8, 9, J ¼ 8.44 Hz),
7.54–7.52 (m, 2H, ArH-6, 7), 7.20–7.14 (m, 2H, ArH-3, 4), 6.91 (d,
Product was recrystallized in ethanol. Hydrotalcite was washed
with ethanol to remove organic impurity and dried.
Characterization
2-Phenyl-1H-benzimidazole 3a. Mp 290–291 ꢁC; Rf ¼ 0.5; ESI-
MS (m/z) ¼ 193 (M ꢀ 1); 1H-NMR (400 MHz, DMSO-d6), 12.79 (s,
1H, NH), 8.19 (d, 2H, ArH-8, 9, J ¼ 4.0 Hz), 7.59–7.57 (m, 2H,
ArH-6, 7), 7.53–7.44 (m, 3H, ArH-3, 4, 5), 7.21–7.17 (m, 2H, ArH-
1, 2); 13C-NMR (75.45 MHz, DMSO) 110.0, 119.2, 122.1, 122.6,
126.3, 129.7, 130.1, 135.8, 136.8, 142.6, 151.1.
42008 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
Fig. 8 SEM image of hydrotalcite at a Mg/Al (3 : 1) at different aging time at 110 ꢁC.
Fig. 10 Basicity of 3.0 hydrotalcite at different temperature.
Fig. 9 Basicity of hydrotalcite with different metal ratios.
119.4, 119.7, 126.2, 127.7, 131.7, 132.4, 133.4, 142.2, 160.3,
164.0.
2H, ArH-1, 2, J ¼ 8.40 Hz), 5.37 (s, 1H, OH); 13C-NMR (75.45
MHz, DMSO) 115.1, 122.1, 128.1, 128.6, 128.7, 128.9, 129.0,
130.7, 131.1, 134.5, 150.1.
2-(2-Hydroxyphenyl)-1H-benzimidazole 3d. Mp 222–224 ꢁC;
Rf ¼ 0.55; ESI-MS (m/z) ¼ 209 (M ꢀ 1); 1H-NMR (400 MHz,
DMSO-d6), 12.97 (s, 1H, NH), 8.21 (d, 2H, ArH-8, 9), 7.50–7.43
(m, 4H, ArH-6, 7, 1, 3, 4), 7.23 (d, 2H, ArH-1, 2, J ¼ 8.24 Hz), 5.52
(s, 1H, OH); 13C-NMR (75.45 MHz, DMSO) 116.6, 117.1, 119.0,
2-(4-Chlorophenyl)-1H-benzimidazole 3e. Mp 288–291 ꢁC; Rf
¼ 0.35; ESI-MS (m/z) ¼ 229 (M + 1); 1H-NMR (400 MHz, DMSO-
d6), 12.91 (s, 1H, NH), 7.91 (d, 2H, ArH-8, 9, J ¼ 8.32 Hz), 7.60–
7.46 (m, 2H, ArH-6, 7), 6.98–7.11 (m, 2H, ArH-3, 4), 6.78–6.89
(m, 2H, ArH-1, 2); 13C-NMR (75.45 MHz, DMSO) 115.1, 122.3,
127.9, 128.1, 128.7, 128.8, 128.9, 129.0, 130.7, 131.1, 134.5,
150.1.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42009

View Article Online
RSC Advances
Paper
2-(4-Methoxyphenyl)-1H-benzimidazole 3f. Mp 180–182 ꢁC;
2-(4-Methoxylphenyl)-benzothiazole 5g. Mp 120–122 ꢁC; Rf ¼
Rf ¼ 0.5; ESI-MS (m/z) ¼ 225 (M + 1); 1H NMR (400 MHz, DMSO- 0.65; ESI-MS (m/z) ¼ 242 (M + 1); 1H NMR (400 MHz, DMSO-d6):
d6): 12.93 (s, 1H, NH), 7.92 (d, 2H, ArH-8, 9, J ¼ 8.0 Hz), 7.58– 8.16–8.32 (m, 2H, ArH-8, 9), 7.48–7.98 (m, 1H, ArH-6), 7.56 (d,
7.75 (m, 1H, ArH-6), 7.48–7.55 (m, 1H, ArH-7), 7.22 (d, 2H, ArH- 2H, ArH-1, 2, J ¼ 7.8 Hz), 7.42–7.50 (m, 1H, ArH-7), 7.15 (d, 2H,
3, 4, J ¼ 7.6 Hz), 7.38–7.47 (m, 2H, ArH-1, 2), 3.81 (s, 3H, OCH3); ArH-1, 2, J ¼ 8.0 Hz), 3.85 (s, 3H, CH3); 13C NMR (75.45 MHz,
13C NMR (75.45 MHz, DMSO-d6): 55.6, 114.6, 115.3, 121.4, DMSO-d6): 54.3, 121.8, 123.7, 125.8, 126.7, 127.4, 130.3, 135.4,
123.0, 123.2, 128.5, 130.2, 138.7, 152.8, 160.7.
