Fe3O4 nanoparticle-bonded β-cyclodextrin as an efficient and magnetically retrievable catalyst for the preparation of β-azido alcohols and β-hydroxy thiocyanate

Article abstract of DOI:10.1007/s11164-015-2037-y

A novel Fe₃O₄ nanoparticle-bonded β-cyclodextrin (β-CD@MNP) has been synthesized and characterized by scanning electron microscopy, vibrating sample magnetometry, and thermogravimetric analysis. It is found that the nanoparticles can

Full text of DOI:10.1007/s11164-015-2037-y

Res Chem Intermed
DOI 10.1007/s11164-015-2037-y
Fe3O4 nanoparticle-bonded b-cyclodextrin
as an efficient and magnetically retrievable catalyst
for the preparation of b-azido alcohols and b-hydroxy
thiocyanate
Soheil Sayyahi1 Sara Mozafari1
•
•
Seyyed Jafar Saghanezhad2
Received: 10 February 2015 / Accepted: 25 March 2015
ꢀ Springer Science+Business Media Dordrecht 2015
Abstract A novel Fe3O4 nanoparticle-bonded b-cyclodextrin (b-CD@MNP) has
been synthesized and characterized by scanning electron microscopy, vibrating
sample magnetometry, and thermogravimetric analysis. It is found that the
nanoparticles can be used as an efficient and magnetically retrievable nanocatalyst
for the preparation of b-azido alcohols and b-hydroxy thiocyanates under ultrasound
irradiation.
Keywords Magnetic nanoparticles Á b-CD@MNP Á Azido alcohols Á Hydroxy
thiocyanate
Introduction
Recently, much attention has been given to develop the application of magnetically
recoverable nanocatalyst systems for sustainable organic synthesis [1–4]. Surface
functionalization of magnetic nanoparticles (MNPs) is a well-designed way to
bridge the gap between heterogeneous and homogeneous catalysis. Ferrite (Fe3O4)
can be used as a versatile support for functionalization of metals, organocatalysts,
N-heterocyclic carbenes, and chiral catalysts. Homogeneous organocatalysts can be
successfully decorated with linkers/ligands on the surface of magnetite or,
alternatively, the organocatalysts can be directly immobilized on the surface of
magnetite [5].
The use of water as a solvent features many benefits such as improving
reactivities and selectivities, simplifying the workup procedures, enabling the
&
Soheil Sayyahi
sayyahi.soheil@gmail.com
1
2
Department of Chemistry, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran
ACECR-Production Technology Research Institute, Ahvaz, Iran
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S. Sayyahi et al.
recycling of the catalyst, and allowing mild reaction conditions and protective-
group free synthesis in addition to being benign itself [6–8]. In addition,
development of organic chemistry in water can lead to uncommon reactivities
and reverse selectivities compared to organic solvents [9].
Epoxides are among the most versatile intermediates in organic synthesis [10].
Also, a number of biologically significant molecules contain these strained three-
membered rings within their structures [11]. A literature survey indicate that there is
a considerable interest in ring-opening reactions of epoxides by nucleophilic
addition for the stereoselective preparation of 1,2-disubstituted products in aqueous
medium, which is due to the special physical properties and structure of water (e.g.
pH control, H-bonding capabilities, and excellent activation of ionic nucleophiles)
[12–16]. Herein we report on the synthesis and application of a magnetically
separable nanoparticle-bonded b-cyclodextrin as a highly efficient heterogeneous
catalyst for the ring-opening reaction of epoxides.
Results and discussion
It has been demonstrated that immobilization of b-cyclodextrin on magnetic
nanoparticles as a hybrid organic–inorganic nanocomposite could be used as
heterogeneous nanocatalyst in organic synthesis [17]. In this study, a Fe3O4
nanoparticle-bonded b-cyclodextrin catalyst was prepared based on the procedures
outlined in Scheme 1.
