Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of 1,3-disulfoimidazolium trifluoroacetate Ionic Liquid (IL) for Three Component Synthesis of 3,4-dihydropyrimidinones

Article abstract of DOI:10.1007/s10562-016-1922-3

Abstract: This report describes the development of six acidic composites of Y-zeolite with 1,3-disulfoimidazolium trifluoroacetate [Dsim][CF₃COO] ionic liquid (IL) and displays the gradual increase of acidic IL mediated dealumination within zeo

Full text of DOI:10.1007/s10562-016-1922-3

Catal Lett
DOI 10.1007/s10562-016-1922-3
Studies on Structural Changes and Catalytic Activity of Y-zeolite
Composites of 1,3-disulfoimidazolium trifluoroacetate
Ionic Liquid (IL) for Three Component Synthesis
of 3,4-dihydropyrimidinones
Pinky Gogoi1 · Arup Kumar Dutta1 · Ruli Borah1
Received: 30 September 2016 / Accepted: 13 November 2016
© Springer Science+Business Media New York 2017
Abstract This report describes the development of six
acidic composites of Y-zeolite with 1,3-disulfoimidazolium
trifluoroacetate [Dsim][CF3COO] ionic liquid (IL) and dis-
plays the gradual increase of acidic IL mediated dealumi-
nation within zeolite framework with increasing loading
in Powder XRD and IR studies. The structural changes of
modified framework of zeolite were analyzed by SEM-
EDX, TEM, TGA, BET and UV–Vis techniques. Out of
the six composites, the more acidic [Dsim][CF3COO]/
NaY=20% (e) composite was evaluated as heterogene-
ous catalyst for multicomponent synthesis of 3,4-dihydro-
pyrimidinones (DHPMs) under neat condition at various
temperature.
Graphical Abstract
Keywords Modified Y-zeolite · Brønsted acidic IL ·
Dealumination · Heterogeneous catalyst · DHPMs
1 Introduction
The concept of “Supported Ionic Liquid Phase” (SILP)
is pervasive and it focuses to transfer the desired proper-
ties of ionic liquid (IL) to support substances by confining
the fluid to the surface mainly through physisorption and
in a few cases by chemisorption. Such immobilization of
IL may generate ‘designer surfaces’ with properties of both
components [1–3]. Many applications of SILP have been
observed in last decade as functional materials for genera-
tion of heterogeneous catalysts, surface modifying agents,
stationary phases in separation techniques and in electro-
chemistry [4–6]. Generally, organic synthesis utilize higher
Electronic Supplementary Material The online version
of this article (doi:10.1007/s10562-016-1922-3) contains
supplementary material, which is available to authorized users.
* Ruli Borah
ruli@tezu.ernet.in
1
Department of Chemical Sciences, Tezpur University,
Napaam, 784028 Tezpur, Assam, India
Vol.:(0123456789)
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P. Gogoi et al.
amount of IL as recyclable greener medium or catalyst in
homogeneous condition with or without any catalyst. The
transfer of unique physicochemical properties of IL on
solid support combines the advantages of both homoge-
neous and heterogeneous catalysis, with facile separation
from the reaction mixture. Furthermore, based on their
capacity to stabilize the catalyst in organic reactions, such
heterogenized catalysts include several advantages over
free IL such as high thermal and water stability, leaching
stability, safe handling and easy recycling through filtra-
tion. Thus, they can effectively resolve the difficulties in
separation of products, and achieve high recoverability and
reusability of catalysts. Studies reveal that the use of immo-
bilized task-specific ILs as catalytic system also modifies
the process of catalytic reactions, affecting reaction rate,
eliminate undesirable reactions, increase product selectivity
and even enantioselective activity of asymmetric reactions
[7, 8]. For preparation of functionalized hybrid material of
ionic liquids, NaY zeolite is considered as suitable choice
for its well organized pore channels, high surface area and
thermal stability in addition to environment friendly nature
[9].
R
O
H3C
O
NH
H3C
N
O
H
Method A/B
O
O
4a-f
R
H3C
O
O
CH3
O
1
H
N
O
O
HN
2
H
H2N
NH2
Method A/B
R
R
O
4k-l
CH3
R
O
3
Method A/B
NH
N
H
Catalyst = 3 mg of 20%(e) composite
etc.
