Fe3O4?Hydrotalcite-NH2-CoII NPs: A novel and extremely effective heterogeneous magnetic nanocatalyst for synthesis of the 1-substituted 1H-1, 2, 3, 4-tetrazoles

Article abstract of DOI:10.1016/j.inoche.2020.108287

In this study, we present a versatile and easy procedure for modifying a ferrite nanoparticles so step by step. A new nanocatalyst was prepared via Co^II immobilized onto an aminated ferrite nanoparticles (Fe₃O₄?HT?AEPH₂-Co^II). The catalyst was fully characterized by FT-IR, EDX, FE-SEM, TGA, XRD, and VSM analyses. In the preparation of 1-substituted-1-H-tetrazole, the corresponding nanocatalyst shown great catalytic activity. The reaction contains expeditious reusable catalyst (Fe₃O₄?AEPH₂-Co^II) that promotes condensation between sodium azide, triethyl ortho-formate, and diversity of heterocyclic/aromatic amines. Also, an environmentally toxic solvent was eliminated. A significant improvement in the synthetic efficacy (95%, yield) was obtained by this new sustainable and eco-friendly protocol as well as high purity. The current procedure as a green protocol offers benefits including a simple operational procedure, an excellent yield of products, mild reaction conditions, minimum chemical wastes, short reaction time, and easy catalyst synthesis. Without any significant reduction in the catalytic performance, up to four recyclability cycles of the catalyst were obtained. The optimization results suggest that the best condition in the preparation of tetrazole derivatives is 0.005 g of the Fe₃O₄?HT?AEPH₂-Co^II catalyst where H₂O is the solvent at 90 °C. The proposed protocol could be applied on a wider scope of the substrate (i.e., electron-deficient and electron-rich).

Full text of DOI:10.1016/j.inoche.2020.108287

Inorganic Chemistry Communications 122 (2020) 108287
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
II
Fe O @Hydrotalcite-NH -Co NPs: A novel and extremely effective
3
4
2
heterogeneous magnetic nanocatalyst for synthesis of the 1-substituted
1
H-1, 2, 3, 4-tetrazoles
*
Mehri Salimi , Farzaneh Esmaeli-nasrabadi, Reza Sandaroos
Department of Chemistry, Faculty of Science, University of Birjand, P. O. Box 97175-615, Birjand, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, we present a versatile and easy procedure for modifying a ferrite nanoparticles so step by step. A
Tetrazole
II
new nanocatalyst was prepared via Co immobilized onto an aminated ferrite nanoparticles (Fe
3
O
4
@H-
Sodium azide
Triethyl orthoformate
II
T@AEPH
2
-Co ). The catalyst was fully characterized by FT-IR, EDX, FE-SEM, TGA, XRD, and VSM analyses. In
the preparation of 1-substituted-1-H-tetrazole, the corresponding nanocatalyst shown great catalytic activity.
One-pot
II
II
3 4 2
The reaction contains expeditious reusable catalyst (Fe O @AEPH -Co ) that promotes condensation between
Fe
3
O
4
@HT@AEPH
2
-Co nanoparticles
sodium azide, triethyl ortho-formate, and diversity of heterocyclic/aromatic amines. Also, an environmentally
toxic solvent was eliminated. A significant improvement in the synthetic efficacy (95%, yield) was obtained by
this new sustainable and eco-friendly protocol as well as high purity. The current procedure as a green protocol
offers benefits including a simple operational procedure, an excellent yield of products, mild reaction conditions,
minimum chemical wastes, short reaction time, and easy catalyst synthesis. Without any significant reduction in
the catalytic performance, up to four recyclability cycles of the catalyst were obtained. The optimization results
Hydrotalcite
suggest that the best condition in the preparation of tetrazole derivatives is 0.005 g of the Fe
3
O
4
@HT@AEPH
O is the solvent at 90 C. The proposed protocol could be applied on a wider scope of the
substrate (i.e., electron-deficient and electron-rich).
2
-
II
◦
Co catalyst where H
2
1
. Introduction
of several drugs approved by the Food and Drug Administration (FDA),
which are important in medicine [15]. It has been reported that cell
penetration and oral bioavailability are improved in a drug via the
lipophilic character of moieties that are tetrazole [16]. In this regard, the
potential therapeutic profile of tetrazole chemistry has occurred so
much attention. In the class of nonpeptide angiotensin-II inhibitors,
losartan, valsartan, and irbesartan are famous antihypertensive drugs
possessing a biphenyl tetrazolyl part in their structure (Fig. 1). Likewise,
there is also a tetrazole ring in the structure of TAK-456 as a wide range
of antifungal drugs (Fig. 1).
