Cu attached functionalized mesoporous MCM-41: a novel heterogeneous nanocatalyst for eco-friendly one-step thioether formation reaction and synthesis of 5-substituted 1H-tetrazoles

Article abstract of DOI:10.1007/s11164-021-04543-2

In the current study, a mesoporous copper-attached functionalized MCM-41 with the DL-Pyroglutamic acid framework has been produced through a post-synthetic method. The MCM-41 functionalization technique has been used to synthesize this novel heterogeneous catalyst. The material has been identified fully using XRD, FT-IR, BET, EDX, elemental mapping, SEM, and TGA. This catalyst displays high catalytic performance in the one-step thioether formation (C–S) reaction and synthesis of 5-substituted 1H-tetrazoles. The main aspects of this economical copper-catalyzed procedure are green synthesis, slighter experimental conditions, and less reaction time with no additives. Further benefits comprise experimental comfort of handling, secure replacement to dangerous, damaging, and poisoning regular Lewis’s acid catalysts, and reusability with constant catalytic performance. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-021-04543-2

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04543-2
Cu attached functionalized mesoporous MCM‑41: a novel
heterogeneous nanocatalyst for eco‑friendly one‑step
thioether formation reaction and synthesis of 5‑substituted
1H‑tetrazoles
Somayeh Molaei1 · Mohammad Ghadermazi1
Received: 13 April 2021 / Accepted: 15 July 2021
© The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract
In the current study, a mesoporous copper-attached functionalized MCM-41 with
the DL-Pyroglutamic acid framework has been produced through a post-synthetic
method. The MCM-41 functionalization technique has been used to synthesize this
novel heterogeneous catalyst. The material has been identifed fully using XRD,
FT-IR, BET, EDX, elemental mapping, SEM, and TGA. This catalyst displays high
catalytic performance in the one-step thioether formation (C–S) reaction and syn-
thesis of 5-substituted 1H-tetrazoles. The main aspects of this economical copper-
catalyzed procedure are green synthesis, slighter experimental conditions, and less
reaction time with no additives. Further benefts comprise experimental comfort of
handling, secure replacement to dangerous, damaging, and poisoning regular Lew-
is’s acid catalysts, and reusability with constant catalytic performance.
Extended author information available on the last page of the article
Vol.:(0123456789)
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S. Molaei, M. Ghadermazi
Graphic abstract
Keywords Thioether formation (C–S) reaction · Synthesis of 5-substituted
1H-tetrazoles · Green synthesis · Cu-grafted functionalized MCM-41 ·
DL-pyroglutamic acid framework
Introduction
A Catalytic procedure involving the thioether formation (C–S) reactions have
appeared as the strong method for the thioether formation reactions. [1–3] Among
thioethers, the diaryl sulfdes are of considerable importance due to their exten-
sive range of therapeutic performances, and they can be utilized for various clinical
usages in the therapy of Alzheimer’s, cancer, and Parkinson’s diseases [4–7]. Difer-
ent kinds of transition metal catalysts can be impressively mediated C–C, C–N, C–O
formation reactions [8–12]. Metal-catalyzed thioether formation (C–S) reaction has
been relatively less investigated than C–N formation reaction and C–O formation
reactions due to the disulfdes reaction and inactivation of metal catalysts via sul-
fur poisoning. Often, thioether formation (C–S) reactions sufer from intense prob-
lems comprising employment of unstable and smelly thiols, which can cause seri-
ous health problems. Some thioether formation (C–S) reactions are carried out using
burnable, poisonous, costly solvents, and their removal has been considered in the
industry. To produce catalytic methods, many attempts have been made to carry out
thioether (C–S) formation reactions with green solvent [13, 14]. To conquer the dif-
fculty of the handling of thiols, diferent methods for the thioether formation have
been proposed [15–17]. In this article, we organize a green approach by molecular
S8 instead of thiols that stops the formation of disulfde. The procedure gives the
required product in good to high yields in a short time. Currently, heterogeneous
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Cu attached functionalized mesoporous MCM-41: a novel…
catalysts are highly recognized for the green origination of any catalytic method
because of their simple recovery, besides the minimization of unwanted poisonous
wastes [18]. The problems generally associated with the homogeneous catalysts can
be simply overcome by heterogenization of homogeneous equivalent onto solid sup-
port [19–24].
