Application and characterization of eggshell as a new biodegradable and heterogeneous catalyst in green synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones

Article abstract of DOI:10.1016/j.catcom.2012.12.013

An efficient and eco-friendly method for the synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones has been developed by using eggshell as a natural and heterogeneous catalyst. A mixture of an appropriate aldehyde, malononitrile and dimedone in the presence of e

Full text of DOI:10.1016/j.catcom.2012.12.013

Catalysis Communications 33 (2013) 70–75
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
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Short Communication
Application and characterization of eggshell as a new biodegradable and
heterogeneous catalyst in green synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones
⁎
Elaheh Mosaddegh , Asadollah Hassankhani
Institute of Material Sciences and Engineering, Graduate University of Advanced Technology, PO Box 76315-117, Kerman, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 October 2012
Received in revised form 10 December 2012
Accepted 14 December 2012
Available online 26 December 2012
An efficient and eco-friendly method for the synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones has been
developed by using eggshell as a natural and heterogeneous catalyst. A mixture of an appropriate aldehyde,
malononitrile and dimedone in the presence of eggshell at ambient temperature in EtOH resulted in 90–98%
yields of the corresponding products. This new and green methodology is of interest due to use of a green,
bioactive and biodegradable catalyst, its short reaction time, high yields without further purification and
the ability to carry out the large scale reactions. Prepared eggshell was characterized by elemental analysis,
infrared spectroscopy, particle size distribution, X-ray diffraction and fluorescence, scanning electron
microscope, thermo gravimetric and BET surface area analysis.
Keywords:
Eggshell
Environmentally friendly
Heterogeneous catalyst
Biodegradable
© 2012 Elsevier B.V. All rights reserved.
Bioactive catalyst
7,8-Dihydro-4H-chromen-5(6H)-ones
1. Introduction
heterogeneous media in the presence of several types of catalysts or
solid supports such as fluorapatite [38], diphosphate Na2CaP2O7 [39],
The synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones and their
derivatives, has been of considerable interest to chemists because they
may contribute to potential pharmacological activities [1], such as
spasmolytic, diuretic, anti-coagulant, anti-cancer, anti-ancaphylactia
activity [2–6]. In addition, they have been shown to act as cognitive
enhancers, for the treatment of neurodegenerative disease, including
Huntington's disease, Alzheimer's disease, amyotrophic lateral Sclerosis,
AIDS associated dementia and Down's syndrome as well as for the
treatment of schizophrenia and myoclonus [7,8]. Numerous synthetic
methods have been reported for the preparation of 7,8-dihydro-4H-
chromen-5(6H)-ones under classical or modified conditions [9–34].
However, some of these methods suffer from expensive reagents, long
reaction times, low yields, use of large quantities of volatile organic
solvents, acidic and harsh reaction conditions, therefore, for the increas-
ing environmental and economical concerns in recent years, it is now
essential for chemists to search environmentally reactions under natu-
ral conditions as many as possible.
natural phosphate [40], animal bone meal [41], and hydroxyapatite
[42].
In continuation of our efforts to develop new, green chemistry
methods as well as our interest on the application of heterogeneous-
catalyzed organic reactions [43], we decided to report the use of
eggshell as a heterogeneous, natural and biodegradable catalyst for
green synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones via a one-pot
three-component tandem Knoevenagel-cyclo condensation reaction.
The reaction was completed with high catalytic activity and reusability
in excellent yields after only a few minutes (Scheme 1). The size and
structure of eggshell powder were characterized by elemental analysis,
X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy
and laser particle sizer.
