An efficient synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4]triazole-1,5-dithiones catalyzed by TiO2-functionalized nano-Fe3O4 encapsulated-silica particles as a reusable magnetic nanocatalyst

Article abstract of DOI:10.1039/c5ra23457c

Immobilization of a nano-TiO₂ catalyst on the surface of a magnetic SiO₂ support was performed through the reaction of a Fe₃O₄@SiO₂ composite with Ti(OC₄H₉)₄via a simple process. The Fe₃O₄@SiO₂-TiO₂ nanocomposite was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and a vibrating sample magnetometer (VSM). The Fe₃O₄@SiO₂-TiO₂ nanocomposite has been found to be an efficient catalyst for the synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4]triazole-1,5-dithiones from the condensation of various aldazines and potassium thiocyanate in acetonitrile solvent at room temperature. It has been found that the nanocatalyst was recycled for up to 6 cycles with minimal loss in catalytic activity. The purpose of this research was to provide an easy method for the synthesis of perhydrotriazolotriazole derivatives by a robust and magnetically recoverable catalyst.

Full text of DOI:10.1039/c5ra23457c

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An efficient synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4]
triazole-1,5-dithiones catalyzed by TiO2-functionalized nano-Fe3O4
encapsulated-silica particles as a reusable magnetic nanocatalyst
Received 00th January 20xx,
Accepted 00th January 20xx
Javad Safari, and Leila Javadian
DOI: 10.1039/x0xx00000x
Immobilization of a nano-TiO2 catalyst on the surface of a magnetic SiO2support was performed through the reaction of
Fe3O4@SiO2 composite with Ti(OC4H9)4 via a simple process. The Fe3O4@SiO2–TiO2 nanocomposite was characterized using
scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS),
X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), and vibrating sample magnetometer (VSM). The
Fe3O4@SiO2–TiO2 nanocomposite has been found to be an efficient catalyst for the synthesis of
perhydro[1,2,4]triazolo[1,2-a][1,2,4] triazole-1,5-dithiones from the condensation of various aldazines and potassium
thiocyanate in acetonitrile solvent at room temperature. It has been found that the nanocatalyst was recycled for up to 6
cycles with minimal loss in catalytic activity. The purpose of this research was to provide an easy method for the synthesis
of perhydrotriazolotriazole derivatives by a robust and magnetic recoverable catalyst.
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They adopt the s-trans conformation due to steric interaction of the
alkyl or aryl substations. So, this conformation does not suffer the
[4+2] cycloaddition known as the Diels-Alder reaction.15 Although,
there are a few papers in the literatures that have described the
synthesis of perhydrotriazolotriazoledithione derivatives, they have
drawbacks such as high catalyst loading, drastic conditions, low
yields and long reaction times. 16,17
1. Introduction
1,3-Dipolar cycloaddition or [3+2] cycloaddition reaction is
fundamental processes in organic chemistry that offers a powerful
synthetic methodology to achieve five-membered heterocyclic
systems in stereo and regiocontrolled approach.1-4 The term “criss-
cross” cycloaddition appeared in 1917 by Bailey and McPherson and
the first paper described the cycloaddition of cyanic acid to
benzalazine.5 Criss-cross cycloaddition reactions are a procedure for
the synthesis of fused heterocyclic rings in an one pot arrangement
that offer two fused five-membered rings.6,7 The formation of
corresponding products was described by Huisgen as the result of
two following 1,3-dipolar cycloadditions in 1963.8 Since then, some
papers have published listing examples of criss-cross cycloaddition
reactions of aldazines and different dipolarophiles such as
thiocyanate.9 In addition to aldazines, the current reactions have
In recent decades, design of magnetically catalysts has attracted a
great deal of attention due to simple separation of catalysts by a
permanent magnetic field. A lot of materials such as FeCo, Fe2O3,
NiFe2O4, Fe3O4, CoFe2O4 and black sand have the magnetic
properties.18-23 Among them, Fe3O4 nanoparticles has been chosen
because of its low toxicity and remarkable magneticproperties.24-26
Fe3O4 nanoparticles have emerged as supports for immobilization
of catalyst which offer an easy separation of the catalyst without
the need of conventional filtration method or tedious work-up
processes. Beside the facile separation, a great feature of Fe3O4
nanoparticles is their surface modification that affords sometimes
higher activity than their homogeneous systems. Fe3O4 core with
shell of silica offers sites for surface modification with various
compounds in catalyst application. Silica layer not only avoids the
oxidation of the Fe3O4 by the outer atmosphere, but also can
prevent the aggregation induced by the magnetic dipolar attraction
between magnetic nanoparticles.27-29 Also, silica enhances a better
dispersion of magnetic nanoparticles in suspension.30 Magnetic
nanoparticles have been used as catalysts or catalyst supports in
many organic reactions including oxidation, reductions,
multicomponent reactions and C-C couplings with a high level of
activity.31-34 It is anticipated that the magnetic properties of catalyst
would be useful to improve the performance of the [3+2]
cycloaddition reaction and provide a support for the solid acid
catalyst. On the other side, extensive attention has been directed
toward the application of solid acids in organic synthesis because
such reagents help prevent release of reaction residues into the
environment. In this regard, nanostructure solid acids show higher
been reported for ketazines10 1,2-diazabuta-1,3-dienes,11,
12
glyoxalimines,13 and hexafluoroacetonazine with many types of
compounds including alkenes.14 The 1,3-dipolar ketazines and
aldazines are 1,3-heterodiene compounds and have double 1,3-
dipolar sites (scheme 1).