Among some immobilization methods, organofunctionalized mesoporous materi-
als can be considered as the most desirable in the scope of catalysis study because
of their high surface area, high absorbency, adjustable pore size distribution, and
great hydrothermal/ mechanical stability [25–30]. In these functionalized materi-
als, the nanoscale pores’ periodicity can approve the simple access of the catalytic
situations and possible dispersion of the reactants and solvent in the support [31].
Mesoporous materials can be functionalized via various organic reactions so that
the organic functional groups play an essential role in covalent bonding of cata-
lytic active sites at the pore surface while maintaining the porous host arrangement
[32–42]. S-arylation reactions have been utilized by diferent transition metals [32,
43–45]. Among them, Cu catalysts have been evaluated as the most useful and desir-
able in the thioether formation (C–S) reactions because of their plenty and environ-
mentally harmless experimental conditions with the lowest waste and safety peril.
A tetrazole is a main group of heterocycles. They have found an extensive scope of
uses in materials science as great density energy materials in therapeutic chemistry,
as a metabolically constant replacement for a carboxylic acid group, in coordina-
tion chemistry as ligands, and in photographic materials as anticoagulants [46–50].
Later methods to generate tetrazoles in the literature generally contain the costly and
poisonous metal, or utilization of hydrazoic acid, which is very poisonous, unstable,
and fammable [51–54]. In this paper, we investigated the synthesis of 5-substituted
1H-tetrazoles in green media with a green catalyst. This new synthesis proposes a
nontoxic, suitable, and eco-friendly synthetic method to tetrazoles. This catalyst
showed excellent catalytic performance for the thioether formation (C–S) reactions
with molecular S8. A novel Copper-containing DL-Pyroglutamic acid-functional-
ized mesoporous MCM-41 catalyst was designed by attaching copper at the surface
MCM-41(Scheme 1).
Experimental
Materials
Cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), DL-
Pyroglutamic acid, and Cu (NO3)2 were obtained from Aldrich. The solvents and
reagents were obtained from Merck and utilized without further purifcation.
Characterization approaches
Copper loading in the MCM-41@DL-Pyroglutamic acid-Cu catalyst was
determined using ICP-OES (inductively coupled plasma-optical emission
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S. Molaei, M. Ghadermazi
HO
O
N
H
O
Water, Reflux,
48hr
MCM-41
Cu(NO3)2
EtOH, Reflux,
16hr
acid
roglutamic
DL-Py
MCM-41@
M=Cu
acid-M
MCM-41@DL-Pyroglutamic
Scheme 1 Schematic representation of MCM-41@DL-Pyroglutamic acid-Cu nanocatalyst
spectrometry) 730-ES Varian. FT-IR (Fourier-transform infrared) spectra were
obtained with a BRUKER VERTEX 80 spectrometer. XRD (X-ray difraction)
patterns were generated by Cu Kα radiation with a MPD difractometer. TGA
(Thermogravimetric) analysis were done with a Shimadzu DTG 60 analyzer.
SEM (Scanning electron microscopy) images were recorded on a FESEM-TES-
CAN MIRA3 microscope equipped with EDX. BET (Nitrogen adsorption–des-
orption) isotherm was obtained on a BLlSORP-MINI II analyzer.
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Cu attached functionalized mesoporous MCM-41: a novel…
Synthesis of mesoporous MCM‑41
The MCM-41 was prepared by the reported method [27]. 3.5 mL of NaOH (2 M)
and 1 g of cetyltrimethylammonium bromide (CTAB) were introduced to 480 mL
of deionized water and stirred at 80 °C. After obtaining a homogeneous solu-
tion, 5 mL of tetraethyl orthosilicate (TEOS) was added drop by drop. After two
hours, the MCM-41 was separated and washed using deionized water. Then, the
mesoporous MCM-41 was dried at 50 °C and calcined at 550 °C (5 h).
Synthesis of DL‑Pyroglutamic acid attached mesoporous MCM‑41 (MCM‑41@
DL‑Pyroglutamic acid)
MCM-41@ DL-Pyroglutamic acid was obtained by the following method: 1.5 g
of DL-Pyroglutamic acid was added to the suspension of 1 g of the mesoporous
MCM-41 in 30 mL of deionized water. Under the stirring condition, the mixture
was refuxed (48 h). The obtained product was separated and washed using deion-
ized water. Then, the mesoporous MCM-41@ DL-Pyroglutamic acid was dried at
50 °C.
Synthesis of MCM‑41@DL‑Pyroglutamic acid‑Cu catalyst
2.5 mmol of Cu (NO3)2 was added to the suspension of 1 g of MCM-41@ DL-
Pyroglutamic acid in 30 mL of ethanol. Under the stirring condition, the mixture
was refuxed (16 h). The obtained product was separated and washed with etha-
nol. Then, the mesoporous MCM-41@ DL-Pyroglutamic acid-Cu was dried at 50
°C.