137.4, 144.4, 154.2, 166.4.
2-(4-Methylphenyl)-1H-benzimidazole 3g. Mp 260–262 ꢁC; Rf
2-Phenyl-benzoxazole 7a. Mp 98–100 ꢁC; Rf ¼ 0.5; ESI-MS (m/
¼ 0.55; ESI-MS (m/z) ¼ 209 (M + 1); 1H-NMR (400 MHz, DMSO- z) ¼ 196 (M + 1); 1H-NMR (400 MHz, CDCl3), 8.24 (d, 2H, ArH-8,
d6), 9.78 (s, 1H, NH), 8.11 (t, 2H, ArH-8, 9, J ¼ 11.04 Hz), 7.57– 9, J ¼ 7.5 Hz), 7.76 (dd, 1H, ArH-5, J ¼ 3.3 Hz, J ¼ 3.0 Hz), 7.52–
7.55 (m, 2H, ArH-6, 7), 7.32 (d, 2H, ArH-3, 4, J ¼ 7.88 Hz), 7.19– 7.60 (m, 4H, ArH-6, 7, 3, 4), 7.34–7.37 (m, 2H, ArH-1, 2); 13C-
7.15 (m, 2H, ArH-1, 2), 2.41 (s, 3H, CH3); 13C-NMR (75.45 MHz, NMR (75.45 MHz, DMSO) 121.6, 122.3, 123.5, 124.6, 125.4,
DMSO) 20.9, 121.9, 126.4, 127.4, 129.3, 129.4, 130.1, 132.2, 129.4, 132.3, 138.5, 150.6, 154.2, 162.2. Anal. calcd for C13H9NO:
139.5, 150.1, 161.11.
C 79.98, H 4.65, N 7.17; found: C 79.87, H 4.51, N 7.06.
2-Phenyl-benzothiazole 5a. Mp 112–114 ꢁC; Rf ¼ 0.65; ESI-MS
2-(4-Chlorophenyl)-benzoxazole 7b. Mp 142–146 ꢁC; Rf ¼
(m/z) ¼ 212 (M + 1); 1H NMR (400 MHz, DMSO-d6): 8.07–8.11 (m, 0.45; ESI-MS (m/z) ¼ 229 (M+); H NMR (400 MHz, DMSO-d6):
3H, ArH-8, 9, 6), 7.91 (d, 1H, ArH-7, J ¼ 7.36 Hz), 7.48–7.52 (m, 8.11–8.19 (m, 2H, ArH-8, 9), 7.65 (d, 2H, ArH-6, 7, J ¼ 7.6 Hz),
4H, ArH-1, 2, 3, 4), 7.39 (t, 1H, ArH-5, J ¼ 8.0 Hz); 13C NMR 7.52–7.60 (m, 1H, ArH-3), 7.35–7.86 (m, 1H, ArH-4), 7.28 (d, 2H,
(75.45 MHz, DMSO-d6): 120.9, 124.3, 125.41, 126.41, 127.92, ArH-1, 2, J ¼ 8.6 Hz); 13C-NMR (75.45 MHz, DMSO) 121.6, 122.3,
1
130.23, 131.67, 133.89, 143.25, 154.78, 168.24.
