Horsetail plant (Equisetum arvense) and horsetail plant ash: application and comparison of their catalytic activities as novel and natural porous lewis acid catalysts for the one-pot green synthesis of 2-amino-4H-chromene derivatives under solvent-free co

Article abstract of DOI:10.1007/s13738-019-01777-1

This study aims to use a new medicinal porous plant having a high content of silica known as horsetail and horsetail ash for the first time as novel, efficient, and environmentally friendly natural mild catalysts. The structure of these catalysts was char

Full text of DOI:10.1007/s13738-019-01777-1

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01777-1
ORIGINAL PAPER
Horsetail plant (Equisetum arvense) and horsetail plant ash:
application and comparison of their catalytic activities as novel
and natural porous lewis acid catalysts for the one‑pot green synthesis
of 2‑amino‑4H‑chromene derivatives under solvent‑free conditions
Nina Hosseini Mohtasham1 · Mostafa Gholizadeh1
Received: 20 March 2019 / Accepted: 30 August 2019
© Iranian Chemical Society 2019
Abstract
This study aims to use a new medicinal porous plant having a high content of silica known as horsetail and horsetail ash
for the frst time as novel, efcient, and environmentally friendly natural mild catalysts. The structure of these catalysts was
characterized by diferent techniques such as FT-IR, XRF, SEM–EDS, N2 adsorption–desorption, XRD, and ICP analysis.
The results obtained from the analysis revealed that both horsetail and horsetail ash could act as a solid acid catalyst. In
addition, a further detailed analysis illustrated that they have a diferent surface area, porosity, and crystalline structure which
can afect their catalytic activities. The synthesis of 2-amino-4H-chromene derivatives was performed via a one-pot three-
component condensation of dimedone, malononitrile, and various aromatic aldehydes to compare their catalytic activities
under solvent-free conditions. Due to its high porosity and high surface area, horsetail ash yields better results compared to
the horsetail itself. FT-IR, mass, 1H-NMR, and 13C-NMR spectroscopies were used to identify the synthesized compounds in
this study. An important advantage of this method is the use of these efective natural catalytic systems with characteristics
such as low cost, mild reaction conditions, nontoxicity, and reusability which resulted in corresponding products in high to
excellent yields and proper reaction times.
Keywords Horsetail plant · Ash · Heterogeneous porous catalyst · One-pot reaction · 2-Amino-4H-chromene
Introduction
synthetic chemist’s toolbox [1]. Academic and industrial
research groups have increasingly focused on multicom-
ponent reactions (MCRs), combining at least three simple
building blocks and providing the most powerful platform
to access many small organic compounds such as biologi-
cally active heterocyclic compounds in a limited number
of reaction steps in one pot [2]. One of the most common
MCRs producing an interesting class of oxygen heterocyclic
compounds is 2-amino-4H-chromene derivatives synthesis,
with attractive pharmacological and biological features, such
as antiallergic [3], antitumor [4], antimicrobial [5], antioxi-
dant [6], anticancer [7], and antifungal properties [8]. Due to
the prominence of 2-amino-4H-chromene derivatives, sev-
eral reagents [9–15] and various synthetic methods [16–19]
have been used for the synthesis of these types of hetero-
cyclic compounds. Although these procedures provide an
improvement in the synthesis of the mentioned compounds,
some of the applied methods have limitations such as harsh
reaction conditions, nongreen solvents, tedious steps for
A brief review of relevant studies has shown that green
chemistry has established a stable context providing
essential design criteria for the development of efcient
chemical syntheses of complex and high-added-value mol-
ecules. On the other hand, multicomponent reactions have
only recently been considered as major expansions of the
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01777-1) contains
supplementary material, which is available to authorized users.
* Mostafa Gholizadeh
m_gholizadeh@um.ac.ir
Nina Hosseini Mohtasham
ninamohtasham77@gmail.com
1
Department of Chemistry, Faculty of Science, Ferdowsi
University of Mashhad, Mashhad 9177948974, Iran
Vol.:(0123456789)
1 3

