Layered double hydroxides@poly(p-phenylenediamine)@Cu as a novel catalyst for the synthesis of pyrrole derivatives: preparation and characterization

Article abstract of DOI:10.1007/s11164-019-04053-2

Abstract: In this research, the synthesis route of ZnCr-layered double hydroxides functionalized with poly(p-phenylenediamine) and Cu(II) was described. LDHs@PpPDA@Cu was synthesized as a novel, green, and recyclable catalyst and characterized by various

Full text of DOI:10.1007/s11164-019-04053-2

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-04053-2
Layered double hydroxides@poly(p‑phenylenediamine)@
Cu as a novel catalyst for the synthesis of pyrrole
derivatives: preparation and characterization
Maryam Mirzaei‑Mosbat1 · Ramin Ghorbani‑Vaghei1 · Zahra Karamshahi1
Received: 23 September 2019 / Accepted: 27 November 2019
© Springer Nature B.V. 2019
Abstract
In this research, the synthesis route of ZnCr-layered double hydroxides functional-
ized with poly(p-phenylenediamine) and Cu(II) was described. LDHs@PpPDA@Cu
was synthesized as a novel, green, and recyclable catalyst and characterized by vari-
ous techniques including Fourier transform infrared spectroscopy, scanning electron
microscopy, thermogravimetry analysis, X-ray difraction, and energy dispersive
X-ray analysis. The catalytic activity of the LDHs@PpPDA@Cu was investigated in
the synthesis of pyrrole derivatives via one-pot four-component coupling of amine,
aldehyde, nitromethane and acetylacetone. The results of analyses demonstrated that
the reactions proceeded to completion which has led to the successful synthesis of
high purity compounds.
Graphic abstract
Keywords Synthesis · Novel · Green · Recyclable · Catalyst · One-pot · Coupling
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-019-04053-2) contains supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0123456789)
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M. Mirzaei-Mosbat et al.
Fig. 1 Examples of pyrroles with biological activities
Introduction
The synthesis of novel heterocyclic compounds is of paramount importance among
research studies, owing to their abundance, and extensive pharmaceutical and indus-
trial application domains [1]. Nitrogen-containing heterocycles as one of the most
substantial categories of heterocyclic compounds are of eclectic pharmacological
and biological performances [2]. Pyrrole and its derivatives are widely circulated
organic molecules having prime signifcance in natural products, synthetic chemis-
try, drugs, and the food industry [3]. Some instances of Pyrrole are known to per-
form as antitumor [4], anti-infammatory [5], antibacterial [6], antioxidant [7], and
antifungal agents (Fig. 1) [8]. Besides, these compounds have been systematically
employed in material science [9]. Thus far, a good number of synthetic routes have
been proposed and developed for the preparation of pyrroles and their derivatives.
The classical methods utilized for the synthesis of pyrroles include Hantzsch [10],
Knorr [11], Paal–Knorr [12], and Clauson-Kaas condensation [13] reactions. How-
ever, despite their utility, such methods frequently sufer from some drawbacks such
as multistep synthetic operations, severe reaction conditions, scarcity of the initi-
ate materials, functional group compatibility, and region-specifcity. To overcome
these challenges, various efcient strategies such as transition metal catalysis [14]
and multicomponent [15] reactions (MCRs) have been developed. MCRs include
reactions in which three or more starting materials react in a one-pot process to form
a new product. The advantages of MCRs extend from high atom economy, the abil-
ity to build complex molecules, avoiding the necessity of isolation and purifcations
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Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
of the intermediates, consistency with the principles of green chemistry, operational
simplicity, and minimizing waste, labor, and cost [16]. Given the mentioned sig-
nifcance and applications of pyrrole and its derivatives, researchers worldwide have
put tremendous eforts to devise and develop the most facile route for synthesizing
these compounds. Heretofore, a variety of methods have been reported for the syn-
thesis of pyrrole in the literature. Among which the routinely applied, one involves
one-pot four-component coupling of amine, aldehyde, nitromethane and acetylac-
etone. A lot of research studies using variant catalysts and reaction settings have
been conducted. Maiti et al. [17], in 2010, reported the preparation of novel deriva-
tives of pyrroles under refux condition, applying FeCl3 catalyst. In 2012, function-
alized pyrrole derivatives were synthesized by Rajeshwar Reddy et al. using I2 as a
catalyst at 90–95 °C. In another research work, Gupta et al. [18], in 2014, reported
the new derivatives of these compounds prepared at 90–95 °C in the presence of
[bmim]HSO4 [19]. In 2015, pyrroles were synthesized by Tang et al. [20] using Fe-
MIL-101 as a catalyst in toluene.