123.5, 124.6, 125.4, 129.4, 132.3, 138.5, 150.6, 154.2, 162.2.
2-(4-Chlorophenyl)-benzothiazole 5b. Mp 104–106 ꢁC; Rf ¼
2-(3,4-Dimethoxy phenyl)-benzoxazole 7c. Mp 109–112 ꢁC; Rf
0.55; ESI-MS (m/z) ¼ 246 (M + 1); 1H NMR (400 MHz, DMSO-d6): ¼ 0.55; ESI-MS (m/z) ¼ 255 (M+); H-NMR (400 MHz, CDCl3),
8.31–8.48 (m, 2H, ArH-8, 9), 7.40–7. 81 (m, 1H, ArH-6), 7.62 (d, 7.77 (d, 1H, J ¼ 1.96 Hz, ArH-8), 7.66–7.69 (m, 2H, ArH-6, 7),
2H, ArH-3, 4, J ¼ 7.6 Hz), 7.48–7.56 (m, 1H, ArH-7), 7.24 (d, 2H, 7.47–7.50 (m, 1H, ArH, 9), 7.23–7.28 (m, 2H, ArH-3, 4), 6.90 (d,
ArH-1, 2, J ¼ 8.26 Hz); 13C NMR (75.45 MHz, DMSO-d6): 121.8, 1H, ArH-4, J ¼ 8.08 Hz), 3.94 (s, 3H, OCH3), 3.89 (s, 3H, OCH3);
125.2, 126.50, 127.52, 128.82, 131.31, 132.67, 134.69, 145.25, 13C-NMR (75.45 MHz, DMSO) 54.8, 55.1, 121.6, 122.4, 123.0,
1
155.78, 167.94.
124.5, 126.7, 128.9, 131.8, 137.4, 150.6, 152.6, 165.0. Anal. calcd
2-(4-Bromophenyl)-benzothiazole 5c. Mp 106–108 ꢁC; Rf ¼ for C15H13NO3: C 70.59, H 5.13, N 5.49; found: C 70.57, H 4.98, N
0.45; ESI-MS (m/z) ¼ 290 (M+); H NMR (400 MHz, DMSO-d6): 5.46.
1
8.26–8.32 (m, 2H, ArH-8, 9), 7.48–7.88 (m, 1H, ArH-6), 7.64 (d,
2-(4-Nitro phenyl)-benzoxazole 7d. Mp 262–264 ꢁC; Rf ¼ 0.5;
2H, ArH-3, 4, J ¼ 7.56 Hz), 7.50–7.58 (m, 1H, ArH-7), 7.31 (d, 2H, ESI-MS (m/z) ¼ 240 (M+); 1H-NMR (400 MHz, CDCl3), 8.43–8.46
ArH-1, 2, J ¼ 8.26 Hz); 13C NMR (75.45 MHz, DMSO-d6): 121.0, (m, 2H, ArH-8, 9), 8.38–8.41 (m, 2H, ArH-6, 7), 7.82–7.84 (m, 1H,
125.1, 126.2, 127.1, 128.2, 131.3, 132.6, 134.6, 145.5, 155.0, ArH-3), 7.63–7.65 (m, 1H, ArH-4), 7.40–7.47 (m, 2H, ArH-1, 2);
167.4.