R1
R1
R2
R1
R2
N
N
R2
N
N
N
N
R2
R1
R1
R2
R1
R2
R1= H, CH3, ...
R2= Alkyl, Aryl
Scheme 1. Azines containing double 1,3-dipolar sites.
Laboratory of Organic Compound Research, Department of Organic Chemistry,
Faculty of Chemistry,University of Kashan, Kashan, P.O.Box: 87317-51167, Kashan,
Iran. Tel:+9831-55912320; E-mail: Safari@kashanu.ac.ir
†
DOI: 10.1039/x0xx00000x
Electronic
Supplementary
Information
(ESI)
available:
See
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activity than their bulk materials due to their particular chemical dropwise into a mixture containing 0.40 g of magnetic Fe3O4@SiO2
and physical properties especially large surface to volume ratio.35 As in 10 ml water/ethanol. The mixture was refluxed at 90 C for about
an extension of our researches on the application of magnetic solid 2 h. Then, the magnetic sample was dried at 60 °C and calcined at
acids in organic transformations, functionalization of Fe3O4 450 °C for 2 h to offer Fe3O4@SiO2-TiO2 nanocomposite.39
nanoparticles with TiO2 has been studied to offer magnetic catalyst
which combines the benefits of TiO2 and Fe3O4 to afford greater 2.4. A typical procedure for the synthesis of aldazines
potential applications.
Aldazines were prepared by the method as described in the
In this contribution, we hope to report an efficient method for the
literature.40 A mixture of the aldehyde (2 mmol), hydrazine sulfate
synthesis of perhydrotriazolotriazoledithions by the condensation
(1 mmol), and triethylamine (1 mmol) was heated at 60 °C for 3–5
of aldazines as 1,3-heterodienes with thiocyanate in [3+2]
min. The completion of the reaction was monitored by thin layer
cycloaddition by a magnetically recyclable catalyst.
chromatography (petroleum ether:ethyl acetate= 7:3).After the
completion of the reaction, the mixture was cooled on ice. The
aldazine was collected by suction filtration. Then, it was washed
2. Experimental
with water, and dried under vacuum. The yellow solid was
recrystallized from ethanol to afford the desired aldazineas cream
to orange crystals.
2.1. General
All the commercially available reagents were obtained from Aldrich
or Merk and were used without further purification. 1H and 13C
NMR spectra were recorded on a Bruker DRX-400 spectrometer.
Chemical shifts are expressed in δ parts per million. The IR spectra
of the compounds were recorded on a Perkin Elmer FT-IR 550
spectrophotometer. All melting points (m.p.) were determined on
an ElectroMK3 apparatus, expressed in °C and are uncorrected.
Analytical thin layer chromatography (TLC) on silica gel plates
containing UV indicator was employed regularly to follow the
course of reactions and to confirm the purity of products. The
Sonication was performed in Shanghai Branson-BUG40-06
ultrasonic cleaner. The obtained nanoparticles were characterized
2.5. A typical procedure for the synthesis of tetrahydro-[1,2,4]
triazolo [1,2-a][1,2,4]triazole-1,5-dithione derivatives
In a typical experiment, KSCN (2 mmol), AcOH (0.18 mL), CH3CN (6
mL) and catalytic amount of Fe3O4@SiO2-TiO2nanocomposite (0.04
g) were stirred at room temperature. After stirring for 5 min,
aldazine (1 mmol) was added to this mixture and the contents were
stirred for an appropriate period while the progress of the reaction
was followed by TLC using petroleum ether:ethyl acetate=7:3) as
eluent. After completion of the reaction, the nanocatalyst was
removed by an external magnet and reused. Then, cold water (50
mL) was added and the solid product was collected by filtration,
was washed successively with CHCl3, dried and recrystallized from
ethanol to afford the pure product. The products were identified by
comparison of their spectroscopic and physical data with those
reported in the literature.
by XRD on
a Bruker D8 Advance X-ray diffraction (XRD)
diffractometer (CuK, radiation, k =0.154056 nm and 40 kV voltage),
at a scanning speed of 2° min-1 from 10° to 100° (2ө). Scanning
electron microscope (SEM) was performed on a FEI Quanta 200
SEM operated at a 20 kV accelerating voltage. Magnetic properties
were characterized by a vibrating sample magnetometer (VSM,
MDKFD, University of kashan, Kashan, Iran) at room temperature.
