Role of basicity and the catalytic activity of KOH loaded MgO and hydrotalcite as catalysts for the efficient synthesis of 1-[(2-benzothiazolylamino)arylmethyl]-2-naphthalenols

Article abstract of DOI:10.1039/c5ra11857c

Novel KOH-loaded MgO and hydrotalcite as basic catalysts have been synthesized and were characterized by XRD, SEM and their basicity. The effect of the KOH wt%, reaction time, basicity and catalyst loading have been investigated in three-component reactio

Full text of DOI:10.1039/c5ra11857c

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: P. Sahu, P. Sahu
and D. Dayal, RSC Adv., 2015, DOI: 10.1039/C5RA11857C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
Graphical Abstract
Role of basicity and catalytic activity of KOH loaded MgO and hydrotalcite as
catalysts for efficient synthesis of 1-[(2-benzothiazolylamino)arylmethyl]-2-
naphthalenols
Pramod K. Sahu,*a, b Praveen K. Sahu,*b Dau D. Agarwala, b
aSchool of Studies in Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh, India
bDepartment of Industrial Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh, India
*To whom correspondence should be addressed: Email: sahu.chemistry@gmail.com, researchdata6@gmail.com (Pramod
K. Sahu); praveensahu1234@gmail.com (Praveen K. Sahu)
1

RSC Advances
Page 2 of 24
View Article Online
DOI: 10.1039/C5RA11857C
Role of basicity and catalytic activity of KOH loaded MgO and hydrotalcite as
catalysts for efficient synthesis of 1-[(2-benzothiazolylamino)arylmethyl]-2-
naphthalenols
Pramod K. Sahu,*a, b Praveen K. Sahu,a, b Dau D. Agarwala, b
aSchool of Studies in Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh, India
bDepartment of Industrial Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh, India
*To whom correspondence should be addressed; Email: sahu.chemistry@gmail.com, researchdata6@gmail.com (Pramod.
K. Sahu)
Abstract
Novel KOH-loaded MgO and hydrotalcite as basic catalysts have been synthesized and were
characterized by XRD, SEM and basicity. Effects of KOH wt %, reaction time, basicity and
catalyst loading have been investigated in three component reaction of aldehydes, 2-amino
benzothiazole and 2-naphthol. Present studies revealed that loading of KOH and reaction time
o
greatly appreciated. Best conversion and yield at 70 C were obtained as 93% and 88%,
respectively. Hydrotalcite could be reused four times without loss of catalytic efficiency. Present
catalytic systems have required short reaction time, non toxic, easy to workup, good catalytic
activity and gives high efficiency.
Keywords: KOH-loaded MgO, Catalytic Activity, Hydrotalcite, Reusability, Multi-component
Synthesis.
1. Introduction
The scaffold decoration of bioactive molecules represents one of the most exciting research
areas in organic chemistry and has a rich history within the realm of fragment-based drug design.
o-Quinone methides (o-QMs) are highly reactive, transient species that have been applied as
2

Page 3 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
intermediates in the synthesis of several natural compounds including flavonoids, isoflavans,
chromenes and benzopyranes.1-4 Multi-component reactions (MCRs) are powerful tool and have
attracted much attention of synthetic organic chemists because of building of complex molecules
with diverse range of complexity which can easily be achieved from readily available starting
materials.5 Such processes enable the rapid elaboration of complex structures in a highly
efficient, higher yield than almost any sequential synthesis of the same target, a single
purification step, time and energy saving, low expenditures, easy adaptation to combinatorial
synthesis and modular manner.6 However, researchers have synthesized the 2-
aminobenzothiazolomethyl naphthol derivatives with many drawbacks such as long reaction
time, higher catalyst loading, low yield, higher reaction temperature and no reusability of
catalyst.7, 8
In recent year, due to increasing concern about environmental impact, tremendous effort
has been made towards the development of new processes that minimize pollution in chemical
synthesis. For this reason and others (catalyst removal, recovery, and recycling), heterogeneous
catalysis is clearly on the rise in industry.9 Heterogeneous catalysts have separated easily from
the reaction mixture by filtration and then reused. In recent year, hydrotalcite and metal loaded
11
catalysts have been investigated more for biodiesel production.10,
Hydrotalcites can be
involved in the preparation of catalysts dedicated to the production of H2,12 wide range of
organic compounds.13 hydrotalcite has also been used as catalyst other than from reactions14 and
showed good catalytic efficiency, recyclability, reaction time, yield etc.
However KOH loaded MgO and hydrotalcite have not been used as catalyst in synthesis
of 2-aminobenzothiazolomethyl naphthols by multi-component reaction. So in present study, we
have used KOH loaded MgO as catalyst in multi-component reaction of 2-amino benzothiazole,
3