Layered double hydroxides (LDHs) have been recognized for over 150 years
since the discovery of the mineral hydrotalcite. Hydrotalcite is a layered double
hydroxide of general formula of Mg6Al2CO3(OH)16·4(H2O), which was frst studied
by Manasse in 1915 [21]. LDHs are reputed as hydrotalcite-like clays of the general
chemical formula:
[
]
2+
M
(1−x)
M
3+(OH)2 (An−
)
x∕n ⋅ zH2O
x
In which M2+ and M3+ are divalent and tri-valent metal cations, An− is the
replaceable interlayer anion and x has usually values between 0.20 and 0.33 (Fig. 2)
[22].
LDHs demonstrate exceptional physical and chemical behaviors such as high
anion exchange capacity, swelling property, memory efect, and high specifc surface
area [23]. Moreover, these materials are cost-efective and stable at a high elevated
temperature (500–600 °C) and harsh pH conditions [24]. The remarkable properties
of these materials presented them as an excellent candidate for such broad felds of
applications including pharmaceutics, electrocatalysts, electrochemistry, photocata-
lysts, and photochemistry [25]. In addition, their utilization in catalytic felds as well
as catalyst supports has been investigated [26].
In this article, an efcient and highly active reusable heterogeneous catalyst was
designed by combining the LDHs, poly-para (phenylenediamine) (PpPDA), and
Cu(OAc)2. Thereafter, its catalytic activity for one-pot synthesis of pyrrole com-
pounds was examined (Scheme 1).
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M. Mirzaei-Mosbat et al.
Fig. 2 Layered double hydroxides structure
Scheme 1 Synthesis of substituted pyrroles using LDHs@PpPDA@Cu
Experimental
Chemicals and instruments
All commercial materials were purchased from Merck and Fluka Companies .1H
NMR and 13C NMR spectra were measured on a spectrometer at 400 MHz and
100 MHz, respectively, in DMSO-d6. Fourier transform infrared (FT-IR) spec-
tra were obtained using the Shimadzu 435-U-04 FT spectrophotometer from KBr
1 3

Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
pellets. Melting points were recorded with a BUCHI 510 apparatus in open capillary
tubes.
General procedure for preparation of LDHs@PpPDA@Cu catalyst
Preparation of layered double hydroxides (LDHs)
LDHs can be synthesized in base solutions using metal salts containing M2+ and
M3+. Initially, an aqueous solution containing Zn2+ and Cr3+ metals were prepared
using precursor salts, i.e., Zn(NO3)2·6H2O and Cr(NO3)3·9H2O in a ratio of 2:1 in
deionized water. Then, NaOH aqueous solution of 2 M was dropped into the solu-
tion and was added dropwise till the pH value of the solution reached 11.5. After-
ward, the mixture was allowed to react for 18 h without stirring at the 65 °C. Finally,
a green slurry was obtained and washed several times with distilled water and dried
in a 60 °C oven for 24 h [27].