Journal of the Iranian Chemical Society
the preparation of catalyst, hazardous and expensive cata-
lysts, strongly acidic conditions, and the use of toxic metals.
Recently, chemists have been interested in the development
of clean and environmentally friendly approaches to substi-
tute hazardous catalysts with more relatively environmental
benign ones. The synthesis of 2-amino-4H-chromene has
become one of the most studied subjects to present new
catalysts with the weakest acids and bases. In addition to
our eforts to develop new and green chemistry methods, as
well as our interest in the application of eco-friendly hetero-
geneous catalysis of organic reactions, this study intends to
report the utilization of horsetail and horsetail ash as novel,
inexpensive, and available heterogeneous natural mild solid
acid catalysts for the frst time to synthesize 2-amino-4H-
chromene derivatives via a one-pot three-component con-
densation of dimedone, malononitrile, and various aromatic
aldehydes in solvent-free conditions regarding the goals of
green chemistry.
of anemia [25], antidiuretic activity [27], antimicrobial
activity [28], an herbal treatment for nail disorders, skin
and hair remedy, relieving rheumatism pain, benefcial for
cardiovascular problems as well as its usefulness to pro-
mote the growth and stability of the skeletal structure [26]
used and studied in Europe and China since ancient times.
Besides, horsetail plant is reported to contain active
components such as phenolic acids (ascorbic acid, ferulic
acid, salicylic acid, malic acid, cafeic acid, gallic acid,
pectic acid, and tannic acid) [29, 30], saponins [31], fa-
vonoids [30, 32], alkaloids [26], enzymes (mainly Thia-
minase) [33], styrylpyrone glucosides [34], and branched
long-chain dicarboxylic acid [35]. It also contains miner-
als such as silicon and silicates [30], potassium, calcium,
aluminum, sulfur, magnesium, manganese, zinc, chrome,
and cobalt [21].
It is reported that the exposure of horsetail plant to high
temperature would result in the production of the horsetail
ash considered to contain better properties and interest-
ingly including higher content of silica, higher surface
area, and porosity compared to horsetail plant [20]. These
facts have been investigated using some analysis which
their results are further discussed.
In general, horsetail can be defned as a species of Equi-
setum arvense. It is a widely distributed plant in almost
all parts of the world; however, it mainly grows in tem-
perate Northern hemisphere areas of Asia, Europe, North
America, and North Africa [20] (Scheme 1). Horsetail is a
source of silica or silicon and it is one of the most densely
silicifed plants in which silica is mostly deposited in the
amorphous form [21] (Fig. 5a). For decades, horsetail has
been extensively applied in medicine, and researchers have
believed that some of the medicinal properties of horsetail
are due to its high silica content [22]. Since it is rich in
silica and silicic acids, horsetail is known as a benefcial
system improving the body’s resistance to infections and
enhancing the elasticity and resistance of the skin and con-
nective tissue. An additional advantage of horsetail is its
interesting pharmacological activities such as pain-reliev-
ing agent [23], hepatoprotective activity [24], treatment
The relevant studies in green chemistry, in which the
application of a novel, eco-friendly, nontoxic, inexpen-
sive, stable, and recyclable catalysts is considered very
signifcant as well as the above-mentioned subjects about
the unique properties of horsetail and horsetail ash (e.g.,
the active compounds and some metals), encouraged us
to apply horsetail and horsetail ash as an abundant, green,
and natural Lewis acid catalysts in organic reactions for
the synthesis of 2-amino-4H-chromene derivatives via
a mild reaction of dimedone (1), malononitrile (2), and
various aromatic aldehydes (3) and consequently make a
comparison between the catalytic activities of horsetail
and horsetail ash (Scheme 2).
Scheme 2 Synthesis of 2-amino-4H-chromene derivatives catalyzed
Scheme 1 Image of horsetail plant, a as reported in the literature, b
by horsetail and horsetail ash
before its application in this research
1 3

Journal of the Iranian Chemical Society
Experimental section
All yields refer to isolated products. Furthermore, the
known products were identifed through comparing their
spectral and physical data with those of the previously
reported data or with the authentic samples.
Materials and analytical methods
All the starting materials used for the synthesis in this
study were purchased from Merck and Sigma-Aldrich
companies and applied without further purifcation. The
purity determination of the substrate and reaction moni-
toring was performed by TLC on silica gel polygram STL
G/UV 254 plates. The melting points of products were
determined by Electrothermal Type 9100 melting point
apparatus. The 1H NMR and 13C NMR spectra were run on
a Bruker Avance, at 300 and 75 MHz, respectively, using
TMS as an internal standard and DMSO-d6 as the solvent.
Mass analysis was performed by Agilent Technology (HP)
5973, mass spectrometer operating at an ionization poten-
tial of 70 eV. The FT-IR spectra were recorded from KBr
disk within the range of 400–4000 cm−1 using an AVA-
TAR 370 FT-IR Therma Nicolet spectrometer. Chemical
compositions of horsetail and horsetail ash were analyzed
using X-ray fluorescence spectroscopy (XRF) (model
PW1410, Philips). Elemental compositions were deter-
mined with a Leo 1450 VP scanning electron microscope
equipped with an SC7620 energy-dispersive spectrometer
(SEM–EDS) presenting a 133 eV resolution at 20 kV.
The surface area, pore volume, and average pore diam-
eter were measured by BELSORP MINI (Quantachrome,
USA). Surface areas of the samples were measured by
adsorption of nitrogen gas at 77 K and the application of
Brunauer–Emmett–Teller (BET) calculation, whereas pore
size and pore size distribution were determined using the
methods proposed by Barrett, Joyner, and Halenda (BJH)
and by Dollimore and Heal (DH). The crystal phases of the
catalyst were examined by X-ray difraction (XRD) using
a D8 ADVANCE Bruker difractometer operated at 40 kV
and 30 mA, using CuKα radiation (k = 0.154 Å), in the 2θ
range from 10° to 80°. Inductively coupled plasma (ICP)
was studied on a SPECTRO ARCOS ICP-OES analyzer
instrument (model 76004555).
Preparation of horsetail and horsetail ash
as catalysts
Horsetail plant was purchased from the market, Mashhad,
Iran, washed several times with distilled water to remove any
adhering and cleaving materials, and dried at room tempera-
ture for 24 h. Then the dried plant was smashed and sieved
(80-mesh size), again washed with distilled water, and dried
at 110 °C for 5 h. After thermal processing of the horsetail at
400 °C for 12 h, the horsetail ash was obtained (Scheme 3).
The removal of the organic matrix (e.g., cellulose, hemi-
cellulose, pectin) by calcination at 400 °C resulted in an
open porosity with a high surface area of about 162 m2/g
for horsetail ash compared to horsetail (Table 3). However,
as the calcination temperature increased, the surface area
decreased continuously to a value close to zero at 750 °C
[20]. Therefore, the optimum calcination temperature
appears to be around 400 °C.
General procedure for the synthesis
of 2‑amino‑4H‑chromene derivatives (4a–r) using
horsetail and horsetail ash as catalysts
In a typical procedure, a mixture of dimedone (1 mmol),
aromatic aldehydes (1 mmol), and malononitrile (1.5 mmol)
was stirred thoroughly in the presence of a catalytic amount
of powdered horsetail (0.05 g) at 80 °C in solvent-free con-
ditions for an appropriate period of time as mentioned in
Table 7. After the reaction was completed (monitored by
TLC: n-hexane/ethyl acetate 4:1 as eluent), hot ethanol
(5 ml) was added, and the catalyst (horsetail) was separated
by fltration, washed two times with ethanol, and dried in
vacuum oven to be reused in subsequent reactions. The fl-
trate was concentrated in vacuum, and upon cooling, a solid
product was obtained. The pure products were obtained in
their crystalline forms by recrystallization from ethanol, and
Scheme 3 Preparation of horse-
tail and horsetail ash
1 3

