Synthesis of mesoporous Ca-MCM catalysts and their use in suitable multicomponent synthesis of polyfunctionalized pyrans

Article abstract of DOI:10.1007/s11164-016-2749-7

Mesoporous Ca-MCM catalysts were prepared using a mixture of CaCO₃, TEOS, cetyl trimethyl ammonium bromide (CTAB), triethanolamine (TEA), ethanol and H₂O. Three catalysts with different CaCO₃ contents, M-Ca 1?%, M-Ca 5?% and M-Ca 10?%, respectively, were prepared and characterized by N₂ physisorption, XRD, FT-IR, XPS, TPD-CO₂ and Pyridine-FTIR. A green and simple protocol was developed for the synthesis of 6-amino-4H-pyran scaffolds through a multicomponent coupling reaction of an aldehyde, malononitrile, and 1,3-dicarbonyl compound in different reaction solvents. This procedure was performed at room temperature (20?°C), obtaining good and excellent yields of 4H-pyran derivatives. The mesoporous materials are insoluble in polar media, which allows easy removal of the reaction products without affecting their catalytic activity. The leaching test showed an excellent stability, and Ca-MCM catalysts can be used three times without appreciable loss of their catalytic activity.

Full text of DOI:10.1007/s11164-016-2749-7

Res Chem Intermed
DOI 10.1007/s11164-016-2749-7
Synthesis of mesoporous Ca-MCM catalysts
and their use in suitable multicomponent synthesis
of polyfunctionalized pyrans
2
Eliana Nope1 Jose J. Martınez Hugo A. Rojas2
•
•
•
´
•
´
Angel G. Sathicq Gustavo P. Romanelli1,3
´
1
Received: 27 June 2016 / Accepted: 30 September 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Mesoporous Ca-MCM catalysts were prepared using a mixture of CaCO3,
TEOS, cetyl trimethyl ammonium bromide (CTAB), triethanolamine (TEA), etha-
nol and H2O. Three catalysts with different CaCO3 contents, M-Ca 1 %, M-Ca 5 %
and M-Ca 10 %, respectively, were prepared and characterized by N2 physisorption,
XRD, FT-IR, XPS, TPD-CO2 and Pyridine-FTIR. A green and simple protocol was
developed for the synthesis of 6-amino-4H-pyran scaffolds through a multicom-
ponent coupling reaction of an aldehyde, malononitrile, and 1,3-dicarbonyl com-
pound in different reaction solvents. This procedure was performed at room
temperature (20 °C), obtaining good and excellent yields of 4H-pyran derivatives.
The mesoporous materials are insoluble in polar media, which allows easy removal
of the reaction products without affecting their catalytic activity. The leaching test
showed an excellent stability, and Ca-MCM catalysts can be used three times
without appreciable loss of their catalytic activity.
Keywords Mesoporous Ca-MCM Á Polyfunctionalized 4H pyrans Á
Multicomponent reaction
´
Jose J. Martınez
jose.martinez@uptc.edu.co
´
&
&
1
Gustavo P. Romanelli
gpr@quimica.unlp.edu.ar
´
Centro de Investigacion y Desarrollo en Ciencias Aplicadas ‘Dr. Jorge J. Ronco’ (CINDECA-
CCT-CONICET), Universidad Nacional de La Plata, Calle 47 No. 257, B1900AJK La Plata,
Argentina
2
3
´
´
Escuela de Ciencias Quımicas, Facultad de Ciencias, Universidad Pedagogica y Tecnologica de
Colombia UPTC, Avenida Central del Norte, Tunja, Boyaca, Colombia
´
´
´
Catedra de Quımica Organica, CISAV, Facultad de Ciencias Agrarias y Forestales, Universidad
Nacional de La Plata, La Plata, Argentina
´
´
123

E. Nope et al.
Introduction
Heterogeneous catalysis plays an important role in the production of chemical
products. The use of heterogeneous catalysis has several benefits; for example, it can
be separated easily by simple filtration, which is a relevant topic for industrial
manufacturing processes due to economical and environmental considerations. The
development of inexpensive, mild, reusable, nontoxic catalysts tolerating a wide range
of temperatures, and easy and safe disposal remains an issue of great interest [1–3].
The need for clean processes imposes the use of different environmentally
friendly reaction conditions such as a procedure at room temperature, the
elimination of toxic solvent, transformation with high atom economy and the use
of a recyclable catalyst [4]. In particular, ethanol is considered a green solvent,
because it poses few human health and environmental risks, and ethanol is mostly
derived from the fermentation of biomass feedstocks [5].
Another aspect that contributes to achieving a cleaner process is the substitution
of inorganic or organic liquid catalysts, such as aqueous sodium and potassium
hydroxide or sodium methoxide or terbutoxide, for a reusable solid basic catalyst
Recently, different materials, such as metal oxides, rare earth oxides, modified
hydrotalcites, clays, natural phosphates, anion exchanger resin, and the alkylam-
monium group on MCM-41, have been used to catalyze different transformations,
under mild reaction conditions, with high selectivity, easy recovery, catalyst
recycling, and simple product isolation [6, 7]. In this direction, Tanabe and
¨
Holderich reviewed the industrial applications of solid acid and base catalysts. They
counted more than 100 industrial processes in which solid acid, base, and acid–base
bifunctional catalysts are used [8].