R
R=NO2, OMe,OH, Cl, H
4g-j
Method A/B :Solvent-free medium at 60oC / solvent-free grinding at ambient temperature
Scheme 1 Synthesis of 3,4-dihydropyrimidinone derivatives 4
chemists are still searching for efficient method under mild
condition with higher yields.
The present work aims to study the immobilization of
–SO3H functionalized 1,3-disulfoimidazolium trifluoroace-
tate [Dsim][CF3COO] in NaY zeolite with different loading
of IL and study their structural changes of basic framework
using Powder XRD, FT-IR, SEM-EDX, TEM, TGA, BET
and UV–Vis techniques. The acidity of each IL compos-
ite is determined from Hammett function and evaluated as
heterogeneous catalyst for three-component preparation of
Biginelli 3,4-dihydropyrimidinones in solvent-free medium
at 60°C and also under solvent-free mechanochemical
method at ambient temperature (Scheme 1). 3,4-Dihyropy-
rimidinones (DHPMs) and their derivatives are well known
heterocycles in the realm of natural and synthetic chemistry
for its diverse therapeutic and pharmacological properties
including antitumor, antiviral, anti-inflammatory and anti-
bacterial activities [10–14]. A large number of traditional
Lewis or Brønsted acids catalysts have been reported for
the formation of DHPMs with various limitations such as
strong acidic condition, high temperature reaction, longer
reaction time, use of organic solvent and non-recycling of
catalyst [15–17]. To overcome those disadvantages, sev-
eral modified protocols have been designed in the follow-
ing years by means of microwave irradiation [18], ultra-
sound irradiation [19], ionic liquids [20], mechanochemical
method [21] and different types of recyclable acidic, nan-
oparticle, metal oxides such as lanthanide triflate [22],
indium(III) halides [23], Sr(OTf)2 [24], nanomagnetic-
supported sulfonic acid [25], FeCl3-supported nanopore
silica [26], nanosilica-supported Sn(II) chloride [27], Fe3O3
[28] and boehmite nanoparticle [29], metal oxide-MWC-
NTs [30], and so on. In spite of their prospective efficacy,
2 Experimental
2.1 General Remarks
The chemicals were purchased from different commercial
suppliers in pure state. Powder XRD patterns of samples
were recorded with a Rigaku (miniflex UK) X-ray diffrac-
tometer using Cu Kα radiation (0.15418 nm) operated at
30 kVand 15 mA at a scan speed of 2° min−1 and 2θ range
1
of 5–70°. The HNMR and 13CNMR were recorded in a
JEOL 400 MHz spectrometer (δ in ppm) in DMSO-d6 sol-
vent. FT-IR spectra were recorded in Perkin-Elmer FT-IR
spectrometer. Hammett acidity of ionic liquid composite
material was measured in a UV 2550 spectrophotometer.
Shimadzu TGA 50 instrument was used for thermogravi-
metric analysis. All elemental analyses were obtained
from Perkin Elmer 20 analyzer. Melting points of DHPMs
were recorded on a Buchi-560 apparatus. Nitrogen adsorp-
tion–desorption isotherm of IL loaded NaY composites
was measured in Quantachrome ASiQWin apparatus.
Scanning electron microscopy (SEM) and Energy-disper-
sive X-ray (EDX) analyses were carried out with a JEOL
JSM-6390LV SEM equipped with an Energy-Dispersive
X-ray analyzer. Transmission electron microscopic (TEM)
images were carried out on a JEM-2010 (JEOL) instrument
equipped with a slow-scan CCD camera and at an acceler-
ating voltage of 200 kV.