RSC Advances
Page 4 of 24
View Article Online
DOI: 10.1039/C5RA11857C
aldehydes and 2-naphthol and found good yield. But due to low catalytic efficiency of recycled
catalyst, this catalyst failed to produce better yield. Further, for removing this problem,
hydrotalcite was used as catalyst and found good catalytic activity and recyclability. Synthesis
was tried with hydrotalcite which is rapid, low reactor corrosive, easy to separate, inexpensive
and highly efficient.15 Herein, first time, we report the synthesis of 2-aminobenzothiazolomethyl
naphthols by three-component reaction of aldehydes, 2-amino benzothiazole and 2-naphthol
using KOH-loaded MgO and hydrotalcite as novel catalysts under solvent free conditions
(Scheme 1).
Scheme 1. Synthesis using hydrotalcite or KOH/MgO at 70 oC.
CHO
R
S
OH
R
N
+
NH
Hydrotalcite or KOH/MgO
At 70 oC
N
H
NH2
OH
S
1
2. Experimental section
General
1
The H NMR spectra were measured by BRUKER AVANCE II 400 NMR spectrometer
o
1
with tretramethylsilane as an internal standard at 20-25 C; data for H NMR are reported as
follow: chemical shift (ppm), integration, multiplicity (s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet and br, broad), coupling constant (Hz). IR spectra were recorded by SHIMADZU,
IR spectrometer of sample dispersed in KBr pellet and are reported in terms of frequency of
absorption (cm-1). E-Merck pre-coated TLC plates and RANKEM silica gel G were used for
preparative thin-layer chromatography. Melting points were determined on electrical melting
point apparatus in open capillary and were uncorrected. 2-Amino benzothiazole was purchased
4

Page 5 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
from Sigma Aldrich and other chemicals were purchased from Himedia, Mumbai India and used
without any further purification.
HPLC separations were carried out using an HPLC system (Water alliance e2695,
separation module, USA) composed a detector (2489 UV/Vis detector), vacuum degasser, a
quaternary pump, injector with 50 µL sample loop, variable wavelength detector (VWD). The
packing materials were dispersed in ethanol and packed in the column under 35 MPa with
ethanol. The HPLC phase consisted of acetonitrile/10mM ammonium acetate buffer pH 4.0
(30/70, v/v). The flow rate was set at 0.25 mL/min and analysis was performed in isocratic mode.
The surface area of hydrotalcite samples was determined from the N2 adsorption data
measured at 77 K using Micromeritics, ASAP 2010. The samples were activated at 80 °C for 4 h
under vacuum prior to N2 adsorption measurements. The specific surface area of the samples was
calculated from the N2 adsorption isotherms according to the BET method.
KOH-loaded catalyst preparation
The catalyst was prepared by magnesia with an aqueous solution of KOH. The catalysts
were dried at 393 K for 16 h and calcined at 773 K for 5 h. X-ray powder diffraction patterns
were obtained from calcined catalyst samples with a PC X-ray diffractometer using Cu Kα
radiation at 40 kV and 40 mA and a scan speed of 2 °C/min. The surface morphology of the
prepared catalysts was investigated by a scanning electron microscope (SEM).
Preparation of hydrotalcite
The catalyst hydrotalcite was synthesized using literature procedure.16
Typical procedure. One-pot hydrothermal reactions at higher temperature and autogenous
pressure in aqueous media were carried out to obtain small and high surface area particles. In a
typical reaction Mg2+ and Al3+ hydroxide (metallic ratio of 3:1) were taken and corresponding
5

RSC Advances
Page 6 of 24
View Article Online
DOI: 10.1039/C5RA11857C
ratio of sodium bicarbonate was added to maintaining the pH 8.5. After aging the slurry, the
precipitate was filtered, washed, and dried.
One-pot three component reaction
Typical procedure with KOH-loaded MgO. A mixture of aldehydes (2 mmol), 2-naphthol (2
o
mmol) and 2-amino benzothiazole (2 mmol) were heated at 70 C under solvent free conditions
using KOH-loaded MgO as a catalyst. The time taken by different aldehydes in reaction has
mentioned in table 2. After completion of the reaction (TLC analysis), the reaction mixture was
cooled to room temperature and filtered. Solid cake was washed with ethyl acetate. Filtrate
having product was washed with water and extracted with ethanol and concentrated the ethanol
to crystallize the product. Recycled KOH/MgO catalyst was washed with ethyl acetate to remove
organic impurity.
Typical procedure using Hydrotalcite.
A mixture of aldehydes (2 mmol), 2-naphthol (2 mmol) and 2-amino benzothiazole (2 mmol)
o
were heated at 70 C under solvent free conditions using hydrotalcite (Mg-Al-CO3, 80 mg) as a
catalyst. The time taken by different aldehydes in reaction has mentioned in table 2. After
completion of the reaction (monitored by TLC), the reaction mixture was cooled to room
temperature and poured in cold water. The solid mass was filtered and dissolved in ethanol then
filtered again so that product was dissolved in ethanol and hydrotalcite has been separated and
concentrated the ethanol to crystallize the product. Recycled hydrotalcite was washed with
ethanol to remove organic impurity.
3. Results and discussion
The powder X-ray diffraction spectra of KOH/MgO catalyst has been prepared are shown in
the figure 1 (A). From figure 1 (A) it can be seen that there are typical characteristic peaks both
6