2. Experimental
2.1. Materials and instruments
Recently, there has been an increasing interest in the development
of clean technologies to replace hazardous reagent with relatively envi-
ronmental benign catalysts. In addition “green chemistry” emphasizes
the optimization of synthetic methodologies to reduce pollution, cost
and tedious work-ups. This new challenge has led to a growing interest
in the field of organic synthesis under green conditions [35–37]. In this
regard numerous organic reactions have been carried out in solid/liquid
All chemicals were of analytical grade, purchased from Merck and
used as received. Melting points were determined on a Gallenkamp
melting point apparatus and are uncorrected. NMR spectra were
recorded at 500 (1H) and 125.77 (13C) MHz on Bruker DRX-500
Avance spectrometer at 500 and 125.77 MHz, respectively. IR spectra
were obtained with MATSON 1000 FT-IR spectrophotometer. X-ray
diffraction (XRD) with a D8 Bruker diffractometer (40 kV and
40 mA) and Cu
radiation (λ=0.154 nm) was used to analyze the
Kα
⁎
Corresponding author. Tel.: +98 3426226617; fax: +98 3426226611 12.
E-mail address: mosaddegh_e@yahoo.com (E. Mosaddegh).
crystal structure of the milled powders. The XRD patterns were
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.12.013

E. Mosaddegh, A. Hassankhani / Catalysis Communications 33 (2013) 70–75
71
Scheme 1. Synthesis of 7,8-dihydro-4H-chromen-5(6H)-one derivatives catalyzed by eggshell at ambient.
recorded in the 2θ range of 20–80º with the step size of 0.01°. The
mean size and size distribution of the eggshell powder were mea-
sured by a dynamic laser light scattering (DLS) apparatus (FRITSCH
Analysette 22 NanoTec Laser Particle Sizer). The chemical composi-
tion of the catalyst was determined by using an X-ray Fluorescence
Microanalyser (Unisantis XMF-104, Germany) with 40 kV, 300 mA
and Mo radiation. TGA experiments were carried out by using a STA
409 PC Luxx thermal analysis machine (NETZSCH, Germany) under
a flow of nitrogen. The sample weight used was about 20 mg, and
the temperature ranged from 25 to 900 °C with a ramping rate of
10 °C/min. The morphology of the cross section of the film was exam-
ined with a scanning electron microscope (SEM) after being fractured
in liquid nitrogen. Dried samples were coated with gold ions by using
an ion coater at 150 s. Surface structure was visualized by scanning
electron microscope (VEGA TS5130MM) by using a 20 kV accelerat-
ing voltage.
(d, 1H, J=16.3Hz, CH-8) 2.24 (d, 1H, J=16.3Hz, CH-8), 2.45 (m,
2H, CH-6), 4.85 (s, 1H, CH-4), 4.63 (s, 2H, NH2), 7.12–7.33 (m, 4H,
ArH).
2-Amino-3-cyano-7,7-dimethyl-4-(3-nitrophenyl)-5-oxo-5,6,7,8-tetra-
4H-chromen (Table 3, entry 6). IR (KBr, cm−1): 3330, 3180, 2957,
2650, 1667, 1617, 1592, 1219, 1145, 797. 1H NMR (500 MHz,
CDCl3, δ/ppm): 1.07 (s, 3H, CH3), 1.15 (s, 3H, CH3), 2.22 (d, 2H, J=
16.4Hz, CH-8), 2.29 (d, 1H, J=18.0Hz, CH-8), 2.47–2.57 (m, 2H,
CH-6), 4.55 (s, 1H, CH-4), 4.78 (s, 2H, NH2), 7.49–8.12 (m, 4H, ArH).
2-Amino-3-cyano-7,7-dimethyl-4-(4-methylphenyl)-5-oxo-5,6,7,8-
tetra-4H-chromen (Table 3, entry 8). IR (KBr, cm−1): 3445, 3180,
2957, 2882, 2187, 1667, 1617, 1592, 1368, 1219, 1145, 1046. 1H
NMR (500 MHz, CDCl3, δ/ppm): 1.04 (s, 3H, CH3), 1.11 (s, 3H,
CH3), 2.29 (S, 3H, CH3), 2.21 (d, 1H, J=16.3Hz, CH-8) 2.26 (d, 1H,
J=16.3Hz, CH-8), 2.44–2.45 (m, 2H, CH-6), 4.37 (s, 1H, CH-4),
4.52 (s, 2H, NH2), 7.08–7.12 (m, 4H, ArH).