The morphology and particle size range of the b-CD@MNP was determined by
SEM images (Fig. 1). The magnetic nanoparticle micrographs show an almost
Scheme 1 Synthesis of b-CD@MNP
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Fe3O4 nanoparticle-bonded b-cyclodextrin as an efficient…
Fig. 1 SEM images of Fe3O4 (a) and Fe3O4-bonded b-cyclodextrin (b)
spherical shape of average particle dimensions approximately 67 9 86 nm, which
indicates that the shell diameter is 46 nm.
We also used thermogravimetric (TG) analysis to study the composition and
thermal stability of the b-CD@MNP (Fig. 2). As depicted from the thermogram,
there are two steps of weight loss in the region from room temperature to 600 ꢁC.
While the small mass loss (*5 % w/w) below 150 ꢁC is associated to the removal
of the adsorbed water, the main mass loss (*30 % w/w) in the range of 250–325
and 325–450 ꢁC may be attributed to the thermal decomposition of b-CD and
linkers, respectively.
In order to investigate the magnetic properties of b-CD@MNP at room
temperature, a vibrating sample magnetometer (VSM) was used. Comparison of the
diagrams indicate that the saturation magnetization of the neat Fe3O4 and b-
CD@MNP changed from 58.5 to 6.4 emu/g because of surface modification and
Fig. 2 TG–DTG analysis for Fe3O4 nanoparticle-bonded b-cyclodextrin
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S. Sayyahi et al.
functionalization of the magnetite particles (Fe3O4) with a non-magnetic SiO2 shell
and bulky b-CD molecules and the linker moiety (Fig. 3).
Next, the catalytic ability of the b-CD@MNP magnetic nanoparticles with
combination of ultrasound promoted ring opening of epoxides was investigated in
aqueous media. The reaction between epoxycyclohexane and sodium thiocyanate in
the present of b-CD@MNP was used as a model for the optimization of reaction
conditions. The use of 1 mmol reactant, 1.2 mmol thiocyanate ions, and 0.05 g of
the catalyst in water showed to be the most effective conditions to perform the
reaction. When the reaction was carried out in the absence of the nanocatalyst or
with Fe3O4 no product was observed, but after a prolonged reaction time, some diol
was isolated (60 min, yield was 15 and 17 %, respectively). It should be noted that
in the presence of b-CD, the reaction was completed in 5 min, but because of the
simpler work-up procedure and recycling b-CD@MNPs catalyst system was
preferred. Also, without sonication the reaction rate was decreased significantly.
Fig. 3 The magnetic curve of Fe3O4 nanoparticles at room temperature (upper curve), b-CD@MNP
(lower curve)
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Fe3O4 nanoparticle-bonded b-cyclodextrin as an efficient…
With these results in hand, various epoxides converted to their corresponding b-
azido alcohols and b-hydroxy thiocyanate in good to excellent yields (Table 1).
In styrene oxide (Table 1, entry 1) epoxide ring opening occurred from both
sides. This is probably because the positive charge on the oxygen appears to be
localized on the more highly substituted benzylic carbon leading to the major
product, whereas in the case of aliphatic epoxides, steric factors predominate over
electronic factors, thereby facilitating attack at the less hindered carbon atom of the
epoxide ring [19]. Otherwise, in the case of cyclohexene oxide (Table 1, entry 6),
the reaction was completely antistereoselective, and the trans product was obtained.
The catalyst recycling and reuse by the magnetic cleansing technique is the major
practical advantage of Fe3O4 supported organocatalysts from the point of view of
green chemistry [20]. Fortunately, b-CD@MNP dispersion showed response to a
magnetic field and the nanoparticles separated from the aqueous reaction media
once an external magnet is approached (Fig. 4). It is noteworthy that in this method
the reusing experiment of the nanoparticles did not show significant loss of their
catalytic activity or magnetic nature (Table 2).
In cyclodextrin chemistry, inclusion complexation is accomplished by the
intermolecular interaction between cyclodextrin and guest, which leads to the
penetration of the guest molecule partly or completely into the cavity of the
cyclodextrin [21]. Accordingly, it is surmised that b-CD@MNP could act as a
microreactor and hydrogen bonding of epoxide to the outer OH of b-CD facilitate
the ring-opening with the nucleophile.