Page 7 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
at 37.0°, 43.0°, and 62.3°, which can be signed to the characteristic peaks of MgO crystalline.17
The XRD analysis of the 1wt % KOH/MgO sample shows the crystalline phase corresponding to
magnesia. This interaction is the main difference between the homogeneous KOH catalyst and
KOH/MgO catalyst. Small crystallite of KOH was also observed at 4 wt % KOH/MgO catalyst
(figure 2).
Fig 1. Effect of different loading amounts on catalyst
1%, (b) 2%, (c) 3%, (d) 4%
Crystallite KOH
d
c
b
a
Fig 2. SEM images of catalysts
1 wt % KOH/MgO
2 wt % KOH/MgO
7
4 wt % KOH/MgO
3 wt % KOH/MgO

RSC Advances
Page 8 of 24
View Article Online
DOI: 10.1039/C5RA11857C
Model reaction starting from benzaldehyde, 2-naphthol and 2-amino benzothiazole have
proved to be a facile method for preparation of 2-aminobenzothiazolo-phenylmethyl-2-naphthol
derivatives. To optimize the reaction conditions, first of all we have investigated different
catalysts for synthesis of 2-aminobenzothiazolo-phenylmethyl-2-naphthol derivatives. Table 1
suggests that without catalyst longer reaction time was necessary (24 hours) with poor yield. The
best result was obtained when KOH-loaded MgO used with maximum yield (Table 1, entry 2).
Other metal catalysts give moderately to significant yield.
Table 1. Screening of catalystsa
Entry Catalyst (in mole)
Time (hrs) Yield% of 1a
1
2
Without catalyst
KOH/MgO
24
15
88
3.0
(40 mg KOH per gram support)
AlCl3 (0.001)
3
4.5
5.0
4.5
6.0
5.0
5.5
4.0
4.5
71
49
57
61
52
69
42
43
4
MgCl2 (0.001)
5
Mg(OH)2 (0.001)
Al(OH)3 (0.001)
Ca(OH)2 (0.001)
MgO (0.001)
6
07
8
9
Al2O3 (0.001)
10
CaO (0.001)
aReaction conditions: benzaldehyde (2 mmol), 2-naphthol (2 mmol) and 2-amino benzothiazole (2 mmol) in presence of various
catalysts under solvent free conditions.
Table 2. Synthesis of 2-aminobenzothiazolomethyl naphthol derivativesa
Entry
Aldehydes
Product
KOH/MgO
Hydrotalcite
M.P. (oC)
Time (h) Yield (%) Time (h) Yield (%) Found
Reported(ref.)
1
2.5
3.0
88
90
2.8
3.0
92
90
203-204 202-2048(c)
194-175 173-1758(f)
1a
CHO
OH
2
1b
OCH3
CHO
8

Page 9 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
3
3.5
85
2.6
89
192-194 192-1948(g)
1c
CH3
CH3
N
CHO
4
3.0
91
2.6
91
190-192 189-1918(a)
1d
NO2
CHO
5
6
2.5
2.5
88
90
2.6
2.8
87
92
162-163 160-1618(f)
172-173 172-1738(c)
1e
1f
OH
CHO
OCH3
CHO
CH3
7
2.5
89
2.6
92
180-181 183-1848(c)
1g
CHO
8
3.0
92
2.8
93
208-209 208-2098(f)
1h
Cl
CHO
9
3.0
2.5
73
84
3.0
2.4
78
88
188-190 188-1908(g)
1i
1j
OH
CHO
Cl
10
>250 242(Dec.)8(f)
Cl
CHO
9

RSC Advances
Page 10 of 24
View Article Online
DOI: 10.1039/C5RA11857C
2.5
81
2.4
81
197-198 197-1988(c)
1k
NO2
11
CHO
aReaction conditions: 2-amino benzothiazole (2 mmol), 2-naphthol (2 mmol) and benzaldehyde (2 mmol),
hydrotalcite or KOH/MgO under solvent free conditions.
To optimize the effect of reaction time on the yield of target product, a model reaction was
carried out at different time under solvent free conditions using KOH-loaded MgO at 70 oC. The
reaction time 3.0 h was found to be optimum time and highest conversion (from 35-93%) and
yield (from 31-88%) was obtained (figure 3). Conversion of starting materials to product was
measured by HPLC analysis. When the loading of catalyst was not enough, the maximum yield
could not be reached. To avoid this kind of problem, an optimum amount of catalyst loading had
to be investigated. For this study, model reaction has been carried out in the presence of different
amount of prepared catalyst (10 mg, 20, mg, 50 mg, 80 mg, 100 mg) respectively (table 3).
Highest yield was obtained with 50 mg of KOH-loaded MgO catalyst. The catalyst loading 50
mg was found to be the optimal quantity and used for further studies.
Fig 3. Effect of reaction time on yield of target product
10

