Preparation and application of highly efficient and reusable TBAPIL@Si(CH2)3@nano-silica-based nano-catalyst for preparation of benzoxanthene derivatives

Article abstract of DOI:10.1007/s13738-021-02211-1

Tetrabutylammonium prolinate ionic liquid (TBAPIL) was prepared, and mesoporous silica nanoparticles (NPs) were synthesized. Both of these were linked through propyltriethoxysilane to prepare a reusable catalyst TBAPIL@Si(CH₂)₃@silica NPs (TBAPILS). The formation of TBAPIL was checked through Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) analysis. X-ray diffraction analysis confirmed the structure of silica NPs and linking of TBPAIL on it. Transmission electron microscopy proved the flourishing development of silica NPs. Scanning electron microscopy graphs exposed the altering in morphology of silica NPs and TBAPILS. FT-IR analysis also confirmed the formation of TBAPILS catalyst. Moreover, the effectiveness of the TBAPILS was also checked for the synthesis of various derivatives of tetrahydrobenzoxanthenes-11-ones. The formation and structure of obtained compounds were confirmed by FT-IR, elemental analysis, ¹HNMR and ¹³C NMR spectral analysis. The catalyst TBAPILS was found to be used successfully up to five cycles without significant loss of activity.

Full text of DOI:10.1007/s13738-021-02211-1

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-021-02211-1
ORIGINAL PAPER
Preparation and application of highly efcient and reusable
TBAPIL@Si(CH2)3@nano‑silica‑based nano‑catalyst for preparation
of benzoxanthene derivatives
Akansha Agrwal1 · Vipin Kumar2 · Virendra Kasana3
Received: 6 April 2020 / Accepted: 1 February 2021
© Iranian Chemical Society 2021
Abstract
Tetrabutylammonium prolinate ionic liquid (TBAPIL) was prepared, and mesoporous silica nanoparticles (NPs) were syn-
thesized. Both of these were linked through propyltriethoxysilane to prepare a reusable catalyst TBAPIL@Si(CH2)3@silica
NPs (TBAPILS). The formation of TBAPIL was checked through Fourier-transform infrared spectroscopy (FT-IR) and
nuclear magnetic resonance (NMR) analysis. X-ray difraction analysis confrmed the structure of silica NPs and linking
of TBPAIL on it. Transmission electron microscopy proved the fourishing development of silica NPs. Scanning electron
microscopy graphs exposed the altering in morphology of silica NPs and TBAPILS. FT-IR analysis also confrmed the
formation of TBAPILS catalyst. Moreover, the efectiveness of the TBAPILS was also checked for the synthesis of various
derivatives of tetrahydrobenzoxanthenes-11-ones. The formation and structure of obtained compounds were confrmed by
FT-IR, elemental analysis, 1HNMR and 13C NMR spectral analysis. The catalyst TBAPILS was found to be used successfully
up to fve cycles without signifcant loss of activity.
Keywords Tetrabutylammonium prolinate ionic liquid · Mesoporous silica nanoparticles · Tetrahydrobenzoxanthene ·
TBAPILS · Transmission electron microscopy · Scanning electron microscopy · X-ray difraction
Introduction
due to the structural and electronic changes which difer-
entiate them from the original materials [3]. Nanoparticles
(NPs) can replace conventional materials and serve as het-
erogeneous catalytic systems or as a material of support for
diferent catalytic systems [4, 5]. Catalyst is a substance
which speeds up the chemical reactions, enhances the prod-
uct yield and shrinks the energy of activation, but a severe
trouble with reactions in catalytic conditions is the parting
of catalytic system from the ongoing reaction mixture so
that it may be used again [6]. To defeat this trouble, a hetero-
geneous catalytic system may be used in synthetic organic
chemistry. Currently, heterogeneous catalytic systems may
be prepared by a variety of substances in a straightforward
way [7]. Heterogeneous catalytic systems may capably be
formed by modifying the support with NPs and combin-
ing these with catalytic system [8, 9]. Recently a range of
methods have been reported for the synthesis of silica NPs
with controlled size and chemical stability with a variety of
applications in drug delivery [10]. Moreover, these silica-
based catalysts have also been used to catalyze a range of
chemical reactions [11, 12].
Nano-catalysis is a very exciting feld which is originated
from nanoscience. Nano-catalysts are gaining importance
increasingly [1]. The main aim of the nano-catalysts is to
control the chemical reactions through changing their size,
morphology and composition of reaction center [2]. The
overall approach opens various areas for designing of nano-
catalysts having a distinct, selective and specifc chemical
activity. The nano-shape, size and a large surface area by
volume ratio provide unique characteristics to nano-catalysts
* Akansha Agrwal
akansha.agrwal90@gmail.com
1
Department of Chemistry, KIET Group of Institutions,
Delhi-NCR, Meerut Road (NH-58), Ghaziabad 201 206,
India
2
Department of Physics, KIET Group of Institutions,
Delhi-NCR, Meerut Road (NH-58), Ghaziabad 201 206,
India
3
Department of Chemistry, Govind Ballabh Pant University
of Agriculture and Technology, Pantnagar, India
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Ionic liquids are salts having melting point lower than
the boiling point of water. Ionic liquids have several alter-
native names such as designer solvents, molten salts and
ionic fuids [13]. Ionic liquids are generally colorless liquids
with moderately low viscosity. Ionic liquids are made up
of two parts positive and negative ions, therefore there is
wide scope to prepare them in large numbers and to fne-
tune their properties according to the requirement. These
advantages are unavailable for single constituent molecular
solvents. In addition to all these properties, ionic liquids can
be readily formed by using commercially accessible reagents
[14]. Ionic liquids also have an important role in cataly-
sis and synthesis [15]. Various methods for the preparation
along with their applications in catalysis have been reported
for tetrabutylammonium prolinate and other ionic liquids
[16–18]. But most of these ionic liquids are associated with
disadvantages like harsh conditions and non-reusability.