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Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of…
2.1.1 General Procedure for Preparation of Six
Composites of [Dsim][CF3COO]/NaY
The synthesis of [Dsim][CF3COO]/NaY composite
involved in two steps. Initial step utilized for synthesis of
1,3-disulfoimidazolium trifluoroacetate [Dsim][CF3COO]
IL according to literature procedure [31]. Wet impregna-
tion method was used to synthesize different composition
of [Dsim][CF3COO]/NaY composite. For this purpose, the
following steps were practiced: (i) NaY zeolite were out-
gassed at 300°C for 12 h, (ii) six different weight/weight
(w/w) ratios (namely 3, 5, 10, 20, 50 and 80%) of [Dsim]
[CF3COO] ionic liquid and the zeolite powder were added
in methanol in a 50 mL round bottom flask, (iii) the suspen-
sion was refluxed in methanol for overnight, (iv) the solvent
was evaporated in rotary evaporator to get the hybrid acidic
catalyst, (v) finally it was treated at 90°C in vacuum oven
Fig. 1 Powder XRD profile of the parent and the [Dsim][CF3COO]
encapsulated NaY zeolite samples: a NaY; b [Dsim][CF3COO]/
for 3 h to remove any traces of unwanted solvent molecule.
NaY=3%;
c [Dsim][CF3COO]/NaY=5%; d [Dsim][CF3COO]/
2.1.2 General Method for the Preparation
of 3,4‑dihydropyrimidinones Derivatives (4)
NaY=10%; e [Dsim][CF3COO]/NaY=20%; f [Dsim][CF3COO]/
NaY=50%; g [Dsim][CF3COO]/NaY=80%
A mixture of aromatic aldehyde (1 mmol), ethyl acetoac-
etate/acetophenone/cyclopentanone (1 mmol) and urea
(1.5 mmol) was treated at 60°C under neat condition (or
solvent-less grinding method using mortar and pestle at
ambient temperature) utilizing 3 mg of 20% loaded [Dsim]
[CF3COO]/NaY composite for the appropriate time until
the reaction was complete. The progress of the reaction
was monitored with thin layer chromatography in presence
of EtOAc and petroleum ether (1:2) as mobile phase. The
mixture was diluted with hot ethanol (3 mL) to dissolve
the crude product. The catalyst was recovered as pure solid
residue after filtration of ethanol solution and then washed
three times with hot ethanol. The product was isolated as
solid precipitate after addition of water to the ethanol solu-
tion with vigorous stirring. Recrystallization of the crude
product from saturated ethanol gave analytically pure
product.
original structure of zeolite was destroyed above 20% (e)
loading in case of 50% (f) and 80% (g) composites which
may be due to acidic IL induced dealumination of Y-zeolite
to some extra framework Al species in presence of higher
amount of ionic liquid. Partial dealumination converted a
small portion of the crystalline zeolite structure into amor-
phous state with significant retention of the crystallinity up
to the loading 20% (e) which is reflected in Fig. 2 through
comparison of percent crystallinity of modified samples
with the parent zeolite. The relative crystallinity differences
of four different composites (b, c, d, e) and the parent zeo-
lite (a) were calculated by taking four high intensity peaks
at 2θ=15.54°, 23.54°, 26.90° and 31.28° using Eq. 1 as
follows:
(
)
% Crystallinity = AS × 100 ∕AR
(1)
where AR is integrated area of the reference material under
the peaks between a set of 2θ limits, AS represents inte-
grated area of the sample under the peaks between the same
set of 2θ limits as that of the reference.
3 Results and Discussion
3.1 Powder XRD Analysis
3.2 FT-IR Analysis
Figure 1 is presented for comparative studies of PXRD pro-
file of the parent zeolite (a) and six samples of the [Dsim]
[CF3COO]/NaY composites with different loading of 3%
(b), 5% (c), 10% (d), 20% (e), 50% (f) and 80% (g) respec-
tively in ascending order. The intensity of basic peaks of
NaY zeolite gradually decreases against increasing load-
ing of acidic [Dsim][CF3COO] up to 20% (e) composite
with complete retention of parent structure of zeolite. The
Figure 3 displays the IR spectra of NaY zeolite and six
composites within the range of 1800–400 cm−1. The IR
spectra of four composites up to 20% loading (e) also
showed slight shifting of fundamental absorption peaks
of NaY zeolite with preservation of the basic framework.
This observation again confirmed that the loaded amount
of –SO3H functionalized IL for four composites (b, c, d,
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P. Gogoi et al.