Recently, mesoporous molecular sieves (such as MCM-41, MCM-48, and SBA-
15) have attracted much attention in catalysis due to the specific characteristics of
these materials that include high surface area, well-defined pore shape, narrow pore
size distribution, and good thermal stability [9].
These materials are very attractive for heterogeneous reactions of large organic
molecules for which microporous zeolites cannot be used. Kubota et al. obtained
excellent results in the Knoevenagel condensation using Si-MCM-41 molecular
sieves. Recently, Pirouzmand and coworkers prepared Ca/MCM-41 via direct and
post-synthesis methods, and they studied the effect of the cationic template and
metal incorporation method on their basicity and catalytic performance in the
transesterification reaction of canola oil [10, 11].
On the other hand, multicomponent reactions (MCRs) are a notable methodology
in heterocyclic synthesis for obtaining molecular diversity. MCRs increase the
reaction efficiency due to their high atom economy, which involves performing
several steps without isolating intermediates or changing the reaction conditions.
MCRs have attracted attention in the area of combinatorial chemistry due to their
efficiency [12, 13].
Furthermore, heterocyclic compounds bearing the 4H-pyran skeleton are an
important family of compounds that play a key role in organic synthesis, because
they are present in a variety of synthetic compounds. Synthetic molecules
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
containing the pyran moiety have interesting pharmacological and biological
properties [14]. These compounds are used as anticancer, spasmolytic, anticoag-
ulant, anti-anaphylactic, neuroprotective, HIV-inhibitory, antimicrobial, antifungal,
antioxidant agents, and some have diuretic activity [15]. 4H-Pyrans containing a
heterocyclic ring are extensively used in pharmacology; for example, 4-phenyl-4H-
pyrans have been identified as potent and specific IKCa channel blockers, and some
2-amino-4H-pyrans are important photoactive materials [16].
The most common synthesis of 2-amino-4-aryl-3-cyano-4H-pyran derivatives is
usually a two-step reaction carried out between a Michael acceptor (arylidene-
malononitriles) and b-dicarbonyl compounds in the presence of a base as catalyst
(piperidine, morpholine or metal alkoxides) using ethanol or other solvents (DMSO,
DMF) as reaction media. Most of these methods involve volatile solvents that
require longer reaction times and the catalyst is difficult to recover [17].
To solve these disadvantages, methods that involve recyclable solid basic
catalysts have been reported. For example, FeNi3–SiO2 [18], potassium phthalimide
(POPI) [19], nanosilica-supported tin (II) chloride [12], imine-based silica-
functionalized copper(II) [20], nanocrystalline ZnO [15], sodium acetate [21]
copper II oxymetasilicate [22], silica nanoparticles [17], sodium borate [23], ZnO/
MgO [24], ammonium acetate [25], and Mg/La mixed oxide [26] afforded excellent
yields of 4H pyrans.
In the present paper, we report the synthesis and characterization of three
mesoporous solids containing CaCO3. In addition, we studied the application of
these recyclable solid catalysts in a simple, convenient, efficient, and eco-friendly
process for the multicomponent preparation of 2-amino-4-aryl-3-cyano-4H-pyran
derivatives (Fig. 1). To the best of our knowledge, this is the first application of this
type of solids in multicomponent reactions using a green and simple protocol at
room temperature for the synthesis of 6-amino-4H-pyran scaffolds.
Experimental section
General
The precursors and additives tetraethyl orthosilicate (TEOS), CaCO3, cetyl
trimethylammonium bromide (CTAB), ethanol (EtOH), NH4OH, and tri-
ethanolamine (TEA) were used in the catalyst preparation. Aromatic aldehydes
1a
2
3a
4a
Fig. 1 Synthesis of 6-amino 4H-pyran derivative via a three-component coupling of benzaldehyde 1a,
malononitrile 2 and ethylacetoacetate 3a
123

E. Nope et al.
such as malononitrile and 1,3-diketo compound were used in the synthesis of 4H-
pyrans. All chemicals were purchased from Aldrich and used without further
purification.
Benzylidene malononitrile was prepared following the procedure described in the
literature [27]. The reaction yields were calculated from pure products. All the
products were identified by comparison of melting point (mp), thin layer
1
chromatography (TLC), and nuclear magnetic resonance (NMR) data. H and 13C
NMR spectra were recorded on a Bruker (400 MHz) spectrometer using TMS as
internal reference. Chemical shifts for 1H NMR and 13C NMR spectra were reported
using (CDCl3) as solvent. 13C NMR spectra were recorded at 100 MHz.
Catalyst syntheses
Ca-MCM solids (M-Ca 1 %, M-Ca 5 % and M-Ca 10 %) were prepared at different
concentrations of CaCO3 using ethanol as co-solvent at room temperature. The
molar composition of the gels was: 1 SiO2: X CaCO3: 0.3 CTAB: 170 H2O: 74.8
EtOH: 4.7 NH4OH: 0.2 TEA. Where, X was the % CaCO3 incorporated (1, 5, and
10 %, respectively). CTAB and TEA were used as template agents. In a typical
procedure, a solution of CTAB and NH4OH and CaCO3 was mixed carefully in
ethanol for 60 min. Then, a solution of TEOS and TEA was added dropwise and
stirred for 24 h. The pH was 10.5. The gels were dried at room temperature and then
calcined in air flow (10 cm3 9 min-1) at 550 °C. Si-MCM was synthetized
following the same procedure.