2-Amino-3-cyano-7,7-dimethyl-4-(3-methoxyphenyl)-5-oxo-5,6,7,8-
tetra-4H-chromen (Table 3, entry 10). IR (KBr, cm−1): 3404, 3329,
3205, 2907, 2187, 1641, 1617, 1567, 1517, 1393, 1368, 1195, 822.
1H NMR (500 MHz, CDCl3, δ/ppm): 1.05 (s, 3H, CH3), 1.11 (s, 3H,
CH3), 3.78 (S, 3H, CH3), 2.23 (d, 1H, J=16.2Hz, CH-8) 2.26 (d, 1H,
J=16.7Hz, CH-8), 2.44 (d, 1H, J=17.1Hz, CH-6), 2.49 (d, 1H, J=
17.6Hz, CH-6), 4.37 (s, 1H, CH-4), 4.57 (s, 2H, NH2), 6.73–7.22 (m,
4H, ArH).
2.2. Catalyst preparation
Empty chicken eggshells were collected from the household and
washed with tap warm water. The adhering membrane is separated
manually. Then, the eggshells are washed with distilled water and
dried at room temperature [44–47]. The clean eggshells were dried
at room temperature. Then the eggshells were crushed and milled
into different particle sizes by mortar. The mean particle size was
obtained with a laser particle sizer.
3. Results and discussion
2.3. General procedure for the preparation of 2-amino-3-cyano-7,7-
dimethyl-4-(4-nitro)-5-oxo-5,6,7,8-tetra-4H-chromene (Table 3, entry 1)
3.1. Characterization of eggshell catalyst
3.1.1. Particle size and chemical composition of eggshell powder
XRF and elemental analysis of eggshell showed high levels of Ca
(32.7%) and carbon (13%), P (0.75%), O (50.04%), with small amounts
of Mg (1.6%), Sr (0.4%), Si (0.5%), K (0.07%), Na (0.06%), Fe (0.03%), Zn
(0.02%), Ni (0.01%), Cl (0.02%), nitrogen (0.30%), and hydrogen
(0.05%). Size distributions were determined by DLS (Fig. 1), the size
of 90% of the eggshell particles is below 100 μm and the mean diam-
eter was 35 μm.
In a typical general procedure, a mixture of 4-nitrobenzaldehyde
(0.15 g, 1 mmol), malononitrile (0.1 g, 1.5 mmol) and dimedone
(0.14 g, 1 mmol) in EtOH (3 mL) at ambient temperature, was stirred
thoroughly in the presence of a catalytic amount of powdered
eggshell (0.1 g) to afford the 7,8-dihydro-4H-chromen-5(6H)-ones
in excellent yields. After completion of the reaction (TLC), the mixture
was filtered and washed with hot EtOH. After cooling, the crude
products were precipitated. Pure 7,8-dihydro-4H-chromen-5(6H)-ones
was obtained in high yields without any use of more purification. All
compounds were known in the literature [9–34] and the NMR and IR
spectra of the products were in agreement with earlier data [9–34].
The selected spectral data of five representative 4-substituted
7,8-dihydro-4H-chromen-5(6H)-one derivatives are given below:
3.1.2. BET surface area analysis
The catalytic activity of the catalysts agreed well with the specific
surface area and catalyst particle size. The higher SBET with smaller
sizes of catalyst particles could provide higher reaction conversion
[48]. Table 1 presents the nitrogen physisorption data of natural
eggshell and pure CaCO3. The surface area of the natural eggshell
was 0. 0253 m2 g−1 (Table 1, entry 1), which indicated that natural
eggshell processed average porosity. The surface area of pure CaCO3
2-Amino-3-cyano-7,7-dimethyl-4-(2,4-dichloroyphenyl)-5-oxo-5,6,7,
8-tetra-4H-chromen (Table 3, entry 4). IR (KBr, cm−1): 3328, 3180,
2957, 2180, 1665, 1592, 1366, 1219, 797. 1H NMR (500 MHz,
CDCl3, δ/ppm): 1.07 (s, 3H, CH3), 1.13 (s, 3H, CH3), 2.19 (d, 2H,
J=16.4Hz, CH-8), 2.26 (d, 1H, J=18.0Hz, CH-8), 2.46 (s, 2H,
CH-6), 4.82 (s, 1H, CH-4), 4.85 (br, 2H, NH2), 7.15–7.36 (m, 4H,
ArH).