The samples for SEM were prepared by spreading a small drop
containing nanoparticles onto a silicon wafer and being dried
almost completely in air at room temperature for 2 h, and then
were transferred onto SEM conductive tapes. The TEM images were
recorded usinga Ziess EM10C transmission electron microscope
operated at a 80 KV accelerating votage.
2.5.1. Spectral data for compounds
2.5.1.1. Tetrahydro-3,7-diphenyl-[1,2,4] triazolo [1,2-a] [1,2,4]
triazole-1,5-dithione (3a): white solid, m.p= 188-189 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) = 0.26; IR (KBr)/ ν (cm-1):
3385, 3180, 1500, 1251; 1H NMR (Acetone-d6, 400 MHz)/ δ
ppm:6.81 (s, 2H, CH), 7.38-7.42 (m, 10H, Ar-H), 11.42 (s, 2H, NH);13C
NMR (DMSO-d6, 100 MHz) δ (ppm): 73 (CH), 126.25 (CH), 127.76
(CH), 128.31 (CH), 129.73 (CH), 184.1 (C=S) ppm; CHNCalculated (%): C
(58.89), H (4.29), N (17.18), S (19.63); CHNFound (%): C (58.82), H
(4.39), N (17.34), S (19.73).17
2.2. Preparation of Fe3O4@SiO2 as a support
First, Fe3O4 nanoparticles were prepared by chemical co-
precipitation of FeCl2 and FeCl3[Fe2+: Fe3+= 1:2] in base solution as
described in the literature.36, Then, Fe3O4-SiO2 composite were
37
2.5.1.2. Tetrahydro-3,7-bis (3-nitrophenyl)-[1,2,4] triazolo [1,2-a]
[1,2,4] triazole-1,5-dithione (3b): white solid, m.p= 190-191 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) =0.15; IR (KBr)/ ν (cm-1):
synthesized through the Stöber method using tetraethyl
orthosilicate as a silica source in a basic water/ethanol mixture at
room temperature under continuous mechanical stirring.38 Briefly,
0.5 g of the Fe3O4nanoparticles was dispersed in 20 ml of distilled
water and 50 ml of ethanol under ultrasound irradiation and then
concentrated aqueous ammonia (1 ml) was added. Finally, 0.2 ml of
tetraethyl orthosilicate diluted in ethanol (10 ml) was added drop-
wisely under continuous mechanical stirring. After stirring for 18 h,
Fe3O4@SiO2 nanoparticles were collected by magnetic separation
and washed three times with water and ethanol. Finally, the
magnetic product was dried at 70 °C for 6 h.
1
3215, 1616, 1529, 1491, 1352, 1247, 1161; H NMR (Acetone-d6,
400 MHz)/ δ ppm:7.25 (s, 2H, CH), 7.80 (t, J= 7.0 Hz, 2H, ArH), 8.00
(d, J= 7.0 Hz, 2H, ArH), 8.31 (d, J= 7.0 Hz, 2H, ArH), 8.39 (s, 2H, ArH),
10.38 (s, 2H, NH) ppm;);13C NMR (Acetone-d6, 100 MHz) δ (ppm):
72.0 (CH), 119.43 (CH), 122.55 (CH), 129.88 (CH), 133.76 (CH),
145.50 (CH), 148.60 (C), 158.09 (C), 184.11 (C=S) ppm; CHNCalculated
(%):C (46.02), H (2.2.87), N (20.13), S (15.62), O (15.36); CHNFound
(%): C (46.45), H (3.01), N (19.18), S (15.35), O (16.01).
2.5.1.3. Tetrahydro-3,7-bis (4-methoxyphenyl)-[1,2,4] triazolo [1,2-
a] [1,2,4] triazole-1,5-dithione (3c): white solid, m.p= 160-162 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) =0.18; IR (KBr)/ υ(cm-1):
3390, 3157, 2960, 1613, 1508, 1249, 1173, 1028; 1H NMR (Acetone-
2.3. Preparation of catalyst
A magnetically separable TiO2 catalyst was prepared by dissolving
1.5 ml of Ti(OC4H9)4 in 30 ml ethanol and adding this solution
2 | J. Name., 2012, 00, 1-3
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d6, 400 MHz)/ δ ppm: 3.72 (s, 6H, OCH3), 6.75 (s, 2H, CH), 6.99 (s,
4H, Ar-H), 7.28-7.30 (d,J= 6.8 Hz, 4H, Ar-H), 11.31 (s, 2H, NH) ppm;
13C NMR (DMSO-d6, 100 MHz) δ (ppm): 55.73 (CH3), 77.03 (CH),
114.76 (CH), 127.67 (CH), 130.0 (C), 160.35 (C), 184.0 (C=S); ppm;
CHNCalculated (%): C (55.96), H (4.66), N (14.51), S (16.58); CHNFound
(%): C (55.93), H (4.76), N (14.72), S (16.68). 17
3. Results and discussion
3.1. Characterization of magnetic nanocatalyst
The synthetic path to the magnetic nanocatalyst is shown in
Scheme 2.