Catalyst characterization
Textural properties
N2-sorption isotherms at 77 K were measured in Micromeritics ASAP 2020
equipment. Samples were previously evacuated at 623 K for 16 h. The surface area
was calculated using a multipoint Brunauer–Emmett–Teller (BET) model in the
range of P/P0 = 0.05 - 0.35 in the adsorption isotherm. The pore volume was
calculated from the amount of N2 adsorbed at the highest relative pressure of 0.99,
and the pore diameter was calculated from the Barrett–Joyner–Halenda (BJH)
equation.
X-ray diffraction
X-ray diffraction studies were performed in a PANalytical X-Pert-Pro diffractome-
˚
ter using nickel filtered Cu ka radiation (k = 1.54056 A). Spectra were obtained in
the range 1.5°–4° and 10°–100° using a count time of 1 s and a step size of 0.05°.
˚
The unit cell parameter (A) was calculated using the formula a = H6d, where
d represents the d (211) reflection.
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
Fourier transform infrared spectroscopy
The FTIR spectra were recorded on KBr pellets on a Perkin–Elmer FTIR 2000
spectrometer.
XPS analysis
The XPS data were obtained in a Thermo Scientific Escalab 250 XI spectrometer.
Measurements were performed at room temperature with monochromatic Al Ka
(hv = 1486.6 eV) radiation. The analyzer was operated at 25 eV pass energy and a
step size 0.05 eV. The pressure in the analytical chamber was 6.3 9 10-9 mBar.
The C 1 s signal (284.6 eV) was used as internal energy reference in every
experiment. The determination of core-level peak positions was accomplished after
background subtraction according to Shirley using peak XPS software. Peaks in a
spectrum were fitted by a combination of Gauss and Lorentz curves, which also
allowed the separation of overlapping peaks.
Temperature-programmed desorption of CO2 (TPD-CO2)
The nature of basic sites was studied by temperature-programmed desorption of
CO2. TPD analysis was performed on a Micromeritics AutoChem 2920. Prior to the
adsorption of CO2, the samples were preheated at 300 °C in He flow (25 mL/min)
for 1 h. Then, the adsorption of CO2 (10 % in helium) at 50 mL/min was carried out
at 120 °C for 30 min. The samples were purged with helium (25 mL/min) for 1 h.
The TPD began at 90 °C K with a heating rate of 10 °C/min to reach 900 °C.
Pyridine adsorption followed by FTIR
The nature of acid sites was studied by pyridine (Pyr) adsorption, followed by FTIR.
Infrared spectra were collected using Nicolet iS50 equipment with an in situ diffuse
reflectance cell (Harrick, Praying Mantis). For the determination of acid sites, a
pretreatment at 573 K was performed with a helium flow of 30 mL/min for 1 h to
clean the surface of possible contaminants. Subsequently, the samples were
gradually cooled down to room temperature and then pyridine adsorption was
performed for 1 h to 10 mL/min. After adsorption, the gas phase was removed by
evacuation with a helium flow at 30 mL/min at 573 K.
General procedure for the synthesis of 4H-pyranes
The catalytic activity of the CaO-MCM catalysts was evaluated in the formation of
4H-pyranes. The reaction was performed in a round bottom flask equipped with a
condenser and immersed in an oil bath. Briefly, a mixture of aldehyde (1 mmol),
malononitrile (1 mmol), 1,3-diketo compound (1 mmol), and the catalysts (30 mg)
was stirred at room temperature (20 °C) in 2 mL ethanol. The progress of the
reaction was monitored by TLC (EtOAc/hexane = 1:1). After completion of the
reaction, 2 mL of ethanol was added to the reaction mixture to remove the catalyst.
123

E. Nope et al.
Upon concentration of the reaction mixture, the desired product crystallized out.
The crude product was recrystallized from ethanol to give a pure product. As the
purity of the product was high, no further recrystallization was required.
Catalyst reuse
Reuse stability tests of the catalysts were carried out by running five consecutive
experiments, under the same reaction conditions. After each test, the catalyst was
separated from the reaction mixture by filtration, washed with ethanol (2 9 2 mL),
dried under vacuum, and then reused.
