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Journal of Inclusion Phenomena andMacrocyclic Chemistryand Macrocyclic Chemistry ISSN 1388-3127Volume 76Combined 3-4 J Incl Phenom Macrocycl Chem (2013)76:363-368DOI 10.1007/s10847-012-0207-8

β-Cyclodextrin conjugated magneticnanoparticles as a novel magneticmicrovessel and phase transfer catalyst:synthesis and applications in nucleophilicsubstitution reaction of benzyl halidesAli Reza Kiasat & Simin Nazari

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ORIGINAL ARTICLE

b-Cyclodextrin conjugated magnetic nanoparticles as a novelmagnetic microvessel and phase transfer catalyst: synthesisand applications in nucleophilic substitution reaction of benzylhalides

Ali Reza Kiasat • Simin Nazari

Received: 16 March 2012 / Accepted: 15 June 2012 / Published online: 8 July 2012

� Springer Science+Business Media B.V. 2012

Abstract This paper presents a feasible protocol for the

preparation of b-cyclodextrin conjugated Fe3O4 magnetic

nanoparticles as an efficient microvessel and host system

for nucleophilic substitution reaction of benzyl halides in

water. No evidence for the formation of by-product for

example isothiocyanate or benzyl alcohol was observed

and the products were obtained in pure form without fur-

ther purification. The characteristics results of FT-IR,

XRD, TGA and SEM shows that b-CD is grafted onto

Fe3O4 nanoparticles. The nanomagnetic catalyst could be

readily separated from solution via application of an

external magnet, allowing straightforward recovery and

reuse.

Keywords Magnetic nanoparticles � b-Cyclodextrin �Nucleophilic substitution � Benzyl thiocyanate �Benzyl azide

Introduction

Nowadays, molecular host–guest systems have been

attracted enormous interest. By careful selection of host

and guest molecules, specific properties of the resulting

inclusion compounds can be targeted. Cyclodextrins (CDs)

are widely used as hosts to form noncovalent inclusion

complexes with a wide variety of organic molecules by

taking up a whole molecule, or some part of it into their

lipophilic cavity [1–7]. Many of the potential applications

of host–guest systems require immobilization of either the

guest molecule or the host molecule [8].

Developing novel materials for immobilizing a catalyst

with the ability to maintain its activity and selectivity is a

task of great economic and environmental importance in

chemical and pharmaceutical industries, especially when

expensive and/or toxic homogenous materials are employed

[9].

In this regard, magnetic nanoparticles (MNPs) emerged

as new catalyst supports because of their specific charac-

teristics. These nanoparticles, because of their high surface

area, biocompatibility and unique magnetic properties,

have a broad range of potential uses in biomedical and

catalyst support applications [10, 11]. More than these,

they can be easily separated by simple application of an

external magnetic field. Iron oxides, magnetite (Fe3O4) and

maghemite (c-Fe2O3) are by far the most used MNPs,

because they are much less toxic than their metallic

counterparts, and they still have high saturation magneti-

zation and superparamagnetic behavior, among which

magnetite is a very promising choice due to its already

proven biocompatibility. Magnetite nanoparticle can be

easily formed at low temperatures under mild conditions

and modified in terms of hydrophilicity/hydrophobicity to

tune its dispersion stability in organic or aqueous media.

For this reasons, In recent years the synthesis of organic/

inorganic hybrid materials composed of iron oxide nano-

particles and organic compounds has gained increasing

attention for emerging applications as sensors, adsorbents,

imaging agents, storage media, and catalysis in biotech-

nology and microelectronics [12–19].

By considering all the above-mentioned points and in

continuation of our research [20–23] to develop green

chemistry by using water as reaction medium and molec-

ular host–guest systems, herein, b-CD grafted onto

A. R. Kiasat (&) � S. Nazari

Chemistry Department, College of Science, Shahid Chamran

University, 61357-4-3169 Ahvaz, Iran

e-mail: akiasat@scu.ac.ir

123

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DOI 10.1007/s10847-012-0207-8

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magnetic nanoparticle (MNPs-bCD) was successfully

prepared and its performance as solid–liquid phase-transfer

catalyst for nucleophilic substitution reactions of benzyl

halides with thiocyanate and azide anions in water was

investigated.