Tetrahydrobenzoxanthen-11-one and its derivatives
are a chief class of bioactive compounds having activities
like anti-infammatory [19], free radical scavenging [20],
mGlu1 receptor enhancing [21], antiplasmodial [22], anti-
tumor [23], inhibitors of recombinant human calpain I [24],
molecular probes in chemical biology [25], antibacterial [26,
27], antiproliferative [28], antineoplastic [29], drug develop-
ment [30, 31], antileukemic [32] and insecticidal [33]. Due
to special spectroscopic properties, these derivatives have
also been used as pH-indicators [34], fuorescent materials in
visualization of molecules [35] and as photodynamic therapy
agents [36]. Various methods have been developed for the
synthesis of tetrahydrobenzoxanthen-11-one using PMA/
SiO2 [37], ZnO [38], InCl3/ionic liquid [39], p-dodecylben-
zenesulfonic acid [40], iron oxide NPs [41], trichloroacetic
acid [42], silica sulfuric acid [43], strontium trifate [44],
PEG [45], bismuth nitrate [46], phenylboronic acid [47],
molecular iodine [48], p-TSA [49] and other heterogeneous
catalysts [50, 51]. Most of them have the limitations such
as low yield, formation of mixture of products, long reac-
tion time and harsh reaction conditions, so it is imperative
to develop new and efcient methods with reduced reaction
time and mild reaction conditions for the synthesis of deriva-
tives of biologically active tetrahydrobenzoxanthen-11-one
compounds. To the best of our knowledge, we are frst to
report the synthesis of tetrahydrobenzoxanthen-11-one in
solvent-less condition by using TBAPILS nano-catalyst.
were made of Borosil. IR spectra were taken on BRUCKER
FT-IR spectrophotometer of BRUCKER. BRUCKER
AVANCE II 400 MHz instrument was used for 1HNMR
analysis with CDCl3 solvent. Decibel digital melting point
equipment was used for recording of melting points. The
progress of reaction and compounds purity was checked by
TLC on silica gel plates with hexane and ethyl acetate sol-
vents and visualized through vapors of iodine and UV light.
JSM-1011 transmission electron microscope was used for
TEM analysis and JEOL (JSM-6610 LV) with a prime ray
power of 5 kV apparatus was used to record SEM analysis.
XRD analysis of powdered samples was recorded at room
temperature (RT) over Rigaku-Geigerfex X-Ray difractom-
eter by using Cu-Ka radiation (k=0.154 nm) in the series of
108–708 at 30 kV and 15 mA with step size 0.05 and step
time of 19.2 s.
Synthesis of mesoporous silica nanoparticles (NPs)
In a round-bottom fask, 100 mL methanol was placed. To
it, 60 mL solution of ammonia (32%) and 1.98 mL water
were mixed. The mixture was stirred up to 5–6 min and
after that 10.40 g tetraethyl orthosilicate (TEOS) was added
drop-wise. The solution was again stirred for 72 h at an
ambient temperature [52, 53]. Then, it was centrifuged for
30 min, after which solvent was evaporated by rotavapor,
washed with ethanol and particles obtained were put in oven
at 250 °C for 1 h.
Synthesis of tetrabutylammonium prolinate ionic
liquid (TBAPIL)
Tetrabutylammonium hydroxide [(TBA)(OH)] aqueous
solution was prepared by modifed literature method [54]
from Tetrabutylammonium bromide (20 mmol) using anion
exchange resin AMBERLITE IRA400 OH. The obtained
[(TBA)(OH)] aqueous solution (10 mmol) was then added
drop-wise with a slightly excess aqueous proline solution
(10 mmol). This combination was stirred at RT for 12 h,
then water was removed in vacuum and obtained residue
was dissolved in CH3CN (40 mL) and the solution was fl-
tered to remove unreacted proline. Filtrate was dried over
anhydrous Na2SO4 and solvent was removed in vacuum to
give the desired TBAPIL as low viscous colorless oil [17].
