Magnetic nanoparticles grafted with β-cyclodextrin-polyurethane polymer as a novel nanomagnetic polymer brush catalyst for nucleophilic substitution reactions of benzyl halides in water

Article abstract of DOI:10.1016/j.molcata.2012.08.012

The polymer coated magnetic nanoparticles has gained significant attention for potential applications in biomedicine, separations, and magnetic storage. In this study, β-cyclodextrin-polyurethane polymer coated Fe ₃O₄ magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was successfully prepared and evaluated as solid-liquid phase-transfer catalyst and molecular host system for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed and the products obtained in pure form without further purification. The nanomagnetic polymer brush catalyst was easily removed from solution via application of a magnetic field, allowing straightforward recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with a mean diameter of 59 nm. The grafting of β-cyclodextrin-polyurethane polymer to Fe₃O₄ magnetic nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).

Full text of DOI:10.1016/j.molcata.2012.08.012

Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Magnetic nanoparticles grafted with ␤-cyclodextrin–polyurethane polymer as a
novel nanomagnetic polymer brush catalyst for nucleophilic substitution
reactions of benzyl halides in water
Ali Reza Kiasat∗, Simin Nazari
Chemistry Department, College of Science, Shahid Chamran University, Ahvaz 61357-4-3169, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 June 2012
Received in revised form 13 August 2012
Accepted 15 August 2012
Available online 25 August 2012
The polymer coated magnetic nanoparticles has gained significant attention for potential applications
in biomedicine, separations, and magnetic storage. In this study, ␤-cyclodextrin–polyurethane polymer
coated Fe3O4 magnetic nanoparticle as a novel class of hybrid organic/inorganic molecular catalyst was
successfully prepared and evaluated as solid–liquid phase-transfer catalyst and molecular host system
for nucleophilic substitution reactions. The nanocomposite has demonstrated the ability to catalytic the
nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in
water. No evidence for the formation of by-products for example isothiocyanate or alcohol was observed
and the products obtained in pure form without further purification. The nanomagnetic polymer brush
catalyst was easily removed from solution via application of a magnetic field, allowing straightforward
recovery and reuse. Results obtained from scanning electron microscopy (SEM) and vibrating sample
magnetometery (VSM) show that the synthesized magnetic nanocomposite are superparamagnetic with
a mean diameter of 59 nm. The grafting of ␤-cyclodextrin–polyurethane polymer to Fe3O4 magnetic
nanoparticle is confirmed by Fourier transform infrared spectroscopy (FT-IR).
Keywords:
␤-Cyclodextrin–polyurethane
Magnetic nanoparticle
Nucleophilic substitution
Benzyl halide
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
surface areas compared to other, more traditional, microp-
orous/mesoporous materials used as catalyst supports, limiting
Magnetic nanoparticles have been attracting increasing atten-
tion among the academic and industrial scientific community
[1–3]. These nanoparticles, because of their high surface area and
unique magnetic properties, have a broad range of potential uses
in biomedical and catalyst support applications [4,5]. Iron oxides,
magnetite (Fe3O4) and maghemite (␥-Fe2O3) are by far the most
used magnetic nanoparticles, because they are much less toxic
than their metallic counterparts, and they still have high satura-
tion magnetization and superparamagnetic behavior, among which
magnetite is a very promising choice due to its already proven bio-
compatibility [6]. In addition, previous investigations have shown
that magnetite has relatively high LD50 values (400 mg/kg in rats)
and polymer-coated magnetite has not shown any acute or suba-
cute toxicity in animal studies [7,8].
the total amount of active sites that can be grafted to the sur-
face. Researchers have shown some success using nanoparticle
supported dendrons and magnetic nanoparticle polymer brush
materials to increase these loadings [9–11].
The functionalization and modification of iron oxide nanopar-
ticles with various biocompatible and biodegradable materials in
many different ways has been demonstrated [6,12,13]. A striking
feature of the MNPs-supported catalysts is that they can be readily
separated using an external magnet, which achieves simple sepa-
ration of the catalysts without filtration.