Experimental

General

Iron (II) chloride tetrahydrate (99 %), iron (III) chloride

hexahydrate (98 %), benzyl halides and other chemical

materials were purchased from Fluka and Merck compa-

nies and used without further purification. b-cyclodextrin

was heated at 80 �C under vacuum for 30 min before use to

remove traces of moisture. Products were characterized 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 spectrometer using TMS as internal standard.

FT-IR spectra were measured on a BOMEM MB-Series

1998 FT-IR spectrophotometer using potassium bromide

pressed disc method, with 4 cm-1 resolution and 15

scanning times.

The purity determination of the products and reaction

monitoring were accomplished by TLC on silica gel Poly

Gram SILG/UV 254 plates. The TGA curve of the b-CD

grafted onto Fe3O4 MNPs 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 25–600 �C. X-ray diffraction (XRD) patterns of

the samples were taken with a Philips X-ray diffractometer

Model PW1840 (Bragg–Brentano configuration) at room

temperature utilizing Cu Ka radiation with the wavelength

of 1.5418 A. The peak position and intensities were

obtained between 10 and 80� with a velocity of 0.02�/s.

The particle morphology was performed by measuring

SEM using a Philips, XL30 scanning electron microscope

operating at 20 kV.

Preparation of b-CD grafted onto Fe3O4 MNPs-bCD

Preparation MNPs-bCD involved three steps. First, super-

paramagnetic nanoparticles (MNPs) were prepared via

improved chemical coprecipitation method [24]. Accor-

ding 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 vac-

uum at 70 �C.

For introducing of isocyanate groups onto the surface of

the magnetic nanoparticles, MNPs-NCS in the second step,

the obtained MNPs powder (0.4 g) was dispersed in DMF

(30 mL) by sonication and then hexamethylene diisocya-

nate (HMDI) (17.6 mL) in 5 mL of dry DMF was added

dropwise to the mixture. After mechanically agitation for

3 h, the suspended substance was separated with external

magnetic field. For removing of unreacted HMDI, the

settlement product was re-dispersed in dry DMF by soni-

cation and isolated with magnetic decantation for three

times. The precipitated product (MNPs-NCS) was used in

the next step.

To graft b-CD onto the surface of MNPs, synthesized

(MNPs-NCS) was suspended in dry DMF (15 mL) and

then two grams of b-CD (1.76 mmol) was dissolved in

15 mL of dry DMF and was added dropwise to mixture.

The reaction mixture was stirred at 70 �C for 3 h. The

precipitate was separated by magnetic decantation and

washed with water and acetone several times. MNPs-bCD

was dried in vacuum for 24 h (Scheme 1).

All the procedures that MNPs was involved in were

carried out under N2 protection to avoid possible oxidiza-

tion during reaction.

Typical procedure for the nucleophilic substitution

of benzyl halides catalyzed by MNPs-bCD

To a mixture of the benzyl halide (1.0 mmol) and NaY (Y:

N3, SCN) (2 mmol) in water (5 ml), MNPs-bCD (0.2 g)

was added. The suspension was magnetically stirred under

reflux conditions 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 9 10

mL). The extracted was dried with CaCl2 and evaporated in

vacuo to give corresponding product. The residual catalyst

in the reaction vessel was washed and dried and then

subjected to the next run directly.

Results and discussion

Synthesis of b-CD grafted onto Fe3O4 MNPs-bCD

and its structural and morphological analysis

Magnetic nano-phase transfer catalysts have the advanta-

ges of both magnetic separation techniques and nano-sized

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materials, which can be easily recovered or manipulated

with an external magnetic field. As the catalysts are usually

immobilized on the surface of the MNPs, easy access of

reactants to the active sites of the nano-complex, can also

be achieved. In present study Fe3O4 MNPs were prepared

by a coprecipitation method from ferrous and ferric ion

solutions in basic media. The MNPs prepared by this

method had significant numbers of hydroxyl groups on the

surface from contact with the aqueous phase. For grafting

b-CD, the isocyanate groups were preliminarily bonded

onto the surface of the MNPs by the reaction of hydroxyl

groups of magnetic NPs with hexamethylene diisocyanate.