Among the known stable heterocycles, tetrazoles belong to a cate-
gory of 5-membered heterocyclic compounds containing nitrogen, in
which nitrogen content is maximum. It is believed that 2-phenyl-2H-tet-
razole-5-carbonitrile to be the first compound having a tetrazole ring
which was synthesized and characterized in 1885 [1].
In recent decades, considerable attention has been received to the
chemistry of N-containing heterocycles (tetrazoles) because of their
hopeful biological properties particularly antifungal [2], antimicrobial
[
3], antiulcer [4], antinociceptive [5], anti-HIV [6], antiallergic [7],
Befitting coordinating properties are endowed by them. For example,
nitrogen-containing heterocyclic ligands can form stable complexes by
numerous metal ions. In organic synthesis, they can act as pioneers to
many different of nitrogen heterocycles [17,18]. For the preparation of
other complex heterocycles, the tetrazole ring is an important interme-
diate through various rearrangements [19]. Inherent acetylcholines-
terase inhibition potency was detected in nitrogen-containing
heterocyclic compounds. Therefore, they are among the most promising
anti-inflammatory [8], antiproliferative [9] and anticancer [10]. It is
also presented that they are potential TNF alpha inhibitors [11], P2X7-
antagonists [12], and inhibitors of anandamide cellular uptake [13].
Because of the application of tetrazole and derivatives thereof as lipo-
philic as spacers and metabolically established substitutes for a car-
boxylic acid in a drug study, their importance of them has augmented in
medicinal chemistry [14]. There are tetrazole moieties in the structures
*
Corresponding author.
E-mail addresses: msalimi@birjand.ac.ir, m_salimi4816@yahoo.com (M. Salimi).
https://doi.org/10.1016/j.inoche.2020.108287
Received 11 August 2020; Received in revised form 30 September 2020; Accepted 3 October 2020
Available online 15 October 2020
1
387-7003/© 2020 Elsevier B.V. All rights reserved.

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
Fig. 1. Drugs in the market with a tetrazole moiety.
candidates for Alzheimer’s disease treatment [20–22]. Therefore, there
is a need to develop efficient protocols to synthase tetrazoles considering
pharmacological applications of them. 1-substituted tetrazoles are
interested due to their wide applications [23,24]. However, their
application in medical practice is restricted due to the lack of convenient
synthesis methods.
stability [34,35]. Therefore, it is needed to design and synthesize
powerful and recyclable nano-magnetic catalysts. Heterogeneous cata-
lysts in chemical processes are interested in the literature. It is due to
their merits including good reusability and easy separation from the
reaction mixture in comparison with homogeneous catalytic systems. It
is important to pay attention to the low activity and selectivity of het-
erogeneous catalysts compared to homogeneous ones due to the low
surface area. It is more important when the immobilization of the active
catalytic kinds onto appropriate support is a case where the active sites
in a supported system are not approached as in the equivalent homo-
geneous due to steric hindrance of the great support. Reducing support
size by a combination of heterogeneous catalytic systems and nano-
technology can be a solution that multiplies the interactions of surface
and reactants increasing the ratio of surface to volume. From the activity
and selectivity point of view, nono chemical technology can be
approached by both heterogeneous and homogeneous catalyst systems.
However, due to the very small dimensions of nanomaterials, major
restrictions are the facile recovery and separation of the catalyst. Mag-
netic nanoparticles are excellent alternatives. By using an external
magnetic modest, they are effortlessly separated from the reaction me-
dium. Besides, an excellent method of the separation of catalysts is the
magnetization of common nano-solid supports. A novel type of hetero-
geneous reusable catalytic system is created by the combination of nano-
chemistry technology, and magnetic solid supports, and heterogeneous
properties. These catalysts have the advantages of homogeneous
However, acid-catalyzed could be cycle added between isocyanides
and hydrazoic acid in the preparation of 1-substituted tetrazoles
[
25,26]. In the presence of acetic acid, it also could be synthesized by
cyclization between triethyl orthoformate, sodium azide, and primary
amines [27]. Other methods include using various catalysts including
natrolite zeolite [28], In(OTf)
3 4
[29], [Hbim]BF [30], SSA [31], Yb
(
OTf) [32]. Disadvantages include the usage of dangerous and costly
3
reagent, prolonged reaction times, and use of the solvent with the high
boiling point, high temperature, dull workup processes, the existence of
highly hydrazic acid, and the problem in the recovery and separation of
the catalyst, toxic waste generation. Therefore, it is important to create
an ecofriendly and more effective procedure which reduce these
disadvantages.