Preparation of LDHs@PpPDA
LDHs@PpPDA were synthesized at room temperature through the emulsion polym-
erization method as follows. In a typical reaction, 0.75 g of LDHs were poured into
a 250 mL fask and then 20 mL chloroform and 30 mL of distilled water were added
to those. In the next step, fask contents were well-dispersed for about 30 min by an
ultrasonic bath in the ambient temperature and then the solution containing PpPDA
monomer (1 g) in 30 mL of HCl (1 M) was added to the aqueous solution. The oxi-
dizing solution was prepared via 1.5 g (6.5 mmol) of APS in 20 mL of deionized
water and was added to the reaction mixture. After 24 h, the resultant precipitate
was washed several times with deionized water. Finally, the precipitate was dried in
vacuum oven at 50 °C for 24 h [28].
Preparation of LDHs@PpPDA@Cu
At frst, 1 g from the LDHs@PpPDA was dispersed in 50 mL EtOH using an ultra-
sonic bath (15 min). Then, 0.5 g of Cu(OAc)2 was dissolved in 5 mL EtOH and
added to the previous mixture. After refuxing the mixture for 24 h, the resulting
precipitate was separated and washed with 50 mL EtOH and dried in an oven.
General procedure for synthesis of pyrrole derivatives
A mixture of aromatic aldehyde (1 mmol), amine (1 mmol), acetylacetone (1 mmol),
nitromethane (1 mL), and LDHs@PpPDA@Cu (0.05 g) was stirred at 100 °C for
an appropriate time. The reaction was monitored by TLC (n-hexane:acetone, 7:1).
After completion of the reaction, the reaction mixture was poured into a centrifuge
tube and the catalyst was separated by centrifugation. The resulting solution was
poured into a petri dish, and the excess nitromethane was removed under vacuum.
Then, resulting precipitates were collected and washed with cold diethyl ether. The
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M. Mirzaei-Mosbat et al.
products were identifed using physical and spectroscopic data (FT-IR, NMR and
CHN).
Analytical data of selected products
1‑(4‑(2,3‑dichlorophenyl)‑2‑methyl‑1‑(p‑tolyl)‑1H‑pyrrol‑3‑yl)ethan‑1‑one (5e) Mp.
90–92 °C. FT-IR (KBr, ν, cm−1): 3010, 2968, 1607, 1501, 1246. 1H NMR
(400 MHz, DMSO-d6, δ, ppm): 7.74 (s, 1H), 7.43–7.15 (m, 6H), 6.55 (s, 1H), 4.02
(s, 3H), 3.82 (s, 3H), 3.46 (s, 3H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 26.17,
31.57, 48.29, 108.09, 113.95, 120.64, 126.06, 130.26, 134.41, 144.02, 150.73,
188.35. Anal. Calcd. For C20H17Cl2NO: C, 67.05; H, 4.78; N, 3.91. Found: C, 66.95;
H, 4.83; N, 3.85.
1‑(4‑(4‑chloro‑3‑nitrophenyl)‑2‑methyl‑1‑phenyl‑1H‑pyrrol‑3‑yl)ethan‑1‑o1ne
(5f) Mp. 106–108 °C. FT-IR (KBr, ν, cm−1): 3072, 2936, 1604, 1509, 1346. H
NMR (400 MHz, DMSO-d6, δ, ppm): 8.87 (s, 1H), 8.49 (s, 1H), 8.17 (s, 1H), 7.48–
7.04 (m, 5H), 6.84 (s, 1H), 3.45 (s, 3H), 3.23 (s, 3H). 13C NMR (100 MHz, DMSO-
d6, δ, ppm): 29.92, 48.75, 104.33, 112.27, 116.47, 118.95, 124.39, 128.98, 131.47,
134.43, 139.44, 150.32, 180.82. Anal. Calcd. For C19H15ClN2O3: C, 64.32; H, 4.26;
N, 7.9. Found: C, 64.28; H, 4.28; N, 7.83.
1‑(4‑(2‑bromophenyl)‑2‑methyl‑1‑(p‑tolyl)‑1H‑pyrrol‑3‑yl)ethan‑1‑one (51 g) Mp.