General process for the synthesis of 5‑substituted 1H‑tetrazoles
MCM-41@DL-Pyroglutamic acid-Cu was added (70 mg) to a mixture of nitrile
(1 mmol), NaN3 (1.2 mmol), and PEG (3 ml) at 120 °C. At the end of the reaction
(checked by TLC), the MCM-41@DL-Pyroglutamic acid-Cu was separated using
a centrifuge and washed repeatedly with EtOAc and distilled water to eliminate
the unreacted reagents. The organic layer was preserved with 10 mL of 5 N HCl.
Then the organic was washed with water and dried by anhydrous Na2SO4 to pro-
duce the wanted products (Scheme 2).
General process for thioether formation (C–S) reaction
At 130 °C, a mixture of KOH (0.7 g), aryl halide (1 mmol), catalyst (70 mg), S8
(1 mmol), and DMSO (3 mL) were stirred. The reaction progress was checked
by TLC. At the end of the reaction, the MCM-41@DL-Pyroglutamic acid-Cu
was separated using a centrifuge and washed repeatedly with EtOAc and distilled
1 3

S. Molaei, M. Ghadermazi
Scheme 2 The applications of MCM-41@DL-Pyroglutamic acid-Cu nanocatalyst toward the synthesis
of 5-substituted 1H-tetrazoles and the thioether formation (C–S) reaction
water to eliminate the unreacted reagents. Then the organic compound was
washed with water and dried over anhydrous Na2SO4 to dryness to produce the
wanted aryl thioethers (Scheme 2).
Selected spectral data
1
(Table 3, Entry 1) 5-(3-Nitrophenyl)-1H-tetrazole. HNMR (400 MHz, DMSO,
ppm): δ 7.90 (t, 2H), 8.39–8.49 (m, 2H), 8.41–8.51 (s, 1H.)
1
(Table 3, Entry 2) 5-(4-Nitrophenyl)-1H-tetrazole HNMR (400 MHz, DMSO,
ppm): δ 8.29–8.33 (d, 2H), 8.44–8.46 (d, 2H).
1
(Table 5, Entry 1) Diphenyl sulfde HNMR (400 MHz, DMSO, ppm): δ
7.29–7.33 (m, 6H), 7.35–7.39 (m, 4H).
1
(Table 5, Entry 4) Bis(4-methylphenyl) sulfde HNMR (400 MHz, CDCl3,
ppm): δ 3.40–3.67 (s, 6H) 7.26–7.38 (m, 8H).
1
(Table 5, Entry 9) Bis(4-hydroxyphenyl) sulfde HNMR (400 MHz, DMSO,
ppm): δ 6.75–6.78 (d, 4H), 7.15–7.18 (d, 4H), 9.66 (s, OH).
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
a
824
457
1066
b
802
451
1675
1381
1074
c
1633
1382
802
453
1084
3900
3400
2900
2400
1900
1400
900
400
-1
Wavenumber (cm )
Fig. 1 FT-IR spectra of MCM-41 (a), MCM-41@DL-Pyroglutamic acid (b), and MCM-41@DL-Pyro-
glutamic acid-Cu (c)
Results and discussion
Characterization
The FT-IR analysis of MCM-41, MCM-41@DL-Pyroglutamic acid, MCM-41@
DL-Pyroglutamic acid-Cu are presented in Fig. 1. The FT-IR spectra of the sam-
ples have three specifc bands at around 1066, 824, and 457 cm−1 which are due to
1 3

S. Molaei, M. Ghadermazi
the asymmetric, symmetric Si−O−Si stretching vibration and bending Si−O−Si
vibration [55], demonstrating that the silica basis persists unchanged upon immo-
bilization [56]. The presence of the organic molecule is recognized by the presence
of stretching vibration of the C–N and C=O bands at around 1381 and 1675 cm−1
,
respectively, which is an indication that DL-Pyroglutamic acid has been attached
successfully into the mesoporous MCM-41. In The FT-IR spectrum of MCM-41@
DL-Pyroglutamic acid-Cu (Fig. 1c), the stretching vibration of the C=O band is
moved to the lower frequency (1633 cm−1), demonstrating coordination of the C=O
with Cu (II). This result indicates that Copper has been attached to the channel of
the MCM-41@DL-Pyroglutamic acid sample.