Fig. 2 Comparison of the
percent crystallinity of modified
samples with the parent zeolite
Table 1 Calculation of Si/Al ratio from IR spectra up to 20% loading
composites
Sample name
υDR (cm−1
)
Si/Al ratio
NaY
568
572
572
580
584
1.93
2.16
2.16
2.74
3.13
[Dsim][CF3COO]/NaY=3%
[Dsim][CF3COO]/NaY=5%
[Dsim][CF3COO]/NaY=10%
[Dsim][CF3COO]/NaY=20%
bands respectively for the composites (b, c, d, e). The
asymmetric T–O (Si or Al) band becomes wider in case
of 50% (f) and 80% (g) loaded composites and showed
another distinct band at 1246 cm−1 by merging of S–O
symmetric and asymmetric stretching vibration of –SO3H
groups at 1222 and 1075 cm−1 [31]. The framework sen-
sitive double-ring vibration peak of TO4 unit at 568 cm−1
shifted to around 572–584 cm−1 for the (b), (c), (d) and
(e) composites [33]. In case of highest loaded compos-
ites i.e. (f) and (g), we observed the appearance of a
small hump at 628–632 cm−1 for S–O bending vibration
of –SO3H group along with T–O–T bending vibration.
These two composites witnessed the maximum dealumi-
nation state in presence of highest amount of acidic IL
through collapsing of the basic double-ring vibration and
bending vibration of TO4 building block at 455–458 cm−1
[34]. The substantial change of absorption patterns of
highest loaded composites 50% (f) and 80% (g) revealed
the existence of large number of extra framework Al
species within these modified zeolite samples [34, 35].
From the double-ring vibration peak of various samples,
we calculated the Si/Al ratio of different composites of
Fig. 3 FT-IR profile of the parent and the [Dsim][CF3COO] sup-
ported NaY zeolite samples: a NaY; b [Dsim][CF3COO]/NaY=3%;
c [Dsim][CF3COO]/NaY=5%; d [Dsim][CF3COO]/NaY=10%; e
[Dsim][CF3COO]/NaY=20%;
[Dsim][CF3COO]/NaY=80%
f [Dsim][CF3COO]/NaY=50%; g
e) was not enough for complete destruction of Y-zeolite
framework via dealumination process. This observation
suggests the maximum permissible loading of the IL to be
20% over NaY zeolite.
The peak at 1640–1638 cm−1 for all the composites
can be assigned for bending vibration of water molecule
attached to the zeolite structure which is overlapping with
–C=N– stretching vibration of imidazolium cation [32].
The fundamental symmetric and asymmetric T–O (Si or
Al) stretching vibrations of TO4 unit of zeolite appeared
at 796–784 and at 1026–1011 cm−1 as weak to strong
1 3

Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of…
[Dsim][CF3COO]/NaY (Table 1) using the empirical
relation (Eq. 2) as proposed by Rüscher et al. [36].
350 and 450°C in Fig. 4. The loss of some water molecules
associated with zeolite structure was also clearly appeared
at high temperature calcination from the gradual decrease
of peak intensity of O–H bending vibration at 1643 cm−1 of
Y-zeolite (Supporting info. Fig. S1).
(
)(
cm−1
)
x = 3.857 − 0.00619 ꢀ
(2)
DR
where Si/Al=(1−x)/x.
The shifting of this band towards higher wavenumber in
case of higher percentage of the ionic liquid loaded com-
posites supports partial modification of the zeolite frame-
work to some EFAl species.
From the IR study, we can infer that during the prepara-
tion of composites: [Dsim][CF3COO]/NaY, the basic zeo-
lite framework was modified to some extent with the for-
mation of extra framework species of Al up to the loading
of 20% (e). Above that extensive dealumination collapsed
the basic structure of NaY in case of (f) and (g) which was
reflected in the IR spectra in the Fig. 3.
The partial preservation of zeolite framework at high
temperature was evidenced from FT-IR spectra of the 20%
(e) loaded composite at three different temperatures 250,
3.3 TGA Analysis
The comparative thermogravimetric analysis of the parent
zeolite, the hybrid materials and the ionic liquid are pre-
sented in Fig. 5A, B. In the Fig. 5A, the TGA profile of
NaY (a), 3% (b), 5% (c) loaded samples shows approximate
18–20% weight loss around 100°C without any further
decomposition up to 600°C which can be accounted for
loss of only Na+ bound water or physisorbed water from the
zeolite framework [37].The amount of such water gradually
reduces to 10–12% in case of 10% (d) and 20% (e) loaded
composites as evident from TGA plot in the Fig. 5B. Partial
dealumination caused by –SO3H moiety imparts a stabiliz-
ing effect in case of (d) and (e) composites by healing of Al
defects with migrating H4SiO4 molecules [38].