100–103 °C. FT-IR (KBr, ν, cm−1): 3001, 2930, 1606, 1508, 1245. H NMR
(400 MHz, DMSO-d6, δ, ppm): 8.51 (s, 1H), 7.75–7.15 (m, 7H), 6.48 (s, 1H), 4.02
(s, 3H), 3.82 (s, 3H), 3.35 (s, 3H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 20.72,
28.26, 44.98, 101.81, 107.66, 114.36, 119.80, 123.13, 126.06, 129.84, 131.92,
138.61, 199.60. Anal. Calcd. For C20H18BrNO: C, 65.23; H, 4.93; N, 3.8. Found: C,
65.15; H, 4.98; N, 3.75.
1‑(4‑(1H‑indol‑3‑yl)‑2‑methyl‑1‑(p‑tolyl)‑1H‑pyrrol‑3‑yl)ethan‑1‑one (5 h) Mp.
1
120–122 °C. FT-IR (KBr, ν, cm−1): 3308, 3067, 2835, 1606, 1509, 1248. H NMR
(400 MHz, DMSO-d6, δ, ppm): 11.96 (s, 1H), 8.8 (s, 1H), 8.04–6.61 (m, 9H), 3.68
(s, 3H), 3.44 (s, 3H), 3.15 (s, 3H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 25.88,
33.36, 50.45, 86.89, 94.83, 97.88, 101.82, 108.87, 112.81, 117.21, 125.14, 129.49,
135.66, 146.62, 151.04, 205.89. Anal. Calcd. For C22H20N2O: C, 80.46; H,6.14; N,
8.53. Found: C, 80.38; H, 6.2; N, 8.47.
1‑(2‑methyl‑1‑phenyl‑4‑(pyridin‑2‑yl)‑1H‑pyrrol‑3‑yl)ethan‑1‑one
(5j) Mp.
88–90 °C. FT-IR (KBr, ν, cm−1): 3032, 2921, 1596, 1502, 1331. 1H NMR (400 MHz,
DMSO-d6, δ, ppm): 8.56 (s, 1H), 7.77 (s, 1H), 7.43–7.14 (m, 8H), 3.83 (s, 3H), 3.35
(s, 3H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 30.36, 49.15, 100.15, 102.23,
109.35, 111.41, 114.77, 119.38, 121.88, 130.68, 134.83, 138.19, 141.95, 147.79,
151.97, 197.12. Anal. Calcd. For C18H16N2O: C, 78.24; H, 5.84; N, 10.14. Found:
C, 78.16; H, 5.93; N, 10.05.
1 3

Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
1‑(2‑methyl‑4‑(pyridin‑2‑yl)‑1‑(p‑tolyl)‑1H‑pyrrol‑3‑yl)ethan‑1‑one
(5i) Mp.
1
114–115 °C. FT-IR (KBr, ν, cm−1): 3028, 2860, 1577, 1410. H NMR (400 MHz,
DMSO-d6, δ, ppm): 8.87 (s, 1H), 8.17 (s, 1H), 7.48–6.6 (m, 7H), 3.66 (s, 3H), 3.43
(s, 3H), 3.21 (s, 3H). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 21.16, 30.76, 43.72,
97.64, 103.06, 109.78, 112.28, 117.27, 121.05, 125.64, 131.51, 135.68, 141.15,
145.70, 181.64. Anal. Calcd. For C19H18N2O: C, 78.59; H, 6.25; N, 9.65. Found: C,
78.53; H, 6.28; N, 9.58.
Results and discussion
The LDHs@PpPDA@Cu was prepared according to the procedure depicted in
Scheme 2. At frst, the LDHs were prepared in accordance with the method previ-
ously reported. After which the LDHs were built, PpPDA was coated on its surface.