H-NMR and 13C-NMR spectra of selected pyranes
Ethyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-3-carboxylate (1) 1H NMR
(400 MHz, CDCl3): d 1.15 (t, 3H, J = 7.2 Hz), 2.41 (s, 3H), 4.00 (m, 2H,
J = 7.2 Hz), 4.40 (s, 1H), 4.63 (s, 2H), 7.22–7.37 (m, 5H); 13C NMR (100 MHz,
CDCl3): d 13.8, 18.5, 38.4, 60.2, 62.3, 108.2, 118.9, 127.3, 127.7, 128.4, 143.6,
156.5, 156.6, 157.5, 165.3
Ethyl 6-amino-5-cyano-2-methyl-4-p-tolyl-4H-pyran-3-carboxylate (2) 1H NMR
(400 MHz, CDCl3): d 1.09 (t, 3H, J = 7.2 Hz), 2.30 (s, 3H), 2.38 (s, 3H), 4.06 (q,
2H, J = 7.2 Hz), 4.39 (s, 1H), 4.54 (s, 2H), 7.10 (m, 4H); 13C NMR (100 MHz,
CDCl3): d 13.7, 18.3, 21.4, 38.2, 60.9, 62.2, 108.2, 119.1, 127.2, 129.1, 136.7,
140.9, 156.5, 157.3, 166.2
Ethyl
6-amino-5-cyano-2-methyl-4-(3-nitrophenyl)-4H-pyran-3-carboxylate
(4) 1H NMR (400 MHz, CDCl3): d 1.12 (3H, t, J = 7.2 Hz), 2.40 (3H, s),
4.00–4.06 (2H, m), 4.55 (1H, s), 4.85 (2H, s), 7.46–7.52 (2H, m), 8.03–8.08 (2H,
m); 13C NMR (100 MHz, CDCl3): d 14.2, 18.8, 39.1, 61.1, 107.1, 118.6, 122.5,
122.6, 129.7, 134.1, 146.3, 148.5, 158.1, 165.5
Ethyl
6-amino-5-cyano-4-(3-hydroxyphenyl)-2-methyl-4H-pyran-3-carboxylate
(5) 1HNMR (400 MHz, CDCl3), d 1.00 (t, 3H, J = 7.2 Hz), 2.37 (s, 3H), 4.05
(q, 2H, J = 7.2 Hz), 4.34 (s, 1H), 4.72 (s, 2H), 6.63–6.69 (m, 3H), 7.10 (t, 1H), 8.80
(s, 1H); 13CNMR (100 MHz, CDCl3), d 13.8, 15.4, 38.8, 58.2, 61.0, 107.1, 112.2,
114.9, 117.4, 121.7, 124.1, 129.8, 143.4, 155.8, 159.1, 167.2
Ethyl 6-amino-5-cyano-2-methyl-4-(3,4,5-trimethoxyphenyl)-4H-pyran-3-carboxy-
late (8) 1H NMR (400 MHz, CDCl3), d 1.12 (t, 3H, J = 7.2 Hz), 2.45 (s, 3H),
3.82 (s, 9H), 4.10 (q, 2H, J = 7.2 Hz), 4.43 (s, 1H), 4.68 (s, 2H), 6.53 (s, 2H); 13C
NMR (100 MHz, CDCl3), d 13.8, 18.8, 56.0, 60.6, 62.4, 104.3, 107.7, 137.1, 139.4,
153.3, 156.1, 157.2, 165.9
Methyl 6-amino-5-cyano-2-methyl-4-phenyl-4H-pyran-3-carboxylate (10) 1H
NMR (400 MHz, CDCl3), d 2.30 (s, 3H), 4.00 (s, 3H), 4.40 (s, 1H), 4.50 (s, 2H),
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
7.15–7.28 (m, 5H); 13C NMR (100 MHz, CDCl3), d 18.0, 38.4, 51.9, 62.0, 107.5,
118.7, 127.2, 127.4, 128.4, 143.5, 157.0, 157.4, 166.5
Methyl
6-amino-4-(2-chlorophenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate
(12) 1H NMR (400 MHz, CDCl3), d 2.30 (s, 3H), 3.60 (s, 3H), 4.53 (s, 1H),
5.00 (s, 2H), 7.08–7.30 (m, 4H); 13C NMR (100 MHz, CDCl3), d 18.0, 36.5, 51.2,
61.1, 106.8, 118.0, 127.3, 128.4, 128.8, 129.8, 133.1, 140.5, 157.7, 157.8, 166.2
Results and discussion
The nitrogen sorption isotherms are shown in Fig. 2. The isotherms are of type IV in
the IUPAC classification. In all samples, the capillary condensation step occurs at a
relative pressure of *0.2. The absence of a hysteresis loop in this region indicates a
high quality mesoporous framework in the Ca-MCM solids. The pore size
distributions calculated according to the Barrett, Joyner and Halenda method (BJH-
method) suggest a very narrow pore size distribution in Si-MCM and Ca-MCM,
which is centered between 2.2 and 2.7 nm depending on the CaCO3 content. This
slight change in pore size is possibly due to the presence of calcium carbonate inside
the channels.
(a)
22
(b)
26
24
22
20
18
16
14
12
10
8
20
18
16
14
12
10
8
6
4
2
0
10
5
0
10
100
1000
10
100
1000
1,0
Pore width (Å)
Pore width (Å)
6
6
0,0
0,2
0,4
0,6
0,8
1,0
0,0
0,2
0,4
0,6
0,8
Relative pressure, p/p°
Relative pressure, p/p°
(c)
(d)
20
18
16
14
12
10
8
16
14
12
10
8
6
4
2
0
4
2
0
10
100
1000
6
10
100
1000
6
Pore width (Å)
Pore width (Å)
4
4
0,0
0,0
0,2
0,4
0,6 0,8
1,0
0,2
0,4
0,6 0,8
1,0
Relative pressure, p/p°
Relative pressure, p/p°
Fig. 2 Nitrogen sorption isotherms of the calcined Ca-MCM solids. a Si-MCM, b Ca-MCM 1 %, c Ca-
MCM 5 %, d Ca-MCM 10 %
123

E. Nope et al.
The textural properties of all prepared solids are summarized in Table 1. In
general, the solids have high surface areas (961–1590 m2 g-1) and pore volumes
between 0.54 and 0.9 cm3 g-1. The thickness of the silica pore walls can be easily
calculated using the reflection angle obtained for each sample and the pore diameter.