Page 11 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
Table 3. Effect of catalyst loading on yielda
Entry
Catalyst loading (mg)
10
Yield
60
76
1
2
3
4
5
20
50
80
100
88
88
88
aReaction conditions: benzaldehyde (2 mmol), 2-naphthol (2 mmol) and 2-amino benzothiazole (2 mmol) in presence of
KOH/MgO catalysts under solvent free conditions.
The reaction temperature can influence the reaction rate and yield because the intrinsic rate
constants are strong functions of temperature.18 In this study, the effects of the reaction
temperature were investigated at four different reaction temperatures, such as room temperature,
o
50, 70 and 100 C temperatures. The catalyst used in this experiment was 4 wt % KOH/MgO.
o
The results are shown in figure 4. Best conversion and yield at 70 C were obtained as 93% and
88%, respectively.
Fig 4. Effect of temperature on conversion and yield of product
To gain the effect of KOH loadings of catalysts on their catalytic activities, different
loadings of KOH ranging from 1 to 5 wt % were studied with model reaction. The results are
demonstrated in figure 5. As loading of KOH was raised from 1 to 4 wt %, the conversion of
starting material was increased. However, by increasing the amount of KOH from 4 to 5 wt %, a
significant change in conversion and yield were not observed. Highest yield was obtained with
loading of KOH of 4 wt % on MgO. It is obvious that change in their catalytic activity was well
11

RSC Advances
Page 12 of 24
View Article Online
DOI: 10.1039/C5RA11857C
correlated to change their basicity as shown in table 4. These results are also in agreement with
the results obtained by D’Cruz et al.19
Fig 5. Effect of KOH loading on conversion and yield
Basicity of the catalyst was determined using Hammett indicator and benzoic acid
titration method.20-22 Model reaction was carried out in the presence of KOH-loaded MgO
catalyst. Excellent catalytic activity has showed using different substituted aromatic aldehydes.
We have studied the different amount of KOH loading on metal and correlate with the basicity of
catalyst. As evident from Table 4, KOH loading on the surface of MgO could induce the basicity
of catalyst. As loadings of KOH were raised from 1 to 4 wt %, the yield of target product was
increased and yield was 88%. Moreover as seen in Table 4, basicity play an important role in
catalytic activity of the catalyst prepared. BET surface area has been demonstrated in table 4
which shows that as KOH loading increases, surface area was decrease.
Table 4. Effect of basicity on yield
Entry Samples
Time ( h) Yield (%) Basicity (mmol/g) BET area (m2/g)
1
2
3
4
5
1% wt KOH/MgO 6.0
57
74
81
88
88
1.065
1.096
1.117
1.187
1.010
22.52
20.01
18.21
17.13
15.50
2% wt KOH/MgO 4.5
3% wt KOH/MgO 3.5
4% wt KOH/MgO 3.0
5% wt KOH/MgO 3.0
12

Page 13 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
The dependence of the activity of KOH/MgO catalysts on the loading amount of KOH has
been investigated with effect of basicity. The most basic properties of catalysts arise when an
alkali base is loaded onto a support. The presence of alkali cations enhances the electron density
of the framework oxygen, thus acting as basic sites. The data clearly demonstrate the
involvement of potassium in the activity and basicity. The incorporation of potassium increased
the basic strength of the pure MgO, resulting in an increase the yield. The results in Table 4 show
that the activity increased by increasing the KOH content (4%) due to presence of highest
number of basic sites or suggesting that basic sites have a very specific environment. But basic
sites may be cover by exceeded KOH when the amount of loaded KOH was from 4-5 wt %,
resultant basic strength and the basic site of the catalyst were not raised, and lower the surface
areas of active components and lower the catalytic activity. At a low loading of KOH, the active
sites are more dispersed on the pure MgO surface and cannot disperse properly with too much
KOH.
The recyclability of the catalyst was also investigated for 4 wt % KOH/MgO catalyst, which
gives the highest yield of 88%. After the reaction, catalyst was separated by filtration and then
reused in the model reaction. It was shown that the reaction catalyzed by a used catalyst provided
70% yield, which was lower than the yield over the fresh catalyst. This indicated that the spent
catalyst was slightly deactivated. Thus, the decrease in catalytic activity probably resulted from
the leaching of the some potassium content. This low activity may be explained by dissolution of
K species in the heterogeneous KOH/MgO catalyst.23
Thus, we have further synthesized and used hydrotalcite (Mg:Al; 3:1) as new
heterogeneous catalyst to removing the drawback of recyclability or leaching of catalyst which
overcome with KOH/MgO catalyst. Mg:Al atomic ratio was measured using X-ray
13

RSC Advances
Page 14 of 24
View Article Online
DOI: 10.1039/C5RA11857C
microanalysis and found 3.16, which is in good agreement with the metallic ratio (3.0) taken in
solution. The value of x [x = MIII/MII + MIII] was found to 0.24, which suggest the purity of
hydrotalcite.24 Powder X-ray diffraction (P-XRD) pattern for sample Mg-Al-CO3 is shown in
2-
figure 6. The presence of CO3 anion in the interlayer gallery of the hydrotalcite is confirmed
by the characteristic basal spacing d003 = 7.76 Ao. This indicates a gallery height of 2.96 Ao
(assuming a thickness of 4.8 Ao for the cationic sheets). The material is reasonably crystalline
and suggests a relatively well-ordered sheet arrangement 25
. Diffraction peaks of the (003) basal
plane that gives the distance between the layers became sharper which indicates higher
crystallinity and order. This fact is supported by the increase in the ratio of the intensities of the
diffraction from the (006) basal plane to that of the (003) one. The crystallite size of this sample
was found 24.87 nm as calculated using Scherrer formula 26
More intensive and sharper
.
reflections of the (003) and (006) planes has found at low 2θ values (11-23º).
Fig 6. P-XRD pattern and SEM image of hydrotalcite
003
006
012
015
018
XRD pattern Mg-Al- 3:1
14