On the other hand, both the curves of 50% (f) and 80%
(g) loaded composites displayed 25% (approx.) weight
loss in two steps below 150 °C followed by continuous
weight loss up to 600 °C. These unusual observations
represent a destabilized zeolite framework for these two
Fig. 4 FT-IR spectra of the composite: [Dsim][CF3COO]/NaY=20%
(e) calcined at 250, 350 and 450°C respectively
Fig. 5 A, B TGA profile of the parent and the [Dsim][CF3COO]
encapsulated NaY zeolite samples: a NaY; b [Dsim][CF3COO]/
NaY=10%; e [Dsim][CF3COO]/NaY=20%; f [Dsim][CF3COO]/
NaY=50%; g [Dsim][CF3COO]/NaY=80%; h [Dsim][CF3COO]
NaY=3%;
c [Dsim][CF3COO]/NaY=5%; d [Dsim][CF3COO]/
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P. Gogoi et al.
composites in the highest dealumination state caused by
the acidic IL during preparation, which is also evident
from the IR and PXRD studies. The most probable cause
may be the loss of some water molecules from Al defects
consisting of four silanols (Si–OH) within the zeolite
framework created during the dealumination process
[39].
3.4 SEM-EDX Analysis
The SEM images portrayed the surface of NaY zeolite to
be consisting of perfectly cube shaped particles. As can
be seen in Fig. 6, the loaded IL particles form small clus-
ters over the zeolite surface (composites b and e) which
reduces the size and uniformity of the zeolite particles.
The distribution of such clusters is observed to be more
disordered for the 3% loaded composite. We found less
clusters on the SEM image of 20% loaded composite with
wide scattering of smaller crystallite size partclies. The
Y-zeolite structure got completely destroyed in case of
highest loaded composite via dealumination of zeolite
framework as observed from the IR study.
Fig. 7 EDX spectra of [Dsim][CF3COO]/NaY=20% (e)
3.5 TEM Analysis
The HRTEM imaging in Fig. 8 was carried out for the 20%
loaded composite. The TEM images displayed the encap-
sulation or accumulation of [Dsim][CF3COO] on the exter-
nal surface of zeolite pores with preservation of crystalline
structure of Y-zeolite framework in this composite as con-
firmed from the PXRD pattern in the Fig. 1.
The EDX spectra of (e) composite showed the pres-
ence of constituent elements of [Dsim][CF3COO] IL as
well as NaY zeolite (Fig. 7).
Fig. 6 SEM images of basic
zeolite and composites: i NaY; ii
[Dsim][CF3COO]/NaY=3%; iii
[Dsim][CF3COO]/NaY=20%;
iv [Dsim][CF3COO]/NaY=80%
1 3

Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of…
Fig. 8 TEM images of 10%
loaded composites
encapsulation of acidic [Dsim][CF3COO] which may
Table 2 Textural properties of NaY zeolite and the composite
reduce the access of zeolite pores for adsorption of N2 gas.
Sample name BET area
(m2/g)a
Micropore Micropore External
volume
area (m2/g) surface area
(m2/g)b
3.7 Acidity Determination by Hammett Plot
(cm3/g)b
NaY(a)
912.6
291.0
0.377
0.153
900.7
287.4
11.92
3.60
The Hammett acidity of four acidic composites up to 20%
loading was determined from UV–Visible Hammett plot in
Fig. 10 according to the standard method using 4-nitroani-
line as basic indicator in ethanol solution [41]. The indi-
cator showed maximum absorbance at 378 nm in ethanol.