The values are between 1.1 and 1.3 nm, indicating the good quality of the
mesoporous structure. However, the thickness of Ca-MCM is less compared with
that of Si-MCM. It is well recognized that the pore wall thickness is related to
longer crystallization times; however, the poor solubility of CaCO3 allows that not
all the CaCO3 is included inside the pores of mesoporous solid, and there is not
incorporation of Ca into MCM framework resulting in a lower thickness of Ca-
MCM compared with Si-MCM. It is possible that in our solids Ca-MCM have some
clusters of CaCO3; however, the activity catalytic shown is similarly independent of
CaCO3 content, and this being the most interesting result in this study.
The X-ray diffraction patterns at low angle range (1.5°–4°, Fig. 3a) of calcined
Ca-MCM are shown in Fig. 1a. A peak at 2h * 2.4° to 2.7° in all samples can be
observed (Table 1). The incorporation of CaCO3 slightly modifies the interplanar
distance in the mesoporous solid sample due to the presence of CaCO3 particles
inside the channels. The XRD pattern at wide angle (Fig. 3b) shows a well-defined
diffraction peak and a broad peak at 22° associated with SiO2. Other peaks perfectly
match the standard calcite pattern (JCPDS 88-1807, red line). The peaks increase
with the calcite contents in the mesoporous structure. The crystal size of CaCO3
using the (1 0 4) reflection peak at 2h = 29.36° is near 3.0 nm. This size is similar
in every catalyst (Fig. 3).
The incorporation of CaCO3 was also followed by FTIR (Fig. 4). In the region of
1050–1100 cm-1 a band assigned to Si–O bond vibration appears [28]. The
displacement at higher wave number of this band is attributed to the interaction Ca–
O–Si, which is more evident with increasing calcite content. This phenomenon also,
has been observed in Ca-SBA [29].
Figure 5 shows the XPS spectra of the Ca 2p core levels for all Ca-MCM
catalysts. The Ca2p3/2 core level binding energy (BE) position appears at 346 eV,
which is characteristic of a calcite structure. This result confirms that the calcination
temperature for preparing the Ca-MCM solids does not modify the CaCO3 structure.
CO2-TPD studies were used to compare the basicity of Ca-MCM solids. Figure 6
depicts the temperature-programmed desorption spectra of two representative Ca-
MCM catalysts (1 and 5 %). The peak observed at around 600 °C could be assigned
to the thermal decomposition of CaCO3, so only CO2 desorption is observed in the
range of 100–400 °C (inset in Fig. 5). The desorption of CO2 at 150 °C showed the
existence of –OH groups associated with weak basic sites, while the signal at around
280 °C corresponds to moderate strength basicity. The signal at 150 °C is well
defined in the Ca-MCM 5 % catalyst (Fig. 4b). According to the integral intensity
of the desorption curves, the total basicity of the Ca-MCM catalysts increases with
the calcite content.
The FTIR spectra of pyridine adsorbed on the surface of MCM and Ca-MCM are
¨
shown in Fig. 7. The solid CaCO3-MCM present both Lewis and Bronsted acid sites
related with the mesoporous framework. The Lewis acid sites (L) on the surface can
be recognized with the bands at 1444 and 1577 cm-1 [30]. This band decreases with
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
123

E. Nope et al.
(a)
(b)
d
c
d
c
b
a
b
a
1,5
3,0
4,5
6,0
20
40
60
80
100
2 theta (degree)
2 theta (degree)
Fig. 3 X-ray diffraction patterns at (a) low-angle range and (b) high-angle range of the calcined Ca-
MCM: a Si-MCM, b Ca-MCM 1 %, c Ca-MCM 5 %, d Ca-MCM 10 %
a.
b.
c.
d.
1600
1400
1200
1000
800
Wavenumber (cm-1)
Fig. 4 FTIR spectra for a Si-MCM, b Ca-MCM 1 %, c Ca-MCM 5 %, d Ca-MCM 10 %
Fig. 5 XPS spectra of the Ca
2p core levels of the calcined
Ca-MCM. a Ca-MCM 1 %,
b Ca-MCM 5 %, c Ca-MCM
10 %
c.
b.
a.
342
344
346
348
350
352
354
356
B.E (e.V)
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
Fig. 6 CO2 desorption patterns
for a Ca-MCM 1 % and b Ca-
MCM 5 %
b.
a.
100
200
300
400
Temperature (°C)
b.
a.