Table 1
BET surface area (SBET and average particle size of eggshell powder and pure CaCO3.
Entry
Sample
Surface areaa (m2 g−1
)
Average particle sizeb (μm)
2-Amino-3-cyano-7,7-dimethyl-4-(2-chlorophenyl)-5-oxo-5,6,7,8-
tetra-4H-chromen (Table 3, entry 5). IR (KBr, cm−1): 3478, 3329,
3180, 2957, 2187, 1666, 1592, 1368, 1219, 797. 1H NMR
(500 MHz, CDCl3, δ/ppm): 1.07 (s, 3H, CH3), 1.11 (s, 3H, CH3), 2.18
1
2
Eggshell
CaCO3
0.0253
0.0145
35
75
a
Determined by N2 adsorption analysis.
Determined by laser particle sizer.
b

72
E. Mosaddegh, A. Hassankhani / Catalysis Communications 33 (2013) 70–75
Fig. 1. Particle size distribution of eggshell.
was 0.0145 m2 g−1 (Table 1, entries 2) that processed low porosity.
So, it is logical that an eggshell can catalyze the reaction more
effectively.
The stretching vibration of the type; ν(C\O); ν3(E′) is observed as a
strong broad band in the range of 1422 cm−1 while the stretching vi-
bration ν(C\O); ν1(A′1) is observed in the region of ~1085 cm−1 as
a medium band. The out of plane of vibration δ(OCO); ν2(A″2) is
observed in the range of 876 cm−1 as a strong band while, the angle
deformation bending vibration δ(OCO); ν4(E′) appear in the range of
710 cm−1 as a medium strong (Fig. 3) [45]. A medium broad band in
2517 cm−1 shows the presence of HCO3. This data confirms the pres-
ence of CaCO3 in the egg shell powder [45] and compare with published
data of 1455–1470/1420–1425 cm−1 (ν3), 1065–1075 cm−1 (ν1),
863–873 cm−1 (ν2) for CaCO3 [51–54]. So, the FTIR spectrum of the
eggshell powder approves the presence of calcite in the catalyst struc-
ture and shows that this product is hygroscopic and clearly has mois-
ture water [55].
The IR spectra of magnesium carbonate and calcium phosphate
are, understandably, very similar but the bands related to calcium
carbonate are broader than Mg carbonate. Magnesium substitution
in the calcite lattice causes an increased structural disorder which
results in additional weak bands at 1085 cm−1 (ν1 overtone band)
[56]. The intensity of these peaks increases with the quantity of Mg
in the calcite structure. The ν4 band additionally shifts to higher fre-
quencies with an increase in Mg substitution [57].
3.1.3. XRD and FTIR analyses
Also, the prepared catalyst was characterized by infrared spectros-
copy (FT-IR) and X-ray diffraction (XRD). One main characteristic
peak for eggshell marked by its indices (30) was observed which con-
firmed the presence of a calcite structure and is similar to a calcium
carbonate mineral (Fig. 2.) [49]. This result was confirmed by FTIR.
The full description of the IR spectra is given in the following.
The strong characteristic phosphate and carbonate bands with
absorbed H2O were observed in the IR spectra. The band related to
the stretching vibration ν(OH) of uncoordinated H2O is observed as
expected in the range of ~3000 cm−1. A broad band of around
3410 cm−1 shows the presence of absorbed H2O. The broad band at
this region results from an overlapping of hydrogen vibrations in
the phosphate group: stretching vibrations of structural -OH and
absorbed H2O. A low intensity band can be observed at 710 cm−1
which is assigned to the stretching vibration of the P–OH group. The
role of phosphorus as phosphate in the eggshell was reported in the
literatures [50].