The X-ray difraction of MCM-41 displays three- difraction peaks [57] a very
sharp refection (d100) and two low-intensity refections (d110 and d200) at 2.47°,
4.18°, and 4.83°, from the well-ordered mesopores hexagonal structure (Fig. 2). The
refections are good-resolved, revealing a high-quality sample. The MCM-41@DL-
Pyroglutamic acid-Cu X-ray difraction exhibits that the three characteristic peaks of
MCM-41 have persisted upon the functionalization of MCM-41(Fig. 3). However,
the intensity of the refections of the MCM-41@DL-Pyroglutamic acid-Cu material
decreased in comparison with that of the MCM-41. This consequence may be due to
the decreasing of order, such as variations in the wall thickness, or may be assigned
to contrast matching between the silicate framework and organic moieties which are
located inside the channels of MCM-41. These results indicate that the structure of
the mesoporous materials remains intact through the grafting procedure [57–60].
16000
d100
14000
12000
10000
8000
6000
4000
d110
d200
2000
0
1
2
3
4
5
6
7
8
9
10
11
2θ (°)
Fig. 2 XRD pattern of MCM-41
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
8000.00
d100
7000.00
6000.00
5000.00
4000.00
3000.00
2000.00
d110
d200
1000.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
2θ (°)
7.00
8.00
9.00
10.00 11.00
Fig. 3 XRD pattern of MCM-41@DL-Pyroglutamic acid-Cu
The presence of organic moieties in such a highly distorted environment in addi-
tion to the limited fexibility compared to O–Si–O may generate a more defective
structure with a broader pore size distribution.
A wide-angle XRD (WXRD) analysis was performed to confrm that copper is
complex with the organic compound. Figure 4 presents a wide-angle XRD pattern
of MCM-41@DL-Pyroglutamic acid-Cu. A signal peak at 2θ = 43.6° in MCM-
41@DL-Pyroglutamic acid-Cu was visible, implying that Cu species (Cu (111))
were incorporated into MCM-41@DL-Pyroglutamic acid-Cu, or they are highly
dispersed to be detected. This is consistent with the observations made by Yu
et al. [61]. The XRD spectra of MCM-41@DL-Pyroglutamic acid-Cu sample also
exhibited two weak difraction peaks at 2θ values around 35.6° and 38.9° attrib-
uted to the CuO crystallites phase (JCPDS 80–1917) [62].
The TGA curves of MCM-41 and MCM-41@DL-Pyroglutamic acid-Cu are
shown in Fig. 5. Two major weight loss processes can be detected for MCM-
41@DL-Pyroglutamic acid-Cu sample. The weight loss below 150 °C can be due
to the removal of adsorbed water [63]. The weight loss between 150 to 600 °C
was assigned to the decomposition of organic molecules [64]. While the weight
loss at the range of 600 to 800 °C was ascribed to the decomposition of silanol
templates, which includes conversion of Si–OH to Si–O–Si with the release of
water (dehydration) [65, 66]. This is evidence that organic groups enter into the
channels.
29Si {1 H} CP-MAS NMR technique characterize the three diferent silicon
atoms that organize the silica framework. Silica framework consists of silicon atoms
without hydroxyl groups Si–(O–Si)4, silicon atoms bearing one hydroxyl group
1 3

S. Molaei, M. Ghadermazi
6000
5500
5000
4500
4000
3500
3000
2500
2000
SiO2
CuO
Cu
20
30
40
50
60
70
80
90
2θ (°)
Fig. 4 Wide-angle XRD pattern of MCM-41@DL-Pyroglutamic acid-CU
(Si–O)3–Si–OH, and silicon atoms bearing two hydroxyl groups (Si–O)2–Si–(OH)2
called geminal silanols. The (Si–O)2–Si–(OH)2 and (Si–O)3–Si–OH species are pre-
sent at the silica surface, while Si–(O–Si)4 species are present in the bulk. Caponetti
9
et al. reported that Si {1 H} CP-MAS NMR and 29Si{1 H} MAS NMR investiga-
tions for Nd–MCM-41 show a Si–(O–Si)4 groups reduction, and a (Si–O)3–Si–OH
groups increase. For this work, these results could be in agreement with the disap-
pearance of the decomposition of MCM-41 in the 600 to 800 °C region and a link-
age between organic groups and silica matrix.