On the other hand, ␤-cyclodextrin–polyurethane polymer form
a whole new family of stationary microvessel and solid–liquid
phase transfer catalyst, which form noncovalent inclusion com-
plexes with a wide variety of lipophilic molecules by taking up
a whole molecule, or some part of it into the lipophilic cavity of
their ␤-cyclodextrin units [14–17]. In that regard and with a cost-
cutting goal, we designed, novel magnetic nanoparticle supported
polymeric phase transfer catalyst through the immobilization
of ␤-cyclodextrin–polyurethane polymer on magnetite, ␤-CDPU-
MNPs, and the preliminary evaluation of its catalytic activity as
solid–liquid phase-transfer catalyst and molecular host system for
nucleophilic substitution reactions.
Magnetite nanoparticle can be easily formed at low tem-
peratures under mild conditions and modified in terms of
hydrophilicity/hydrophobicity to tune its dispersion stability in
organic or aqueous media. Unfortunately, it often has lower
∗
Corresponding author. Tel.: +98 611 3331746; fax: +98 611 3331746.
E-mail address: akiasat@scu.ac.ir (A.R. Kiasat).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.08.012

A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
81
2. Experimental
2.1. General
Iron (II) chloride tetrahydrate (99%), iron (III) chloride hexahy-
drate (98%), benzyl halides and other chemical materials were
purchased from Fluka and Merck and used without further purifica-
tion. ␤-Cyclodextrin was heated at 80 ◦C under vacuum for 30 min
before use to remove traces of moisture. Products were charac-
terized by comparison of their physical data, IR and 1H NMR and
13C NMR spectra with known samples. NMR spectra were recorded
in CDCl3 on a Bruker Advance DPX 400 MHz instrument spec-
trometer using TMS as internal standard. The purity determination
of the products and reaction monitoring were accomplished by
TLC on silica gel polygram SILG/UV 254 plates. The FT-IR spec-
tra of CDPU-MNPs was measured as potassium bromide discs on
a BOMEM MB-Series 1998 FT-IR Spectrophotometer. The particle
morphology was examined by a SEM. The TGA curve of the ␤-
cyclodextrin–polyurethane polymer grafted onto Fe3O4 magnetic
nanoparticles was recorded on a BAHR, SPA 503 at heating rates of
10 ◦C min−1. The thermal behavior was studied by heating 1–3 mg
of samples in aluminum-crimped pans under nitrogen gas flow,
over the temperature range of 25–500 ◦C.
Fig. 1. FT-IR spectra of (a) HMDI, (b) ␤-CDPU, (c) MNPs and (d) ␤-CDPU-MNPs.
catalyst in the reaction vessel was washed and dried and then sub-
jected to the next run directly.
3. Results and discussion
3.1. Investigation around the approach of ˇ-CDPU-MNPs
2.2. Preparation of ˇ-cyclodextrin–polyurethane polymer grafted
onto Fe3O4 magnetic nanoparticles (ˇ-CDPU-MNPs)
preparation and its structural and morphological analysis
Among all iron oxide NPs, magnetite (Fe3O4) exhibits the most
interesting properties because the presence of non-equivalent iron
cations in two valence states, Fe2+ and Fe3+, in the crystal struc-
ture gives rise to a unique magnetic structure [19]. Magnetite is
easily prepared by adding a base to an aqueous mixture of Fe2+
and Fe3+ chloride. The chemical reaction of Fe3O4 nanoparticles
precipitation is given in Scheme 1.
The magnetic nanoparticles prepared by this method had sig-
nificant numbers of hydroxyl groups on the surface from contact
with the aqueous phase. For grafting ␤-cyclodextrin–polyurethane
polymer, the isocyanate groups were preliminarily bonded onto the
surface of the magnetic nanoparticles by the reaction of hydroxyl
groups of magnetic NPs with hexamethylene diisocyanate. Then ␤-
cyclodextrin, was polymerized with hexamethylene diisocyanate
in dry dimethylformamide and in the presence of modified mag-
netic nanoparticles (Scheme 2).
