Immobilization of β-cyclodextrin onto Dowex resin as a stationary microvessel and phase transfer catalyst

Article abstract of DOI:10.1016/j.catcom.2009.12.005

In this study, immobilization of β-cyclodextrin onto commercial Dowex resin by covalent bond was reported. The efficiency of this biocatalyst system as a stationary microvessel and new solid-liquid phase transfer catalyst in reduction of epoxides by NaBH₄ was studied.

Full text of DOI:10.1016/j.catcom.2009.12.005

Catalysis Communications 11 (2010) 484–486
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Immobilization of b-cyclodextrin onto Dowex resin as a stationary microvessel
and phase transfer catalyst
*
Ali Reza Kiasat , Soheil Sayyahi
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:
In this study, immobilization of b-cyclodextrin onto commercial Dowex resin by covalent bond was
Received 21 September 2009
Received in revised form 28 November 2009
Accepted 3 December 2009
Available online 6 December 2009
reported. The efficiency of this biocatalyst system as a stationary microvessel and new solid–liquid phase
transfer catalyst in reduction of epoxides by NaBH
4
was studied.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
b-Cyclodextrin
Immobilization
Inclusion complex
Ring-opening reaction
Reduction
1
. Introduction
flow methods could be employed, making the technique particu-
larly attractive for industrial applications [17].
The use of cyclodextrins (CDs) as microvessels to perform
chemical reaction has attracted the interest of chemist since the
960s [1]. Cyclodextrins have hydrophobic cavities into which or-
ganic molecules of appropriate size and shape can be incorporated
mainly through hydrophobic interactions in aqueous solutions [2–
]. Although water has many unique properties, it has not tradi-
tionally been the solvent of choice in which to perform organic
reactions. One reason has been that the nonpolar nature of organic
molecules results in low or no solubility in water [6].
Recently, as part of our efforts to introduce novel PTC systems
for the synthesis of organic compounds [18,19]; we have reported
grafting of the poly(ethylene glycol) onto Dowex resins [20], as an
efficient and reusable catalyst in the regioselective azidolysis of
epoxides in water. Taking into account all this; we decided to
immobilize b-CD as a stationary microvessel and new phase trans-
fer system for organic transformation.
1
5
2. Experimental
As is well known, the solubility of apolar guest compounds in
water is (in general) increased when they form inclusion com-
plexes with CDs [7–11]. Thus, cyclodextrins are potent phase
transfer catalysts (PTC) [12,13].
On the other hand, the practical utility of CDs could be ex-
tended further if they can be rendered water insoluble. Different
strategies have been explored in the literature including poly-
merization procedures and immobilization onto solid particles
such as silica, PEGylated Merrifield resins, and inside nanoporous
oxides [14–16].
2.1. General remarks
Epoxides and other chemical materials were purchased from
Fluka and merck and used without further purification. Dowex
+
H resin (mesh 30–40) was washed with cold methanol, dried un-
der vacuum at 50 °C and stored in airtight container. b-cyclodex-
trin was heated at 80 °C under vacuum for 30 min before use to
remove traces of moisture. Products were characterized by com-
1
parison of their physical data, IR and H NMR spectra with known
Immobilization of the phase transfer catalyst on an insoluble
polymeric matrix has considerable advantages. Not only would
the catalyst recovery and product isolation be greatly simplified
but also, owing to the three-phase nature of the system, continuous
samples. NMR spectra were recorded in CDCl on a Bruker Advance
DPX 400 MHz instrument spectrometer using TMS as internal stan-
3
dard. IR spectra were recorded on a BOMEM MB-Series 1998 FT-IR
spectrometer. The purity determination of the products and reac-
tion monitoring were accomplished by TLC on silica gel polygram
SILG/UV 254 plates. GLC analyses were performed on a Shimadzu
GC-12 A chromatograph equipped with a 3-m Thermon-1000
column.
*
Corresponding author. Tel./fax: +98 611 3331746.
E-mail address: akiasat@scu.ac.ir (A.R. Kiasat).
1
566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2009.12.005