Iron-oxide nanoparticles were prepared via co-precipitation and
modified with a thin layer of amorphous silica by Stöber method
through sol–gel method. The Fe3O4@SiO2 -supported TiO2 magnetic
catalyst obtained after addition of Ti(OC4H9)4 into the Fe3O4@SiO2
magnetic composite. Silica layer was utilized to encapsulate the
Fe3O4 NPs to prevent any decrease in catalytic property when it was
incorporated into the TiO2 structure. Because silica as a shell can
decrease the electronic interactions at the point of contact.19
The magnetic nanoparticles were characterized by X-ray diffraction
(XRD), Fourier transform infrared (FT-IR), scanning electron
microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and
vibrating sample magnetometer (VSM).
2.5.1.4. Tetrahydro-3,7-bis (2-chlorophenyl)-[1,2,4] triazolo [1,2-a]
[1,2,4] triazole-1,5-dithione (3d):white solid, m.p= 197 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) =0.32; IR (KBr) ν (cm-1):
3433, 3183, 2929, 1498,1251; 1H NMR (DMSO-d6, 400 MHz) δ
(ppm): 7.16 (s, 1H, CH), 7.34-7.36 (m, 1H, Ar-H), 7.43-7.47 (m, 2H,
Ar-H), 7.54-7.61 (m, 1H, Ar-H), 11.48 (s, 1H, NH); 13C NMR (DMSO-
d6, 100 MHz) δ (ppm): 74.86 (CH), 128.14 (CH), 128.63 (CH), 130.62
(CH), 131.87 (CH), 132.48 (C), 134.01 (C), 185.19 (C=S) ppm;
CHNCalculated (%): C (48.60), H (3.04), N (14.18), S (16.20), Cl (17.72);
CHNFound (%): C (47.99), H (3.58), N (14.76), S (16.09), Cl (17.58).
2.5.1.5.Tetrahydro-3,7-bis (3-chlorophenyl)-[1,2,4] triazolo [1,2-a]
[1,2,4] triazole-1,5-dithione (3e): white solid, m.p= 194-195 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) = 0.35; IR (KBr)/ ν (cm-1):
3427, 3191, 2927, 1501, 1247 ;1H NMR (Acetone-d6, 400 MHz)/ δ
ppm: 7.07 (s, 1H, CH), 7.47-7.51 (m, 3H, Ar-H), 7.55 (s, 1H, Ar-H),
10.14 (s, 1H, NH);13C NMR (DMSO-d6, 100 MHz) δ (ppm): 76.62
(CH), 124.88 (CH), 126.39 (CH), 128.12 (CH), 131.84 (CH), 134.15 (C),
139.76 (C), 184.47 (C=S) ppm; CHNCalculated (%): C (48.60), H (3.04), N
(14.18), S (16.20), Cl (17.72); CHNFound (%): C (48.32), H (3.13), N
(14.31), S (16.29), Cl (17.81). 17
NaOH, EtOH
Fe3O4
FeCl2. 4H2O FeCl3. 6H2O
1)
Ar
SiO2
TEOS, NH3
Fe3O4
2)
Fe3O4
2.5.1.6. Tetrahydro-3,7-bis (4-chlorophenyl)-[1,2,4] triazolo [1,2-a]
[1,2,4] triazole-1,5-dithione (3f): white solid, m.p= 201-203 °C; Rf
(petroleum ether:ethylacetate)= 7:3 (v/v)) =0.31; IR (KBr)/ ν (cm-1):
TiO2
SiO2
1) Ti(OEt)4, EtOH
2 h, 90 oC
SiO2
3)
1
Fe3O4
Fe3O4
3438, 3168, 2925, 1629, 1492, 1249, 1157; H NMR (Acetone-d6,
2) 2 h, 450 oC
400 MHz)/ δ ppm:6.84 (s, 2H, CH), 7.39 (s, 4H, ArH), 7.51 (s, 4H,
ArH), 11.48 (s, 2H, NH) ppm;13C NMR (DMSO-d6, 100 MHz) δ (ppm):
75.50 (CH), 128.4 (CH), 130.45 (CH), 133.21 (CH), 133.8 (CH), 184.1
(C=S) ppm; CHNCalculated (%): C (48.60), H (3.04), N (14.18), S (16.20),
Cl (17.72); CHNFound (%): C (58.82), H (4.39), N (17.34), S (19.73). 17
Scheme 2. Preparation steps of magnetic catalyst.
The phase and purity of three samples (Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2-TiO2) were plotted by The X-ray diffraction patterns
(Figure 1).