Ultimately, the LDHs@PpPDA@Cu catalyst was synthesized utilizing Cu(OAc)2
precursor and the characterization analyses were also performed using Fourier trans-
form infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), thermo-
gravimetry analysis (TGA), and X-ray difraction (XRD). The concentration of cop-
per in LDHs@PpPDA@Cu, which was 9.17 wt%, was determined by inductively
coupled plasma optical emission spectrometry (ICP-OES).
Study of the FT‑IR spectra
The FT-IR spectra of LDHs, LDHs@PpPDA, LDHs@PpPDA@Cu are repre-
sented in Fig. 3. Notably, the IR spectra of LDHs are illustrated in (a) section
of Fig. 3 and the characteristic peaks of 3400 cm−1, 1400 cm−1, and 500 cm−1
−
were related to O–H, NO3 anion, and metal–oxygen stretching vibrations,
Scheme 2 Total procedure for synthesis of LDHs@PpPDA@Cu
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M. Mirzaei-Mosbat et al.
Fig. 3 FT-IR spectra of LDHs (a), LDHs@PpPDA (b), LDHs@PpPDA@Cu (c)
respectively. The IR spectra of LDHs@PpPDA are shown in (b) section of Fig. 3
and the characteristic peaks of 3371 cm−1, 1568 cm−1, 1501 cm−1, and 1285 cm−1
were attributed to N–H, C=N, C=C, and C–N stretching vibrations, respectively.
As could be observed, the intensity as well as the geometry of O–H stretching
vibration in Fig. 3a was dramatically changed as a result of bonding formation
between PpPDA on LDHs which approves the successful synthesis of PpPDA on
the LDHs. Besides, the existing of Cu–N absorption band in 520 cm−1 in Fig. 3c
along with the decrement of N–H peak intensity demonstrates that LDHs@
PpPDA@Cu catalyst was efectively prepared.
Study of the X‑ray difraction
X-ray difraction spectroscopy was applied to investigate the crystal structure of
LDHs, LDHs@PpPDA and LDHs@PpPDA@Cu. Figure 4c shows the XRD pat-
tern of LDHs and the series peaks including 2θ: 10°, 30°, 40° which is consistent
with earlier reported research works [29]. The characteristic peaks (2θ: 10°, 30°)
spotted in XRD pattern of LDHs@PpPDA (Fig. 4b) manifestly attests the coating
of PpPDA on LDHs [30]. Moreover, the syntheses of LDHs@PpPDA@Cu are con-
frmed through taking a comparison among the XRD patterns for LDHs@PpPDA@
Cu (Fig. 4a), LDHs and LDHs@PpPDA. The emerging of the peaks related to Cu
in 2θ: 15°, 17°, 19° as well as a diferent pattern in 24° also shows the formation of
Cu in LDHs@PpPDA. In the end, the average crystal size of LDHs@PpPDA@Cu is
calculated using Debye–Scherrer’s (D=Kλ/(βcosθ)) formula.
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Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
Fig. 4 XRD pattern of LDHs (c), LDHs@PpPDA (b), LDHs@PpPDA@Cu (a)
Study of the thermal gravimetric (TGA) properties
In order to evaluate the thermal stability of LDHs@PpPDA@Cu catalyst, ther-
mogravimetry analysis (TGA) was performed. As remarked in Fig. 5, three mass-
loss regions were detected within the curves. In the frst fracture of the diagram at
100–200 °C, a weight loss is taken place, which might be attributed to the loss of
water, residual monomer and other solvent in the catalyst. In addition, the second
mass-loss appeared at 200–300 °C, which could be due to the decomposition of
PpPDA oligomers. In the last step, after 350 °C, the cleavage and decomposition
of PpPDA polymeric chains and Cu/polymer complex in the catalyst have begun
Fig. 5 TGA curve of LDHs@PpPDA@Cu
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M. Mirzaei-Mosbat et al.
to occur. As a result, the optimum temperature for employing LDHs@PpPDA@
Cu as a catalyst could be up to 300 °C.