The X-ray elemental mapping images show the homogenous distribution of
copper element on the MCM-41@DL-Pyroglutamic acid-Cu catalyst. Also, the
ligand functionalization is demonstrated through the presence of N, O, and C
atoms (Fig. 6). This has been further approved by the EDX spectrum of the cat-
alyst. The exact amount of Cu attached to the nanocomposite was determined
by the ICP-AES analysis, and it was obtained to be 1.7 mmol g−1. The parti-
cle shape and surface texture were specifed from SEM images. Figure 7 dis-
plays the images of MCM-41@DL-Pyroglutamic acid-Cu catalyst. The particles
are nanometric in spherical morphology. The average diameter of the catalyst
is approximately 107 nm. The inherent constitution of MCM-41@DL-Pyro-
glutamic acid-Cu catalyst was revealed by TEM measurement (Fig. 8). In this
sample, the TEM image showed the presence of ordered mesostructures, and it
shows the Cu deposition.
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Cu attached functionalized mesoporous MCM-41: a novel…
110
100
90
80
70
60
50
25
125
225
325
425
525
625
725
825
925
Temperature (°C)
Fig. 5 TGA curves of MCM-41 (up) and MCM-41@DL-Pyroglutamic acid-Cu (down)
1 3

S. Molaei, M. Ghadermazi
6000
5000
4000
3000
2000
SiKα
O Kα
1000
0
CuLα
CuKβ
CuKα
keV
0
5
10
15
20
Fig. 6 EDX spectrum and X-ray elemental mapping images of MCM-41@DL-Pyroglutamic acid-Cu
Reaction Study
In continuation of this work on the evolution of efective, reusable catalysts using
MCM-41@DL-Pyroglutamic acid-Cu, we described a very simple, green, and efec-
tive procedure for the synthesis of 5-substituted 1H-tetrazoles by mixing nitriles and
NaN3 with eco-friendly MCM-41@DL-Pyroglutamic acid-Cu as a new catalyst. In
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
Fig. 7 SEM images of MCM-41@DL-Pyroglutamic acid-Cu
the quest regarding eco-friendly and cost-efective metal-catalyzed methods, Cop-
per-catalyzed methods are favorable.
To optimize the experimental conditions and to investigate the catalytic perfor-
mance of MCM-41@DL-Pyroglutamic acid-Cu, 3- nitrobenzonitrile and NaN3 were
chosen as trial substrates. The efect of the diferent experimental parameters like
temperature, solvent, and catalyst amount was evaluated, and the consequences are
shown in Table 1. Solvent has an outstanding efect on the yield. The experimen-
tal results exhibit that PEG, DMSO, and DMF are good solvents in the synthesis
of 5-substituted 1H-tetrazoles, while ethanol is not appropriate for this reaction. A
1 3

S. Molaei, M. Ghadermazi
Fig. 8 The TEM images MCM-41@DL-Pyroglutamic acid-Cu
rise in temperature from 80 to 120 °C raises the speed of the reaction to provide the
required product in high yield. The infuence of the amount of catalyst on the reac-
tion was also estimated. A good yield is attained on rising the quantity of catalyst.
To compare per site activity of the heterogeneous catalyst and to choose the best cat-
alyst, the diferent catalysts were tested. When the catalytic reaction was performed
with MCM-41@DL-Pyroglutamic acid as a catalyst, no satisfactory results were
obtained under this condition. We then performed the reaction using MCM-41 @Cu
as the catalyst, it was observed that the reaction proceeded with good results giving a
product yield of 80%. This demonstrates that the catalytic performance is generated
from copper sites. Compared to MCM-41@DL-Pyroglutamic acid-Cu, the loading
of the metals is decreased in the MCM-41@Cu. Because the ligand coordinates with
Cu ions in such a way that the Cu act as active catalytic sites. So, when the reaction
has proceeded with MCM-41@DL-Pyroglutamic acid-Cu as a catalyst, excellent
results (high yield in the shorter period) were obtained. Therefore, the experimental
conditions have been recognized as 120 °C in PEG with 70 mg of MCM-41@DL-
Pyroglutamic acid-Cu catalyst. To recognize the scope and overview of MCM-41@