Designing and using appropriate center cores and catalytic species,
novel approaches concern the maintainable growth of extremely selec-
tive nanostructured catalysts [33]. In the preparation of catalyst based
on nano-magnetic, silica derivative has been used as a coating agent.
This is due to many prominent features including great selectivity and
good activity, effective recovery and good recyclability, excellent
2

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
II
3 4 2
Scheme 1. Preparation of catalyst (Fe O @HT@AEPH -Co ).
catalysts, like excellent selectivity and activity [35–37].
nanoparticles [38–46].
Nowadays, Organic synthesis is explored considering the principle of
green. Therefore, it is important to use an eco-friendly catalyst and
moderate reaction circumstances. Hydrotalcite (HTs) and magnetic
hydrotalcite (MHTs) have been investigated extensively to enhance the
long-term stability and activity of catalysts. In organic reactions, they
are investigated as a hopeful material for the catalyst support. Hydro-
talicte is a layer double hydroxide (LDH) with abundant surface hy-
It is difficult to separate the catalysts based on hydrotalcite from the
reaction medium by conventional centrifugation and filtration separa-
tion methods [40]. Using of a magnetic separation approach is a suitable
technique [47] that can be applied using a simple magnetic bar when
magnetic nanoparticles are incorporated into the hydrotalcite structure
[41,42]. It also prevents the agglomeration of MNPs, as well.
In this paper, an amino-functionalized Fe
rier is prepared. It was prepared with 2-aminoethyl dihydrogen phos-
phate (AEPH ). It is a short-chained bifunctional organic molecule. It
also has both an amino group and a phosphate group. For binding by
3 4
O @HT nanoparticle car-
2
3
ꢀ
droxyl groups, Mg-Al mixed oxides, and anionic (CO ) interlayers. The
2
+
3+
x+
general formula of a layer double hydroxide is [M (1-x)M x(OH) ]
2
2
n- x
x-
2+ 3+
[
A
/n⋅mH
is the interlayer anion. Plentiful surface hydroxyl groups are made of
2
O] . M is di metal ion, M is a trivalent metal ion, and
n-
II
A
Fe
3 4 2
O @HT NPs, the phosphate group of AEPH is useful. Co immobi-
II
2
16
+
lized onto aminated Fe O @HT (Fe O @HT@AEPH -Co ) was also
3
4
3
4
2
alternating cationic layers ((MgMg 6AlAl22(OHMg Al2(OH)) as the
6
6
studied. Because in the bonding of several metal ions, the amino group
can perform as a point of anchor. In the preparation of 1-substituted 1H-
tetrazoles, a new magnetically reusable heterogeneous catalyst was
brucite-like). Mg-Al mixed oxide is chemically active sites to be used for
the catalytic reaction. They as well as acts as an anchoring site for metal
3

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
Table 1
II
Preparation of tetrazole derivatives using Fe
3
O
4
@HT@AEPH
2
-Co catalyst.
Entry
1
Substrate
Product
Time (h)
1
Yield (%)
95
2
3
70
3
4
5
6
7
8
9
2.5
2.5
3
85
85
45
90
82
95
70
3
3
3
3
1
0
2.5
75
1
1
1
2
3
60
2.5
30
(
continued on next page)
4

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
Table 1 (continued)
Entry
Substrate
Product
Time (h)
Yield (%)
1
3
3
40
1
1
4
5
3
3
80
60
II
◦
C
Reaction Conditions: amine (1.0 mmole), sodium azide (1.0 mmol), triethyl orthoformate (1.2 mmol), Fe
3
O
4
@HT@AEPH
2
-Co , H
2
O, 90
investigated. It was Fe
3
O
4
@HT@AEPH
2
-CoII that was prepared using
by an external magnetic field. Then, it was washed with 2 × 100 mL
standard procedures according to the literature (Scheme 1).
distilled water. When the pH reached 7, for 12 h, Fe
3
O
4
@HT was dried
◦
at 50 C.