Page 15 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
SEM image Mg-Al- 3:1
A typical SEM image of Mg-Al-CO hydrotalcite is shown below in figure 6. This
3
figure indicates the existence of lamellar particles looks like rounded hexagonal shape and
typical of hydrotalcite like material. The material was found mesoporous with the
surface area 90 m2/g
.
Basicity of hydrotalcite is a key for the preparation of material with high performance.27
It can be achieved by changing the nature of M2+/M3+ metals.28 As far as Mg-Al mixed oxides of
hydrotalcite is concerned, a correlation can be established between the composition and the
basicity; when the amount of Al increases, the total number of basic sites decreases.15, 29 The
decrease in basic site density observed in Mg-Al mixed oxide derived from hydrotalcites when
increasing the Al content is reported to be the reason for decreasing activity in the Knoevenagel
condensation reaction between glyceraldehydes acetonide and ethyl acetoacetate.30 The
performance of Mg-Al mixed oxide in the methanolysis of soyabean oil was shown to be
dependent on the Mg/Al ratio.11(g) Numerous authors have tried to identify the best composition
of Mg-Al mixed oxide catalysts in the case of various reactions. A set of Mg-Al hydrotalcite-like
precursors with different Mg/Al atomic ratios were studied by Diez et al.31 The optimum Mg/Al
molar ratio is dependent on the target reaction and more precisely, on the basic strength needed
15

RSC Advances
Page 16 of 24
View Article Online
DOI: 10.1039/C5RA11857C
to activate the reactant. By encouraging from previous results,32 it is clear that among the all
metallic ratio of hydrotalcites, 3:1 ratio of hydrotalcite (Mg-Al-CO3) gives better results.
Resultant, in this communication we have synthesized hydrotalcite catalyst (Mg-Al-CO3, 3:1)
and used in present reaction.
In order to evaluate the appropriate catalyst loading, reaction of benzaldehyde (2 mmol), 2-
amino benzothiazole (2 mmol) and 2-naphthol (2 mmol) was carried out using 20 mg, 50 mg, 80
o
mg, 100 mg and 120 mg of hydrotalcite as catalyst at 70 C under solvent free conditions. The
catalyst loading 80 mg was found to be the optimal quantity (Table 5). Catalyst was reused and
the results show that the hydrotalcite (Mg-Al-CO3) can be reused as such without significant loss
in yield (Table 6). A variety of electron donating and electron withdrawing groups on aromatic
aldehydes have been studied (Table 2). It was found that meta substituted aldehyde give the
lower yield as compared to ortho and para substituents (Table 2, entry 9, 11).
Table 5. Effect of Catalyst [Mg-Al-HT (Mg/Al=3:1)] Loadinga
Entry
Catalyst loading (mg)
20
Time (min)
180
170
160
160
Yield (%)
1
2
3
4
5
40
76
92
92
92
50
80
100
120
160
aReaction conditions: Benzaldehyde (0.0025), 2-amino benzothiazole (0.0025 mol) and 2-naphthol (0.0025 mol), hydrotalcite (80
mg), temp. at 70 oC.
Table 6. Recyclability of hydrotalcite [Mg-Al-HT (Mg/Al=3:1)]a
Product Fresh HT
92
Reuse (I)
92
Reuse (II)
91
Reuse (III)
90
Reuse (IV)
90
1a
aReaction conditions: benzaldehyde (0.0025 mol), 2-amino benzothiazole (0.0025 mol) and 2-naphthol (0.0025 mol), hydrotalcite
(80 mg), temp. at 70 oC.
A model reaction has been carried out using of benzaldehyde (0.0025 mol), 2-amino
benzothiazole (0.0025 mol) and 2-naphthol (0.0025 mol) for recyclability and reusability of
16

Page 17 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
hydrotalcite as catalyst by incorporating 80 mg of catalyst. After completion of reaction, the
contents were filtered to recycle the hydrotalcite catalyst through whatman filter 42. Recycled
hydrotalcite washed with 5 ml ethanol to remove organic impurities. Hydrotalcite catalyst can be
readily recovered and reused for at least four runs without any significant loss of activity.
Fig 7. XRD pattern of recovered hydrotalcite
003
006
012
015
018
XRD data of recovered hydrotalcite (figure 7) which showed the similar profile as fresh
catalyst which confirmed that layered structure of hydrotalcite was maintained after the reaction.
4. Conclusion
In conclusion, 4 wt. % KOH/MgO and hydrotalcite as catalysts, which have the highest yield
of target product and gave the best catalytic activity for multi-component reaction of substituted
o
aldehydes, 2-amino benzothiazole and 2-naphthol at 70 C under solvent free conditions.
Loading of KOH with 4 wt % gave the highest basicity and best catalytic activity. Highest
conversion and yield of product were obtained at 3.0 h of reaction time. After recycling,
KOH/MgO could not better perform than fresh catalyst due to leaching of basic sites but this
drawback has been removed by using hydrotalcite as catalyst. Morphology and characterization
of catalysts are characterized by XRD and SEM. Hydrotalcite and KOH-loaded MgO have
showed better results as compared to simple metal catalysts used. Present methodology involves
17