Journal of the Iranian Chemical Society
Results and discussion
Characterization of catalysts
FT‑IR analysis of the catalysts
Figure 1 shows the FT-IR spectra of horsetail and horse-
tail ash. As illustrated in Fig. 1a, the broadband at around
3500–3400 cm−1 is assigned to the stretching vibration of
Si–O–H band and the H–O–H vibration of water molecule
adsorbed on the silica surface [36]. The doublet bands at
about 2923 and 2851 cm−1 are related to the C–H stretch-
ing from aliphatic saturated compounds [37]. A weak peak
around 1734 cm−1 was proposed to be attributed to the C=O
stretching of the related organic compounds [38]. Further-
more, the band detected at about 1640–1620 cm−1 comes
from the bending vibration of water molecules. The strong
peaks between 1100 and 1025 cm−1 are due to the asym-
metric stretching vibration of the structural siloxane band,
Si–O–Si. The bands at 805–800 and 475–460 cm−1 in all
spectra are assigned to the Si–O–Si symmetric stretching
vibration and Si–O–Si bending vibration, respectively [39].
As shown in Fig. 1b, the exposure of horsetail plant to high
temperature resulted in the removal of all organic group
peaks forming the horsetail ash.
Fig. 1 FT-IR spectrum of a horsetail and b horsetail ash
no more purifcation was required. All the products were
known compounds which were identifed by the charac-
terization of their melting points (as indicated in Table 7)
in comparison with those authentic literature samples and
also in some cases by their FT-IR, mass, 1H NMR, and 13
C
NMR spectral data. Also, owing to the catalytic properties
of horsetail ash, it was decided to carry out the reaction
again in the presence of horsetail ash as the catalyst. After-
ward, the results obtained from horsetail and horsetail ash
as two diferent catalytic systems were compared to under-
stand which of them could act as a better catalytic system for
catalyzing this reaction. The obtained results revealed that in
comparison with horsetail, only a small amount of horsetail
ash was needed as a catalyst (0.01 g), and the reaction could
also be carried out at room temperature. These results could
be due to the high surface area and high porosity of horsetail
ash considered as its main characteristics rather than the
horsetail plant that provides a good reaction condition. The
results were compared with each other and then are sum-
marized in Table 7.
XRF analysis of the catalysts
XRF technology provides one of the simplest and most accu-
rate procedures for the determination of chemical composi-
tions of many types of materials.
The chemical composition of horsetail ash that was deter-
mined by XRF showed a high value of silica content for
the sample (up to 85%). Horsetail ash also includes other
compositions such as Al2O3, Fe2O3, SO3, P2O5, K2O, Na2O,
and CaO as a very small proportion of metallic elements
(Table 1). Also, the main components of horsetail were
also determined and are listed in Table 2. As it is shown in
Table 2, the amount of silica is higher than other elements.
According to the results presented in Tables 1 and 2, it can
Table 1 Chemical composition of horsetail ash obtained from X-ray fuorescence analysis (wt%)
SiO2
Al2O3
0.07
Na2O
0.09
MgO
4.32
K2O
0.43
TiO2
0.03
MnO
0.04
CaO
6.24
P2O5
0.90
Fe2O3
0.75
SO3
1.62
85.39
Table 2 Chemical composition
of horsetail obtained from X-ray
fuorescence analysis (wt%)
SiO2 Al2O3 Na2O MgO K2O TiO2 MnO CaO P2O5 Fe2O3 SO3 Cl
15 0.04 0.12 0.82 5.89 0.01 0.02 4.92 0.42 0.51
aLoss on ignition
LOIa
4
0.85 68
1 3

Journal of the Iranian Chemical Society
be concluded that the amount of silica in horsetail ash is
higher than that of horsetail. The result also illustrated that
the presence of such elements in both horsetail and horsetail
ash results in their function as Lewis acid catalytic system.
EDS analysis of the catalysts
The energy-dispersive spectrum (EDS) of horsetail (Fig. 2a)
indicated that it included signifcantly high concentrations
of carbon related to its organic compounds (e.g., cellulose,
hemicellulose, pectin) and alkali and alkaline earth metals,
for instance, Si, Ca, K, Mg, S, Al, as the main components
[40]; however, the concentration of silica was revealed to be
higher than that of other metals. In EDS analysis of horsetail
ash (Fig. 2b), achieved at a high temperature (400 °C), the
peak related to organic parts has not been observed, indicat-
ing that all organic compounds have been removed. Also, a
high concentration of Si was detected which is consistent
with the XRF results.
Fig. 2 EDS spectrum of a horsetail and b horsetail ash
Fig. 3 SEM images of a horsetail and b horsetail ash
1 3

Journal of the Iranian Chemical Society
SEM analysis of the catalysts
removal of organic compounds resulted in the development
of a higher surface area and porosity for horsetail ash in
which it could provide a larger contact area for catalyzing
the reaction in better conditions rather than that of horsetail.
In further analyses of this research, the scanning electron
microscope (SEM) was considered as a useful tool to ana-
lyze the surface morphology of the horsetail compared to
horsetail ash (Fig. 3).
N2 adsorption–desorption studies
As illustrated, silicon was found at its highest amount
in the outer edge of both horsetail and horsetail ash [40].
Moreover, it seemed as if the horsetail ash (Fig. 3b) perfectly
retained the original structure of the horsetail plant (Fig. 3a).
Also, as indicated in Fig. 3b, it can be estimated that the
The nitrogen adsorption–desorption isotherms and pore
size distribution curves of horsetail and its ash are shown
in Fig. 4a–d. As indicated in Fig. 4a, horsetail showed
Fig. 4 N2 adsorption–desorption isotherms and pore size distributions of horsetail plant (a, b) and horsetail ash (c, d)
1 3