13C-NMR (75.45 MHz, DMSO) 120.9, 121.8, 122.8, 124.9, 126.8,
2-(4-Nitrophenyl)-benzothiazole 5d. Mp 226–228 ꢁC; Rf ¼ 0.4; 130.0, 131.7, 137.5, 151.6, 153.2, 163.2. Anal. calcd for
ESI-MS (m/z) ¼ 256 (M + 1); 1H NMR (400 MHz, DMSO-d6): 8.28–
C13H8N2O3: C 65, H 3.33, N 11.66; found: C 64.78, H 3.40, N
8.44 (m, 2H, ArH-8, 9), 7.48–7.98 (m, 1H, ArH-6), 7.62 (d, 2H, 11.58.
ArH-3, 4, J ¼ 7.6 Hz), 7.45–7.53 (m, 1H, ArH-7), 7.25 (d, 2H, ArH-
2-(4-Hydroxyphenyl)-benzoxazole 7e. Mp 284–286 ꢁC; Rf ¼
1, 2, J ¼ 8.26 Hz); 13C NMR (75.45 MHz, DMSO-d6): 120.09, 0.6; ESI-MS (m/z) ¼ 211 (M+); 1H NMR (400 MHz, DMSO-d6): 9.42
124.12, 125.25, 126.05, 128.08, 131.09, 132.60, 134.36, 145.05, (s, 1H, OH), 8.16–8.32 (m, 2H, ArH-8, 9), 7.41–7. 57 (m, 1H, ArH-
155.88, 167.99.
6), 7.56 (d, 2H, ArH-3, 4, J ¼ 7.6 Hz), 7.42–7.50 (m, 1H, ArH-7),
2-(4-Hydroxyphenyl)-benzothiazole 5e. Mp 220–222 C; Rf ¼ 7.27 (d, 2H, ArH-1, 2, J ¼ 8.4 Hz); 13C-NMR (75.45 MHz,
ꢁ
0.6; ESI–MS (m/z) ¼ 228 (M + 1); 1H NMR (400 MHz, DMSO-d6): DMSO) 121.0, 121.8, 122.0, 123.9, 125.8, 130.9, 131.7, 137.2,
10.23 (s, 1H, –OH), 8.08 (d, 1H, ArH-8, J ¼ 7.8 Hz), 7.92–7.99 (m, 152.6, 153.2, 163.8.
ꢁ
3H, ArH-6, 7, 9), 7.50 (t, 1H, ArH-2, J ¼ 7.56 Hz), 7.40 (t, 1H, ArH-
2-(4-Methylphenyl)-benzoxazole 7f. Mp 122–124 C; ESI-MS
1, J ¼ 7.36 Hz), 6.93 (d, 2H, ArH-3, 4, J ¼ 8.4 Hz); 13C NMR (75.45 (m/z) ¼ 209 (M+); H NMR (400 MHz, DMSO-d6): 8.06–8.22 (m,
1
MHz, DMSO-d6) 116.1, 122.1, 122.3, 124.0, 124.9, 126.5, 129.1, 2H, ArH-8, 9), 7.24–7.74 (m, 1H, ArH-6), 7.56 (d, 2H, ArH-3, 4, J ¼
134.1, 153.7, 160.6, 167.5.
7.6 Hz), 7.41–7.49 (m, 1H, ArH-7), 7.26 (d, 2H, ArH-1, 2, J ¼ 8.0
2-(4-Methylphenyl)-benzothiazole 5f. Mp 84–86 ꢁC; Rf ¼ 0.5; Hz), 2.31 (s, 3H, CH3); 13C NMR (75.45 MHz, DMSO-d6): 21.3,
ESI–MS (m/z) ¼ 226 (M + 1); 1H NMR (400 MHz, DMSO-d6): 8.21– 110.7, 119.6, 123.4, 124.8, 126.4, 127.4, 129.6, 138.4, 141.5,
8.37 (m, 2H, ArH-8, 9), 7.42–7.92 (m, 1H, ArH-6), 7.54 (d, 2H, 150.4, 162.2.