RSC Advances
Page 18 of 24
View Article Online
DOI: 10.1039/C5RA11857C
the operational simplicity, short reaction times, simple catalyst system, higher yield and ease of
work-up procedure.
Characterization data
1-[(2-Benzothiazolylamino)phenylmethyl]-2-naphthalenol (1a)
White powder, mp 203-204oC; IR (KBr) (υmax, cm-1): 3381 (OHstr), 1599 (C=Cstr), 1542 (N-Hben),
1
1515 (C-Hben), 1449 (C-Hben); H NMR (400 MHz, DMSO): δH 6.69-7.93 (16H, m, 15H-arom
and 1H-CH), 8.67 (1H, s, NH), 10.11 (1H, s, OH); 13C NMR (100 MHz, DMSO): 53.36, 118.02,
118.57, 118.81, 120.49, 120.84, 122.27, 123.58, 125.23, 126.04, 127.83, 128.34, 128.56, 129.28,
130.59, 132.12, 142.25, 151.96, 153.19, 166.33; ESI-MS: m/z Calculated for C24H18N2OS 382;
Found [M+H]+ 283.3.
1-[(2-Benzothiazolylamino)(4-nitrophenyl)methyl]-2-naphthalenol (1d)
White powder, mp 120-122oC; IR (KBr) (υmax, cm-1): 3348 (OHstr), 2933 (C-Hstr), 1625 (C=Cstr),
1510 (N-Hben), 1267(C-Nstr), 962-812 (C-Hdef); 1H NMR (400 MHz, DMSO): δH 6.88-7.75 (15H,
m, 14H-arom and -CH), 8.65 (1H, s, NH), 10.00 (1H, s, OH); 13C NMR (100 MHz, DMSO):
53.43, 117.81, 118.31, 118.58, 119.59, 120.41, 121.46, 122.54, 122.91, 123.24, 122.98, 125.20,
125.33, 126.65, 127.32, 128.57, 128.98 129.89, 145.99, 150.68, 153.38, 166.69; ESI-MS: m/z
Calculated for C24H17N3O3S 427.2 Found [M+H]+ 428.1.
1-[(2-Benzothiazolylamino)(2-hydroxyphenyl)methyl]-2-naphthalenol (1e)
Off white powder, mp 162-163oC; IR (KBr) (υmax, cm-1): 3504 (OHstr), 2941 (C-Hstr), 1627
(C=Cstr), 1508 (N-Hben), 1280 (C-Nstr), 962-813 (C-Hdef); 1H NMR (400 MHz, DMSO): δH 6.68-
7.49 (15H, m, 14H-arom and -CH), 8.68 (1H, s, NH), 10.04 (1H, s, OH), 10.34 (1H, s, OH); 13C
NMR (100 MHz, DMSO): 51.82, 116.74, 116.95, 117.76, 118.84, 119.40, 120.60, 121.11,
18

Page 19 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
121.24, 125.54, 122.52, 126.31, 128.20, 128.98, 129.80, 131.73, 132.12, 136.31, 150.86, 152.65,
154.47, 160.83, 166.54; ESI-MS: m/z Calculated for C24H18N2O2S 398.2 Found [M+H]+ 399.1.
1-[(2-Benzothiazolylamino)(4-methoxyphenyl)methyl]-2-naphthalenol (1f)
Off white powder, mp 172-173oC; IR (KBr) (υmax, cm-1): 3510 (OHstr), 3012 (C-Hstr), 2922 (C-
1
Hstr), 1625 (C=Cstr), 1500 (N-Hben), 1278 (C-Nstr); H NMR (400 MHz, DMSO): δH 3.69 (3H, s,
OCH3), 6.69-7.87 (15H, m, 14H-arom and -CH), 8.51 (1H, s, NH), 10.53 (1H, s, OH); 13C NMR
(100 MHz, DMSO): 54.81, 59.12, 113.33, 118.11, 119.03, 119.12, 120.58, 122.53, 125.52,
126.22, 127.42, 128.47, 128.79, 129.38, 130.22, 132.16, 133.56, 151.69, 153.35, 158.00, 166.84;
ESI-MS: m/z Calculated for C25H20N2O2S 412.2 Found [M+H]+ 413.1.
1-[(2-Benzothiazolylamino)(4-methylphenyl)methyl]-2-naphthalenol (1g)
White powder, mp 180-181oC; IR (KBr) (υmax, cm-1): 3007 (C-Hstr), 2922 (C-Hstr), 1625 (C=Cstr),
1
1510 (N-Hben), 1267 (C-Nstr); H NMR (400 MHz, DMSO): δH 2.23 (3H, s, CH3), 6.75-7.80
(15H, m, 14H-arom and -CH), 8.66 (1H, s, NH), 10.14 (1H, s, OH); 13C NMR (100 MHz,
DMSO): 20.60, 53.33, 118.00, 118.66, 118.92, 120.51, 120.85, 122.27, 125.26, 126.03, 128.34,
128.50, 128.60, 129.22, 130.55, 132.13, 135.17, 139.13, 151.97, 153.20, 166.39; ESI-MS: m/z
Calculated for C25H20N2OS 396.2 Found [M]+ 396.1.
1-[(2-Benzothiazolylamino)(4-chlorophenyl)methyl]-2-naphthalenol (1h)
White powder, mp 208-209 oC; IR (KBr) (υmax, cm-1): 3504 (OHstr), 1627 (C=Cstr), 1267 (C-Nstr),
1122 (C-Hben); 1H NMR (400 MHz, DMSO): δH 6.97-7.98 (15H, m, 14H-arom and -CH), 8.57
(1H, s, NH); 13C NMR (100 MHz, DMSO): 53.48, 117.71, 118.13, 118.44, 118.96, 120.95,
121.12, 122.43, 122.47, 125.81, 126.82, 127.30, 127.78, 128.22, 129.54, 130.32, 131.39, 134.52,
138.16, 151.61, 153.28, 155.11, 166.89; ESI-MS: m/z Calculated for C24H17N2OClS 416.4 Found
[M+H]+ 417.2.
19