Preparation of TBAP@Si(CH2)3@nano‑silica
(TBAPILS) catalyst
Experimental
Materials and methods
The supporting of the TBAPIL on propyl silane-grafted
silica nanoparticles is shown in Scheme 1. Silica NPs (1 g)
and 3-chloropropyltriethoxysilane (3 mmol) were added
to 20 mL of dry toluene and then refuxed for 12 h. The
resultant grafted SiO2@Si(CH2)3Cl was fltered, washed
All reagents and chemicals were of L.R. grade and procured
from Hi-media and Molychem and directly used with no
additional purifcation. The glasswares used during the study
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Journal of the Iranian Chemical Society
Scheme 1 Synthesis of [TBA][Pro] @Si(CH2)3@nano-silica catalyst
thrice with dry toluene and with dry diethyl ether and
dried at 75 °C for 6 h in vacuum oven. Then, TBAPIL
(10 mmol) was added to the round-bottom fask containing
SiO2@Si(CH2)3Cl (1 mmol), K2CO3 (5 mmol) in 50 mL
of dry toluene. The mixture was refuxed for 24 h. The
resultant solid was then fltered, washed and dried to give
TBAPILS. After the usual workup and washings, the mate-
rial was dried at 75 °C for 5 h in a vacuum oven.
Results and discussion
TBAPILS catalyst
TEM analysis of Mesoporous Silica NPs
The size of silica NPs was characterized from TEM. The
results are shown in Fig. 3a, b. The size of silica NPs was
found to be 40–50 nm.
1H NMR of TBAPIL 1H NMR (CDCl3, 400 MHz): δppm
3.28 (t, 2H), 3.26 (t, 1H), 2.33 (t, 2H), 1.93(s, 1H), 1.62
(m, 2H), 1.58 (m, 2H), 1.56 (m, 2H), 1.37 (m, 2H), 0.91(t,
3H) (Fig. 1).
Synthesis of tetrahydrobenzoxanthen‑11‑one
derivatives using TBAPILS catalyst
β-naphthol (10 mmol)/α-naphthol(10 mmol), cyclic 1,3
dicarbonyl compound (10 mmol) and benzaldehyde deriv-
ative (10 mmol) were mixed with TBAPILS (5 mol%). The
mixture of was stirred vigorously at 80 °C (Scheme 2)
and progress of reaction was observed using TLC (ethyl
acetate: n-hexane:: 3:7 v/v). After completion of reaction,
cold water was added to the reaction mixture to ease the
precipitation of product. The solid obtained was dissolved
in ethyl alcohol and fltered. The catalyst obtained as solid
was washed three times with alcohol to remove any traces
of product and then dried in vacuum oven at 70 °C to
be used for next cycle. Solvent was distilled of from fl-
trate to get the solid product. The crude product was then
recrystallized from dichloromethane to give pure product.
FT‑IR analysis
The functional groups of the prepared TBAPILS catalyst
and its precursors were characterized by FT-IR technique,
as shown in Fig. 2. In mesoporous nano-silica, two char-
acteristic bands by the side of 963 cm−1 and 783 cm−1 are
for Si–O–Si symmetric and asymmetric stretching, and at
3562 cm−1 due to surface Si–OH stretching. Two bands at
459 and 1633 cm−1 are due to Si–O–Si and Si–OH bend-
ing, respectively (Fig. 2a). The characteristic bands of
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Journal of the Iranian Chemical Society
Scheme 2 Synthesis of Tetrahydrobenzoxanthen-11-one derivatives
SEM analysis silica NPs and TBAPILS catalyst
The surface morphology of silica NPs and TBAPILS cata-
lyst was characterized by SEM. Silica nanoparticles dem-
onstrate a porous morphology (Fig. 4a). TBAPILS grafted
on silica nanoparticles fll the pores in the surface thereby
making a diferent topological arrangement which gives
rise to changed morphology (Fig. 4b). Perusal of Fig. 4a,
b clearly indicates the diference in surface morphology
of silica NPs and TBAPILS (Fig. 4a, b).
XRD analysis
Fig. 1 Structure of tetrabutylammonium prolinate ionic liquid
The XRD pattern of silica NPs clearly conforms to the
amorphous nature of it with the broad peak (2θ) at 23.70.
The XRD results are in well agreement with the reported
facts JCPDS card number (00-049-1711) [55]. The change
in intensity in TBAPILS (Fig. 5b) in comparison with sil-
ica NPs (Fig. 5a) clearly indicates the linking of TBAPIL
on surface of silica NPs. These XRD results are sup-
ported by the SEM results whereby changed morphology
is observed after grafting on the silica NPs.
chloropropylsilane-coated silica appearing at 1057, 1237
and 2965 cm−1 are due to the Si–O–Si stretching, C–H
bending and stretching, respectively (Fig. 2b). The char-
acteristic bands at 1359, 1625, 3524, 2938 cm−1 are due
to –C–OH, –C = O, –NH and –C–H stretching. The bands
by the side of 1455 and 735 cm−1are due to the –C–H
and –C = O bending (Fig. 2c). The presence of groups in
TBAPILS catalyst such as Si–O–Si, –C = O, –C–H is con-
frmed by bands at 461, 791, 1121, 1241, 1681, 2986 and
3600 cm−1 (Figs. 2d, 3).