DL-Pyroglutamic acid-Cu catalyzed synthesis of 5-substituted 1H-tetrazoles, dif-
ferent benzonitriles were used as substrates under our optimal conditions, as pre-
sented in Table 2. The synthesis continued to end within 150 min, and 5-substituted
1H-tetrazoles were separated in good to high yields. This reveals the potential efec-
tiveness of this procedure for preparative purposes. To investigate whether the com-
pounds in Table 3 entries 3 and 4 were obtained di-tetrazole or not, FT-IR analysis of
these compounds was investigated. The FT-IR spectra of these compounds showed
a group of bands at 3449 cm−1 (N–H) 2924 and 2856 cm−1 (which appointed to the
stretching vibrations of C-H bonds) 1460 (C-H), 1276 (N–N=N-), 1217, 1123, and
1078 cm−1 resulted from the existence of the secondary amino group and tetrazole
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Cu attached functionalized mesoporous MCM-41: a novel…
Table 1 Optimization of reaction parameters for the model reaction using a catalyst
Entry a Catalyst
Solvent Catalyst (mg) Tem. (°C) Time(min) Yield (%) b
1
MCM-41@DL-Pyroglutamic
ETOH 70
H2O 70
DMSO 70
80
130
130
130
130
130
130
130
130
130
180
180
40
56
61
69
72
79
89
69
57
10
80
acid-Cu
2
MCM-41@DL-Pyroglutamic
100
120
120
80
acid-Cu
3
MCM-41@DL-Pyroglutamic
acid-Cu
4
MCM-41@DL-Pyroglutamic
DMF
PEG
PEG
PEG
PEG
PEG
PEG
PEG
70
70
70
70
50
30
70
70
acid-Cu
5
MCM-41@DL-Pyroglutamic
acid-Cu
6
MCM-41@DL-Pyroglutamic
100
120
120
120
120
120
acid-Cu
7
MCM-41@DL-Pyroglutamic
acid-Cu
8
MCM-41@DL-Pyroglutamic
acid-Cu
9
MCM-41@DL-Pyroglutamic
acid-Cu
10
MCM-41@DL-Pyroglutamic
acid
11
MCM-41@Cu
aReactions conditions: Nitrile (1 mmol), NaN3, (1.2 mmol), catalyst, and solvent (3 ml) at temperature
bIsolated yield
ring and the existence of band at 2200 cm−1 owing to CN group [67]. So, these
results show that the compounds in Table 3 entries 3 and 4 were not obtained di-
tetrazole. Figure 9 shows the FT-IR of 5-(isocyanomethyl)-1H-tetrazole (entry 4).
The thioether formation reaction was performed in a very simple protocol. MCM-
41@DL-Pyroglutamic acid-Cu catalyst has been utilized in the thioether formation
(C–S) reactions using molecular S8 and KOH at 120 °C. To optimize reaction condi-
tions, thioether formation (C–S) reactions of iodobenzene were selected as a repre-
sentative model. The efect of the diverse experimental parameters like temperature,
catalyst amount, base, and the solvent were evaluated, and the consequences are
shown in Table 3.
First, the representative thioether formatio (C–S) reaction was performed with
any catalyst; blank cycle provided insignifcant product. To investigate the infuence
1 3

S. Molaei, M. Ghadermazi
Table 2 Optimization of reaction parameters for the model reaction using MCM-41@DL-Pyroglutamic
acid-Cu catalyst
Entry a catalyst
Solvent Base Catalyst (mg) Tem (℃) Time (min) Yield (%) b
1
2
3
4
5
6
MCM-41@DL-Pyro- DMSO KOH
glutamic acid-Cu
–
130
130
130
100
80
100
100
100
100
100
100
N. R
N. R
N. R
N. R
N. R
12
MCM-41@DL-Pyro- Toluene KOH 70
glutamic acid-Cu
MCM-41@DL-Pyro- PEG
glutamic acid-Cu
KOH 70
KOH 70
KOH 70
KOH 70
MCM-41@DL-Pyro- H2O
glutamic acid-Cu
MCM-41@DL-Pyro- ETOH
glutamic acid-Cu
MCM-41@DL-Pyro- DMF
130
glutamic acid-Cu
7
MCM-41@DL-Pyro- DMSO KOH 70
glutamic acid-Cu
80
100
100
100
100
100
100
30
45
78
55
31
80
8
MCM-41@DL-Pyro- DMSO KOH 70
100
130
130
130
130
glutamic acid-Cu
9
MCM-41@DL-Pyro- DMSO KOH 70
glutamic acid-Cu
10
11
12
MCM-41@DL-Pyro- DMSO KOH 50
glutamic acid-Cu
MCM-41@DL-Pyro- DMSO KOH 30
glutamic acid-Cu
MCM-41@DL-Pyro- DMSO KOH 90
glutamic acid-Cu
13
14
15
16
17
MCM-41@DL-Pyro- DMSO NaOH 70
glutamic acid-Cu
130
130
130
130
130
100
100
100
240
240
20
MCM-41@DL-Pyro- DMSO Na2CO3 70
N. R
N. R
12
glutamic acid-Cu
MCM-41@DL-Pyro- DMSO K2CO3 70
glutamic acid-Cu
MCM-41@DL-Pyro- DMSO KOH 70
glutamic acid
MCM-41@Cu
DMSO KOH 70
66
aReaction conditions: Iodobenzene (1 mmol), base (0.7 g), S8 (1 mmol), solvent (3 mL), and catalyst at