ArH-2, 3, J ¼ 7.8 Hz), 7.40–7.48 (m, 1H, ArH-7), 7.18 (d, 2H, ArH-
2-(4-Methoxy phenyl)-benzoxazole 7g. Mp 98–100 ꢁC; Rf ¼
1, 2, J ¼ 8.0 Hz), 2.31 (s, 3H, CH3); 13C NMR (75.45 MHz, DMSO- 0.6; ESI-MS (m/z) ¼ 226 (M + 1); 1H-NMR (400 MHz, CDCl3);
d6): 21.3, 121.7, 123.2, 125.2, 125.5, 126.4, 132.9, 133.5, 135.1, 8.11–8.13 (m, 2H, ArH-8, 9), 7.65–7.67 (m, 1H, ArH-6), 7.46–7.49
138.9, 154.1, 168.7.
(m, 1H, ArH-7), 7.23–7.26 (m, 2H, ArH-3, 4), 6.94–6.96 (m, 2H,
ArH-1, 2), 3.81 (s, 3H, OCH3); 13C-NMR (CDCl3, 75.45 MHz):
42010 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
54.2, 109.3, 113.3, 118.5, 120.5, 124.7, 125.6, 128.3, 141.0, 149.5,
162.1, 163.7. Anal. calcd for C14H11NO2: C 74.65, H 4.92, N 6.22;
found: C 74.42, H 4.79, N 6.11.
B. R. Vishnuvajjala, A. D. Westwell and M. F. G. Stevens, J.
Med. Chem., 2002, 45, 744.
5 (a) V. Kannan and K. Sreekumar, J. Mol. Catal. A: Chem.,
2013, 376, 34; (b) J. Yuan, Z. Zhao, W. Zhu, H. Li, X. Qian
and Y. Xu, Tetrahedron, 2013, 69, 7026; (c) Y. H. Cho,
C. Y. Lee and C. H. Cheon, Tetrahedron, 2013, 69, 6565; (d)
G. Bramhachari, S. Laskar and P. Barik, RSC Adv., 2013, 3,
14245; (e) A. Teimouri, A. N. Chermahini, H. Salavati and
L. Ghorbanian, J. Mol. Catal. A: Chem., 2013, 373, 38; (f)
S. Santra, A. Majee and A. Hajra, Tetrahedron Lett., 2012,
53, 1974; (g) M. M. Guru, M. A. Ali and T. Punniyamurthy,
J. Org. Chem., 2011, 76, 5295; (h) J. P. Wan, S. F. Gan,
J. M. Wu and Y. Pan, Green Chem., 2009, 11, 1633.
Conflicts of interest
Author has no conict of interest.
Acknowledgements
We are grateful thanks to Chandigarh and Punjab University,
Chandigarh for spectral analytical data.
6 (a) N. B. Valentin, J. B. Patrick, A. M. John, J. S. Colin and
L. Stuart, J. Org. Chem., 2013, 78, 1471; (b) H. C. Yeon,
Y. L. Chun, C. H. Deok and H. C. Cheol, Adv. Synth. Catal.,
2012, 354, 29926; (c) S. Hashem, A. Mahdi and
M. D. Mohammad, J. Iran. Chem. Soc., 2012, 9, 189; (d)
R. Yassin, M. Rachid, A. Rachid, E. H. Mohammadine,
R. Sylvain, G. Geraid and L. Said, Tetrahedron Lett., 2011,
52, 3492; (e) W. Ying, S. Kathy, R. S. Daryl and
W. D. Stevan, Tetrahedron Lett., 2006, 47, 4823.
7 (a) R. J. Perry, B. D. Wilson and R. J. Miller, J. Org. Chem.,
1992, 57, 2883; (b) D. Alagille, R. M. Baldwin and
G. D. Tamagnan, Tetrahedron Lett., 2005, 46, 1349; (c)
C. Benedi, F. Bravo, P. Uriz, E. Fernandez, C. Claver and
S. Castillon, Tetrahedron Lett., 2003, 44, 6073; (d)
R. S. Varma, R. K. Saini and O. Prakash, Tetrahedron Lett.,
1997, 38, 2621; (e) R. S. Varma and D. Kumar, J. Heterocycl.