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Journal of the Iranian Chemical Society
Fig. 2 FT-IR of a SiO2 NPs, b
Si(CH2)3@SiO2, c TBAPIL and
d TBAPILS catalyst
Fig. 3 TEM images of silica
NPs: a low magnifcation and b
high magnifcation
Fig. 4 a SEM of silica NPs and
b SEM of TBAPILS catalyst
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Journal of the Iranian Chemical Society
Fig. 5 a XRD of silica NPs and
b XRD of TBAPILS catalyst
R2
R2
(A)
TBAPILS
O
O
H
O
TBAPILS
R1
TBAPILS
R1
H
R1
1
OH
H
H
O
O
O
1a
1b
R2
R2
O
O
R1
R2
R2
R1
R1
H
H
O
OH
O
O
R2
TBAPILS
H
O
R2
H2O
1e
1c
1d
TBAPILS
Scheme 3 Plausible mechanism for the synthesis of tetrahydrobenzoxanthene-11-one derivatives
oxygen of the carbonyl group of aldehyde which increases
the electrophilicity of carbonyl group and anion activates
the nucleophile b-naphthol, consequent upon this nucleo-
philic attack of β-naphthol at carbonyl carbon is facilitated
and ortho-quinone methide intermediates (1a) is formed.
Mechanism
A plausible mechanism has been proposed for the prepa-
ration of tetrahydrobenzoxanthen-11-one derivatives using
TBAPILS catalyst (Scheme 3). The cation is attached to the
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Journal of the Iranian Chemical Society
After removal of a water molecule, 1b is formed. With the
removal of a water molecule, the catalyst TBAPILS which
is attached to oxygen of carbonyl group of aldehyde is
detached and now it interacts with active methylene group
containing compound (A) via oxygen and makes it more
reactive while anion interacts with enolic –OH of bicarbo-
nyl. Due to combined efect of these activations, Michael
addition is facilitated. Ring closure step, next to Michael
addition step, is also facilitated by the catalyst. Here also,
solvent less condition to optimize temperature. No yield was
obtained at RT even up to 10 h stirring. After this, the reac-
tion was tried at diferent temperatures from 40 to 100 °C
with a diference of 10 °C. As a result of rising temperature,
the yield increased and the reaction time decreased. After
80 °C, no rise in yield was observed. Time also remained
constant. So, 80 °C was taken as the optimum temperature
for the reaction.
electrophilicity of carbonyl carbon of bicarbonyl is increased Scope of substrate
due to its interaction with cation and interaction of anion
with –OH group of naphthol moiety assists in removal of
hydrogen thus facilitating ring closure. After ring closure,
dehydration takes place and fnal product (1e) is obtained
(Scheme 3). The mechanism proposed is the modifcation to
the mechanism reported in the literature [47, 51] in which
interaction of anion and combined efect of cation and anion
are not discussed. In our view, it is simultaneous interaction
of cation as well as anion of the catalyst with substrates in
each step that makes the catalyst more active. Comparison
of the activity of catalyst with those of tetrabutylammonium
bromide and proline supports this view (Table 3).
Derivatives of substituted tetrahydrobenzoxanthen-11-one
were produced by the reaction between substituted α/β-
naphthol, benzaldehyde derivative and cyclic 1, 3 dicarbo-
nyl. The substituted group, % yield, M.P. and reaction time
are displayed in Table 1. To inspect the scope of substrate, a
range of benzaldehyde derivative was used. All the products
were obtained in good to excellent yield. The reaction was
completed within 15 to 180 min. The reaction was viable
for electron-withdrawing as well as for electron-donating
groups substituted on the benzene ring of benzaldehyde. The
reaction could be carried out well for both α-naphthol and
β-naphthol which clearly establishes broad substrate scope
of the reaction catalyzed by TBAPIS (Table 1). Turn over
number (TON) and turn over frequency (TOF) values of
catalyst for all the products have been calculated and are
presented in Table 1. TON values were obtained in the range
Optimization of reaction conditions
A model reaction of β-naphthol, benzaldehyde and cyclic
1,3 dicarbonyl was carried out using TBAPILS under
Table 1 Substituted
tetrahydrobenzoxanthen-11-one
derivatives
Code –R1
–R2
Yield (%)a TON TOF (min−1
)
M.P. (°C) M.P. (°C) Ref Time (min)
A1
A2
A3
A4
A5
A6
A7
A8
A9
–H
3-NO2
4-Cl
–CH3 92
–CH3 88
–CH3 84
–CH3 80
–CH3 82
184
176
168
3
2
6
150–152 151–153 [57] 60
170–172 168–170 [47] 90
175–177 176–179 [42] 30
210–215 218–220 [58] 15
4-NH(CH3)2
3-OH
3,4- (OCH3)2 –CH3 88
2,4-(Cl)2 –CH3 85
4-OH,3-OCH3 –CH3 80
2-OH,3-OCH3 –CH3 80
160 11
164
176
170
160
160
176
180
144
160
164
5
2
8
5
4
3
1
1
2
5
225–227
165–168
240–241 [57] 30
90
173–175 175–178 [59] 20
196–198 213–215 [57] 30
215–217 213–215 [59] 40
A10 4-F
A11 –H
A12 3-NO2
A13 4-Cl
A14 –H
A15 3-NO2
A16 4-Cl
A17 –H
A18 3-NO2
A19 4-Cl
–CH3 88
180–182
190–192
184–185 [47] 60
202–203 [58] 180
–H
–H
–H
–CH3 82
–CH3 81
–CH3 82
–H
–H
–H
90
72
80
210–215 230–232 [60] 120
208–210 204–206 [58] 90
160–162 155–157 [58] 30
170–172 167–170 [61] 15
215–218 185–187 [61] 15
156–158 173–175 [58] 60
162 11
164 11
84
86
85
168
192
190
3
2
2
178–180 167–170
90
170–172 175–177 [58] 120
aIsolated yield
bReaction conditions: β-naphthol (10 mmol)/α-naphthol(10 mmol), benzaldehyde derivative (10 mmol)
and cyclic 1,3 dicarbonyl (10 mmol) in the absence of solvent with TBAPILS (5 mol%) at 80 °C
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Journal of the Iranian Chemical Society
Table 2 Optimization of the amount of TBAPILS catalyst for the for-
144–192. The values clearly indicate that catalyst is quite
stable. The TOF values calculated per minute were obtained
in the range 1–11 indicating variable efciency of the cata-
lyst for diferent reactants.