The Hammett acidity was expressed as decreasing order
against their observed H0 values as included in supporting
documents (Tables S1–S3): [Dsim][CF3COO]/NaY=20%
(e) >[Dsim][CF3COO]/NaY=3% (b) > [Dsim][CF3COO]/
NaY=10% (d) > [Dsim][CF3COO]/NaY=5% (c). The
higher acidity of 20% (e) loaded composite can be expected
from gaining of extra stabilization through healing effects
as mentioned in the TGA analysis (Fig. 5) as well as lower
rate of clustering of smaller size particle which is clearly
visible in the SEM image (Fig. 6). The unusual order of
other three composites 3% (b), 5% (c) and 10% (d) can be
accounted for different rate of clustering and their effects
on blocking the active sites of composites for interaction
[Dsim]
[CF3COO]/
NaY=20%
aMultipoint BET, bt-plot method
3.6 BET Analysis
The BET surface area measurement was performed for the
20% (e) loaded composite and NaY zeolite to check the
change in porosity of the supported material. As evident
from the Table 2, the composite witnessed rapid loss in
surface area and pore volume compared to the basic NaY
zeolite as calculated from t-plot method (Fig. 9) [40]. The
abrupt decrease in surface area and micropore volume in
case of the 0.2 (e) composite mainly refers to modifica-
tion of zeolite framework into non-porous surface through
1 3

P. Gogoi et al.
Fig. 9 I N2 physisorption Isotherms for NaY and composite (e); II pore size distribution plot for NaY; III pore size distribution plot for com-
posite (e); IV t-plot for NaY; V t-plot for composite (e)
1 3

Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of…
Fig. 10 Hammett plots of the composites (b) [Dsim][CF3COO]/
NaY=3%; (c) [Dsim][CF3COO]/NaY=5%; (d) [Dsim][CF3COO]/
NaY=10%; (e) [Dsim][CF3COO]/NaY=20% in three conditions; A
Hammett plot by mixing equal concentration of the indicator and the
composites; B Hammett plot by mixing 1:4 ratio of the indicator and
the composites; C Hammett plot by mixing 2:3 ratio of the indicator
and the composites
with the basic indicator. The order of Hammett acidity did
not change in Fig. 10B, C against the mixing of 1:4 and 2:3
ratio of the indicator and the respective four composite.
of four composites namely 3% (b), 5% (c), 10% (d) and 20%
(e) with 10 mg under solvent-free method at 80°C. Though
there was small difference in the time required for comple-
tion of the reaction, the 20% loaded composite afforded the
best result (entries 2–4). With the sole IL, it took 15 min
to complete the reaction (entry 1). By reducing the amount
of 20% loaded composite at 80 and 60°C (entries 6–8), we
observed excellent results in both cases (entry 7, 8) using
3 mg of the composite [Dsim][CF3COO]/NaY=20% (e)
for 2–10 min reaction.
3.8 Catalytic Performance
To evaluate the activity of the catalysts under different con-
ditions systematically, we choose the three component reac-
tion of ethyl acetoacetate (1 mmol), benzaldehyde(1 mmol)
and urea (1.5 mmol) as the model reaction under solvent
free condition at different temperatures and the results are
presented in Table 3. Due to small difference in acidity of
the synthesized catalysts as determined through the Ham-
mett plots (Fig. 10A), we tested the catalytic performance
For the sake of much milder condition to be devel-
oped, the reaction was carried out at room temperature
using mechanical energy. It only took 15 min to com-
plete the reaction with an excellent yield of 93% (entry
1 3

P. Gogoi et al.
Table 3 Optimization of
the reaction condition for the
synthesis of model compound
(4a)
Entry
Catalyst
Amount of the
catalyst (mg)
Temp. (°C)
Time (min)
Product
yielda (4a)
(%)
1
2
3
4
5
6
7
8
9
[Dsim][CF3COO]
[Dsim][CF3COO]/NaY=3%
[Dsim][CF3COO]/NaY=5%
[Dsim][CF3COO]/NaY=10%
10
10
10
10
10
5
3
3
3
80
80
80
80
80
80
80
60
10
4
7
5
2
2
2
10
15
93
94
91
92
97
96
94
96
95
[Dsim][CF3COO]/NaY=20%
-do-
-do-
-do-
-do-
r.t. grinding
aIsolated yields
9). Therefore, we extended our studies for the preparation
of other derivatives of DHPMs through variation of aro-
matic aldehydes and keto compound in presence of 3 mg
of 20% (e) loaded catalyst under solvent-free medium at
60 °C and at mild condition using grinding method. All
these observations were included in Table 4.