2.5.1.7. Tetrahydro-3,7-bis (3-hydroxyphenyl)-[1,2,4] triazolo [1,2-a]
[1,2,4] triazole-1,5-dithione (3g): white solid, m.p= 165-167 °C; Rf
(petroleum ether:ethylacetate= 7:3 (v/v)) =0.12; IR (KBr)/ ν (cm-1):
3423, 3177, 2958, 1601, 1505, 1250; 1H NMR (Acetone-d6, 400
MHz) δ (ppm): 6.95 (s, 4H, Ar-H), 7.24 (s, 1H, CH), 8.62 (s, 1H, OH),
9.97 (s, 1H, NH) ppm;13C NMR (Acetone-d6, 100 MHz) δ (ppm): 73
(CH), 112.01 (CH), 113. 88 (CH), 119.03 (CH), 130.0 (CH), 145.50
(CH), 158.09 (C), 184. 0 (C=S) ppm;CHNCalculated (%): C (53.70), H
(3.88), N (15.04), S (17.68), O (9.70); CHNFound (%): C (53.76), H
(3.58), N (15.34), S (17.74), O (9.66).
The XRD pattern of Fe3O4 MNPs exhibit the peaks at 2θ= 30.1, 35.5,
43.2, 53.5, 57.0, 62.8 and 74.3° (Figure 1a). It is in agreement with
the JCPDS card No. 19–0629.36The coating of amorphous phase SiO2
does not change the structure of Fe3O4nanoparticles (Figure 1b).
Also, the position and relative intensities of peaks indicate that the
structure of Fe3O4@SiO2 can be remained after the surface
modification with TiO2. The XRD pattern of the Fe3O4@SiO2-TiO2
MNPs shows peaks at 2θ =25.2, 30.3, 35.6, 43.4, 48.2, 53.5, 57.2
63.1 and 74.4°(Figure1c). The peaks at around 25° and 48° conform
to the (1 0 1) and (2 0 0) Bragg reflection planes which indicates the
existence of tetragonal anatase TiO2.
2.5.1.8. Tetrahydro-3,7-bis (3-hydroxy-4-methoxyphenyl)-[1,2,4]
triazolo [1,2-a][1,2,4]triazole-1,5-dithione (3h): white solid, m.p=
177-180 °C; Rf (petroleum ether:ethylacetate= 7:3 (v/v)) =0.06; IR
1
(KBr)/ ν (cm-1): 3422, 2929, 1510, 1278, 1133; H NMR (Acetone-d6,
The elemental composition is calculated from the energy dispersive
X-ray. The EDAX image confirmed the existence of Fe, Si, O and Ti
elements in the magnetic catalyst (Figure 2). The elemental
compositions of Fe3O4@SiO2-TiO2nanocatalystwere 14.9, 70.3, 6.7,
and 7.9 wt % for Fe, O, Si, and Ti, respectively. The presence of Ti
inthe composites indicates that the titanium dioxide nanoparticles
have been deposited on the surface of Fe3O4@SiO2.
400 MHz)/ δ ppm:3.81 (s, 6H, OCH3), 6.86 (s, 2H, CH), 6.96-7.40 (m,
6H, ArH), 7.89 (s, 2H, OH), 9.88 (s, 2H, NH) ppm; 13C NMR (Acetone-
d6, 100 MHz) δ (ppm): 55.40 (OCH3), 77.09 (CH), 111.54 (CH), 112.79
(CH), 117.32 (CH), 129.98 (C), 146.91 (C), 148.37 (C), 185.00
(C=S);CHNCalculated (%): C (51.52), H (4.29), N (13.35), S (15.55), O
(15.29); CHNFound (%): C (51.34), H (4.83), N (12.88), S (14.98), O
(15.97).
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( 1 0 1)
(2 0 0)
( 4 4 0)
(5 3 3)
(3 1 1)
(2 2 0)
(511)
(400)
(422)
Figure 1. The XRD patterns of (a) Fe3O4 (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-
TiO2.
Figure 2. The EDAX of Fe3O4@SiO2-TiO2 nanocatalyst.
Scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) were recorded to understand morphological
changes occurring on the magnetic catalyst and also the size and
shape of the nanoparticles.
The SEM and TEM images of synthesized samples are shown in
Figure 3. The SEM image of Fe3O4 MNPs have a mean diameter
lower than 20 nm a nearly spherical shape (Figure 3a). Figure 3b
shows that Fe3O4@SiO2 nanoparticles keep the morphological
properties of Fe3O4 MNPs except for a larger particle size and
smoother surface. The TEM image shown in Fig. 3d demonstrates
that silica is successfully coated on the Fe3O4NPs with a thin layer of
different phase to form silica shell. So, Fe3O4@SiO2 is nearly in core-
shell structure.
Then, the chemical nature of the magnetic catalyst was surveyed.