Chem., 1998, 35, 1533; (f) K. Bougrin, A. Loupy and
M. Souuaoui, Tetrahedron, 1998, 54, 8055; (g)
T. Yoshiyuki, Y. Kazuaki and K. H. Hokkaido Daigaku
Koagakubu, Chem. Abstr., 1980, 93, 45–49204537k; (h)
L. S. Gadekar, B. R. Arbad and M. K. Lande, Chin. Chem.
Lett., 2010, 21, 1053; (i) M. Lei, L. Ma and L. Hu, Synth.
Commun., 2012, 42, 2981; (j) R. Fazaeli and H. Aliyan, Appl.
Catal., A, 2009, 353, 74; (k) C. Mukhopadhyay and A. Datta,
Heterocycles, 2007, 71, 1837; (l) D. L. Boger, J. Org. Chem.,
1978, 43, 2296; (m) M. Kodomari, Y. Tamaru and
References
1 (a) C. Chen and Y. J. Chen, Tetrahedron Lett., 2004, 45, 113;
(b) N. Siddiqui, A. Rana, S. A. Khan, M. A. Bhat and
S. E. Haque, Bioorg. Med. Chem. Lett., 2007, 17, 4178; (c)
C. J. Lion, C. S. Matthews, G. Wells, T. D. Bradshaw,
M. F. G. Stevens and A. D. Westwell, Bioorg. Med. Chem.
Lett., 2006, 16, 5005; (d) S. T. Huang, I. J. Hsei and
C. Chen, Bioorg. Med. Chem., 2006, 14, 6106.
2 (a) J. L. Girardet and L. B. J. Townsend, J. Org. Chem., 1999,
64, 4169; (b) C.-M. Yeh, C.-L. Tung and C.-M. Sun, J. Comb.
Chem., 2000, 2, 341; (c) J. J. Chen, Y. Wei, J. C. Drach and
L. B. Townsend, J. Med. Chem., 2000, 43, 2449; (d)
D. Tumelty, K. Cao and C. P. Holmes, Org. Lett., 2001, 3,
83; (e) J. Mann, A. Baron, Y. Opoku-Boahen, E. Johansson,
G. Parkinson, L. R. Kelland and S. Neidle, J. Med. Chem.,
2001, 44, 138; (f) B. Raju, N. Nguyen and G. W. Holland, J.
Comb. Chem., 2002, 4, 320; (g) H. Akamatsu, K. Fukase and
S. Kusumoto, J. Comb. Chem., 2002, 4, 475; (h) C. E. Hoesl,
A. Nefzi and R. A. Houghten, J. Comb. Chem., 2003, 5, 155;
(i) D. Vourloumis, M. Takahashi, K. B. Simonsen,
B. K. Ayida, S. Barluenga, G. C. Winters and T. Hermann,
Tetrahedron Lett., 2003, 44, 2807.