Journal of the Iranian Chemical Society
Table 3 Specifc surface area (SBET), pore volume, and mean pore
close examination of the data listed in Table 3 determined
the higher surface area of the horsetail ash compared to the
horsetail due to its exposure to high temperature, resulting in
the successful removal of all organic compounds. Also, it is
shown that pore volume and mean pore diameter of horsetail
ash both increased after burning the horsetail plant [20].
Therefore, all obtained data determined that the presence
of horsetail ash in the reaction resulted in the formation of
better reaction conditions due to its high surface area and
porosity, confrming the SEM analyses results.
diameter of horsetail and horsetail ash
Sample
SBET (m2 g−1
)
Pore volume
Mean pore
diameter
(nm)
(cm3 g−1
)
Horsetail
Horsetail ash
2.025
162.98
0.0094
0.311
7.633
18.574
the characteristics of type II isotherm with H3-type hys-
teresis loops which confrm the existence of porous struc-
ture (mesoporous or macroporous structure) according
to the classifcation presented by IUPAC [41]. Further-
more, the pore size distribution curves (based on the Bar-
rett–Joyner–Halenda (BJH) method) displayed that the pore
size distribution is rather broad compared to that of its ash
having considerable irregular pore size distribution (Fig. 4b).
Also, as shown in Fig. 4c, a typical type IV isotherm with an
H1 hysteresis loop was present for horsetail ash, indicating
the characteristic of mesoporous silica network [42]. Also,
the BJH pore size calculations demonstrated a uniform pore
size distribution with a high-intensity peak, which proves
the high regularity of the mesostructure (Fig. 4d). The spe-
cifc surface area, pore volume, and mean pore diameter for
both horsetail and horsetail ash are shown in Table 3. A
X‑ray difraction (XRD) analysis of the catalysts
The XRD patterns of the horsetail and horsetail ash are
shown in Fig. 5. In horsetail pattern (Fig. 5a), a broad peak
appeared around 2θ equal to 22°, indicating that the silica
of the horsetail was mainly in the form of amorphous [43].
This area is also overlapped by broad refections from cel-
lulose compounds. As observed in Fig. 5b, when horsetail
was exposed to heat intervention, the broad region attributed
to amorphous silica in Fig. 5a disappeared, and some minor
and new sharp refections form of the silica started to appear
revealing the fact that most amorphous silica has been trans-
formed into α-quartz (SiO2). Also, no cellulose refections
Fig. 5 XRD patterns of a horsetail and b horsetail ash
1 3

Journal of the Iranian Chemical Society
Table 4 Elemental analysis for both horsetail and horsetail ash
Table 6 Optimization of the amount of catalyst, solvent, and tempera-
ture in a one-pot synthesis of the model reaction
Element
Elemental content of horse- Elemental content of
tail plant (ppm)
horsetail plant ash
(ppm)
Entry Amount of Solvent Temperature Time (min) Yielda (%)
catalyst (g)
Ca
Al
K
Mg
Na
P
Ba
S
Fe
Zn
Cu
Sr
40,121.5
28,979.8
26,814.1
18,375.3
1098.65
9771.83
9659.63
2962.2
39,551.0
23,672.7
9936.2
28,767.1
8295.2
13,273.3
8585.5
2433.6
2640.2
701.8
68.4
487.5
27.6
288.1
1
2
3
4
5
6
7
8
–
–
–
–
–
–
–
–
–
–
r.t.
110 °C
r.t.
110 °C
110 °C
110 °C
80 °C
60 °C
80 °C
Refux
70
70
70
60
45
25
25
35
25
30
30
35
30
45
60
70
78
90
90
85
90
85
87
85
0.01
0.01
0.03
0.05
0.05
0.05
0.07
0.05
0.05
0.05
1487.6
9
–
H2O
EtOH Refux
CH2Cl2 Refux
767.271
111.149
279.427
19.239
280.3
60,979.1
10
11
12
Sb
Mn
Si
Reaction condition: 4-nitrobenzaldehyde (1 mmol), malononitrile
(1.5 mmol), dimedone (1 mmol) when horsetail was used as a catalyst
303,456.6
aIsolated yield
Table 5 Optimization of the amount of catalyst, solvent, and tempera-
The obtained results confrmed the presence of some ele-
ments in both horsetail and horsetail ash, creating an acidic
property for both of them. The results also confrm that the
amount of silica in horsetail ash is higher than that of horse-
tail. These results are in good agreement with those obtained
from XRF and EDS analyses.
ture in a one-pot synthesis of the model reaction
Entry Amount of Solvent Temperature Time (min) Yielda (%)
catalyst (g)
1
2
3
4
5
6
7
8
9
–
–
–
–
–
–
–
–
–
H2O
r.t.
110 °C
r.t.
60 °C
110 °C
r.t.
70
70
10
10
10
10
25
20
15
30
30
45
99
99
99
98
80
80
90
83
0.01
0.01
0.01
0.03
0.005
0.01
0.01
0.01
Catalytic test
Based on the data obtained from the present study on horse-
tail and horsetail ash, and according to their unique proper-
ties, we estimated that they might be used as efcient green
natural herbal heterogeneous mild solid acid catalysts. To
follow our interest and evaluate their catalytic performances,
we intended to employ them for the frst time as natural
mild solid acid catalysts to catalyze a mild and simple reac-
tion for the synthesis of 2-amino-4H-chromene derivatives
(Scheme 2).
r.t.
Refux
EtOH Refux
CH2Cl2 Refux
10
Reaction condition: 4-nitrobenzaldehyde (1 mmol), malononitrile
(1.5 mmol), dimedone (1 mmol) when horsetail ash was used as a
catalyst
aIsolated yield
To this end, we aimed to identify the best reaction condi-
tions for the synthesis of these compounds. Following this,
4-nitrobenzaldehyde (1 mmol), malononitrile (1.5 mmol),
and dimedone (1 mmol) were chosen as a model reaction,
and parameters such as the efect of catalysts, type of solvent
system as well as temperature were systematically exam-
ined. Initially, diferent amounts of catalysts at the range of
25–110 °C under solvent-free conditions were investigated.
The obtained results showed that in the absence of catalysts,
only a trace amount of products was detected (Entries 1 and
2, Tables 5 and 6).
were detected in horsetail ash pattern, illustrating that all
organic substances were successfully removed after heating.
These results confrmed the ones obtained from FT-IR,
EDS, and XRF analyses.
Elemental analysis of the catalysts
The elemental contents of both horsetail and horsetail ash
(0.1 g) were determined and characterized using inductively
coupled plasma (ICP) technique presenting the following
output (Table 4).
Also, as can be seen, the optimum amounts of the
horsetail and horsetail ash for completing the reac-
tion were 0.05 and 0.01 g, respectively. Notably, lower
1 3