mation of A1
Entry
Catalyst (mol %) Time (min)
Yield (%)a
1
2
3
4
5
6
7
1
2
3
4
5
6
7
240
220
180
120
60
60
60
40
50
65
80
92
92
92
Loading of TBAPILS catalyst
To optimize the amount of catalyst, model reaction of
β-naphthol (10 mmol), benzaldehyde derivative (10 mmol)
and cyclic 1,3 dicarbonyl (10 mmol) was tried in the pres-
ence of various amounts of catalyst such as 1, 2, 3, 4, 5, 6
and 7 mol%, there is an increase in yield and decrease in time
aIsolated yield
with increase in the amount of catalyst up to 5 mol% (Fig. 6).
No further signifcant increase in yield was observed in by
further increasing the catalyst amount (Table 2). The results
showed that 5 mol% of the catalyst and 80 °C temperature
was the best combination to aford product A1 in excellent
yield.
Table 3 Optimal conditions for the synthesis of A1 catalyzed by
TBAPILS
Entry Catalyst
Solvent Tem-
Time (h) Yield (%)a
perature
(°C)
1
2
3
4
5
6
7
8
–
–
–
–
–
80
10
10
10
10
10
10
10
10
10
10
5
–
–
–
–
–
–
–
–
–
–
30
–
20
92
92
Ethanol RT
Ethanol 80
Water
Structure and catalytic ability relationship
of TBAPILS catalyst
RT
80
RT
80
RT
80
RT
80
–
Water
Perusal of structure of the catalyst TBAPILS reveals that
it is a bifunctional ionic liquid organocatalyst. It contains
cation (tetrabutylammonium) and an efective anion which
also contains base (–N). These features make it excellent
and task specifc for this reaction. These features are lack-
ing in tetrabutylammonium bromide and proline. Though
tetrabutylammonium bromide contains same cation, it does
not have an efective anion or a base. Proline contains both
acidic as well as basic group but it lacks efective cation.
This is supported by experimental observations (Table 3).
The catalyst prepared by us has activity much higher than
tetrabutylammonium bromide and proline. The interaction
of the catalyst with substrates at diferent stages of reaction
is explained to understand its structure activity relationship.
Cation of the catalyst is efective in catalyzing the reaction
of benzaldehyde and b-naphthol by interacting with the car-
bonyl group of benzaldehyde via oxygen while its base/anion
interacts with the nucleophile (b-naphthol) via hydrogen of
–OH group of naphthol. Then, in the reaction between the
intermediate formed thus and dicarbonyl compound, cation
interacts in the same way with the carbonyl group of the
intermediate and anion/ base interacts with the dicarbonyl
facilitating Michael addition. Finally, in the cyclization
step, carbonyl group of bicarbonyl moiety and OH group
of b-naphthol moiety interact with cation and base/ anion,
respectively. Thus, in every step, catalyst functions as acid
as well as a base. Jimenez et al. [56] have explained these
interactions of bifunctional organocatalyst containing thio-
urea moiety working as Lewis acid and amine working as
Silica NPs
Silica NPs
SiO2@Si(CH2)3Cl
SiO2@Si(CH2)3Cl
TBABr
TBABr
Proline
Proline
TBAPIL
TBAPILS
–
–
–
–
–
–
–
–
–
–
9
10
11
12
13
14
15
RT
80
80
10
4
1
80
1
aIsolated yield
Catalyst (mol%)
Time (Min)
Yield (%)
240
250
200
150
100
50
220
180
120
80
92
60
92
60
92
60
65
50
40
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
Reacꢀon
Fig. 6 Recycling study of TBAPIL up to fve cycles for the synthesis
of A1
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Journal of the Iranian Chemical Society
base on the basis of electron density topological analysis
using quantum chemical technology.
decreased signifcantly (Fig. 7). By these results, we can
say that catalyst successfully may be used up to fve cycles
without signifcant loss of activity.