temperature
bIsolated yield
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Cu attached functionalized mesoporous MCM-41: a novel…
Table 3 Reactions of the nitriles and NaN3 using MCM-41@DL-Pyroglutamic acid-Cu Catalyst
of solvents on the catalytic performance of the MCM-41@DL-Pyroglutamic acid-
Cu, diferent solvents e.g., H2O, ETOH, DMSO, DMF, toluene, and PEG were
examined. Among the diverse solvents examined, the highest yield was achieved
using DMSO. Then, the infuence of temperature was estimated, with an increase
from 80 to 130 °C, a rise in catalytic performance was detected. To study the efect
of the amount of the catalyst in the reaction, the diferent amount of catalyst was
investigated. By changing the amount of catalyst, it was found that 70 mg of the
catalyst is an appropriate quantity. To determine the appropriate base, diferent bases
e.g., K2CO3, Na2CO3, NaOH, and KOH was studied. It was found when KOH was
utilized, the outstanding yield was gained. Then, diferent catalysts were tested.
When the catalytic reaction was performed with MCM-41@DL-Pyroglutamic acid
as a catalyst, no signifcant results were obtained. We then performed the reaction
using MCM-41 @Cu as the catalyst, it was observed that the reaction proceeded
with good results. Therefore, the experimental conditions have been recognized as
130 °C in DMSO with 70 mg of MCM-41@DL-Pyroglutamic acid-Cu catalyst.
1076
1284
1120
837
1217
2370
1728
1625
761
1460
1381
2860
3444
3900
2927
3400
4400
2900
2400
1900
1400
900
400
Wavenumber (cm-1)
Fig. 9 FT-IR spectra of 5-(Isocyanomethyl)-1H-tetrazole
1 3

S. Molaei, M. Ghadermazi
Table 4 Reactions of the aryl halides with S8 and KOH base using MCM-41@DL-Pyroglutamic acid-Cu
Catalyst
Thioether formation (C–S) reaction under optimized condition (aryl halide, S8,
KOH (0.7 g) catalyst (7 mg), and DMSO (3 mL) at 130 °C was studied toward
diverse aromatic halides. The consequences of Table 4 show that MCM-41@DL-
Pyroglutamic acid-Cu provides a good activity for the thioether formation (C–S)
reactions using molecular S8.
Scheme 3 Plausible mechanism for MCM-41@DL-Pyroglutamic acid-Cu catalyzed thioether formation
(C–S) reactions using molecular S8
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
Based on previous articles and this study, for this synthesis, a probable mechanis-
tic path has been considered and shown in Scheme 3. The S8 molecule decomposes
to form the potassium disulfde salt in the presence of the KOH base. This molecule
attaches to the catalyst, making a bicyclic ring. Aryl halide later adds: It forms a
complex bridge structure that decomposes on-site by an intermediate. In addition,
the second molecule, aryl halide, is thus added, eventually releasing the thiourea,
which maintains the catalytic site for reuse [68].
Recyclability study
As reusability is signifcant for industrial purposes of a proper catalyst, recycling
of MCM-41@DL-Pyroglutamic acid-Cu was studied. This study was performed
with MCM-41@DL-Pyroglutamic acid-Cu catalyst in the synthesis of 5-substi-
tuted 1H-tetrazoles. Firstly, 1 mmol of 4-nitrobenzonitrile was consumed with
1.2 mmol of NaN3 using a 70 mg catalyst. At the end of the reaction, the catalyst
was collected by centrifuge. To remove any organic materials, the catalyst was
washed with EtOAc, then it was dried at 60 °C, and recycled in the next runs. The
consequences are presented in Fig. 10. We could employ the catalyst for seven
consecutive times without noteworthy decrease in catalytic performance. The
FT-IR, and SEM, analysis of the catalyst after the 7th cycle was done and shown
in Fig. 11. The SEM and FT-IR analysis show that the structure of the catalyst
has been persisted unchanged after seven cycles.
To investigate the thermal stability of the catalyst, TGA analysis of reused
MCM-41@DL-Pyroglutamic acid-Cu after seven runs were performed (Fig. 12).