2
. Experimental section
2
.4. Fe
3
O
4
@HT@AEPH
2
synthesis
2
.1. General methods
Fe
3
O
4
@HT (1 g) was added to a mix of deionization water/ethanol
All chemical reagents and solvents were purchased from Merck and
(50 mL). Then, 1.69 g (12 mmol) of 2-aminoethyl dihydrogen phosphate
was added to the mixture. It was dissolved in deionized water (20 mL).
Sigma-Aldrich chemical companies and were used as received without
further purification. The purity determinations of the products were
accomplished by TLC on silica gel polygram STL G/UV 254 plates. The
FT-IR spectra were recorded on pressed KBr pellets using a Nicoet 800
FT-IR spectrometer at room temperature in the range between 4000 and
◦
Stirring continuously of the solution at 25 C for 48 h. Subsequently,
deionized water and ethanol were used to wash the consequential
nanoparticles (2-aminoethyl dihydrogen phosphate-functionalized
Fe O @HT) repeatedly. Then, they were separated by an external
3
4
ꢀ 1
4
00 cm . The NMR spectra were obtained on Brucker Avance 300 MHz
instruments in DMSO‑d . All the yields refer to isolated products after
purification by thin-layer chromatography or recrystallization.
magnetic field and dried.
6
-CoII synthesis
2
2
.5. Fe
3
O
4
@HT@AEPH
2
.2. Synthesis of hydrotalcite (HT)
0.99 g (4.2 mmol) of CoCl ⋅6H O was added to a mixture of 1 g of
2
2
3 4 2
Fe O @HT@AEPH and 50 mL of ethanol. Vigorous stirring was used to
II
The aqueous solution with a volume of 60 mL was spilled in a 250 mL
3 4 2
reflux the mixture. It took 48 h to obtain Fe O @HT@AEPH -Co . An
flask. It was contained Al(NO
3
)
3
⋅9H
2
O (20 mmol, 7.50 g) and Mg
external magnet and ethanol were used to collect and repeatedly wash
◦
(
NO O (40 mmol, 10.25 g). Then, 60 mL of the mixed solution
3
)
2
⋅6H
2
the product, respectively. Then, it was dried in a vacuum for 6 h at 25 C.
added to the solution dropwise. The vigorous stirring was also applied at
◦
6
0 C. It was contained NaHCO
3
(7.5 g) and NaOH (10.25 g). The pre-
2
.6. General synthesis for the preparation of 1-substituted 1H-tetrazoles
◦
pared suspension was stirred at 60 C for 24 h. The resulted white solid
was filtered and then washed using deionized water. To remove the
alkali metal ions the final pH was reached 7. The resulted Mg-Al
II
In a round-bottomed flask, 0.005 g of Fe
3
O
4
@HT@AEPH
2
-Co , 1.2
mmol of triethyl orthoformate, 1 mmol of sodium azide, and 1 mmol of
◦
hydrotalcite (I) was dried for 12 h at 100 C. Its molar ratio was Mg/
◦
◦
amine were placed. The mixture was stirred at 90 C. TLC was used to
Al = 2.
monitor the reaction. The mixture was cooled to 25 C when the reaction
was completed. Then, it was diluted with 3 × 20 mL of ethyl acetate. An
2
.3. Synthesis of Fe
3
O
4
@Hydrotalcite (Fe
3
O
4
@HT):
external magnet was used to remove the catalyst. Then, it was dried over
anhydrous Na
2
SO
4
. Using EtOAc–hexane with a ratio of 1:9, a crystal-
1
A mixture containing 1.05 g (5.2 mmol) of FeCl
mmol) of FeCl O was dissolved in deionized water with a volume of
⋅6H
00 mL. A three-necked 500 mL round-bottom flask was used. It was
2
⋅4H
2
O and 2.1 g (8
lization step was carried out after concentration. Melting points, H
3
2
NMR, and FT-IR were utilized for the characterization of products. The
synthesized compounds spectral data are reported.
1
equipped with dropping funnel and argon gas inlet tube. Under the Ar
◦
atmosphere and at 80 C, the mixture was stirred for 5 to 10 min. Then,
2.6.1. Analytical data
1
00 mL of NaOH solution (5%) and 4 g of hydrotalcite were concurrently
1-phenyl-1H-tetrazole (Compound 1, Table 1): yellow solid; m.p =
◦
ꢀ 1
2
added into the solution. 24 h stirring of the suspension was the next step
65–67 C, IR (KBr)/ V (cm ): 3063 (C-H, sp stretch Ar), 1681 (C = N),
1591, 1463 (C = C); (3122, 3063, 2918, 1747, 1681, 1591, 1500, 1463,
◦
at 80 C. The resulted from brown powder (Fe
3
O
4
@HT) was separated
5

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
II.