Journal of the Iranian Chemical Society
amounts of catalysts resulted in lower yields (Entry 7,
Table 5 and Entries 4 and 5, Table 6); however, higher
amounts did not affect the reaction times and yields
(Entry 6, Table 5 and Entry 9, Table 6). Concerning the
solvent system, to compare the results of the solution
with that of solvent-free conditions, the model reaction
was examined using 0.01 g of horsetail ash and 0.05 g of
horsetail with H2O, EtOH, and CH2Cl2 under reflux con-
ditions. As shown in Tables 5 and 6, the best results were
achieved under solvent-free conditions. Consequently, as
indicated in Tables 5 and 6, the best results were obtained
through the use of 0.01 g horsetail ash at room tempera-
ture (Entry 3, Table 5) and 0.05 g of horsetail at 80 °C
(Entry 7, Table 6) under solvent-free conditions.
80 °C) and horsetail ash (0.01 g at room temperature) with
various aromatic aldehydes, dimedone, and malononitrile to
give a series of 2-amino-4H-chromene derivatives under sol-
vent-free conditions (Table 7). As shown in Table 7, various
aromatic aldehydes containing both electron-withdrawing
and electron-releasing substituents on their aromatic rings
were utilized well in this reaction and successfully converted
to a wide range of substituted 2-amino-4H-chromenes with
good to excellent yields. The data in Table 7 indicate that
horsetail ash is not only very efective in minimizing the
reaction time, but also highly efcient in terms of catalyst
amount and product yields. These advantages can be attrib-
uted to its high level of activity due to its high porosity and
high surface area. The formation and purity of the prod-
ucts were confrmed by their melting points determination,
which were in good accordance with the literature values.
Moreover, the structures of some of the products were well
After identifying the optimized reaction conditions, we
aimed to study the application of these catalysts and compare
their activity, efciency, and scope by extending our study
under these optimized conditions using horsetail (0.05 g at
Table 7 Synthesis of 2-amino-4H-chromene derivatives catalyzed by horsetail and horsetail ash
Entry
Ar
Product
Horsetail
Timea/yieldb
Horsetail ash
Timea/yieldb
Melting point (°C)
Found
Reported (ref.)
1
2
3
4
5
6
7
8
C6H5
4-Cl-C6H4
4-NO2-C6H4
3-NO2-C6H4
4-Br-C6H4
4a
4b
4c
4d
4e
4f
4 g
4 h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
30/83
35/85
25/90
30/89
25/91
25/89
35/86
30/88
30/85
35/87
30/85
30/90
35/80
25/91
50/83
45/85
40/86
35/91
15/95
10/98
10/99
15/97
10/98
12/97
15/95
15/93
10/96
20/95
15/94
15/96
25/93
15/100
30/91
20/93
25/95
25/94
227–228
205–207
174–175
210–212
206–208
226–228
214–215
220–222
207–209
229–231
244–245
199–201
214–215
240–241
222–224
215–217
214–216
192–194
232–234 [44]
206–208 [45]
178–179 [46]
209–211 [47]
207–209 [48]
229–230 [49]
216–218 [50]
224–225 [49]
210–212 [50]
226–228 [45]
247–249 [50]
201–202 [51]
213–215 [52]
241–243 [45]
226–228 [52]
216–218 [53]
216–218 [54]
190–193 [55]
3-Br-C6H4
4-Me-C6H4
3-Me-C6H4
4-OH-C6H4
3-OH-C6H4
2-OH-C6H4
4-MeO-C6H4
4-Me2N-C6H4
3, 4-di-OH-C6H3
2-Furyl
9
10
11
12
13
14
15
16
17
18
2-Thienyl
1-Naphthyl
5-Br-2OH-C6H3
aThe reaction completion time
bThe yields refer to pure isolated products
1 3