RSC Advances
Page 20 of 24
View Article Online
DOI: 10.1039/C5RA11857C
Acknowledgements
We are grateful thanks to Punjab University, Chandigarh for spectral analytical data.
References
1. Y. Chiang, A. J. Kresge, Y. Zhu, Pure. Appl. Chem. 2000, 72, 2299.
2. S. H. Mashraqui, M. B. Patil, H. D. Mistry, S. Ghadigaonkar, A. Meetsmay, Chem. Lett.
2004, 33, 1058.
3. M. J. Adler, S. W. Baldwin, Tetrahedron Lett. 2009, 50, 5075.
4. J. S. Yadav, B. V. S. Reddy, K. Sadashiv, B. Padmavani, Catal. 2004, 346, 607.
5. (a) C. O. Kappe, Curr. Opin. Chem. Biol. 2002, 6, 314; (b) V. Nair, C. Rajesh, A. Vinod,
U. S. Bindu, A. R. Streekenth, S. Mathen, L. Balagopal, Acc. Chem. Res. 2003, 36, 899;
(c) D. J. Ramon, M. Yus, Angew. Chem., Int. Ed. 2005, 44, 1602; (d) A. A. Domling,
Chem. Rev. 2006, 106, 17.
6. (a) S. Benetti, R. Romagnoli, C. De Risi, G. Spalluto, V. Zanirato, Chem. Rev. 1995, 95,
1065; (b) P. Langer, Chem.-Eur. J. 2001, 7, 3858; (c) P. Langer, Synthesis 2002, 441; (d)
C. Simone, T. Constantieux, Rodriguez, J. Eur. J. Org. Chem. 2004, 4957.
7. A. Shaabani, A. Rahmati, E. Farhangi, Tetrahedron Letters 2007, 48, 7291.
8. (a) A. Kumar, M. S. Rao, V. K. Rao, Aust. J. Chem. 2010, 63, 1538; (b) K. N.
Venugopala, M. Krishnappa, S. K. Nayak, B. K. Subrahmanya, J. P. Vaderapura, R. K.
Chalannavar, R. M. Gleiser, B. Odhav, Eur. J. Med. Chem. 2013, 65, 295; (c) L. Yang, J.
Chem. 2012, 9, 2424; (d) P. K. Kalavagunta, R. Pala, U. R. Pathipati, N. Ravirala, J.
Agric. Food Chem. 2014, 62, 6571; (e) Y. Yu, H. Guo, Chin. J. Org. Chem. 2011, 31, 96;
(f) S. Javanshir, A. Ohanian, M. M. Heravi, M. R. Naimi-Jamal, F. F. Bamoharram, J.
20