More, the IR spectra and XRD have been used to determine the
structure of the catalyst both before and after the reaction (Figs. 2
and 3). The peak position and intensity distributions in the IR and
XRD pattern of the catalysts are similar to the fresh one. So, the re-
covered catalyst had no obvious change in the structure, referring to
Fresh
Reused
3500
3000
2500
2000
1500
1000
500
Wavenumber cm-1
Fig. 3. FT-IR spectra for the comparison of the fresh eggshell and the five-times reused
Fig. 2. XRD patterns of eggshell (a) black line: reused; (b) red line: fresh one.
eggshell.

E. Mosaddegh, A. Hassankhani / Catalysis Communications 33 (2013) 70–75
73
Table 2
Effect of solvents and temperature in the synthesis of 2-amino-3-cyano-7,7-dimethyl-
4-(4-nitro)-5-oxo-5,6,7,8-tetra-4H-chromen.
Entry
Conditions
Time
Yield (%)a
1
2
3
4
5
6
H2O, r.t
H2O, 45 °C
EtOH, r.t
EtOH, 45 °C
EtOH, r.t, non-catalyst
EtOH, r.t, CaCO3 (0.1 g)
70 min
95 min
20 min
17 min
5 h
87b
88b
96b
90b
–
5 h
70
a
Yields refer to the isolated products.
The products were synthesized in the presence of eggshell (0.1 g).
b
the XRD patterns and the FT-IR spectra in comparison with the fresh
one.
Fig. 5. SEM image of eggshell powder.
3.1.4. Thermo gravimetric analysis (TGA)
In order to explain the effect of calcination temperature, we inves-
tigated the calcination process of eggshell with thermal gravimetric
analysis (Fig. 4). The DSC thermal curves representing the carbonate
mineral are characterized by exothermic peaks caused by the evolu-
tion of carbon dioxide. The TGA result showed the temperatures, at
which the eggshell precursors decomposed when heated in a con-
trolled environment at a given ramp rate. The measured weight loss
that was 1.0% below 600 °C reached to 46.2% between 600 °C and
847 °C. The weight loss of the eggshell attributed to the decomposition
of CaCO3 to CO2 and CaO.
The nature of the solvent has an important effect on the outcome
of the reaction so its choice has a crucial effect on the activity [58,59].
To develop optimum conditions, first, we carried out control reactions
in different solvents. The results show that EtOH at room temperature
provides the best reaction conditions. Next, the effect of temperature
on the rate of the reaction was studied for the preparation of
7,8-dihydro-4H-chromen-5(6H)-one. An increase in temperature
did not have any significant effect on the product yield or reaction
time (Table 2).
The effect of the surface hydrophobicity on catalyst performance
was observed by Namba et al. [60] As shown in the FTIR analysis,
the eggshell is highly hydrophilic and preferentially adsorbs H2O ver-
sus alcohol with less polarity and hydrogen bonds. The hydrophilic
character of the eggshell would form stable complexes between
solvents with the active and positive sites (Ca, Mg, Si, Sr, K, Na, Ni,
Fe, and Zn ions) in the eggshell in detriment of the organic substrate
adsorption over the surface of the eggshell and then would decrease
the activity for the reaction.
3.1.5. Scanning electron microscope (SEM)
SEM analysis is another useful tool for the analysis of the surface
morphology of a catalyst. Fig. 5 clearly shows the SEM images of the
catalyst which illustrate the porous nature of the eggshell catalyst.
In general, the high porosity of the micro porous eggshell powder
provides a large contact area for catalyzing the reaction (Fig. 5).
3.2. Synthesis of 7,8-dihydro-4H-chromen-5(6H)-ones
So, when eggshell is used as a catalyst, H2O is preferentially
absorbed on the active sites in the catalyst, competing very favorably
with alcohol. This causes a decrease in the number of active sites and
then a reduction in the reaction rate. Also, the basic sites in the egg-
shell are of Lewis type and correspond to framework oxygen, and
the basicity of given oxygen will be related to the density of the neg-
ative charge. The negative sites in the eggshell can be stabilized by a
proton. It seems logical that the structure will determine the number
of hydrogen bonds that the “protonated transition complex” can form
in order to get the minimum energy configuration. So the reaction
rate is slower in the presence of H2O than in EtOH.