Experimental
Materials and instruments
All the chemicals and reagents were used as received from the supplier, except
toluene and dimethylformamide (DMF), which were dried prior to use. Thin-layer
chromatography was performed on aluminum-backed silica gel 60 F254 plates
(0.2 mm thickness, Merck). SEM images were obtained from a Philips XL30
instrument. Thermogravimetric analysis was performed under nitrogen with a
heating rate of 10 ꢁC/min using a Perkin-Elmer, Pyris 1 TGA.
Preparation of Fe3O4 nanoparticle-bonded b-cyclodextrin
Fe3O4 and silica-coated nanoparticles were synthesized based on the known
common methods [22, 23]. For the synthesis of compound 1, Fe3O4@SiO2 (0.5 g)
were dispersed in dry toluene (20 mL) by sonication for 15 min, and then (3-
chloropropyl)triethoxysilane (1.5 mL, 6.25 mmol) was added. The whole mixture
was stirred and refluxed for 48 h under nitrogen atmosphere. After cooling to room
temperature, the solid materials were filtered off, washed with acetone and dried in a
vacuum. For the synthesis of compound 2, b-cyclodextrin (1.13 g, 1 mmol) was
dissolved in anhydrous DMF (25 mL) to which NaH(0.2 g) was added. The mixture
was stirred at room temperature until no gas was produced [24]. After removing
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Table 1 Preparation of b-azido alcohols and b-hydroxy thiocyanate catalyzed by Fe3O4 nanoparticle-
bonded b-cyclodextrin
Entry
1
Epoxide
Producta
Time (min)
Yield (%)b
84 (>10)c
85 (5)c
92
N3
OH
O
Ph
+
5
15
5
Ph
+
OH
O
N3
O
2
O
10
91
OH
O
N3
O
3
4
5
6
25
10
10
20
5
96
87
91
88
92
91
85
O
OH
O
N3
10
10
OH
N3
O
20
86
a
Products were identified by comparison of their physical and spectral data with those of authentic
samples [14, 18, 19]
b
Isolated yields
c
According to GC analysis
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Fe3O4 nanoparticle-bonded b-cyclodextrin as an efficient…
Fig. 4 Photographs of b-CD@MNP dispersed in reaction medium (a) and separated with a NbFeB
magnet (b)
Table 2 Catalyst recycling and reuse for successive four run
Run
1
2
3
4
Time (min)
Yield (%)
20
86
20
84
20
80
20
80
Reaction conditions: epoxycyclohexane (1 mmol), NaSCN (1.2 mmol), H2O (3 mL), ultrasound
excessive NaH by filtration, precursor 1 was added to the filtrate and stirred at 90 ꢁC
for 12 h. The obtained nanoparticles (b-CD@MNP) were separated with a magnet
and washed thoroughly with water and dried at room temperature.
General procedure for the ring opening of epoxides
A mixture of epoxide (1.0 mmol), NaN3 or NaSCN (1.2 mmol), b-CD@MNP
catalyst (0.05 g) and water (5 mL) were transferred to a glass test tube. Under
ultrasonic irradiation (220 W, 50 kH), the reaction was allowed to proceed at room
temperature for the time shown in Table 1. After completion of the reaction as
monitored by thin layer chromatography [using n-hexane/ethylacetate (5:1) as
eluent], the catalyst was magnetically separated and washed with diethyl ether
before reusing. The filtrate was extracted with ethylacetate (3 9 5) and then the
combined organic phase was washed with water; dried over CaCl2 and evaporated
under vacuum to give the desire product in 84–96 % isolated yields.
Conclusion
It can be concluded that this novel magnetic nanocatalyst (b-CD@MNP) can be
applied successfully in the ring-opening of epoxides with azide and thiocyanate as
nucleophiles. The magnetic nanoparticles not only promote the reaction rate,but also
simplify the work-up procedure. In addition, the nanocatalyst acts as a microreactor
and gathers the reactants together and speed up the reaction rate. The advantages of
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b-CD@MNP are short reaction times, high yield of the products, facile reaction
work-up, utilizing green solvent, and eco-friendly procedure.
Acknowledgments We are sincerely grateful to the Mahshahr Branch, Islamic Azad University for the
financial support of this project.
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