Page 21 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
Saudi Chem. Soc. 2011, DOI: 10.1016/j.jscs.2011.10.013; (g) P. K. Sahu, P. K. Sahu. D.
D. Agarwal, RSC Advances 2014, 4, 40414.
9. (a) J. M. Thomas, W. J. Thomas, in Principles and Practice of Heterogeneous Catalysis,
VCH,Weinheim, 1997; (b) H. U. Blaser, A. Baiker, R. Prins, in Heterogeneous Catalysis
and Fine Chemicals IV, Elsevier, Netherlands, 1997.
10. Y. Xi, R. J. Davis, J. Catal. 2008, 254, 190.
11. (a) O. Ilgen, A. N. Akin, Energy & Fuels 2009, 23, 1789; (b) W. Xie, X. Huang, H. Li,
Bioresource Tech. 2007, 98, 936; (c) P. Intarapong, A. Luengnaruemitchai, S. Jai-In, Int.
J. Renew. Energy Res. 2011, 1, 271; (d) W. Xie, H. Peng, L. Chen, Appl. Catal. A: Gen.
2006, 300, 67; (e) H. Kim, B. Kang, M. Kim, Y. Park, D. Kim, J. Lee, K. Lee, Catal.
Today 2004, 93, 315; (f) W. Xie, H. Li, J. Mol. Catal. A: Chem. 2006, 255, 1; (g) W. Xie,
H. Peng, L. Chen, J. Mol. Catal. A: Chem. 2005, 246, 24; (h) G. J. Suppes, M. A. Dasari,
E. J. Doskocil, P. J. Mankidy, M. J. Goff, Appl. Catal. A: Gen. 2004, 257, 213; (i) X. Li,
G. Lu, Y. Guo, Y. Guo, Y. Wang, Z. Zhang, X. Liu, Y. Wang, Catal. Commun. 2007, 8,
1969; (j) R. S. Watkins, A. F. Lee, K. Wilson, Green Chem. 2004, 6, 335.
12. M. Turco, G. Bagnasco, U. Costantino, F. Marmottini, T. Montanari, G. Ramis, G.
Busca, J. Catal. 2004, 228, 56.
13. B. F. Sels, D. E. De Vos, P. A. Jacobs, Catal. Rev. Sci. Eng. 2001, 43, 443.
14. S. K. Yun, T. J. Pinnavaia, Chem. Mater. 1995, 7, 348.
15. A. Corma, S. Iborra, S. S. Miquel, J. Primo, J. Catal. 1998, 173, 315.
16. S. Gupta, D. D. Agarwal, S. Banerjee, Indian J. Chem., Sect. A 2008, 47, 1004.
17. G. Duan, X. Yang, J. Chen, G. Huang, L. Lu, X. Wang, Powder Technol. 2007, 172, 27.
18. X. Liu, X. Piao, Y. Wang, S. Zhu, Energy Fuels 2008, 22, 1313.
21

RSC Advances
Page 22 of 24
View Article Online
DOI: 10.1039/C5RA11857C
19. A. D’Cruz, M. G. Kulkarni, L. C. Meher, A. K. Dalai, J. Am. Oil Chem. Soc. 2007, 84,
937.
20. H. Hattori, J. Japan Petroleum Inst. 2004, 47, 67.
21. J. J. Di Cosimo, V. K. Di’ez, M. Xu, E. Iglesia, C. R. Apesteguia, J. Catal. 1998, 178,
499.
22. T. Nakatsuka, H. Kawasaki, S. Yamashita, S. Kohjiya, Bull. Chem. Soc. Jpn. 1979, 52,
2449.
23. G. Arzamendi, E. Arguinarena, I. Campo, S. Zabala, L. M. Gandia, Catal. Today 2008,
133, 305.
24. F. Cavani, F. Trifiro, A. Vaccari, Catal. Today 1991, 11, 173.
25. F. M. Labojos, V. Rives, M. A. Ulibarri, J. Mater. Sci. 1992, 27, 1546.
26. A. S. Bookin, A. Dritis, Clays Clay Miner. 1993, 41, 551.
27. B. M. Choudary, M. L. Kantam, V. Neeraja, K. K. Rao, F. Figueras, L. Delmotte, Green
Chem. 2001, 3, 257.
28. (a) S. K. Sharma, P. A. Parikh, R. V. Jasra, J. Mol. Catal. A: Chem. 2007, 278, 135; (b)
V. R. L. Constantino, T. Pinnavaia, J. Inorg. Chem. 1995, 34, 883.
29. (a) A. Corma, V. Fornes, R. M. Martinaranda, F. Rey, J. Catal. 1992, 134, 58; (b) M. J.
Climent, A. Corma, S. Iborra, J. Primo, J. Catal. 1995, 151, 60.
30. C. O. Veloso, C. N. Perez, B. M. De Souza, E. C. Lima, A. G. Dias, J. L. F. Monteiro, C.
A. Henriques, Microporous Mesoporous Mater. 2008, 107, 23.
31. V. K. Diez, C. R. Apesteguia, J. I. Di Cosimo, J. Catal. 2003, 215, 220.
22

Page 23 of 24
RSC Advances
View Article Online
DOI: 10.1039/C5RA11857C
32. (a) J. Lal, M. Sharma, S. Gupta, P. Parashar, P. Sahu, D. D. Agarwal, J. Mol. Catal. A:
Chem. 2012, 352, 31; (b) P. K. Sahu, P. K. Sahu, R. Jain, R. Yadav, D. D. Agarwal,
Catal. Sci. Technol. 2012, 2, 2465.
23

RSC Advances
Page 24 of 24
View Article Online
DOI: 10.1039/C5RA11857C
Figure Legends
Fig 1. XRD pattern of KOH/MgO with different loading amounts:
1%, (b) 2%, (c) 3%, (d) 4%
Fig 2. SEM images of catalysts
Fig 3. Effect of reaction time on yield of target product
Fig 4. Effect of temperature on conversion and yield of product
Fig 5. Effect of KOH loading on conversion and yield
Fig 6. P-XRD pattern and SEM image of hydrotalcite (Mg-Al-3:1)
Fig 7. XRD pattern of recovered hydrotalcite
Scheme Captions
Scheme 1. Synthesis using hydrotalcite or KOH/MgO at 70 oC.
24