0
200
400
600
800
1000
Temperature (°C)
Fig. 7 FTIR spectra of pyridine
adsorbed for a MCM, b Ca-
MCM 1 %, c Ca-MCM 5 % and
d Ca-MCM 10 %
L
B
L
NI
B
B
B-L
a
b
c
d
1650
1600
1550
1500
1450
1400
Wavenumber ( )
cm-1
the presence of CaCO3. The bands at 1540 and 1596 cm-1 in MCM are associated
with Bronsted acid sites (B). The band at 1540 cm-1 is attributed to formation of the
¨
pyridinium ion, and the signal at 1596 cm-1 corresponds to Bronsted acid sites,
¨
which are not strong enough to protonate pyridine, but these sites could form
hydrogen bonded adducts [31]. It is interesting to note that these bands decrease in
Ca-MCM solids, but a new band at 1560 cm-1 appears also, and this has been
-1
associated with Bronsted acid sites [32]. The signal in 1490 cm is characteristic
¨
of Lewis–Bronsted acid sites (B–L) [29].
¨
Catalytic test
Initially, we focused on the evaluation of different catalysts for the model reaction
between benzaldehyde (1a), malononitrile (2) and ethylacetoacetate (3a) in ethanol
at room temperature. We used Ca-MCM 1, 5 and 10 % to improve the yield for the
synthesis of 2-amino-4H-pyran compounds. The reaction without catalyst (Table 2,
entry 1) gives only the product of condensation between benzaldehyde and
malononitrile. When commercial bulk CaCO3 is used, a yield of 4H-pyran is
123

E. Nope et al.
Ca content
Table 2 Optimization of reaction conditions using different synthetized catalysts
Yield intermediate I
Yield 4H-pyran
Blank
95
5
0
90
98
86
86
0
CaCO3
100
0.9
4.2
8.6
Ca-MCM 1 %
Ca-MCM 5 %
Ca-MCM 10 %
7
6
7
Reaction conditions Benzaldehyde (1 mmol), malononitrile (1 mmol), and ethyl acetoacetate (1 mmol)
were stirred in 2 mL of ethanol in the presence of 30 mg of M-Ca 1 % at room temperature (20 °C) for
12 h
obtained (Table 2, entry 2), indicating that the presence of a catalyst is necessary to
improve the reaction. As shown in Table 2, a most interesting result is obtained with
MCM-Ca 1 %. In this case, the yield to 4H-pyran is 84 % at room temperature
(20 °C) in 12 h, and the calcium content is very low, only 0.9 % (Table 2, entry 3).
Finally, the yields for 4H-pyran using Ca-MCM 5 and 10 % catalysts are similar
and independent of the load of CaCO3 (Table 2, entries 4 and 5). This indicates that
less than 1 % of calcium is sufficient to perform the reaction with excellent yields
and selectivity.
Then, we performed the reaction in various solvents in order to optimize the
reaction conditions using Ca-MCM 1 % as catalyst (Table 3). The results confirmed
that the solvent has a great effect on the catalytic activity of Ca-MCM. The reaction
was favored by the presence of polar solvents such as ethanol, methanol or water
(Table 3, entries 1–3), and the yields were very low when we used less polar
solvents such as toluene or chloroform, 38 and 45 %, respectively (Table 3, entries
5 and 6). The highest yield was obtained with ethanol, 98 % (Table 3, entry 1).
The reuse of the catalyst was evaluated under the same reaction conditions and
proportions (1 mmol each substrate, 2 mL of ethanol, 30 mg of Ca-MCM 1 %,
20 °C, 12 h) in five consecutive cycles of reaction. The separation is by simple
filtration due to the hydrophobicity of the Ca-MCM solid in comparison with
Table 3 Solvent screening for the model reaction
Entry
Solvent
Yields (%)
1
2
3
4
5
6
Ethanol
98
91
85
45
38
35
Methanol
Water
Acetone
Toluene
Chloroform
Reaction conditions Benzaldehyde (1 mmol), malononitrile (1 mmol), and ethyl acetoacetate (1 mmol)
were stirred in 2 mL of ethanol in the presence of 30 mg of M-Ca 1 % at room temperature (20 °C) for
12 h
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
Table 4 Catalyst reuse, effect on 4H-pyran (%)
Entry
Catalytic cycle
Yield (%)
1
2
3
4
5
1
2
3
4
5
98
95
95
94
93
Reaction conditions Benzaldehyde (1 mmol), malononitrile (1 mmol), and ethyl acetoacetate (1 mmol)
were stirred in 2 mL of ethanol in the presence of 30 mg of M-Ca 1 % at room temperature (20 °C) for
12 h
CaCO3. After completion of the reaction, the recovered catalyst is washed with hot
ethanol (2 9 3 mL) and dried in vacuum. The results, which are given in Table 4,
suggest no appreciable variations when the catalyst is reused five consecutive times.
In order to evaluate the possible catalyst solubilization, an additional test was
performed. The Ca-MCM 1 % sample (30 mg) was refluxed in ethanol (5 mL) for
12 h, filtered at high temperature and dried in vacuum till constant weight. The
activity of the treated catalyst is practically the same as that of the fresh catalyst
(97 % yields in 12 h). The refluxed ethanol was used as solvent for attempting the
reaction without adding the catalyst. After 12 h of reaction, appreciable amounts of
benzylidene-malononitrile intermediate, and Knoevenagel condensation product
between benzaldehyde and ethyl acetoacetate, and only traces of product were
detected.