Hot fltration test
Comparison of the efciency of TBAPILS catalyst
with other reported catalysts
To confrm the heterogeneity of TBAPILS catalyst and in
order to prove that tetrabutylammonium ionic liquid was not
leaching out from the TBAPILS catalyst, the hot fltration
test was performed with the model reaction of β-naphthol,
benzaldehyde derivative and cyclic 1,3 dicarbonyl under
optimized reaction conditions. After 30 min which is half
of the reaction time, the catalyst was fltered of and 45%
yield was obtained and fltrate was allowed to react further
but no signifcant amount of product was obtained. These
results show that immobilized ionic liquid is not leached
out from the coated silica NPs and the TBAPILS catalyst is
heterogeneous in nature.
To prove the superiority of TBAPILS catalyst (Table 4), we
compared our results with some of those catalysts reported
in the literature for compound A1. The results clearly indi-
cate the superiority of the catalyst developed by us. Moreo-
ver, solvent less condition makes the reaction economic.
1HNMR, 13CNMR and elemental analysis
of tetrahydrobenzoxanthen‑11‑one derivatives
A1‑9,9‑dimethyl‑12‑phenyl‑9,10‑dihydro‑8H‑benzo[a]xan‑
then‑11(12H)‑one Anal. Calcd. For C25H22O2: C, 84.74;
H,6.21; N, Nil; O,9.03 Found: C, 82.58; H, 5.96; N, Nil;
O,10.28% 1H NMR (CDCl3, 400 MHz): δppm 8.10 (d,1H,–
Ar), 7.74–7.80 (m,2H, –Ar), 7.43–7.31 (m, 5H, –Ar),7.21–
7.14(m, 2H, –Ar), 7.06 (m, 1H, –Ar), 5.71 (s,1H, –CH),
2.57 (s, 2H, –CH2), 2.26(m, 2H, –CH2), 1.11 (s, 3H, –CH3),
0.96 (m, 3H, –CH3); 13CNMR (CDCl3,100 MHz,δppm):
197.10, 164.06, 147.81, 144.82, 131.57, 128.93, 128.52,
127.10, 126.33, 124.99, 123.76, 117.78, 117.13, 50.94,
41.48, 34.78, 32.36, 29.40, 27.24.
Recycling studies of TBAPILS catalyst
After completion of reaction, the catalyst was fltered of the
reaction mixture, washed, dried and used for the next cycle
in the synthesis of A1. The process was repeated constantly
up to seven cycles and observed not a major reduction in
yield until ffth cycle. In sixth and seven cycles, the yield
92
A 2 ‑ 9 , 9 ‑ d i m e t hy l ‑ 1 2 ‑ ( 3 ‑ n i t ro p h e ny l ) ‑ 9 , 1 0 ‑ d i hy‑
dro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
100
90
80
70
60
50
40
30
20
10
0
90
89
87
85
1
400 MHz): δppm 8.10 (m, 1H, –Ar), 7.92–7.94 (dd, 1H,
–Ar), 7.84 (d, 1H, –Ar),7.82–7.79(m, 3H, –Ar), 7.45–7.35
(m, 4H, –Ar), 5.81 (s, 1H, –CH), 2.61 (s, 2H, –CH2), 2.26
(m, 2H, –CH2), 1.13 (s, 3H, –CH3), 0.98 (m, 3H, –CH3).
A3‑9, 9‑ dimethyl‑12‑(4‑ chlorophenyl)‑9, 10‑ dihy‑
dro‑8H‑benzo[a]xanthen‑11(12H)‑one 1H NMR (CDCl3,
400 MHz): δppm 7.91 (d,1H, –Ar), 7.80–7.76 (m,2H, –Ar),
7.44–7.38 (m, 2H, –Ar),7.33–7.26 (m, 2H, –Ar), 7.17–7.11
(m, 2H, –Ar), 6.99 (s,1H, –Ar), 5.68 (s,1H, –CH), 2.52 (s,
2H, –CH2), 2.29 (m, 2H, –CH2), 1.10 (s, 3H, –CH3), 0.96
(s, 3H, –CH3).
1
2
3
4
5
Cycles
Fig. 7 Optimization of the amount of TBAPILS catalyst for the for-
mation of A1
Table 4 Comparison of the
efciency of TBAPILS catalyst
with other reported catalyst in
the synthesis of A1
Entry
Catalyst
Condition
Time (h)
Yield (%)a
References
1
2
3
4
5
6
Sr(OTf)2
Phenylboronic acid
–
Proline trifate
PWA
TBAPILS
ClCH2CH2Cl 80 °C
EtOH
PEG 120 °C
H2O/Refux
60 °C
5
4
6.5
3
1.17
1
85
79
87
85
86
92
[44]
[47]
[45]
[62]
[63]
Our work
Solvent less
aIsolated yield
1 3

Journal of the Iranian Chemical Society
A4‑9,9‑dimethyl‑12‑(N,N‑dimethylphenyl)‑9,10‑dihy‑
dro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
A 1 1 ‑ 1 2 ‑ p h e n y l ‑ 9 , 1 0 ‑ d i h y d r o ‑ 8 H‑ b e n z o [ a ] x a n ‑
then‑11(12H)‑one H NMR (CDCl3, 400 MHz): δppm
1
1
400 MHz): δppm 7.92 (d,1H, –Ar), 7.80–7.70 (m,2H, –Ar),
7.43–7.30 (m, 5H, –Ar),7.17–6.99 (m, 2H, –Ar), 5.67 (s,1H,
–CH), 2.97 (s, 6H, –CH3), 2.57 (s, 2H, –CH2), 2.27 (s, 2H,
–CH2), 1.14 (s, 3H, –CH3), 0.97 (s, 3H, –CH3).