The SEM and TEM images in Fig. 3c and 3eshow that Fe3O4@SiO2-
TiO2 nanocatalyst have
a
larger particle size than
Fe3O4@SiO2nanoparticles (about 30 nm in size) and nearly spherical
shape. The nanocatalyst shows some aggregation, which was due to
calcination at 450 °C.39
Figure 3. SEM image of the a) Fe3O4, b) Fe3O4@SiO2and c) Fe3O4@SiO2-TiO2.
TEM image of the d) Fe3O4@SiO2 and e) Fe3O4@SiO2-TiO2.
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In order to explore the molecular structures of Fe3O4, Fe3O4@SiO2, Room temperature specific magnetization versus applied magnetic
and Fe3O4@SiO2– TiO2, the FT-IR analysis was investigated. Figure 4 field curve measurements of the Fe3O4@SiO2-TiO2 indicated the
saturation magnetization value (Ms) of 31 emu g-1, which is slightly
lower than of the Fe3O4@SiO2 (46.94 emu g-1) and uncoated Fe3O4
MNPs (55.70 emu g-1).
shows the FT-IR spectra recorded in the range of 4000–400 cm-1.
The main absorption peaks 3423 and 570 cm−1 were assigned to O-
H and Fe-O stretching vibration modes of pure Fe3O4 NPs,
respectively (Figure 4a). The absorption peak of SiO2-coated sample
at 450 cm-1 is due to the Si-O-Fe bond.
3.2. Application of Fe3O4@SiO2-TiO2nanocomposite as a
heterogeneous catalyst in the synthesis of tetrahydro-[1,2,4]
triazolo [1,2-a][1,2,4] triazole-1,5-dithione derivatives.
In this research, we tried to prepare tetrahydro-[1,2,4] triazolo [1,2-
a][1,2,4] triazole-1,5-dithione derivatives from the reaction
between aldazine derivatives and potassium thiocyanate under
mild conditions. Titanium dioxide anchored on the surface of the
Fe3O4@SiO2 nanoparticles and carried out successfully the
cycloaddition reaction. Initially, in order to optimize the reaction
conditions, the model reaction was proceeded from the
condensation of benzaldazine and potassium isothiocyanate in a 1:2
ratio at room temperature for the synthesis of compound 3ausing
TiO2, Fe3O4 or Fe3O4@SiO2-TiO2as a catalyst. Fe3O4@SiO2-TiO2 acted
as
a
highly efficient magnetic catalyst to synthesize
perhydro[1,2,4]triazolo[1,2-a][1,2,4] triazole-1,5-dithione (3a) and
afforded the product in higher yield and lower reaction time
compared with other catalysts (Table 1). Also, other advantages of
the current catalyst are simple separation and recoverable of
Fe3O4@SiO2-TiO2 compared with reported catalysts. With notice to
above results, the importance of Fe3O4@SiO2-TiO2 composite
nanoparticles as a heterogeneous catalyst was revealed in this
study and therefore it was selected as the efficient catalyst for
further work.
Figure 4. FT-IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2-TiO2.
The bands at 1073 cm-1 and 803 cm-1 are characteristic peaks of the
symmetrical and asymmetrical vibrations of Si-O-Si (Figure 4b). The
peak at 451 cm-1 is an indication of the presence of Si-O-Fe. Figure
4c show the IR spectra of TiO2 modified Fe3O4@SiO2 NPs. From this
spectrum, the appearance of a new peak at 636 cm-1 indicates the
formation of Si-O-Ti surface structures and successful linking of the
TiO2 onto the Fe3O4@SiO2 MNPs. There was no evidence for
interaction between Ti and Fe in the IR spectra. It indicates that
Fe3O4 is encapsulated by the SiO2 layer well. So, the catalytic
property of Fe3O4@SiO2-TiO2 is not reduced by this interaction.
Table 1. The synthesis of tetrahydro-3,7-diphenyl-[1,2,4] triazolo
[1,2-a] [1,2,4] triazole-1,5-dithione by various catalysts.
H
H
N
S
Ph
H
Ph
AcOH, Catalyst
CH3CN, r.t.
N
H
N
N
N
2 KSCN
Ph
Ph
S
N
H
The magnetization curves of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-
TiO2 were recorded in Figure 5. The magnetic property of the
Fe3O4@SiO2-TiO2 magnetic catalyst were examined and were
compared with the magnetic properties of Fe3O4and Fe3O4@SiO2.
VSM study indicated a decrease in the magnetic saturation of
Fe3O4@SiO2-TiO2 composite due to the non-magnetic nature of the
shell NPs.