3 4 2
Scheme 2. Synthesis of tetrazoles derivatives catalyzed by Fe O @HT@AEPH -Co
II.
3 4 2
Fig. 3. TGA curve of Fe O @HT@AEPH -Co
morphology of the catalyst.
In this study, an environmentally benign heterogeneous catalyst was
used to synthesize 1-substituted-1Htetrazole derivatives 4(a–o). H
2
O
was the solvent. Advantages include catalyst stability and recyclability,
purity, and yield of products, reaction times, and useful methods. It has a
wide range of applications. It is also compatible with various functional
groups (electron-withdrawing/electron-donating) (Scheme 2).
3
.1.1. FT-IR spectroscopy:
The catalyst structure was defined using FT-IR spectroscopy to
confirm the existence of the bonded species. Fig. 2 represents the FT-IR
spectra of HT, Fe @HT, Fe @HT@AEPH and Fe @H-
- Co . For HT, the broadbands which were displayed in the
3
O
4
3
O
4
2
,
3 4
O
Fig. 2. FT-IR spectra of (a) HT, (b) Fe
3
O
4
@HT (c) Fe
3
O
4
@HT@AEPH
2
and (d)
II
T@AEPH
2
II
Fe
3
O
4
@HT@AEPH
2
-Co .
ꢀ
1
range of 3130–3627 cm were assigned to OH group stretching and the
ꢀ 1
absorption band which was around 1633 cm was caused by the flex-
ural oscillation peaks of interlayer water molecules [48]. Also, the ab-
1
391, 1205, 1090, 1051, 995, 962, 912, 881, 762, 684, 506); 1H NMR
CDCl
, 300 MHz) δ (ppm): 7.52–7.76 (m, 5H, Ar), 9.11 (s, 1H tetrazole).
-benzyl-1H-tetrazole (Compound 15, Table 1): White solid; m.p =
(
3
ꢀ 1
sorption peaks around 1369 cm were considered to be caused by the
1
2
3
ꢀ
asymmetric stretching bond of intercalated NO [49]. This indicates
◦
ꢀ 1
2
1
32–133 C; IR (KBr)/ V (cm ): 3061 (C-H, sp stretch Ar), 1644 (C =
the presence of a small number of carbonate ions in the LDH phase.
N), 1535, 1454 (C = C). (3272, 2929, 2857, 1592, 1458, 1406, 1360,
ꢀ
1
Al–OH stretching may be responsible for the bond at 667 and 733 cm
1
3
297, 1244, 1200, 1130, 1001, 955, 880, 752, 695); 1H NMR (CDCl
00 MHz) δ (ppm) 4.46–4.48 (s, 2H), 7.29–7.40 (m, 5H), 8.25 (s, 1H).
,2-di (1-H-tetrazole-1-yl) benzene (Compound 2, Table 1): White
3
,
[
50]. The lattice vibration of metal–oxygen bonds (Mꢀ O) was respon-
ꢀ 1
sible for the absorption peaks around 550–770 cm (Fig. 2a) [51].
In Fig. 2b, the principal bands were observed at 3250–3400 cm
1
ꢀ 1
◦
ꢀ 1
2
solid; m.p = 169–173 C, IR (KBr)/ V (cm ): 3060 (C-H, sp stretch,
Ar), 1620 (C = N) 1455, 1589 (C = C); (3315, 3060, 3003, 2934, 2857,
which is a broad absorption band attributed to stretching frequencies of
hydroxyl groups and bound water on the surface of Fe
3
O
4
NPs, 1010 and
1
7
617, 1586, 1457, 1409, 1360, 1297, 1244, 1200, 1133, 1004, 955, 882,
ꢀ 1
8
64 cm which are asymmetric and symmetric stretching vibrations
1
50, 632); H NMR (CDCl
3
, 300 MHz) δ (ppm): 7.11–7.62 (m, 4H), 8.22
ꢀ 1
characteristic of Fe–O–H bond, and 580–620 cm which is attributed to
the vibrational frequency of Fe–O bond [52–54].