3 (a) D.-F. Shi, T. D. Bradshaw, S. Wrigley, C. J. McCall,
P. Lelieveld, I. Fichtner and M. F. G. Stevens, J. Med.
Chem., 1996, 39, 3375; (b) X. Beebe, D. Wodka and
T. J. Sowin, J. Comb. Chem., 2001, 3, 360; (c) A. Hari,
C. Karan, W. C. Rodrigues and B. L. Miller, J. Org. Chem.,
2001, 66, 991; (d) R. S. Pottorf, N. K. Chadha, M. Katkevics,
V. Ozola, E. Suna, H. Ghane, T. Regberg and M. R. Player,
Tetrahedron Lett., 2003, 44, 175; (e) F. Chen, C. Shen and
D. Yang, Tetrahedron Lett., 2011, 52, 2128.
4 (a) M.-S. Chua, D.-F. Shi, S. Wrigley, T. D. Bradshaw,
I. Hutchinson, P. N. Shaw, D. A. Barrett, L. A. Stanley and
M. F. G. Stevens, J. Med. Chem., 1999, 42, 381; (b)
E. Kashiyama, I. Hutchinson, M.-S. Chua, S. F. Stinson,
L. R. Phillips, G. Kaur, E. A. Sausville, T. D. Bradshaw,
A. D. Westwell and M. F. G. Stevens, J. Med. Chem., 1999,
42, 4172; (c) I. Hutchinson, M.-S. Chua, H. L. Browne,
V. Trapani, T. D. Bradshaw, A. D. Westwell and
M. F. G. Stevens, J. Med. Chem., 2001, 44, 1446; (d)
W. Leng, Y. Zhou, Q. Xu and J. Liu, Macromolecules, 2001,
34, 4774; (e) I. Hutchinson, S. A. Jennings,
´
T. Aoyama, Synth. Commun., 2004, 34, 3029; (n) S. E. Lopez,
´
J. Restrepo, B. Perez, S. Ortiz and J. Salazar, Bull. Korean
Chem. Soc., 2009, 30, 1628; (o) V. R. Devalla and
K. Ethirajulu, J. Chem. Soc., 1995, 1497; (p) A. Teimouri,
A. N. Chermahini, H. Salavati and L. Ghorbanian, J. Mol.
Catal. A: Chem., 2013, 373, 38; (q) D. Yang, X. Zhu, W. Wei,
N. Sun, L. Yuan, M. Jiang, J. You and H. Wang, RSC Adv.,
2014, 4, 17832; (r) D. Yang, X. Zhu, W. Wei, M. Jiang,
N. Zhang, D. Ren, J. You and H. Wang, Synlett, 2014, 25,
0729; (s) D. Yang, K. Yan, W. Wei, L. Tian, Y. Shuai, R. Li,
J. You and H. Wang, Asian J. Org. Chem., 2014, 3, 969; (t)
D. Yang, P. Liu, N. Zhang, W. Wei, M. Yue, J. You and
H. Wang, ChemCatChem, 2014, 6, 3434.
8 N. Ahmet, Z. K. Birgul and M. Z. Luis, Z. Anorg. Allg. Chem.,
2009, 635, 1470.
9 (a) M. S. Newton, J. D. Morrison, R. D. Pennell, N. P. Phodes
and A. J. To, US Pat., Appl., 203152, 2010; (b) V. Rives,
Layered double hydroxides: present and future, Nova Science
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 42000–42012 | 42011

View Article Online
RSC Advances
Paper
Publishers, New York, 2001; (c) S. K. Sharma, P. A. Parikh and
R. V. Jarra, J. Mol. Catal. A: Chem., 2007, 278, 135; (d)
C. O. Veloso, C. N. Perez, B. M. de Souza, E. C. Lima,
A. G. Dias, J. L. F. Monteiro and C. A. Henriques,
Microporous Mesoporous Mater., 2008, 107, 23.
and D. D. Agarwal, RSC Adv., 2014, 4, 40414; (g) P. K. Sahu,
P. K. Sahu, Y. Sharma and D. D. Agarwal, J. Heterocycl.
Chem., 2014, 51, 1193; (h) P. K. Sahu, P. K. Sahu and
D. D. Agarwal, J. Indian Chem. Soc., 2015, 92, 169.
19 S. J. Palmer, T. Nauyen and R. L. Frost, Coord. Chem. Rev.,
2009, 253, 250.
10 (a) W. Kagunya, Z. Hassan and W. Janes, Inorg. Chem., 1994,
35, 5970; (b) M. Ulibarri, F. M. Labajos, V. Rives, 20 S. J. Palmer and R. L. Frost, Ind. Eng. Chem. Res., 2011, 50,
R. Trujillano, W. Kagunya and W. Janes, Inorg. Chem.,
1994, 33, 2592.