Morphological study
The morphological evaluation as well as the average particle size examination of
LDHs@PpPDA@Cu was performed via SEM technique. According to Fig. 6, the
LDHs@PpPDA@Cu composite catalyst possess a consistent structure which indi-
cates that the synthetic procedure resulted in uniformity of the samples. Besides,
referring to the images, it could also be implied that the catalyst particles are of a
layered–layered composite confguration.
Study of the energy dispersive X‑ray (EDX) spectrum
Energy dispersive X-ray analysis of the LDHs@PpPDA@Cu is shown in Fig. 7. The
presence of C, O, N, Cu, Cr, and Zn was validated through this spectrum. The pres-
ence of Cu signal indicates that the LDHs@PpPDA has suitably been covered with
Cu.
Synthesis of pyrrole derivatives using LDHs@PpPDA@Cu as catalyst
In green chemistry, it is of fundamental importance to make use of a suitable cat-
alyst for the synthesis of organic compounds. In light of this, the catalytic activity
of LDHs@PpPDA@Cu was investigated in the one-pot four-component coupling
of amine, aldehyde, nitromethane, and acetylacetone. At frst, the catalytic activ-
ity of LDHs@PpPDA@Cu was compared with that of other catalysts reported
in the literature and the results are tabulated in Table 1. Based on these data,
the LDHs@PpPDA@Cu catalyst is one of the most efective catalysts in the syn-
thesis of pyrroles. In this catalyst, owing to the presence of Cu, its free orbitals
perform as a Lewis acid and activate the carbonyl groups through the interaction
with oxygen. Thereafter, the reaction of benzaldehyde (1 mmol), 4-methyl aniline
Fig. 6 SEM images of LDHs@PpPDA@Cu
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Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
Fig. 7 EDX spectrum of LDHs@PpPDA@Cu
Table 1 Comparison of various catalysts for the synthesis of pyrrole derivatives
Entry
Catalyst
Temp. (°C)
Time (h)
Yield (%)
Ref.
1
2
3
4
5
6
[bmim]HSO4
Montmorillonite clay K10
FeCl3
Fe-MIL-101
CoFe2O4@SiO2-PrNH2-Mo(acac)2
90–95
60
Refux
100
90
100
3
10
7
20
4
87
70
56
85
90
98
[19]
[31]
[17]
[13]
[32]
This work
LDHs@PpPDA@Cu
3
(1 mmol), acetylacetone (1 mmol) and nitromethane (1 mL) was selected as a
model reaction in which diverse temperature and diferent catalyst amounts were
utilized to fnd out the optimized condition for the reaction. The optimization of
the reaction conditions was examined as shown in Table 2. According to these
data, no reaction was observed in the absence of a catalyst. As regards the purity
of the products, the reaction time, and the product yields, 0.05 g of the catalyst
is an adequate amount for complementation of this reaction. Besides, reducing
the amount of catalyst has decreased the reaction efciency, whereas its further
increment had no considerable impact in the progression of the reaction (Table 2,
entries 2–4). Then, various temperatures were monitored within the model reac-
tion. The highest yield of the product was achieved at a temperature of 100 °C.
Therefore, the best result was achieved under the optimized conditions using
0.05 g of catalyst and a temperature of 100 °C (Table 2, entries 5).
In order to evaluate the efect of diferent substitution, this reaction was inves-
tigated under optimum condition employing various aldehydes and amines pos-
sessing diferent electron-withdrawing and electron-donating groups and the
results are presented in Table 3. From the results obtained, it was concluded that
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M. Mirzaei-Mosbat et al.