(
s, 1HTetrazole).
In the FT-IR spectrum of Fe
3
O
4
@AEPH
2
(Fig. 2c) due to the
@AEPH
2
3
. Results and discussion
stretching vibration of P = O, the characteristic band of Fe
3
O
4
ꢀ
1
ꢀ 1
appears at 1128 cm . Two absorption bands at 1034 and 977 cm
asymmetric and symmetric stretching vibrations) confirm the presence
3
.1. Characterization
(
of the P–O–Fe bond. Also, absorption bands at 1093, 984, and 570–605
Thermogravimetric analysis (TGA), scanning electron microscopy
ꢀ 1
cm are attributed to the asymmetric and symmetric stretching and
(
SEM), FT-IR, energy-dispersive X-ray spectroscopy (EDX), and powder
bending vibrations of O–P–O bond, respectively. The broad character-
X-ray diffraction (XRD) were utilized to investigate the structure and
ꢀ 1
istic band of Fe–O at around 580–620 cm covers the latter absorption
6

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
II.
3 4 2
Fig. 4. SEM images of Fe O @HT@AEPH -Co
II.
3 4 2
Fig. 5. Energy dispersive X-ray analysis (EDAX) of Fe O @AEPH -Co
band. Two absorption bands at 3564 and 3590 cm 1 correspond to –NH
ꢀ
a conformation for the AEPH
surface [53].
covalent bonding on the Fe
O
NPs’
2
2
3
4
stretching frequencies. Two other absorption bands at 1617 and 1289
ꢀ
1
cm are also assigned to–NH bending vibration and –CN stretching
vibration, respectively (Fig. 2c) [53].
3.1.3. SEM-EDS images and SEM image combined EDS-elemental mapping:
ꢀ 1
II
The presence of an absorption band at 447 cm in the FT-IR spec-
3 4 2
Fe O @HT@AEPH -Co size and morphology was studied with field
II
II
trum of Fe
nated Fe
absorption due to Co–N vibration (Fig. 2d). Upon coordination of Co on
aminated Fe stretching bands are
NPs, the intensities of –NH
decreased significantly [53].
3
O
4
@AEPH
2
-Co , confirms the coordination of Co on ami-
emission electron microscopy (FE-SEM). Fig. 4 presents the images.
According to Fig. 5, the results of EDX analysis confirms C, P, O, Mg, Fe,
3
O
4
NPs. Structural vibrations of Fe
3 4
O
NPs covers this
II
II
Co, and Al presence. It was also confirmed that Co is supported on
3
O
4
2
aminated Fe
3 4
O NPs.
3 4 2
O @AEPH
-CoII have
The special structure of the synthesized Fe
been studied by elemental mapping evaluation of the nanoparticle
affirmed the existence of P, O, Al, Ca, Fe, Mg, and Co in construction
occurred (Fig. 6).
3
.1.2. Thermal gravimetric analysis (TGA)
Two weight losses were observed in the Fe
TGA thermogram (Fig. 3). Hydrogen and by physically bonded water in
3 4 2
O @HT@AEPH
-CoII
II
the Fe
3
O
4
@HT@AEPH
2
-Co structure is responsible for the weight loss
3.1.4. X‑ray diffraction (XRD) analysis:
◦
3 4 3 4 2
The crystalline structure of HT, Fe O @HT, and Fe O @AEPH
-CoII
by 15% at 27–250 C. On the other hand, the organic segment decom-
position anchored to the surface of the Fe
weight loss by 20% at 250–450 ◦C. According to the thermogram, the
AEPH amount combined on Fe NPs is 20% (wt%). Therefore,
Fe -Co high thermal stability is confirmed by the
removal of the pendent organic group at the elevated temperature that is
3
O
4
NP is responsible for the
was identified by XRD. The characteristic diffraction peaks of a well-
crystallized HT phase (JCPDS NO. 22–0452) was presented by MgAl-
◦
◦
◦
◦
2
3
O
4
LDH at 2θ of 11.69 , 35.05 , 61.04 , and 62.03 , corresponding to the
reflections of planes (001), (100), (110), and (111), respectively. The
successful synthesize of the HT was determined by the diffraction peaks
II
3 4 2
O @HT@AEPH
7

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
II.
3 4 2
Fig. 6. Elemental mapping analysis of Fe O @AEPH -Co
II.