Preparation ␤-CDPU-MNPs involved two steps. First, super-
paramagnetic nanoparticles (MNPs) were prepared via improved
chemical coprecipitation method [18]. According to this method,
FeCl2·4H2O (3.1736 g, 1.6 mmol) and FeCl3·6H2O (7.5684 g,
2.8 mmol) were dissolved in 320 mL of deionized water, such that
Fe2+/Fe3+ = 1/1.75. The mixed solution was stirred under N2 at 80 ◦C
for 1 h, 40 mL of NH3·H2O was injected into the reaction mixture
rapidly, stirred under N2 for another 1 h and then cooled to room
temperature. The precipitated particles were washed five times
with hot water and separated by magnetic decantation. Finally,
magnetic NPs were dried under vaccum at 70 ◦C.
For introducing of isocyanate groups onto the surface of the
magnetic nanoparticles, in the second step, the MNPs powder
(0.4 g) was dispersed in DMF (30 mL) by sonication and then hex-
amethylene diisocyanate (2.96 g, 17.6 mmol) in 5 mL of dry DMF
was added dropwise to the mixture. After mechanically agitation
of mixture for 3 h, to graft ␤-cyclodextrin–polyurethane polymer
onto the surface of MNPs, in the last step, two grams of ␤-CD (2 g,
1.76 mmol) was dissolved in 15 mL of dry DMF and was added drop-
wise to reaction mixture. The mixture was stirred at 70 ◦C for 3 h.
The precipitate was separated by magnetic decantation and washed
with water and acetone several times. ␤-CDPU-MNPs was dried in
vacuum for 24 h.
The grafting of ␤-cyclodextrin–polyurethane polymer on sur-
faces of magnetic nanoparticles was verified by FT-IR studies. Fig. 1
shows the FT-IR spectra of HMDI, ␤-cyclodextrin–polyurethane,
MNPs and ␤-cyclodextrin–polyurethane polymer grafted onto
Fe3O4 magnetic nanoparticles in the 500–4000 cm−1 wavenum-
ber range. It shows that the characteristic absorption band
of Fe
O
bonds in the tetrahedral sites is 580 cm−1 [20]
which is shifted to 594 cm−1 after surface modification with
cyclodextrin–polyurethane polymer. The IR spectrum of the ␤-
CDPU-MNPs show characteristic adsorption bands at 3360 and
1630 cm−1 correspond to NH and C O groups. The NHCO stretching
2.3. Typical procedure for the nucleophilic substitution of benzyl
halides catalyzed by ˇ-CDPU-MNPs
was also observed at 1570 cm−1
.
The presence as well as the degree of crystallinity of magnetic
iron oxide (Fe3O4) in ␤-CDPU-MNPs was obtained from XRD mea-
surements (Fig. 2). The pattern of ␤-CDPU-MNPs displays a most
intense at 2ꢀ = 34.56. This line corresponds that of pure Fe3O4 [21],
confirming the presence of Fe3O4. The observed sharpness and
higher intensity of that line relative to that of pure Fe3O4, indicating
the higher degree of crystallinity of Fe3O4 particles in ␤-CDPU-
MNPs.
To a mixture of the benzyl halide (1.0 mmol) and MY (Y:N3,
SCN, OAc, CN) (2 mmol) in water (5 ml), ␤-CDPU-MNPs (0.1 g) was
added. The suspension was magnetically stirred under reflux con-
ditions for the time shown in Table 1. After complete consumption
of starting material as judged by TLC (using n-hexane–ethylacetate
as eluent), the catalyst was concentrated on the sidewall of the
reaction vessel using an external magnet, the aqueous phase was
separated by decantation and extracted with diethyl ether (2×
10 mL). The extracted was dried with calcium chloride (CaCl2) and
evaporated in vacuo to give corresponding product. The residual
In addition, XRD pattern of ␤-CDPU-MNPs exhibits some peaks
at around 2ꢀ from 22 to 26 degree that are attributed to the
cyclodextrin–polyurethane polymer [22,23].

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A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
Table 1
Optimization of experimental conditions for nucleophilic substitution reaction of benzyl chloride with NH4SCN in water.
Entry
NH4SCN (mmol)
␤-CDPU-MNPs (g)
Temperature
Time (min)
Yield (%) a
1
2
3
4
5
6
2
2
2
1
2
2
0.05
0.1
0.15
0.1
0.1
0.1
90 ◦
90 ◦
90 ◦
90 ◦
60 ◦
r.t.
C
C
C
C
C
55
10
8
60
45
60
87
85
84
Not completed reaction
85
Not completed reaction
a
Isolated yields.