Table 2 Optimization of the
reaction conditions for the
synthesis of pyrrole derivatives
using the LDHs@PpPDA@Cu
catalyst
Entry Catalyst
Temp. (°C) Time (h) Yield (%)
1
–
100
100
100
100
100
90
24
3
3
3
3
3
3
3
3
3
3
Trace
60
88
98
98
2
0.02
3
0.04
4
0.08
5
0.05
6
0.05
90
7
0.05
80
78
8
0.05
70
56
9
0.05
60
45
10
LDHs (0.05)
100
Trace
11
LDHs@PpPDA (0.05) 100
40
Table 3 Synthesis of pyrrole derivatives using the LDHs@PpPDA@Cu catalyst
5c (4:00, 87%)[19]
5b (3:30, 93%)[32]
5a (3:00, 98%)[32]
5d (4;30, 75%)[17]
5f (3:10, 82%)
5e (3:40, 89%)
5g (4:00, 80%)
5h (3:00, 85%
5i (3:40, 90%)
5j (3;20, 94%)
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Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
the reaction proceeds to a higher degree of completion when utilizing an alde-
hyde electron-withdrawing and an amine electron-donating group.
One of the most signifcant features of the catalyst of this study lies in its retriev-
ability and reusability. For this purpose, the model reaction was investigated in the
presence of 0.05 g of catalyst and temperature of 100 °C. After which the catalyst
preparation was completed, it was separated from the reaction, washed several times
with warm deionized water and ethanol and then was placed in an oven for dry-
ing. The results of the recycling for the catalyst are presented in Fig. 8. It was real-
ized that the catalyst holds the potential to be reused for 5 successive cycles without
any considerable loss of its initial catalytic activity. The catalyst activity was also
examined after 5 times using EDX mapping technique. The mapping analysis of the
recycled catalyst demonstrated the stability of the LDHs@PpPDA@Cu during the
recycling procedure (Fig. 9).
A possible mechanism for the synthesis of pyrrole derivatives using LDHs@
PpPDA@Cu catalyst, via a four-component reaction is depicted in Scheme 3. As
reported in the literature, pyrroles can be synthesized from Michael reaction of
β-enamino ketones or esters and nitroalkenes followed by cyclization [33]. Nitroalk-
enes (intermediate I) from aldehyde and nitroalkane and β-enamino ketones or esters
(intermediate II) from acetylacetone and amines could be generated in the presence
of a catalyst. These two intermediates reacted via Michael addition which in turn
formed a fve-membered cyclic intermediate III, followed by intramolecular cycliza-
tion with the elimination of nitroxyl (HNO) and water to lead to the fnal product.
Conclusion
In this research, β-enamino ketones or esters and nitroalkenes could be gener-
ated simultaneously from available abundant starting materials in the presence
of LDHs@PpPDA@Cu catalyst. Through Michael reaction between these two
components followed by cyclization, functionalized pyrroles have been success-
fully synthesized. The utilization of procedure in this study ofers several benefts
Fig. 8 Recyclability test of LDHs@PpPDA@Cu
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M. Mirzaei-Mosbat et al.
Fig. 9 Results of EDX map patterns: LDHs@PpPDA@Cu
Scheme 3 Suggested reaction mechanism for the synthesis of pyrrole derivatives
including facile reaction work-up, short reaction duration, applicability, cost-
efectiveness, high yield, as well as green and mild reaction conditions. The main
advantages of the catalyst are facile preparation route, easy separation from the
reaction medium, recyclability and reusability. Finally, the chemical and physi-
cal structure of catalyst and the synthesized derivatives were analyzed and their
structure was confrmed.
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Layered double hydroxides@poly(p‑phenylenediamine)@Cu…
Acknowledgements The authors would like to appreciate Bu-Ali Sina University, Center of Excellence
in Development of Environmentally Friendly Methods for Chemical Synthesis (CEDEFMCS) for their
fnancial supports of this study.
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M. Mirzaei-Mosbat et al.
Afliations
Maryam Mirzaei‑Mosbat1 · Ramin Ghorbani‑Vaghei1 · Zahra Karamshahi1
*
Ramin Ghorbani-Vaghei
rgvaghei@yahoo.com
1
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University,
Hamedan 6517838683, Iran
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