Fig. 7. XRD patterns of (a) HT, (b)Fe
Fig. 7a) [47]. Fig. 7b presents that all the diffraction peaks can be
3 4 3 4 2
O @HT, (c)Fe O @HT@AEPH -Co
(
CoII and Fe
zation curves. The saturation magnetizations are 7.21 and 18.83 emu.
3 4
O NPs is concluded from the room-temperature magneti-
indexed to (2, 2, 0), (3, 1, 1), (4, 0, 0), (4, 2, 2), (5, 1, 1) and (4, 4, 0)
reflections which match well with the characteristic peaks of cubic
structure (JCPDS 19–0629). We can conclude that the crystalline
ꢀ 1
II
g
for Fe -Co and Fe
bound AEPH -Co presence was confirmed by a decrease in the
Fe @AEPH
2
-CoII saturation magnetization.
3
O
4
@AEPH
2
3 4
O @HT, respectively. The surface-
II
2
structure of Fe
AEPH
and CoII because the peak positions of Fe
unchanged during the production of Fe @AEPH
the Debye–Scherrer equation d = K λ/β cos θ, the average crystallite
3
O
4
NPs is conserved after the surface modification with
3
O
4
2
3 4
O
NPs (Fig. 7b) are
II
3
O
4
2
-Cu (Fig. 7c). Using
3.2. Optimization of the reaction conditions
II
sizes, d, of HT, Fe
3
O
4
@HT, and Fe
3
O
4
@AEPH
2
-Cu calculated to be
0.01, 0.008, 0.005, 0.003, and 0.001 g (Fig. 9) of the catalyst were
about 18.3, 30.3 and 45.6 nm, respectively [53].
investigated to obtain the optimum catalyst concentration. These
◦
different concentrations were investigated at 90 C where H
2
O was the
3
.1.5. Vibrating sample magnetometer (VSM) analysis
Fig. 8 presents the Fe @HT, and Fe @AEPH
solvent.
3
O
4
3
O
4
2
-CoII Mꢀ H hys-
In the absence of a catalyst, the model reaction was completed in 6 h
with a poor yield of 5% (see Fig. 9). Then, 0.01, 0.008, 0.005, 0.003, and
3 4 2
teresis curves. The superparamagnetic characteristic of Fe O @AEPH -
8

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
results.
Condensation of electron-withdrawing and electron-donating groups
contained anilines was carried out. The groups include chloro, bromo,
acetyl, and methyl. The reaction times were short and the isolated yields
were excellent. The results are better in the case of the para-position
anilines (see Table 1, entry 6) compared to the ortho-position anilines
(
see Table 1, entry 7). The steric hindrance on product formation is more
for the ortho-position anilines compared to the para-position anilines.
The spectral and physical data of all known compounds were compared
Fig. 8. Mꢀ H hysteresis curves of Fe
3 4 3 4
O @HT (red curve), and Fe O @H-
II
T@AEPH
2
-Co (black curve). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)
0
.001 g of the catalyst were investigated in terms of yield and time. An
increase by 70–95% was obtained in the yield by any subsequent in-
crease in the catalyst concentration by 0.001 g. Fig. 4 suggests that the
optimum yield is achieved using 0.005 g (0.00015 mol%) of the catalyst
◦
at 90 C. When the catalyst content is less than 0.005 g (0.00015 mol%),
the yield is in the range of 70–90%, and the reaction time is higher.
When the catalyst content is more than 0.005 g, better yield didn’t
achieve. The catalyst surface saturation is the possible reason.
Various temperatures were also investigated to optimize the reaction
Fig. 10. The effect of diverse temperatures in the preparation of tetrazoles by
II
Fe
3
O
4
@AEPH
2
-Co . Conditions of reaction: aniline (1 mmol), triethyl ortho-
formate (1.2 mmol), sodium azide (1 mmol), in
2
H O, 0.005 g of
II
3 4 2
Fe O @AEPH -Co .
2
temperature. The solvent was H O. The yield was better and the reaction
◦
◦
time was shorter increasing the temperature from 25 C to 90 C. At
◦
2
5
C, the yield and time were 5% and 4.5 h. The yield is better
increasing the temperature together with stirring (5–97%) (Fig. 10). But,
◦
no improvement was observed increasing the temperature up to 110 C.
◦
Therefore, 90 C was considered as the optimal temperature.