After removing of unreacted hexamethylene diisocyanate,

b-CD was reacted with modified MNPs (Scheme 1).

The chemical structure of synthesized material was

characterized using FT-IR, XRD, SEM, and TGA analyses.

The IR spectrum of the MNPs-bCD show characteristic

adsorption bands at 3,330 and 1,630 cm-1 correspond to

NH and C=O groups. The NHCO stretching was also

observed at 1,570 cm-1. In addition, all the significant

peaks of b-CD in the range of 900–1,200 cm-1 are present

in the spectrum of MNPs-bCD with a small shift. It is

Fe3O4

OCONH(CH2)6NHCO OH2C

Fe3O4

OH

OHHO

HO

OH

OCN(CH2)6NCO

DMF/ r.t/ 3hFe3O4

OCONH(CH2)6NCO

CH2OHHOH2C

DMF/ 70 oC/ 3 h

Fe2+ + 2Fe3+ NH4OH, N2

80 oC, 1h

Fe3O4

OH

OHHO

HO

OHScheme 1 Synthesis of b-CD

grafted onto Fe3O4 magnetic

nanoparticles (MNPs-bCD)

Table 1 Nucleophilic substitution reaction of benzyl halides with thiocyanate and azide anions in water catalyzed by MNPs-bCD

Entry Benzyl halide Nucleophile Time (min) Yield (%)

1Br

SCN 15 86

N3 35 84

2Cl

SCN 25 81

N3 50 83

3

ClCl

ClSCN 100 80

N3 150 78

4

Br

BrSCN 150 80

N3 180 82

5Cl

SCN 40 83

N3 50 79

6

ClMeO SCN 65 83

N3 80 82

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worthy to note that disappearance of the isocyanate peak in

the IR spectrum at about 2,280 cm-1 was also observed.

The infrared band at 575 cm-1 were associated with the

stretching and torsional vibration modes of the magnetite

Fe–O bonds in tetrahedral sites [15] which is shifted to

594 cm-1 after surface modification with CD. Thus, all the

above results indicate that b-CD has been grafted suc-

cessfully on MNPs.

Figure 1 shows powder XRD patterns of b-CD, MNPs

and MNPs-bCD. The XRD pattern of b-CD showed intense

and sharp peaks, indicating its crystalline nature. Whereas,

it can be observed that when the CD is incorporated into

Fe3O4 MNPs it completely disrupts the fine structure

crystallinity of the CD materials. No distinct peaks char-

acteristic of the CD crystals were observed for MNPs-bCD

which indicate that the CD molecules are distributed

homogeneously in this compound without forming any

phase separated crystal aggregates. The pattern of MNPs-

bCD displays a most intense at 2h = 36.56. This line

corresponds that of pure Fe3O4 confirming the presence of

Fe3O4 [25].

Figure 2 shows the TGA analysis of MNPs-bCD. TGA

thermogram exhibits the first weight loss of 7 % below

220 �C which might be due to the loss of residual water

adhering to the sample surface and adsorbed in the CD

cavities. The second weight loss step of about 60 % in the

region of 290–390 �C was due to the breakdown and

decomposition of CD moieties [16]. Thus, the TGA curves

also convey the obvious information that the b-CD mole-

cules are successfully grafted onto the magnetic surface.

The morphology and the particle size distribution of

MNPs-bCD nanostructure were performed by measuring

SEM using a Philips XL30 scanning electron microscope.

As shown in the images (Fig. 3), nanoparticles in all the

samples have spherical shapes indicating the MNPs-bCD

has large surface area. The samples have homogeneous

distributions of nanoparticles and the magnetite particle

size distribution has an average of 62 nm.

Application of MNPs-bCD as nanomagnetic phase

transfer catalyst for nucleophilic substitution reactions

in water

To evaluate the catalytic activity of MNPs-bCD as phase

transfer catalyst in the nucleophilic substitution reaction,

the reaction of benzyl halides with thiocyanate anion in

water was examined to determine whether the use of b-CD

conjugated MNPs was efficient and to investigate the

optimized conditions.