3.9 Recyclability Profile of the Catalyst
The recyclability profile of 20% loaded composite (e) was
evaluated for the preparation of 4a from the mixture of
3 mmol of β-keto ester and benzaldehyde with 4.5 mmol
of urea under the optimized condition and it was found
that the catalyst maintains very good activity up to 6th
repetitive cycle (Fig. 12). After the reaction was over,
the catalyst surface was washed with cold water and
hot EtOH and then it was dried in oven 70 °C to make
it ready for the next cycles of reactions. With increased
number of cycles, the catalyst slowly lost its efficiency
which was reflecting in decreasing percentage yields of
Single crystal X-ray analysis was performed on the
3,4-dihydropyrimidine derivative 4f (Table 4, entry 6)
which confirmed the presence of basic DHPM unit in
Fig. 11 [44].
Table 4 Substrate scope study
Entry
β-ketoester/ketone
Aldehyde
Time (min)
(method)
Product yield
for DHPMs derivatives using
20% loaded catalyst
(%)a,b,c (4a−l)
A
B
A
B
1
2
3
4
5
6
7
8
CH3COCH2COOC2H
-do-
-do-
-do-
-do-
-do-
C6H5COCH3
-do-
-do-
-do-
Cyclopentanone
-do-
C6H5CHO
10
15
20
18
30
35
15
20
15
28
25
25
15
18
24
25
30
35
30
30
30
35
32
35
96
94
92
93
94
92
94
89
95
85
92
93
93
92
90
93
91
90
89
85
92
82
87d
88
4-NO2C6H4CHO
4-OCH3C6H4CHO
4-OHC6H4CHO
4-ClC6H4CHO
2,4-ClC6H3CHO
C6H5CHO
4-NO2C6H4CHO
4-CH3OC6H4CHO
1-Naphthaldehyde
C6H5CHO
9
10
11
12
4-NO2C6H4CHO
aIsolated yields
bMethod A: reactions were performed at 60°C, Method B: reactions were conducted using mortar and pes-
tle under solvent-free grinding at ambient temperature
cMelting points of known compounds were compared with the literature values in supporting file [26, 27,
42, 43]
dUsing 2 equivalent of aldehydes
1 3

Studies on Structural Changes and Catalytic Activity of Y-zeolite Composites of…
Fig. 11 Single crystal structure of 4f
Fig. 13 FT-IR spectra for the reused catalyst
4 Conclusion
In this study, we analyzed the structural changes of par-
ent NaY zeolite within the framework of modified com-
posites [Dsim][CF3COO]/NaY using different analytical
techniques from which we identified 20% (e) loading
as the best acidic composite from the Hammett func-
tion with thermal stability up to 450 °C. Loading above
this percentage was harmful for the zeolite framework
because of maximum dealumination as evidenced from
the FT-IR and PXRD patterns of the 50% (f) and 80%
(g) loading. Formation of EFAl species on loading of the
acidic IL affected the Si/Al ratio of the composites which
in turn may also affect the acidity scale of the compos-
ites. The strong acidic composite 20% (e) was examined
as heterogeneous catalyst for synthesis of DHPMs deriva-
tives under solvent-free medium at 60 °C and at ambient
temperature using solvent-free grinding method.
Fig. 12 Recyclability profile for the composite: [Dsim][CF3COO]/
NaY=20% (e)
expected product with gradual rise of reaction time for
completion of the reaction.
3.10 Characterization of the Spent Catalyst
Acknowledgements The authors are thankful to Sophisticated
Analytical Instrumentation Centre, Tezpur University for analyses of
various samples for this work and also acknowledge University Grant
Commission, India for granting Junior Research Fellowship (NF-
OBC) to P. Gogoi.
The spent catalyst was again subjected for FT-IR analysis
(Fig. 13) after every alternate cycle to observe the effect
of repeated thermal treatment and washing with hot eth-
anol on the ratio of Si/Al for dealumination which may
slightly decrease the catalytic activity of spent catalyst
in next consecutive cycles. Table S4 in supporting file
shows the retention of initial Si/Al ratio up to 4th cycle
after that it indicates a higher value of Si/Al ratio due to
formation of extraframework Al species from 6th cycle
onward.
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