The activity of the green catalyst was tested using a one-pot
three-component condensation of different aromatic aldehydes
(1 mmol) with dimedone (1 mmol) and malononitrile (1.5 mmol) at
ambient temperature to obtain the corresponding 7,8-dihydro-4H-
chromen-5(6H)-ones. Without the addition of the catalyst, the reaction
produced only alkene 5 and no 7,8-dihydro-4H-chromen-5(6H)-one 4
was formed even after 5 h in the reaction conditions (Fig. 6). This
proves the essential effect of the eggshell as a mild and efficient catalyst
in the reaction.
The length of hydrogen bonds depends on bond strength and tem-
perature [61]. As the temperature of the liquid solvent (water and
TG/%
DSC /(mW/mg)
ex
100
95
90
85
80
75
70
65
60
55
2.0
Table 3
Synthesis of 7,8-dihydro-4H-chromen-5(6H)-one derivatives catalyzed by eggshell at
ambient temperature.
1.5
1.0
0.5
0.0
Entry
Ar
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
4-O2N-C6H4
4-Br-C6H4
4-Cl-C6H4
2,4-Cl2-C6H3
2-Cl-C6H4
3-O2N-C6H4
4-(CH3)2N-C6H4
4-CH3-C6H4
4-HO-C6H4
3-CH3O-C6H4
20
11
20
25
20
6
10
7
5
96
97
92
98
93
90
94
90
94
91
100
200
300
400
500
600
700
800
Temperature /°C
10
10
a
Fig. 4. TGA of eggshell catalyst.
Yield refers to isolated pure product.

74
E. Mosaddegh, A. Hassankhani / Catalysis Communications 33 (2013) 70–75
NC
NC
Ar
Table 4
Synthesis of 2-amino-3-cyano-7,7-dimethyl-4-(4-nitro)-5-oxo-5,6,7,8-tetra-4H-chromen
using different reagents and reaction conditions.
Entry Reagent
Conditions
Time
Yield
(%)ref
5
Fig. 6. Benzilidene malononitrile intermediate.
1
Tetrabutylammonium bromide
(10 mol%)
ZnO–beta zeolite (0.1 g)
ionic liquids (TSILs), (0.5 mmol)
SiO2-Pr-SO3H (0.03 g)
PPA-SiO2 (0.1 g)
H2O/ reflux
45 min 9323
2
3
4
5
6
7
EtOH, reflux
H2O, 90 °C
H2O, reflux
H2O, reflux
H2O, reflux
EtOH/H2O, reflux
50 min 8724
alcohol) increases, the number of the intermolecular hydrogen bond-
ing decreases and its entropy increases due to the increased molecu-
lar motion and the loss in density. This causes an increase in the
interaction of the solvents with the active sites in the eggshell by
hydrogen bond forming. So, by increasing the temperature, the cata-
lytic activity of the eggshell decreases.
Since almost 90% of the eggshell is composed of calcium carbonate
and it is the main active site of the eggshell catalyst, we carried out a
comparative reaction in the presence of CaCO3 (0.1 g) in the same
conditions. It was of interest that only 70% of the product can be
obtained after 5 h and the natural eggshell catalyst showed a higher
yield in comparison with CaCO3 (Table 2, entry 6). This is most likely
because the bulk calcium carbonates have particles with a low aspect
ratio and low surface area. So they can be used at very high loadings
[62], while, as seen in the BET and SEM analyses, the eggshell is very
porous and its calcium carbonates have a much higher surface area.
Also, the eggshell contains a small amount of different ions (Ca, Mg,
Si, Sr, K, Na, Ni, Fe, Zn, Cl and phosphate) which can catalyze the
reaction.
1 h
9325
15 min 9326
8 min 8527
20 min 8628
30 min 8729
Ni(NO3)2.6H2O (10 mol%)
Triethylenetetraammonium
trifluoroacetate (5 mol%)
PhB(OH)2 (5 mol%)
8
9
EtOH/H2O, reflux
Solvent-free, r.t
30 min 8830
4 min 8631
[H3N+-CH2-CH2-OH][HCOO−
(0.27 mmol)
]
10
11
12
13
Ce1MgxZr1−xO2 (0.2 g)
porcine pancreas catalyst (30 mg) EtOH/H2O, 35 °C
[Et3N-SO3HCl (25 mol%)
Eggshell powder (0.1 g)
EtOH, reflux
40 min 9032
1 h
Solvent-free, 80 °C 35 min 9734
EtOH, r.t
20 min 96a
9733
a
Referred to the present work.