Scheme 1. Preparation of Fe3O4 magnetic nanoparticles.
Scheme 2. Synthesis of ␤-CDPU-MNPs.
Fig. 3. TGA curve of ␤-CDPU-MNPs.
Fig. 2. XRD pattern of (a) Fe3O4 and (b) ␤-CDPU-MNPs.

A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
83
The magnetic properties of the uncoated magnetic iron oxide
(Fe3O4) and ␤-cyclodextrin–polyurethane polymer coated Fe3O4
nanoparticles were measured by vibrating sample magnetometer,
VSM, at room temperature (Fig. 7). The VSM technique is used
to measure the magnetization value of magnetic particles under
applied magnetic field. For particles with superparamagnetic prop-
erties, when the applied magnetic field is removed, they should
exhibit no coercivity and remanence. In Fig. 6, the hysteresis loops
that are characteristic of superparamagnetic behavior can be clearly
observed for both MNPs and ␤-CDPU-MNPs. Superparamagnetism
is the responsiveness to an applied magnetic field without retaining
any magnetism after removal of the applied magnetic field. From M
vs. H curves, the saturation magnetization value (Ms) of uncoated
MNPs was found to be 68 emu g−1. For ␤-CDPU-MNPs, the mag-
netization obtained at the same field was 7 emu g−1, lower than
that of uncoated Fe3O4. This is mainly attributed to the existence
of nonmagnetic materials (␤-cyclodextrin–polyurethane polymer)
on the surface of nanoparticles. This interesting magnetic prop-
erty could ensure that this superparamagnetic composite is easily
manipulated by a magnet in the separation process. In addition, the
combination of the magnetic properties of iron oxide with guest-
host inclusion complexing behavior of ␤-CD suggests that this nano
composite has great potential to be used as phase transfer catalyst
in organic synthesis.
Fig. 4. SEM images of Fe3O4 nanoparticles.
Fig. 3 shows the TGA analysis of ␤-CDPU-MNPs. One can observe
from the thermogram that the sample exhibits a three-stage degra-
dation pattern over the range of 30–600 ◦C. The first weight loss of
10% below 300 ◦C which might be due to the loss of the adsorbed
water as well as dehydration of the surface OH groups. The second
weight loss step of about 58% in the region of 305–370 ◦C was due to
the cleavage of the urethane linkage, which is quite high compared
to conventional polyurethanes which generally start to decompose
around 200–220 ◦C. The enhanced thermal stability of ␤-CDPU-
MNPs is attributed to the crosslinked nature. The last stage of
degradation in the region of 370–500 ◦C, probably, is due to thermal
decomposition of cyclodextrin. Thus, the TGA curves also confirm
the successful grafting of ␤-cyclodextrin–polyurethane polymer
onto the magnetic surface.
3.2. Application of ˇ-CDPU-MNPs as nanomagnetic polymer
brush catalyst for nucleophilic substitution reactions in water
Even though some anticancer natural products, drug candidates,
synthetic intermediates, antiasthmatic, biocidal and insecticides
possess thiocyanate, cyanide, azide or acetate functional groups,
there are few reported practical synthetic routes in the literature
for these class of compounds [24–28].
The total weight loss over the full temperature range is esti-
mated to be 83% due to the loss of the adsorbed water and organic
units. The amount of magnetic iron oxide (Fe3O4) was evaluated by
deducting the total weight loss, whose value was obtained from the
TGA curve. From these data, the amount of MNPs is estimated to
be 17%. This value could be confirmed by atomic absorption spec-
troscopy.Atomic absorption spectroscopy (A.A.S.) was also applied
to assess the organic content over the support surface of the syn-
thesized nanocomposite.
Owing to the widespread applications of the described com-
pounds, and in continuation of our previous research on using
water as reaction medium [25,29–31] and our interest in devel-
oping
a true water tolerant catalyst using inexpensive and
nonpolluting reagents [30–32], herein we report the synthetic
applicability of ␤-CDPU-MNPs as novel nanomagnetic polymer
brush catalyst for the rapid, and efficient preparation of benzyl thio-
cyanates, cyanides, azides and acetates in water by nucleophilic
substitution reaction (Scheme 3).