Initially, the mixture of benzyl bromide and NH4SCN in

water was chosen as the model reaction. After some

experiments, it was found that the use of 2 equiv of

NH4SCN per benzyl bromide in the presence of MNPs-

bCD (0.2 g) in water were the best condition and after

stirring for 15 min at 90 �C, the clean formation of a

Fig. 1 XRD pattern of a b-CD, b MNPs and c MNPs-bCD Fig. 2 TGA curve of MNPs-bCD

366 J Incl Phenom Macrocycl Chem (2013) 76:363–368

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product was observed. For comparison the result with

nonsupported catalyst, this nucleophilic substitution reac-

tion was performed under similar conditions using b-CD. It

should be pointed out that, although the results were sim-

ilar, the preparation process using b-CD grafted onto Fe3O4

MNPs-bCD could offer some superiority. This is mainly

because the catalyst can be easily separated by means of an

external magnet and recycling of the catalyst may be

achieved with no loss of activity.

The success of the conversion of benzyl bromide to

benzyl thiocyanate using MNPs-bCD as nanomagnetic

phase-transfer catalyst and molecular host system encour-

aged us to enlarge the scope of the reaction to other benzyl

halides (Scheme 2, Table 1). 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 isothio-

cyanates were observed and the products obtained in pure

form without further purification. 13C resonance of the

SCN and NCS groups at *111 and *145 ppm, respec-

tively, are very characteristic for thiocyanate and isothio-

cyanate functionalities [26].

Cyclodextrins (CDs) are trous-shaped cyclic oligosac-

charides with the hydrophilic outer surfaces and an interior

hydrophobic cavity. Thus in water, central cavities of b-CD

units in MNPs-bCD can be act as microvessel and

accommodate nonpolar benzyl halides. In addition the

hydrophilic exterior due to the outer OH of the b-CD cavity

formed complexes with cation and these complexes cause

the anion to be activated.

However, when an immobilized biocatalyst is prepared,

it should be considered that the main goal of enzyme

immobilization should be the reuse of the biocatalyst. It is

worthy to note that MNPs-bCD does not suffer from

extensive mechanical degradation after operating and could

be quantitatively recovered without filtration since the

MNPs-bCD was rapidly concentrated as soon as an exter-

nal 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 three times for the

nucleophilic substitution reaction of benzyl bromide with

thiocyanate anion. The results were shown that the catalyst

does not show any loss in its activity and produced benzyl

thiocyanate in 86, 81 and 83 % yield, respectively.

With this promising result in hand and establishing the

advantages of MNPs-bCD as nano magnetic phase transfer

catalyst, we focused our attention in the another nucleo-

philic substitution reaction, conversion of benzyl halides to

the corresponding azides. Table 1 summarizes the data and

clearly shown that the desired products, benzyl azides,

were formed in good isolated yields and no side products

were observed. The structures of all of the benzyl thiocy-

anate and azides products were determined from their

analytical and spectral (IR, 1H & 13C NMR) data and by

direct comparison with authentic samples.

Conclusion

In the present work, b-CD grafted onto Fe3O4 MNPs was

successfully prepared and their performance as solid–liquid

phase-transfer catalyst for nucleophilic substitution reactions

of benzyl halides in water was investigated. The new catalytic

system can combine the advantages of homogeneous and

Fig. 3 SEM images of b-CD conjugated magnetic nanoparticles

0.2g MNPs-βCDCH2X

G

NH4SCNWater/ 90

CH2SCN

G

+°C

Scheme 2 Preparation of

benzyl thiocyanate catalyzed by

MNPs-bCD

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heterogeneous catalysts and therefore they can be selective,

reactive and recyclable. With the host effects of b-CD and

superparamagnetism of iron oxide, MNPs-bCD are expected

to have higher potential applications in substitution reactions

of benzyl halides. In conclusion, this method offers several

advantages including easy way to operate, short reaction

times, clean reaction profiles, high isolated yields, safe and

cost-effective procedure for the preparation of benzyl thio-

cyanates and azides, which make it a useful and attractive

process to synthesis of benzyl thiocyanates and azides.

Acknowledgments We are grateful to the Research Council of

Shahid Chamran University for financial support.

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