Journal of the Iranian Chemical Society
Table 8 Comparison of results
obtained in this research with
some of those reported in the
literature for the synthesis of
compound 4c
Entry Catalyst
Reaction condition
Time (min) Yielda (%) References
1
2
3
4
PhB(OH)2 (5 mol%)
EtOH/H2O, refux
EtOH, r.t.
Ball milling at r.t.
EtOH, refux
80 °C
Water+ethanol (1:1,3 ml) 60
EtOH, r.t.
30
30
88
97
92
96
95
90.2
93
95
90
90
85
85
92
94
87
93
75
65
90
99
[56]
[57]
[51]
[58]
[53]
[59]
[60]
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
[69]
–
SiO2 NPs (5 mg)
Piperazine (15 mol%)
TMU-17-NH2 b (6 mol%)
SILCc (0.05 g)
27
240
15
5
6
7
8
9
20Ca-Zr-O2 (50 mg)
OPSF (5 mg)
12
10
15
20
30
240
30
10
MSNsd (10 mg)
EtOH/60 °C
[DiEG(mim)2][OH]e2 (10 mol%) H2O, r.t., K2CO3
10
11
12
13
14
15
16
17
18
19
20
SB-DABCO f (0.06 g)
SO42−@MCM-41 (25 mg)
I2 (10 mmol%)
EtOH, r.t.
EtOH, refux
DMSO, 120 °C
Solvent free
EtOH, refux
Grinding, r.t.
EtOH, refux
Solvent free, 80 °C
Solvent free, r.t.
Solvent free, 80 °C
Solvent free, r.t.
NH4H2PO4–Al2O3 (0.03 g)
TSAg (10 mg)
K2CO3 (20 mol%)
NH4Al(SO4)2.12H2O (0.2 g)
Pure SiO2 (0.05 g)
Pure SiO2 (0.01 g)
Horsetail (0.05 g)
16
130
35
55
–
25
10
This work
This work
Horsetail ash (0.01 g)
Reaction condition: 4-nitrobenzaldehyde, malononitrile, and dimedone
aIsolated yield, b(Zn(NH2-BDC)(4-bpdb))-2DMF (TMU-17-NH2, TMU corresponds to Tarbiat Modares
University), csupported ionic liquid catalyst, dwell-ordered mesoporous silica nanoparticles, ediethylene
f
glycol-bis(3-methylimidazolium) dihydroxide, silica-bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane
chloride, gnano-titania sulfuric acid
characterized using FT-IR, mass, 1H NMR, and 13C NMR
spectral data.
assumed that a Knoevenagel condensation between malon-
onitrile (2) with the carbonyl group of aldehyde (3) which
is activated via the solid acid catalysts led to the formation
of intermediate (5) followed by a dehydration step (6). After
that, dimedone (1) was converted to its enol form after tau-
tomerization and attacked the electrophilic center of (6) as
Michael acceptor to form intermediate (7). Finally, tautom-
erism and intramolecular cyclocondensation of (7) produced
(8), which was converted to the desired product (4). Herein,
all metallic ions existing in both horsetail and horsetail ash
are responsible for catalyzing the reaction efectively, but
in the case of horsetail ash due to its specifc structural and
textural properties, it could provide larger interfacial surface
area for reaction and thus enhance its activity.
Finally, a comparison was made between the protocol
reported in previous studies and that of the current study
for the synthesis of 4c, as a model compound. The results
summarized in Table 8 revealed that the protocol introduced
in this research, which uses horsetail ash, could also be the
best protocol of choice for the synthesis of these compounds.
Besides, we decided to use pure silica under the exact condi-
tion in which horsetail and horsetail ash were applied, and
the results are given in Table 8 (Entries 17 and 18). Interest-
ingly, the consequence of using pure silica as catalyst was
not satisfying, indicating that horsetail and horsetail ash are
good acidic catalysts since not only they contain silica, but
also they contain some metallic elements (e.g., Ca, K, Mg,
etc.) making them better acidic catalysts compared to the
pure silica, itself.
Recyclability of the catalysts
As the properties of an efcient heterogeneous catalyst, its
reusability is a principal advantage to be considered that
is very important for commercial and industrial applica-
tions. Hence, this study intended to investigate the reus-
ability of these catalytic systems (horsetail and horsetail
ash). For this purpose, as mentioned before, dimedone
(1 mmol), 4-nitrobenzaldehyde (1 mmol), and malononi-
trile (1.5 mmol) were used as a model reaction. When the
Proposed the probable mechanism
The suggested mechanism for the synthesis of 2-amino-4H-
chromene derivatives which is shown in Scheme 4 includes
three major steps: Knoevenagel condensation, Michael addi-
tion, and fnally intramolecular ring closure [70]. First, we
1 3

Journal of the Iranian Chemical Society
Scheme 4 Proposed mechanism for the synthesis of 2-amino-4H-chromene derivatives in the presence of horsetail and horsetail ash as catalysts
reaction fnished, the mixture was diluted with hot EtOH,
and the catalysts were easily separated from the product by
simple fltration. These remaining catalysts were further
washed with ethanol to remove the residual products and
were dried at 50 °C overnight. Then, the reused catalysts
were exploited in another reaction indicating that horsetail
and horsetail ash were reusable catalysts; however, a slight
decrease in the yields of the products was observed after
fve cycles (Fig. 6).
Conclusion
The present study ofered an introduction of horsetail plant
with its unique properties. The aim of the study was to raise
awareness about this cheap, natural, and herbal green plant.
According to the results of the current study, the exposure
of horsetail to a high temperature resulted in the production
of the horsetail ash containing better properties and advan-
tages rather than the horsetail, itself. Furthermore, diferent
analytical techniques were employed to identify properties
and chemical compositions of each of which, specifcally.
The results have shown that both horsetail and horsetail ash
could act as good solid acid catalytic systems. Therefore, to
make a comparison between their catalytic properties, both
of them were employed for the frst time in the organic reac-
tion to synthesize the 2-amino-4H-chromene derivatives.
Consequently, it was found that in the presence of horsetail
ash, the reaction took place in better conditions due to its
high surface area and high porosity, providing a large contact
area for catalyzing the reaction. The promising points of this
Fig. 6 Catalytic activity of reused horsetail ash versus horsetail in
fve cycles for the synthesis of compound 4c
1 3