This method offers significant improvements with regard to the
scope of the transformation, simplicity, and green aspects by avoiding
expensive or corrosive catalysts.
3.3. Catalyst recovery and reusability
In order to improve the yield, the optimum amount of the eggshell
catalyst was evaluated in the range of 0.02–0.2 g. The highest yield
was obtained with 0.1 g of eggshell powder and an increase in the
amount of the eggshell up to 0.2 g did not have any significant effect
on the product yield or reaction time.
The reusability of catalysts is one of the most important benefits
and makes them useful for commercial and industrial applications.
Thus, the recovery and reusability of the eggshell were investigated.
After completion of the reaction, the mixture was filtered and washed
with hot EtOH. The eggshell is wholly insoluble in common solvents.
So, the solid catalyst was easily reused after washing with CHCl3 and dry-
ing at room temperature. The recycled catalyst could be re-used in the
next run in the reaction between 4-nitrobenzaldehyde, malononitrile
and dimedone (Fig. 7).
It was very beneficial that the eggshell could be re-used in 5 cycles
without any loss of its catalytic activity. Thus, the new procedure is
environmentally friendly, cost effective, clean and more efficient
than the reported methods. This claim is justified through representa-
tive examples from a more recently published literature, illustrated in
Table 4.
Under these optimized reaction conditions, a wide range of alde-
hydes were applied to study the generality of this procedure. As
seen from Table 3, the procedure was highly effective for the prepara-
tion of 7,8-dihydro-4H-chromen-5(6H)-ones. It was of interest that
the aromatic aldehydes with electron-withdrawing groups in ortho
or para position, took longer to form the respective products (1–5,
Table 3). It may be because of the intrinsic electronegativity induction
effect of substituted halogens. These effects are caused by the removal
of electrons from the aromatic ring through carbon–halogen sigma
bonds. Then, the aromatic ring is deactivated that causes a reduction
on the reaction rate. So it is logical that the presence of two substituted
halogens on the aromatic ring, leads to a further reduction on the reac-
tion rate. Also, the nitro group bonds to the aromatic ring via atoms
having π orbital. The π electrons of the aromatic ring can be unstabilized
in the substituent. This will also disable the aromatic ring and thus
reduce the reaction rate. However, in all cases, the reactions gave the
corresponding products in excellent yields (90–98%) and in very short
reaction times (5–25 min) (Table 3).
3.4. Large-scale synthesis
To assess the feasibility of applying this method in a large scale
synthesis especially in a chemical laboratory, a typical reaction was
performed on a 100 mmol scale with respect to the one mentioned
in the Experimental section (Table 3, entry 1). After stirring the reac-
tion mixture of 4-nitrobenzaldehyde (15.1 g, 1 equiv), dimedone
(14.0 g, 1 equiv), malononitrile (10.0 g, 1.5 equiv) and the eggshell
catalyst (10 g) in EtOH (50 mL) at room temperature for 80 min,
the corresponding product was exactly obtained in 96% isolated
yield in a very short reaction time. The combination of readily avail-
able, stability and safety of the heterogeneous eggshell catalyst
allowed the process to be rapidly scaled-up into the industrial scale.
100
80
60
40
20
0
4. Conclusion
In conclusion, the eggshell can be used as a green and efficient
catalyst for simple and eco-friendly synthesis of 7,8-dihydro-4H-
chromen-5(6H)-ones at ambient temperature. The eggshell catalyst
was reused several times without any loss of its catalytic activity.
Other benefits which include easy availability, safe conditions, excel-
lent yields of products, very short reaction time and large scale
synthesis make this methodology a green catalytic system for the
1
2
3
4
5
Runs
Fig. 7. Recycling experiment of eggshell.

E. Mosaddegh, A. Hassankhani / Catalysis Communications 33 (2013) 70–75
75
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