7.97–7.95 (d, 1H, J=7.96 Hz, –Ar), 7.79–7.75 (m, 2H, –
Ar),7.42–7.32 (m, 5H, –Ar),7.19–7.15 (m, 2H, –Ar),7.08–
7.06 (m, 1H, –Ar),5.74 (s, 1H, –CH), 2.73–2.71 (m, 2H,
–CH2), 2.37–2.44 (s, 2H, –CH2), 2.01–2.04 (m, 2H, –CH2);
13C NMR(CDCl3,100 MHz,δppm): 197.26, 165.76, 147.78,
145.08, 131.51, 128.89, 128.42, 127.04, 126.32, 124.93,
123.71, 117.72, 117.01, 115.55, 37.08, 34.67, 27.75, 20.26.
A5‑9,9‑dimethyl‑12‑(3‑hydroxyphenyl)‑9,10‑dihy‑
1
dro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
400 MHz): δppm 8.19 (d,1H, –Ar), 7.96–7.90 (m, 2H, –Ar),
7.72–7.78 (m, 1H, –Ar),7.47–7.36 (m, 1H, –Ar), 7.29–7.24
(m, 5H, –Ar), 5.96 (s, 1H, –OH), 5.66 (s, 1H, –CH), 2.59 (s,
2H, –CH2), 2.26 (m, 2H, –CH2), 1.10 (s, 3H, –CH3), 0.96
(s, 3H, –CH3); 13CNMR(CDCl3,100 MHz,δppm): 194.26,
161.98, 155.51, 145.67, 144.54, 129.47, 127.27, 126.81,
125.30, 123.22, 121.66, 117.44, 115.84, 115.50, 113.71,
111.85, 48.80, 38.23, 32.52, 30.35, 27.39, 25.04.
A
12‑12‑(3‑nitrophenyl)‑9,10‑dihydro‑8H‑benzo[a]xan‑
1
then‑11(12H)‑one H NMR (CDCl3, 400 MHz): δppm
8.07 (m,1H, –Ar), 7.93–7.91 (m, 1H, –Ar),7.81–7.78 (m,
4H, –Ar),7.40–7.34 (m, 2H, –Ar),5.82 (s, 1H, –CH), 2.75–
2.71(m, 2H, –CH2), 2.39–2.43 (s, 2H, –CH2), 2.05–2.06(m,
2H, –CH2).
A6‑9,9‑dimethyl‑12‑(3,4‑dimethoxyphenyl)‑9,10‑dihy‑
dro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
A
13‑12‑(4‑chlorophenyl)‑9,10‑dihydro‑8H‑benzo[a]xan‑
1
then‑11(12H)‑one 1H NMR (CDCl3, 400 MHz): δppm
7.86 (d, 1H, J = 6.4 Hz, –Ar), 7.80–7.76 (m, 2H, –Ar),7.44–
7.38 (m, 2H, –Ar),7.31 (d, 1H, J = 6.4 Hz, –Ar), 7.26–7.24
(s, 2H, –Ar),7.15–7.11 (m, 2H, –Ar), 5.71(s, 1H, –CH),
2.73–2.67(m, 2H, –CH2), 2.45–2.38 (s, 2H, –CH2), 2.08–
1.97 (m, 2H, –CH2); 13CNMR(CDCl3,100 MHz,δppm):
197.26, 165.91, 147.72, 143.56, 132.20, 131.51, 131.18,
129.92, 129.15, 128.52, 127.14, 125.05, 123.48, 117.01,
115.07, 109.46, 36.99, 34.19, 31.32, 27.72, 20.25.
400 MHz): δppm 8.00 (d, 1H, –Ar), 7.79–7.70 (m, 2H, –
Ar), 7.43–7.37 (m, 2H, –Ar),7.30 (d, 1H, –Ar), 6.96 (d, 2H,
–Ar), 6.76–6.74 (dd, 1H, –Ar), 6.41 (s, 1H, –Ar), 5.66 (s,
1H, –CH), 3.79 (s, 3H,–OCH3), 3.74 (s, 3H, –OCH3), 2.56
(s, 2H, –CH2), 2.29 (m, 2H, –CH2), 1.11 (s, 3H, –CH3), 0.97
(s, 3H, –CH3).