5346.
21 M. Valcheva-Traykova, N. Davidova and A. Weiss, J. Mater.
11 C. M. Jinesh, C. A. Antonyraj and S. Kannan, Catal. Today,
2009, 141, 176.
Sci., 1993, 28, 2157.
22 F. Cavani, F. Triro and A. Vaccari, Catal. Today, 1991, 11,
12 (a) M. A. Ulibarri, I. Pavlovic, C. Barriga, M. C. Hermosin and
173.
J. Cornejo, Appl. Clay Sci., 2001, 18, 17; (b) G. Centi and 23 F. M. Labojos, V. Rives and M. A. Ulibarri, J. Mater. Sci., 1992,
S. Perathoner, Microporous Mesoporous Mater., 2008, 107, 3. 27, 1546.
13 K. Motocura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani, 24 A. S. Bookin and A. Dritis, Clays Clay Miner., 1993, 41, 551.
K. Htsukawa and K. Kanedar, Chem.–Eur. J., 2006, 12, 8228. 25 W. T. Reichle, CHEMTECH, 1986, 16, 58.
14 M. Turco, G. Bagnasco, U. Costantino, F. Marmottini, 26 K. R. Kottapalli, G. Monique, S. V. Jaime and F. Francois, J.
T. Montanari, G. Ramis and G. Busca, J. Catal., 2004, 228, 56.
Catal., 1998, 173, 115.
15 B. F. Sels, D. E. De Vos and P. A. Jacobs, Catal. Rev.: Sci. Eng., 27 (a) Y. Liu, E. Lotero, J. J. Goodwin and X. Mo, Appl. Catal., A,
2001, 43, 443.
2007, 331, 138; (b) P. Chauyplod and W. Trakarnpruk, Ind.
Eng. Chem. Res., 2009, 48, 4177.
28 (a) D. G. Cantrell, L. J. Gillie, A. F. Lee and K. Wilson, Appl.
Catal., A, 2005, 287, 183; (b) J. M. Fraile, N. Garcia,
J. A. Mayoral, E. Pires and L. Rodan, Appl. Catal., A, 2009,
364, 87; (c) H. J. Hattori, J. Jpn. Pet. Inst., 2004, 47, 67.
16 Y. Xi and R. J. Davis, J. Catal., 2008, 254, 190.
17 S. K. Yun and T. Pinnavaia, J. Mater. Chem., 1995, 7, 348.
18 (a) P. K. Sahu, P. K. Sahu, S. K. Gupta, D. Thavaselvam and
D. D. Agarwal, Eur. J. Med. Chem., 2012, 54, 366; (b)
P. K. Sahu, P. K. Sahu, D. Thavaselvam, A. M. Alafeefy and
D. D. Agarwal, Med. Chem. Res., 2015, 24, 725; (c) 29 J. J. Di Cosimo, V. K. Di'ez, M. Xu, E. Iglesia and
P. K. Sahu, P. K. Sahu and D. D. Agarwal, RSC Adv., 2013, C. R. Apesteguia, J. Catal., 1998, 178, 499.
3, 9854; (d) P. K. Sahu, P. K. Sahu, S. K. Gupta and 30 (a) T. Nakatsuka, H. Kawasaki, S. Yamashita and S. Kohjiya,
D. D. Agarwal, Ind. Eng. Chem. Res., 2014, 53, 2085; (e)
P. K. Sahu, P. K. Sahu, S. K. Gupta and D. D. Agarwal,
Catal. Sci. Technol., 2013, 3, 1520; (f) P. K. Sahu, P. K. Sahu
Bull. Chem. Soc. Jpn., 1979, 52, 2449; (b) C. T. Fishel and
R. Davis, Langmuir, 1994, 10, 159.
42012 | RSC Adv., 2017, 7, 42000–42012
This journal is © The Royal Society of Chemistry 2017