The scope and generality of this procedure is illustrated by various examples
using different aldehydes and methyl or ethylacetoacetate, and the results are
summarized in Table 5. According to the results of optimization experiments for the
reaction conditions, the reactions are carried out in the presence of catalyst (30 mg)
at room temperature (20 °C) using ethanol as reaction solvent, and the correspond-
ing 2-amino-4H-pyran derivatives are obtained in very good yields (Table 5, entries
1–7).
The workup and catalyst recovery are simple, and all reactions have very high
selectivity toward the corresponding 2-amino-4H-pyran. The TLC analysis shows
only trace amounts of by-products. After completion of the reaction (monitored by
TLC, eluent; EtOAc:hexane mixtures), the catalyst was separated by centrifugation
and washed with ethanol. After ethanol evaporation, the crude product was easily
isolated in almost pure state. Further purification was performed by recrystallization
from ethanol. The reaction solvent can be recovered by simple distillation and
1
reused. The products are known compounds and were characterized by H-NMR
and 13C-NMR spectroscopy. The characterization details of all compounds are
shown in the experimental methods section.
A plausible reaction mechanism similar to that proposed by Das and coworkers
using ZnO as catalyst can be considered [15]. We assume that our materials are
bifunctional catalysts with acid sites provided by the MCM material surface and
basic sites due to the presence of CaCO3. As Fig. 8 shows, the reaction involves
123

E. Nope et al.
Table 5 Synthesis of polyfunctionalized 2-amine-4H-pyran catalyzed by Ca-MCM 1 %
Entry
Ar
R
M. P.
Yield
Found
Lit.
Found
Lit.
1
C6H5
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3CH2–
CH3–
182–183
155–156
162–164
178–179
160–161
179–180
150–151
183–184
143–144
157–159
162–163
144–145
178–179 [21]
158 [15]
98
75
70
90
83
77
83
58
71
98
73
90
90
92
83
97
71
91
79
88
68
96
93
97
2
4–CH3–C6H4
2–NO2–C6H4
3–NO2–C6H4
3–OH–C6H4
2–Cl–C6H4
3
163–165 [21]
181 [33]
4
5
163–165 [33]
179–181 [21]
147–148 [34]
181–183 [21]
142–144 [35]
160–162 [36]
164–165 [36]
148–150 [36]
6
7
3–OCH3–C6H4
3,4,5–(OCH3)3–C6H2
4–OCH3–C6H4
C6H5
8
9
10
11
12
4–CH3–C6H4
2–Cl–C6H4
CH3–
CH3–
Reaction conditions Benzaldehyde (1 mmol), malononitrile (1 mmol), and ethyl acetoacetate (1 mmol)
were stirred in 2 mL of ethanol in the presence of 30 mg of M-Ca 1 % at room temperature (20 °C) for
12 h
Fig. 8 Plausible mechanism for the synthesis of 4H-pyrans over Ca-MCM catalysts
123

Synthesis of mesoporous Ca-MCM catalysts and their use in…
successive Knoevenagel condensation, Michael addition, and finally intramolecular
ring closure leading to the formation of 4H-pyran. In the first step, the Knoevenagel
condensation between benzaldehyde and malononitrile was through bifunctional
MCM-Ca, which removed the acidic proton from the methylene group present in the
malononitrile acting as a base and in the dehydration acting as acid catalyst. In the
ring closure, the catalyst acts as an acid, minimizing the repulsion between the
germinal nitrile groups. Also, this activates one of the nitrile groups by polarization
and facilitates the intramolecular nucleophilic attack by the enolic OH group,
leading to the formation of the final product and catalyst regeneration.
Conclusion
In this paper, we report the synthesis and characterization of three mesoporous Ca-
MCM catalysts with different calcium contents (1, 2, and 5 %), which were
characterized by atomic absorption, XRD, FT-IR, XPS, TPD-CO2, and textural
properties (SBET). A green and simple protocol was developed for the synthesis of
6-amino-4H-pyran scaffolds through a multicomponent coupling reaction of an
aldehyde, malononitrile, and 1,3-dicarbonyl compound in different reaction
solvents. This procedure was performed at room temperature (20 °C), so good
and excellent yields of 4H-pyran derivatives were obtained. The mesoporous
materials are insoluble in polar media, which allows easy removal of the reaction
products without affecting their catalytic activity. A series of substituted 4H-pyrans
was synthesized using these materials and ethanol as solvent. This methodology
requires a reaction time of approximately 12 h and room temperature (20 °C); using
these conditions, excellent yields of 4H-pyran derivatives were obtained. The Ca-
MCM catalysts are insoluble in polar media, which allows easy removal of the
reaction products without affecting their catalytic activity. The applications of these
catalysts in biomass valorization through multicomponent reactions are in progress
in our laboratory.
Acknowledgments This work was supported by CONICET (PIP 003), ANPCyT (PICT 0409) and La
Plata University. Also, the authors thank Colciencias for financial support under the project
110965843004. Contract: Colciencias-UPTC 047-2015. GPR and AGS are CONICET members. J. J.
´
Martınez thanks CONICET-OEA for a short fellowship in the UNLP.