A GBC (Avanta) Atomic Absorption spectrometer fitted with
a Fe hollow cathode lamp (Unicam, Franklin, MA) was used to
perform atomic absorption measurements. The wavelength of
248.3 nm and spectral bandpass of 0.50 nm were used throughout.
An air–acetylene flame was used for the determination of the Fe
ions. The atomic absorption measurements of ␤-CDPU-MNPs dis-
plays about 10.4% Fe at 0.1 g of sample. So it is clear that there are
nearly 85.6% of cyclodextrin–polyurethane polymer on the Fe3O4
particles.
The structural and morphological characterization of Fe3O4 and
␤-CDPU-MNPs nanostructure were performed by measuring SEM
using a Philips XL30 scanning electron microscope. The surface
morphologies of the uncoated Fe3O4 nanoparticles and ␤-CDPU-
MNPs were shown in Figs. 4 and 5. As shown in Fig. 5, ␤-CDPU-MNPs
gives thin plates with imbedded Fe3O4.
In order to investigate the possible catalytic properties of ␤-
CDPU-MNPs in the nucleophilic substitution reaction, the reaction
of benzyl halides with thiocyanate anion in water was chosen. Ini-
tially, the mixture of benzyl chloride and NH4SCN in water was
chosen as the model reaction to determine whether the use of
polymeric phase transfer catalyst was efficient and to investigate
the optimized conditions. After some experiments (Table 1), it was
found that the use of 2 equiv. of NH4SCN per benzyl chloride in
the presence of ␤-CDPU-MNPs (0.1 g) in water were the best con-
dition and after stirring for 10 min at 90 ◦C, the clean formation of
a product with lower Rf value was observed.
It should be pointed out that in the absence of ␤-CDPU-MNPs,
the reaction was sluggish and even after prolonged reaction time a
considerable amount of starting material was remained. Moreover,
the reaction mixture was contaminated with alcohol.
TEM micrographs provide more accurate information on the
particle size, morphology and loading of polymers on the support
surface. These nanoparticles consist of irregular ␤-CDPU polymers
and have a narrows size distribution (mostly between 17 and
20 nm) with an average diameter of 18 nm, much smaller than the
sizes obtained from the SEM measurements.
As shown in Fig. 6, the fabricated nanocomposite have high load-
ing of polymers on the support surface that could be prohibited real
close contact of nanoparticles to reduce their mutual attraction.
The success of the conversion of benzyl chloride to benzyl
thiocyanate using ␤-CDPU-MNPs as nanomagnetic solid–liquid
phase-transfer catalyst and molecular host system encouraged us
to enlarge the scope of the reaction to other benzyl halides and
nucleophiles (Table 2). In all cases, a very clean reaction was
observed. It is noteworthy that no evidence for the formation of
by-products such as alcohols or isothiocyanates were observed
and the products obtained in pure form without further purifi-
cation. 13C resonance of the SCN and NCS groups at ∼111 and

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A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
Fig. 5. SEM images of ␤-CDPU-MNPs.
Fig. 6. TEM images of ␤-CDPU-MNPs.
Fig. 7. VSM magnetization curve of Fe3O4 nanoparticles and ␤-CDPU-MNPs.
Scheme 3. Nucleophilic substitution reaction of benzyl halides with different anions catalyzed by ␤-CDPU-MNPs.

A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
85
Table 2
Nucleophilic substitution reaction of benzyl halides with thiocyanate, azide, cyanide and acetate anions in water catalyzed by ␤-CDPU-MNPs.
Entry
Benzyl halide
Nucleophile
Time (min)
Yield (%)a
1
2
3
SCN
N3
CN
OAc
SCN
N3
CN
OAc
SCN
5
89
82
79
80
85
78
82
80
80
Br
10
25
40
10
15
35
40
40
Cl
Cl
N3
CN
OAc
SCN
N3
55
75
84
82
–
Cl
Br
Cl
Br
Not completed reaction
4
5
6
70
80
85
115
15
15
25
35
35
40
50
80
80
81
81
79
83
88
81
75
84
81
87
83
CN
OAc
SCN
N3
Cl
CN
OAc
SCN
N3
CN
OAc
MeO
Cl
a
Isolated yields.
Table 3
Comparison of the efficacy of ␤-CDPU-MNPs catalyst with some of those reported in the literature.