A8‑9,9‑dimethyl‑12‑(4‑hydroxy,3‑methoxyphenyl)‑9,10‑di‑
1
hydro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
A14 10,10‑dimethyl‑7‑phenyl‑10,11‑dihydro‑7H‑benzo[c]
xanthen‑8(9H)‑one 1H NMR (CDCl3, 400 MHz): δppm
8.34 (d,1H, –Ar), 8.12 (d, 1H, J = 8.72 Hz, –Ar),7.88 (d,
2H, –Ar),7.78 (d,2H, –Ar), 7.61–7.43 (m, 3H, –Ar),7.29–
7.12 (m, 4H, –Ar), 5.14 (s,1H, –CH), 2.64–2.76 (m, 2H,
–CH2), 2.30 (d, 2H, –CH2), 1.54 (m, 3H, –CH3), 1.08(s,
3H, –CH3).
400 MHz): δppm 8.00 (d, 1H, –Ar), 7.79–7.74 (m, 2H, –
Ar), 7.62 (dd, 1H, –Ar),7.43–7.37 (m, 3H, –Ar), 6.69–6.60
(m, 2H, –Ar), 5.65 (s, 1H, –CH), 5.51 (s, 1H, –OH),3.79 (s,
3H, –OCH3), 2.55 (s, 2H, –CH2), 2.05 (s, 2H, –CH2), 1.11
(s, 3H, –CH3), 0.97 (s, 3H, –CH3).
A9‑9,9‑dimethyl‑12‑(2‑hydroxy,3‑methoxyphenyl)‑9,10‑di‑
1
hydro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
A15
‑
10,10‑dimethyl‑7‑(3‑nitrophenyl)‑10,11‑dihy‑
400 MHz): δppm 7.83–7.73 (m, 3H, –Ar), 7.41–7.26 (m,
3H, –Ar),6.62–6.55 (m, 2H, –Ar), 6.32–6.30 (m, 1H, –Ar),
5.82 (s, 1H, –CH),5.29 (s, 1H, –OH), 3.85 (s, 3H, –OCH3),
2.62 (s, 2H, –CH2), 2.36 (m, 2H, –CH2), 1.13 (s, 3H, –CH3),
0.99 (s, 3H, –CH3).
dro‑7H‑benzo[c]xanthen‑8(9H)‑one 1H NMR (CDCl3,
400 MHz): δppm 8.29 (d, 1H, J = 8 Hz, –Ar), 8.00–7.95
(m, 2H, –Ar),7.78–7.50 (m, 4H, –Ar),7.44–7.36 (m, 3H,
–Ar), 5.24 (s, 1H, –CH), 2.67–2.80 (m, 2H, –CH2), 2.04
(s, 2H, –CH2), 1.26 (m, 3H, –CH3), 0.98 (s, 3H, –CH3).
A16
‑
10,10‑dimethyl‑7‑(4‑Chlorophenyl)‑10,11‑dihy‑
A
10‑9,9‑dimethyl‑12‑
(4‑fuorophenyl)‑9,10‑dihy‑
dro‑7H‑benzo[c]xanthen‑8(9H)‑one 1H NMR (CDCl3,
400 MHz): δppm 8.27 (m,2H, –Ar), 7.80–7.71 (m, 2H,
–Ar),7.47–7.39 (m, 3H, –Ar),7.26–7.18 (m,3H, –Ar),
5.48 (s,1H, –CH), 2.75–2.61 (m, 2H, –CH2), 2.04 (s, 2H,
–CH2), 1.20 (m, 3H, –CH3), 1.08(s, 3H, –CH3).
1
dro‑8H‑benzo[a]xanthen‑11(12H)‑one H NMR (CDCl3,
400 MHz): δppm 7.93–7.91 (d, 1H, J=8 Hz, –Ar), 7.79–
7.76 (m, 2H, –Ar),7.44–7.38 (m, 2H, –Ar),7.31–7.26 (m,
2H, –Ar), 6.89–6.82 (m, 2H, –Ar), 5.69 (s, 1H, –CH),
3.85(s, 3H, –OCH3), 2.56 (s, 2H, –CH2), 2.22–2.33(m, 2H,
–CH2), 1.12(s, 3H, –CH3), 0.96(s, 3H, –CH3).
1 3

Journal of the Iranian Chemical Society
A 1 7 ‑ 1 0 , 1 1 ‑ d i h y d r o ‑ 7 ‑ p h e n y l ‑ 7 H‑ b e n z o [ c ] x a n ‑
then‑8(9H)‑one 1H NMR (CDCl3, 400 MHz): δppm 7.28
(d, 1H, –Ar), 7.27–7.26 (m, 2H, –Ar), 7.25–7.16 (d, 3H,
J = 8 Hz, –Ar), 7.11–7.09 (m, 5H, –Ar), 5.47 (s, 1H, –
CH), 2.80 (m, 2H, –CH2), 2.60 (m, 2H, –CH2), 2.02 (m,
2H, –CH2).
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Conclusion
Tetrabutylammonium prolinate ionic liquid (TBAPIL) was
grafted on silica NPs through propyltriethoxysilane linkage
to aford supported catalyst TBAP@Si(CH2)3@nano-silica
(TBAPILS). SEM results revealed the successful grafting of
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of the size of 40–50 nm and well matched with the val-
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JCPDS card number. The preparation of the catalyst was also
confrmed by FT-IR analysis. The prepared catalyst TBAP-
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Acknowledgements We are thankful to Govind Ballabh Pant Univer-
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