In the end, the influences of various solvents were investigated on the
model reaction. Some organic solvents including ethanol, acetonitrile,
H
2
O, and DMSO were investigated. According to Fig. 11, the most
effective solvent for the preparation of tetrazoles is H O.
2
Scheme 2 presents the general procedure of the experiment. The
reaction of sodium azide and triethyl orthoformate was carried out with
various amines using optimized reaction conditions. Short reaction
times and high to excellent yields were achieved producing the corre-
sponding 1-substituted 1H-tetrazoles. The reaction of several anilines
Fig. 11. The effect of diverse solvents in the preparation of tetrazoles by
II
3 4 2
Fe O @AEPH -Co . Conditions of reaction: aniline (1 mmol), triethyl ortho-
with sodium azide and triethyl orthoformate was carried out in the
II
II
3 4 2
formate (1.2 mmol), sodium azide (1 mmol), 0.005 g of Fe O @AEPH -Co .
presence of 0.005 g of Fe
3
O
4
@HT@AEPH
2
-Co . Table 1 summarizes the
II
Fig. 9. The effect of diverse catalysts in the preparation of tetrazoles by Fe
O
3 4
@AEPH
2
-Co . Conditions of reaction: aniline (1 mmol), triethyl orthoformate (1.2
◦
mmol), sodium azide (1 mmol), in H
2
O, at 90 C.
9

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
II.
3 4 2
Scheme 3. The suggested mechanism for the synthesis of tetrazoles with Fe O /HT-NH -Co
to the literature to be characterized.
3
.3. Mechanism
3 4 2
Scheme 3 presents the possible Fe O @HT@AEPH
-CoII catalyzed
the mechanistic pathway for the tetrazole derivatives synthesis. There is
a possible important role for the catalyst Co (II) in the cyclization pro-
cedures promotion. It is believed that the ethoxy group of triethyl ortho-
II
formate is activated by Fe
3
O
4
@HT@AEPH
2
-Co . Besides, its elimination
is facilitated using the catalyst. Cleaving the triethyl ortho-formate C–O
bond is the mechanism to generate carbenium ion (I). The oxygen atom
of other ethoxy groups and nucleophilic attack of the amine stabilized it.
Then, the second ethoxy group producing carbenium ion (II) expulses.
The neighboring N or O atom can stabilize it. Stabilizing takes place
forming either the iminium (B) or oxonium (A) cation, respectively.
Because of the greater basicity of nitrogen, an iminium cation formation
is preferred. Then, the proposed imidoylazide intermediate (III) is
formed by the azide anion sequential attack [34,35]. Cyclized tetrazoles
II
3 4 2
Fig. 12. Recyclability of Fe O @HT@AEPH -Co in the preparation of tetra-
zole. Conditions of reaction: aniline (1 mmol), triethyl orthoformate (1.2
◦
mmol), sodium azide (1 mmol), at 90 C, H
2
O as a solvent, 0.005 g of
II
3 4 2
Fe O @AEPH -Co .
1
0

M. Salimi et al.
Inorganic Chemistry Communications 122 (2020) 108287
Table 2
can be easily carried out from the reaction medium. On the other hand,
with no significant catalytic activity deterioration, the catalyst could be
reused 6 times.
II
Comparison of results by Fe
3
O
4
2
@HT@AEPH -Co with various catalysts.
Entry
Catalyst
Reaction
Time
(h)
Yield
(%)
Ref.
conditions
1
2
Natrolite zeolite
Solvent free ꢀ
4
3
80–94
83–95
[28]
[56]
Declaration of Competing Interest
◦
1
20
C
Cu NPs/bentonite
Solvent free ꢀ
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
◦
1
20
C
3
4
NHTf
2
Glycerol – r.t.
3
84–95
56–78
[57]
[58]
ZnS nanoparticle
Solvent free ꢀ
3–7
◦
1
30
C
5
6
ZnS nanoparticle
US, DMF, r.t.
0.5
0.5
70–92
85–93
[59]
[60]
Acknowledgements
Ag
2
O
AcOH ꢀ
◦
1
00
C
The authors are grateful to the University of Birjand for its financial
support.
7
8
Fe
acid
Fe
3
O
4
@silica sulfonic
@HT@AEPH
Solvent free ꢀ
0.5 – 3
78–97
[61]
◦
100
C
H
2
O – 90 ◦
C
1
95
This
3
O
4
2
-
II
Co
work
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Mehri Salimi Department of chemistry, University of Birjand, Birjand, Iran.
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