Journal of the Iranian Chemical Society
18. S. Tu, H. Jiang, Q. Zhuang, C. Miao, D. Shi, X. Wang, Y. Gao,
Chin. J. Org. Chem. 23, 488 (2003)
work are referred to as simple experimental procedures, total
removal of problems associated with organic solvents, and
the use of green, inexpensive, and nontoxic natural material
as catalysts, along with its ease of preparation presenting
it as a useful and attractive strategy in view of economic
and environmental advantages. It is recommended that the
horsetail ash could be used as a support for the preparation
of various types of catalysts due to its high surface area and
high silica content that could act as a natural silica resource
having mesoporous structure. As a result, studies on practi-
cal applications of horsetail ash as good support for further
modifcations and production of various types of catalysts
and their applications in other organic reactions are currently
in progress in our laboratory.
19. O.H. Qareaghaj, S. Mashkouri, M.R. Naimi-Jamal, G. Kaupp,
RSC Adv. 4, 48191 (2014)
20. L. Sapei, Characterisation of silica in Equisetum hyemale and its
transformation into biomorphous ceramics, pp. 1–158 (2007)
21. G. Holzhüter, K. Narayanan, T. Gerber, Anal. Bioanal. Chem. 376,
512 (2003)
22. D. Cloutier, A.K. Watson, Weed Sci. 33, 358 (1985)
23. F.H.M. Do Monte, J.G. dos Santos, M. Russi, V.M.N.B. Lanziotti,
L.K.A.M. Leal, G.M. de Andrade Cunha, Pharmacol. Res. 49, 239
(2004)
24. H. Oh, D.H. Kim, J.H. Cho, Y.C. Kim, J. Ethnopharmacol. 95,
421 (2004)
25. H. Mekhf, M. El Haouari, A. Legssyer, M. Bnouham, M. Aziz,
F. Atmani, A. Remmal, A. Ziyyat, J. Ethnopharmacol. 94, 317
(2004)
26. N.S. Sandhu, S. Kaur, D. Chopra, Asian J. Pharm. Clin. Res. 3,
146 (2010)
Acknowledgements We are thankful to Ferdowsi University of Mash-
had Research Council for fnancial support to this work (Grant No:
3/45801).
27. S. Soleimani, F.F. Azarbaizani, V. Nejati, Pak. J. Biol. Sci. 10,
4236 (2007)
28. N. Radulović, G. Stojanović, R. Palić, Phytother. Res. 20, 85
(2006)
29. M. Veit, C. Weidner, D. Strack, V. Wray, L. Witte, F.C. Czygan,
Phytochemistry 31, 3483 (1992)
Compliance with ethical standards
30. A. Carnet, C. Petitjean-Freytet, D. Muller, J. Lamaison, Plants
Med. Phytother. 25, 32 (1991)
Conflict of interest The authors declare that they have no confict of
interest.
31. J.G. dos Santos Junior, F.H.M. do Monte, M.M. Blanco,
VMdNB Lanziotti, F.D. Maia, L.K. de Almeida Leal, Pharma-
col. Biochem. Behav. 81, 593 (2005)
32. M. Veit, K. Bauer, H. Geiger, F.C. Czygan, Planta Med. 58, 697
(1992)
References
33. B. Fabre, B. Geay, P. Beaufls, Plantes Med. Phytother. 26, 190
(1993)
1. R.C. Cioc, E. Ruijter, R.V.A. Orru, Green Chem. 16, 2958 (2014)
2. T.J.J. MŘller, R.V.A. Orru, V.A. Chebanov, Y.I. Sakhno, V.E.
Saraev, E.A. Muravyova, A.Y. Andrushchenko, S.M. Desenko,
V.R. Akhmetova, G.R. Khabibullina, Multi-component Reactions
In Heterocyclic Chemistry (Springer, New York, 2011), pp. 31–73
3. K. Görlitzer, A. Dehne, E. Engler, Arch. Pharm. 316, 264 (1983)
4. S.J. Mohr, M.A. Chirigos, F.S. Fuhrman, J.W. Pryor, Cancer Res.
35, 3750 (1975)
34. C. Beckert, C. Horn, J.P. Schnitzler, A. Lehning, W. Heller, M.
Veit, Phytochemistry 44, 275 (1997)
35. T. Řezanka, Phytochemistry 47, 1539 (1998)
36. F. Adam, K. Kandasamy, S. Balakrishnan, J. Colloid Interface
Sci. 304, 137 (2006)
37. B.M. Cherian, L.A. Pothan, T. Nguyen-Chung, G. Mennig, M.
Kottaisamy, S. Thomas, J. Agric. Food Chem. 56, 5617 (2008)
38. X. Sun, F. Xu, R. Sun, P. Fowler, M. Baird, Carbohydr. Res.
340, 97 (2005)
5. T. Raj, R.K. Bhatia, R.K. Sharma, V. Gupta, D. Sharma, M.P.S.
Ishar, Eur. J. Med. Chem. 44, 3209 (2009)
39. D. An, Y. Guo, Y. Zhu, Z. Wang, Chem. Eng. J. 162, 509 (2010)
40. L. Sapei, N. Gierlinger, J. Hartmann, R. Nöske, P. Strauch, O.
Paris, Anal. Bioanal. Chem. 389, 1249 (2007)
41. P. Yuan, P.D. Southon, Z. Liu, M.E.R. Green, J.M. Hook, S.J.
Antill, C.J. Kepert, J. Phys. Chem. C 112, 15742 (2008)
42. M. Thommes, Chem. Ing. Tech. 82, 1059 (2010)
43. N. Yalcin, V. Sevinc, Ceram. Int. 27, 219 (2001)
44. M.G. Dekamin, M. Eslami, Green Chem. 16, 4914 (2014)
45. M.A. Zolfgol, N. Bahrami-Nejad, F. Afsharnadery, S. Baghery,
J. Mol. Liq. 221, 851 (2016)
6. P. Vats, V. Hadjimitova, K. Yoncheva, A. Kathuria, A. Sharma,
K. Chand, A.J. Duraisamy, A.K. Sharma, A.K. Sharma, L. Saso,
S.K. Sharma, Med. Chem. Res. 23, 4907 (2014)
7. M.K. Manion, D. Hockenbery, Cancer Biol. Ther. 2, 104 (2003)
8. Z.Q. Xu, K. Pupek, W.J. Suling, L. Enache, M.T. Flavin, Bioorg.
Med. Chem. 14, 4610 (2006)
9. E. Mosaddegh, A. Hassankhani, G. Mansouri, E.-J. Chem. 8, 529
(2011)
10. A. Khazaei, F. Gholami, V. Khakyzadeh, A.R. Moosavi-Zare, J.
Afsar, RSC Adv. 5, 14305 (2015)
46. A. Rostami, B. Atashkar, H. Gholami, Catal. Commun. 37, 69
(2013)
11. Y. Ren, W. Zhang, J. Lu, K. Gao, X. Liao, X. Chen, RSC Adv. 5,
79405 (2015)
47. S. Rostamnia, A. Nuri, H. Xin, A. Pourjavadi, S.H. Hosseini, Tet-
rahedron Lett. 54, 3344 (2013)
12. H.R. Safaei, M. Shekouhy, S. Rahmanpur, A. Shirinfeshan, Green
Chem. 14, 1696 (2012)
48. S. Balalaie, M. Bararjanian, M. Sheikh-Ahmadi, S. Hekmat, P.
Salehi, Synth. Commun. 37, 1097 (2007)
13. M.R. Islami, E. Mosaddegh, Phosphorus Sulfur 184, 3134 (2009)
14. X.-S. Wang, D.-Q. Shi, S.-J. Tu, C.-S. Yao, Synth. Commun. 33,
119 (2003)
49. R.-Y. Guo, Z.-M. An, L.-P. Mo, R.-Z. Wang, H.-X. Liu, S.-X.
Wang, Z.-H. Zhang, ACS Comb. Sci. 15, 557 (2013)
50. M.A. Zolfgol, M. Safaiee, N. Bahrami-Nejad, New J. Chem. 40,
5071 (2016)
15. S. Balalaie, M. Sheikh-Ahmadi, M. Bararjanian, Catal. Commun.
8, 1724 (2007)
16. S.-J. Tu, Y. Gao, C. Guo, D. Shi, Z. Lu, Synth. Commun. 32, 2137
(2002)
51. M. Amirnejad, M.R. Naimi-Jamal, H. Tourani, H. Ghafuri,
Monatsh. Chem. 144, 1219 (2013)
17. I. Devi, P.J. Bhuyan, Tetrahedron Lett. 45, 8625 (2004)
1 3