H
Entry
Catalyst
BF3
SbCl3
ZrCl4
TiCl4
Yield (%)
Time (min)
1
2
3
4
5
6
7
85
88
82
97
97
96
98
21 [Ref. 16]
21 [Ref. 16]
21 [Ref. 16]
21 [Ref. 16]
31
TiO2
Fe3O4 NPs
Fe3O4@SiO2-TiO2NPs
20
17
60
40
20
0
The obtained results of the reaction to determine the optimum
amount of magnetic catalyst are shown in Table 2. The reaction
slowly proceeded in low yield without catalyst. The higher yield of
the corresponding product was obtained in shorter time with an
increase in the amount of magnetic nanocatalyst. As can be seen
from Table 1, comparison of the results shows a better yield using
0.04 g of catalyst to synthesize of tetrahydro-[1,2,4] triazolo [1,2-
a][1,2,4] triazole-1,5-dithiones in the presence of Fe3O4@SiO2-TiO2.
While a higher amount of the catalyst did not show any change in
reaction time and yield of the corresponding product.
-20
Fe3O
4
-40
Fe3O ꢀSiO
4
2
Fe3O ꢀSiO ꢀTiO
2
4
2
-60
-10000 -8000 -6000 -4000 -2000
0
2000 4000 6000 8000 10000
Applied Field(Oe)
To demonstrate the advantage of the present work, we compared
the results of Fe3O4@SiO2-TiO2 magnetic catalyst as a catalyst in the
synthesis of tetrahydro-[1,2,4] triazolo [1,2-a][1,2,4] triazole-1,5-
dithiones in the presence of various solvents (Table 3). It can be
Figure 5. Magnetization curves for the Fe3O4 (red line), Fe3O4@SiO2 (blue
line) and Fe3O4@SiO2-TiO2 (green line) at room temperature.
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seen from Table 2 that the present CH3CN was found to be the most synthesized. This is possibly due to tautomeric phenomena of these
efficient solvent among tested solvents in term of reaction time of compounds.
the desired products in the presence of Fe3O4@SiO2-TiO2.
Table 4. The synthesis of tetrahydro-[1,2,4] triazolo [1,2-a][1,2,4] triazole-
1,5-dithiones in the presence of Fe3O4-SiO2-TiO2 MNPs.a
Table 2. The synthesis of tetrahydro-3,7-diphenyl-[1,2,4] triazolo [1,2-
H
a] [1,2,4] triazole-1,5-dithione under different amounts of the magnetic
catalyst.a
H
N
N
S
R
R
H
R
Fe3O4@SiO2-TiO2
AcOH, CH3CN, r.t.
N
H
N
N
H
2 KSCN
(2)
H
N
N
R
S
Ph
H
S
Ph
Fe3O4@SiO2-TiO2
AcOH, CH3CN, r.t.
N
H
H
N
H
N
N
2 KSCN
Ph
(1)
(3)
M.P.
Ph
S
N
H
Entry
R
Product
Time
Yield
H
(min) (%)
(°C)
Entry
Catalyst loading (g)
Time (min)
Yield (%)
1
2
3
4
5
6
blank
0.01
0.02
0.03
0.04
0.05
60
35
23
17
17
17
32
1
C6H5
3a
3b
3c
3d
3e
3f
3g
3h
-
17
30
98
88
98
77
92
94
90
95
-
189-190
197-199
165-166
190-192
194-196
197-200
167-169
170-173
-
79
2
3-NO2 C6H4
4-OCH3 C6H4
2-Cl C6H4
96
3
15
97
4
43
98
5
3-Cl C6H4
20
98
6
4-Cl C6H4
16
a Reaction condition: aldazine (1 mmol), KSCN (2 mmol) AcOH (0.18 mL) and
CH3CN (6 mL) at room temperature.
7
3-OH C6H4
25
8
3-OH, 4-OCH3 C6H3
2-OH, 4-CH3 C6H3
2-OH C6H4
19
Table 3. The solvent effects on time and yield of tetrahydro-3,7-diphenyl-
[1,2,4] triazolo [1,2-a] [1,2,4] triazole-1,5-dithione in the presence of
magnetic catalysta
9
240
240
.
H
N
H
S
Ph
H
10
-
-
-
Ph
Fe3O4@SiO2-TiO2
solvent, AcOH, r.t.
N
H
N
N
N
2 KSCN
a Reaction conditions: aldazine (1 mmol), KSCN (2 mmol), AcOH (0.18 mL),
Fe3O4-SiO2-TiO2 (0.04 g) and CH3CN (6 mL) at room temperature.
Ph
Ph
S
N
H
H
Entry
Solvent
DMSO
CH3CN
H2O
Time (min)
Yield (%)
Tetrahydro-[1,2,4] triazolo [1,2-a][1,2,4] triazole-1,5-dithiones as
products in a green method were prepared using of potassium
thiocyanate and various aldazines in the presence of catalytic
amount of Fe3O4-SiO2-TiO2 MNPs (0.04 g) at room temperature. The
structure of the described products was confirmed by physical and
spectroscopic data. The infrared spectra of the tetrahydro-[1,2,4]
triazolo [1,2-a][1,2,4] triazole-1,5-dithiones exhibits a band at about
3400 cm-1 and another band at about 1250 cm-1 due to NH and C=S
1
2
3
4
5
20
17
25
25
37
92
98
63
89
45
EtOH
1
related to the fused five membered rings, respectively. In the H
NMR spectra the signal around δ= 8–11 ppm is assigned to NH
hydrogen atom.