The TGA data of the catalyst after the seven reaction cycles showed the same
profle as the fresh catalyst, attesting to the stability of the catalyst.
Fig. 10 Recyclability study of the MCM-41@DL-Pyroglutamic acid-Cu catalyst in the preparation of
5-(4- nitrophenyl)-1H-tetrazole
1 3

S. Molaei, M. Ghadermazi
1.2
1
0.8
0.6
0.4
0.2
0
3900
3400
2900
2400
1900
1400
900
400
-1
Wavenumber (cm )
Fig. 11 FT-IR spectra (up) SEM images and (down) of reused MCM-41@DL-Pyroglutamic acid-Cu
Leaching Study
The leaching study was done to recognize the nature of the MCM-41@DL-Pyro-
glutamic acid-Cu catalyst in the synthesis of aryl thioether reaction. The Cu con-
tent of the catalyst was determined before and after reusing the catalyst by the
ICP-AES technique. Furthermore, the ICP-AES technique for the recycled catalyst
approves that minimal leaching of Cu occurred during the reaction. (Scheme 3) It
was obtained that the content of Cu in the fresh catalyst is 1.7 mmol g−1 and Cu
,
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
110
100
90
80
70
60
50
25
125
225
325
425
525
625
725
Temperature (°C)
Fig. 12 TGA curves of reused MCM-41@DL-Pyroglutamic acid-Cu
content has been slightly decreased to 1.6 mmol g−1 after the 7th catalytic reaction
(Table 5). Thus, MCM-41@DL-Pyroglutamic acid-Cu catalyzed thioether forma-
tion (C–S) reactions are completely heterogeneous.
These experimental results suggested no signifcant leaching of Cu happened dur-
ing the reaction, and Cu is covalently grafted with the organic functional groups
in the mesoporous silica. So, during the catalyst recycling, the decreased activity
ascribed to the low leaching of Cu from the catalyst and experimental error.
Hot fltration tests
For the leaching study, the hot fltration test was performed for the synthesis of
5-substituted 1H-tetrazoles as a model reaction by MCM-41@DL-Pyroglutamic
acid-Cu (under optimal conditions) to evaluate whether Cu acts as a homogene-
ous catalyst in the solution or not. After 30 min from the start of the reaction,
a yield of 40% of the reaction was obtained with MCM-41@DL-Pyroglutamic
acid-Cu and then the catalyst was separated from the reaction mixture. Then, the
reaction was continued for another 30 min without increasing the yield. Based on
these results, it can be concluded that there is no leaching of Cu from the support
MCM-41, and the present catalysts are truly heterogeneous.
Table 5 Metal amounts (mmol
Sample
Fresh
1.7
7st Regeneration
1.6
g−1) analysis of fresh and
recovered catalysts
MCM-41@DL-Pyroglutamic acid-Cu
1 3

S. Molaei, M. Ghadermazi
1 3

Cu attached functionalized mesoporous MCM-41: a novel…
The comparison of the catalyst with catalysts reported in the literature for the
synthesis of 5-(4-chlorophenyl)-1H-tetrazole and diphenyl sulfde are presented in
Table 6. The MCM-41@DL-Pyroglutamic acid-Cu exhibits better reaction time
and yield under mild conditions and is more importantly it is a green catalyst.
Conclusion
In conclusion, the efective, atom-economical thioether formation (C–S) reactions
by molecular S8 with KOH at 130 °C, and synthesis of 5-substituted 1H-tetrazoles
are described for the frst time by the green MCM-41@DL-Pyroglutamic acid-Cu
catalyst. This simple, eco-friendly catalysis carry out with no additives and needs
shorter reaction times with moderate to high yields. The present C–S coupling reac-
tion, cycloaddition, and the preparation of disulfdes are associated with some bene-
fts like easier process, slighter reaction conditions, and a replacement to dangerous,
damaging, and poisoning regular Lewis’s acid catalysts. Its reusability with constant
catalytic efcacy for seven runs is determined, showing MCM-41@DL-Pyroglu-
tamic acid-Cu as a greener catalyst, can be used instead of other heterogeneous cata-
lysts or metal salts, and it has high value for industrial uses.
Acknowledgements We gratefully acknowledge the Iran National Science Foundation for fnancial sup-
port of this project under contract (98020716).
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Authors and Afliations
Somayeh Molaei1 · Mohammad Ghadermazi1
* Mohammad Ghadermazi
mghadermazi@yahoo.com
Somayeh Molaei
somayeh.molaei@yahoo.com
1
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
1 3