References
1. M. Bowker, Catal. Lett. 142, 1411 (2012)
2. R.A. Sheldon, Chem. Soc. Rev. 41, 1437 (2012)
3. J.M. Thomas, W.J. Thomas, Principles and Practice of Heterogeneous Catalysis (Wiley, London,
2014)
´
4. M.E. Perez, D.M. Ruiz, M. Schneider, J.C. Autino, G. Romanelli, Cienc. Desarro. 4, 83 (2013)
5. C. Capello, U. Fischer, K. Hungerbuhler, Green Chem. 9, 927 (2007)
6. H. Hattori, Chem. Rev. 95, 537 (1995)
7. H. Hattori, A. Satoh, J. Catal. 45, 32 (1976)
¨
8. K. Tanabe, W.F. Holderich, Appl. Catal. A-Gen. 181, 399 (1999)
123

E. Nope et al.
9. J. Tantirungrotechai, P. Thananupappaisal, B. Yoosuk, N. Viriya-empikul, K. Faungnawakij, Catal
Commun. 16, 25 (2011)
10. Y. Kubota, Y. Nishizaki, H. Ikeya, M. Saeki, T. Hida, S. Kawazu, M. Yoshida, H. Fujii, Y. Sugi,
Micropor. Mesopor. Mater. 70, 135 (2004)
11. M. Pirouzmand, B. Nikzad-kojanag, S.K. Seyed-Rasulzade, Catal. Commun. 69, 196 (2015)
12. J. Safaei-Ghomi, R. Teymuri, H. Shahbazi-Alavi, A. Ziarati, Chin. Chem Lett. 24, 921 (2013)
13. G. Evano, N. Blanchard, M. Toumi, Chem. Rev. 108, 3054 (2008)
14. A. Akbari, Z. Azami-Sardooei, A. Hosseini-Nia, J. Korean Chem. Soc. 57, 455 (2013)
15. P. Bhattacharyya, K. Pradhan, S. Paul, A.R. Das, Tetrahedron Lett. 53, 4687 (2012)
16. D. Armesto, W.M. Horspool, N. Martin, A. Ramos, C. Seoane, J. Org. Chem. 54, 3069 (1989)
17. S. Banerjee, A. Horn, H. Khatri, G. Sereda, Tetrahedron Lett. 52, 1878 (2011)
18. M.A. Nasseri, S.M. Sadeghzadeh, J. Iran. Chem. Soc. 10, 1047 (2013)
19. M.G. Dekamin, M. Eslami, Green Chem. 16, 4914 (2014)
20. M. Gupta, M. Gupta, V.K. Gupta, New J. Chem. 39, 3578 (2015)
21. M.S. Pandharpatte, K.B. Mulani, N.N.G. Mohammed, J. Chin. Chem. Soc. 59, 645 (2012)
22. M.M. Heravi, Y.S. Beheshtiha, Z. Pirnia, S. Sadjadi, M. Adibi, Synth. Commun. 39, 3663 (2009)
23. A. Molla, E. Hossain, S. Hussain, RSC Adv. 3, 21517 (2013)
24. H. Valizadeh, A.A. Azimi, J. Iran. Chem. Soc. 8, 123 (2011)
25. F.M. Abdelrazek, M.H. Helal, A.S. Hebishy, S.M. Hassan, J. Heterocycl. Chem. 52, 1026 (2015)
26. N. Seshu Babu, N. Pasha, K.T. Venkateswara Rao, P.S. Sai Prasad, N. Lingaiah, Tetrahedron Lett.
49, 2730 (2008)
27. M.L. Deb, P.J. Bhuyan, Tetrahedron Lett. 46, 6453 (2005)
28. B. Tian, X. Liu, C. Yu, F. Gao, S. Xie, B. Tu, D. Zhao, Chem. Commun. 11, 1186 (2002)
29. H. Sun, J. Han, Y. Ding, W. Li, J. Duan, P. Chen, H. Lou, X. Zheng, Appl. Catal. A Gen. 390, 26
(2010)
´
30. G. Eimer, S. Casuscelli, C. Chanquia, V. Elıas, M. Crivello, E. Herrero, Catal. Today 133, 639 (2008)
31. C. Otero-Arean, M. Rodrıguez-Delgado, V. Montouillout, J.C. Lavalley, C. Fernandez, J.J. Cuart
´
´
Pascual, J.B. Parra, Micropor. Mesopor. Mater. 67, 259 (2004)
32. P.A. Jacobs, B.K.G. Theng, J.B. Uytterhoeven, J. Catal. 26, 191 (1972)
33. F.K. Behbahani, F. Alipour, GU J. Sci. 28, 387 (2015)
34. A. Moshtaghi Zonouz, I. Eskandari, D. Moghani, Chem. Sci. Trans. 1, 91 (2012)
´
´
´
35. A. Sanchez, F. Hernandez, P.C. Cruz, Y. Alcaraz, J. Tamariz, F. Delgado, M.A. Vazquez, J. Mex.
Chem. Soc. 56, 121 (2012)
36. R.M.N. Kalla, M.R. Kim, I. Kim, Tetrahedron Lett. 56, 717 (2015)
123