Journal of the Iranian Chemical Society
52. S. Gao, C.H. Tsai, C. Tseng, C.-F. Yao, Tetrahedron 64, 9143
62. K. Niknam, M. Khataminejad, F. Zeyaei, Tetrahedron Lett. 57,
361 (2016)
(2008)
53. P. Sharma, M. Gupta, R. Kant, V.K. Gupta, RSC Adv. 6, 32052
63. A. Hasaninejad, M. Shekouhy, N. Golzar, A. Zare, M.M. Dorood-
mand, Appl. Catal. A Gen. 402, 11 (2011)
(2016)
54. B. Sadeghi, A. Hassanabadi, S. Bidaki, J. Chem. Res. 35, 666
64. M. Abdollahi-Alibeik, F. Nezampour, React. Kinet. Mech. Catal.
108, 213 (2013)
(2011)
55. H. Naeimi, M. Farahnak Zarabi, Appl. Organomet. Chem. 32,
65. R.S. Bhosale, C.V. Magar, K.S. Solanke, S.B. Mane, S.S. Choud-
hary, R.P. Pawar, Synth. Commun. 37, 4353 (2007)
66. B. Maleki, S.S. Ashraf, RSC Adv. 4, 42873 (2014)
67. D. Azarifar, S.M. Khatami, M.A. Zolfgol, R. Nejat-Yami, J. Iran.
Chem. Soc. 11, 1223 (2014)
e4225 (2018)
56. S. Nemouchi, R. Boulcina, B. Carboni, A. Debache, C. R. Chim.
15, 394 (2012)
57. S. Banerjee, A. Horn, H. Khatri, G. Sereda, Tetrahedron Lett. 52,
1878 (2011)
68. R. Heydari, R. Rahimi, M. Kangani, A. Yazdani-Elah-Abadi, M.
Lashkari, Acta Chem. Iasi 25, 163 (2017)
58. V. Safarifard, S. Beheshti, A. Morsali, CrystEngCommun 17, 1680
(2015)
69. A.A. Mohammadi, M.R. Asghariganjeh, A. Hadadzahmatkesh,
Arab. J. Chem. 10, S2213 (2017)
59. S. Pradhan, V. Sahu, B.G. Mishra, J. Mol. Catal. A Chem. 425,
297 (2016)
70. P. Bhattacharyya, K. Pradhan, S. Paul, A.R. Das, Tetrahedron Lett.
53, 4687 (2012)
60. A. Maleki, R. Ghalavand, R. Firouzi Haji, Appl. Organomet.
Chem. 32, e3916 (2018)
61. Y. Sarraf, E. Mehrasbi, A. Vahid, M. Tajbakhsh, Chin. J. Catal.
33, 1486 (2012)
1 3