CHCl3
a The catalyst sonicated for 20 min before utilization.
From a green chemistry perspective, the stability of Fe3O4-SiO2-TiO2
magnetic catalyst has been investigated by the possibility of
reusability. Upon completion of the reaction, to evaluate the
catalytic stability of the catalyst, the magnetic catalyst recycled
readily by an external magnet, was rinsed with ethyl acetate several
times and was dried. It was utilized to a second run of the reaction.
The prepared nanocatalyst was stable without the need for
surfactant stabilizers. Although the yield decreased from 98 to 96 %
after six runs, the catalytic activity was still acceptable (Table 5).
After establishing the optimal conditions, the scope of the
cycloaddition reaction between potassium thiocyanate and several
aldazine derivatives were carried out at ambient temperature
according to the general experimental procedure (Table 4). As can
be seen from this Table, benzaldazine bearing ortho substituent
(Table 4, entry 4) slightly afford lower yield than benzaldazines
bearing meta or para substituents. This is possibly due to the steric
effect. There is more steric hindrance for the 2-substituted
benzaldazine on the product formation than the 3- or 4-substituted Table 5. The cycloaddition reaction using the recycled Fe3O4-SiO2-TiO2
magnetic catalyst.
benzaldazines.
Run
Yield
(%)
1
2
3
4
5
6
7
In the case of aldazine derivatives with a hydroxyl group at 2-
position (Table 4, entries 9 and 10), the desired products were not
98
98
97
97
97
96
93
6 | J. Name., 2012, 00, 1-3
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3.3. The proposed reaction mechanism
References
One of the significant advantage of the present catalyst is a large
number of empty d-orbitals of the TiO2 and the low amount of
nanocatalyst used in the reaction. The magnetically separable TiO2
catalyst show great catalytic activity. The features of the Ti4+centres
on the surface of TiO2 nanoparticles play an important role in
increasing activation of thiocyanate. In fact, titanium dioxide
grafted onto the Fe3O4@SiO2 could catalyze the reaction by the
coordination of the unfilled orbitals of TiO2. Thus, it is obvious that
Fe3O4@SiO2-TiO2 catalytic system increases the rate of reaction.
The formation of the corresponding products can be explained by a
proposed mechanism (Scheme 3). According to above reason,
enhancing the electrophilic property of the thiocyanate has
occurred using titanium dioxide supported on Fe3O4@SiO2. Then,
aldazine react as dipoles with two molecules of activated
thiocyanate as a dipolarophile to form tetrahydro-[1,2,4] triazolo
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Conclusions
In this research, we have been described the synthesis of
tetrahydro-[1,2,4] triazolo [1,2-a][1,2,4] triazole-1,5-dithiones via 30 Q. Dai, J. Wang, J. Yu, J. Chen and J. Chen, Appl. Cat. B: Environmental
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condensation of different kinds of aldazine derivatives with
31 M. Shokouhimehr, Y. Z. Piao, J. Y. Kim, Y. J. Jang and T. HyeonAngew.
potassium isothiocyanate using Fe3O4-SiO2-TiO2 composite
nanoparticles as a magnetic nanocatalyst. The reaction in the
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presence of recent magnetic catalyst indicated a lot of significant
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advantages such as eco-friendly and recyclable catalyst, excellent
product yields, low reaction times and simplicity of work-up.
1837
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Acknowledgements
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The authors are grateful to University of Kashan for supporting this
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Graphical abstract:
An efficient synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4] triazole-
1,5-dithiones catalyzed by TiO2-functionalized nano-Fe3O4
encapsulated-silica particles as a reusable magnetic nanocatalyst
Javad Safari and Leila Javadian
Immobilization of a nano-TiO2 catalyst on the surface of a magnetic SiO2 support was performed through the reaction of Fe3O4@SiO2
composite with Ti(OC4H9)4 via a simple process. The Fe3O4@SiO2–TiO2 nanocomposite was characterized using scanning electron
microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier
transform infrared spectra (FTIR), and vibrating sample magnetometer (VSM). The Fe3O4@SiO2–TiO2 nanocomposite has been found to be
an efficient catalyst for the synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4] triazole-1,5-dithiones from the condensation of various
aldazines and potassium thiocyanate in acetonitrile solvent at room temperature. It has been found that the nanocatalyst was recycled for
up to 6 cycles with minimal loss in catalytic activity. The purpose of this research was to provide an easy method for the synthesis of
perhydrotriazolotriazole derivatives by a robust and magnetic recoverable catalyst.