Entry
Substrate/nucleophile
Catalyst/solvent/temperature
Time (h)
Yield (%)
Ref.
−
1
2
3
4
5
6
7
8
9
Benzyl bromide/N3−
Tetramethylammonium bromide pillared clays/petroleum ether–water/100 ◦
C
6
2.5
1
6.5
10
1
10 min
35 min
5 min
84
87
80
88
88
98
82
82
89
[34]
[35]
[25]
[36]
[37]
[38]
This work
This work
This work
Benzyl bromide/N3
Benzyl bromide/SCN−
Benzyl chloride/CN−
Benzyl chloride/CN−
Benzyl bromide/SCN−
Surfactant pillared clay materials and sonochemistry/hexane–water/5 ◦
Tetramethylammonium bromide/water/40 ◦
C
C
Poly [N-(2-aminoethyl) acrylamido] trimethyl ammonium chloride/water/100 ◦
C
Ph3P,Pd(OAc)2/K4[Fe(CN)6], Na2CO3/140 ◦
C
n-Bu4NF-TMSNCS/THF/r.t.
−
Benzyl bromide/N3
␤-CDPU-MNPs/water/100 ◦
␤-CDPU-MNPs/water/100 ◦
␤-CDPU-MNPs/water/100 ◦
C
C
C
Benzyl chloride/CN−
Benzyl bromide/SCN−
∼145 ppm, respectively, are very characteristic for thiocyanate and
isothiocyanate functionalities [25]. However, when an immobi-
lized biocatalyst is prepared, it should be considered that the main
goal of enzyme immobilization should be the reuse of the biocat-
alyst [33]. It is worthy to note that ␤-CDPU-MNPs does not suffer
from extensive mechanical degradation after operating and could
be quantitatively recovered without filtration since the ␤-CDPU-
MNPs was rapidly concentrated as soon as an external magnet was
set close to the sidewall of the reaction vessel. The residual catalyst
was washed with water and methanol and dried, then immediately
reused for the next run. The recovered resin has been reused ten
times for the nucleophilic substitution reaction of benzyl chloride
with thiocyanate anion. The results illustrated in Graph 1 showed
that the catalyst can be used ten times without appreciable loss in
its activity (Graph 1).
With this promising result in hand and establishing the
advantages of ␤-CDPU-MNPs as nanomagnetic solid–liquid phase-
transfer catalyst, we focused our attention in the other nucleophilic
substitution reactions, conversion of benzyl halides to the corre-
sponding cyanides, azides and acetates. Table 2 summarizes the
data and clearly shown that the desired products were formed in
good isolated yields and no side products were observed.A com-
parison of the efficacy of ␤-CDPU-MNPs catalyst with some of
those reported in the literature is presented in Table 3. As it is
seen in addition to having the general advantages attributed to the
nanocatalysts, ␤-CDPU-MNPs is an equally or more efficient cata-
lyst for nucleophilic substitution reaction of benzyl halides in terms
Graph 1. Recyclability of catalyst.
of yield and reaction rate.The catalytic activity of ␤-CDPU-MNPs in
nucleophilic substitution reaction could be attributed to the fact
that ␤-CD unit in nanocomposite consists of seven d-glucopyranose
monomers covalently bound by ␣-1,4-linkages. From a topological
point of view, this macrocycle can be described as a truncated cone,
in which the narrow rim (∼6.4 A) bears the primary hydroxyl group
whereas the wide rim (∼15.4 A) bears the secondary OH groups
[39]. Since no hydroxyl group is present within the toroidal cavity
of ␤-CD, this zone of the molecule has a pronounced hydrophobic

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A.R. Kiasat, S. Nazari / Journal of Molecular Catalysis A: Chemical 365 (2012) 80–86
character. Thus in water, hydrophobic central cavities of ␤-CD units
in ␤-CDPU polymer can be act as microvessel and accommodate
nonpolar alkyl halides. On the other hand, the interior of the ␤-
CD cavity may be more hydrophobic because nonbonding electron
pairs of the glycosidic oxygen are present along with a high elec-
tron density and Lewis-base properties. Thus the outer OH of the
␤-CD cavity formed complexes with cations and these complexes
cause the anion to be activated.
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