A.R. Kiasat, S. Sayyahi / Catalysis Communications 11 (2010) 484–486
485
2
.2. Typical procedure for immobilizing of b-cyclodextrin to Dowex
is no example about application of supported cyclodextrin in the
ring-opening reaction of epoxide with sodium borohydride in
aqueous media. In order to investigate the efficiency of the
Maraton C
An oven dried 50 mL flask equipped with a magnetic stirrer is
immobilized b-Cyclodextrine onto polymer as a solid–liquid
phase transfer catalyst, 2, 3-epoxypropyl phenyl ether was cho-
sen as a model compound and reacted with Dowex-b-CD and
+
charged with dried Dowex H resin (2 g) under nitrogen atmo-
sphere. Then freshly distilled SOCl (5.0 mL, 67 mmol) was added
2
slowly to the flask through an addition funnel and the reaction
mixture was stirred under reflux conditions. After stirring for 6 h,
the excess unreacted thionyl chloride was distilled out. Under
nitrogen atmosphere, a solution of freshly dried b-cyclodextrin
4
NaBH in water. TLC analysis of the mixture showed completion
of the reaction in 8 h. The products, 1-phenoxypropan-2-ol (1a)
and 3-phenoxypropan-1-ol (1b) were achieved after extraction
and no evidence for the formation of diol as byproduct of the
reaction was observed. This reaction was also tested, using
(
3.4 g, 3 mmol) in dried pyridine (10 mL) was added dropwise to
the resulting polymer. The solution was mixed at room tempera-
ture until no HCl was produced. The solid was filtered off and
washed thoroughly with acetone and water. Then, the Dowex-b-
CD was collected and dried in vacuum.
4
Dowex and NaBH ; the reaction was not completed and re-
quired much longer reaction time for the complete conversion.
Also, the product, 3-phenoxypropan-1-ol was contaminated by
diol. The promoting effect of supported catalyst was definitely
confirmed by reaction of 2, 3-epoxypropyl phenyl ether under
similar reaction condition, without adding catalyst, the substrate
2.3. Typical procedure for the ring opening of epoxides
did not react with NaBH
0% of the substrate was recovered.
To confirm the effect of acidic sites on Dowex-b-CD in the rate
4
, even after two days and more than
9
4
NaBH (4.0 mmol) was added gradually to a mixture of epoxide
(
1.0 mmol) and Dowex-b-CD (0.1 g) in water (5.0 mL). The suspen-
and regioselectivity of the reduction reaction, the resin was first
treated with 0.1 M NaOH solution and the reduction of 2, 3-epoxy-
propyl phenyl ether by NaBH was investigated with the inacti-
4
vated acidic sites resin. GLC analysis of the reaction mixture was
clearly shown that the reaction completed in 12 h associated with
remarkable decreasing in 1b, whereas the main product of the
reaction was 1a (Table 1).
This method has been found to be applicable to a series of epox-
ides, under similarly mild experimental reaction conditions, and
the results are illustrated in Table 2.
sion was magnetically stirred at room temperature for the time
shown in Table 2. After complete consumption of epoxide as
judged by TLC (using n-hexane/ethylacetate (5:1) as eluent), the
insoluble PTC was filtered off and the filtrate was extracted with
ether (3 Â 5). The extract was dried over Na
2 4
SO , and evaporated
in vacuo to give the alcohols. The crude products were purified
by silica gel column chromatography.
3
. Results and discussion
The catalytic property of the polymeric matrix, Dowex-b-CD, is
due to the inclusion complex formation of epoxides via hydrogen
bonding of the epoxide oxygen to the outer OH of the b-CD which
then reacts with BH4 anion to form alcohol. Likewise, acidic media
promote activation of the epoxide and increase the rate of the
reduction by sodium borohydride (Scheme 2).
However, when an immobilized biocatalyst is prepared, it
should be considered that the main goal of enzyme immobiliza-
tion should be the reuse of the biocatalyst [24]. It is worthy to
note that Dowex-b-CD does not suffer from extensive mechani-
cal degradation after operating and could be quantitatively
recovered by simple filtration and washing with water and
methanol. The recovered resin has been reused three times for
the reduction of cyclohexene oxide. The results were clearly
shown that the catalyst does not show any loss in its activity
and produced corresponding alcohol in 85%, 82% and 80% yield,
respectively.
b-CD, a cyclic oligosaccharide composed of seven a-(1–4) linked
D-glucopyranose units [21,22], can be easily immobilized to Dow-
ex Maraton C resin in the reaction depicted in Scheme 1. In the first
step, sulfonic acid functional groups of resin were converted to sul-
fonyl chloride. Cyclodextrine can be efficiently immobilized on the
resin by reaction of sulfonyl chloride functional groups with b-CD.
The reaction is very clean and does not require any work-up proce-
dure because the evolved HCl gas can be removed from the reac-
tion vessel immediately.
À
To determine the amount of b-CD supported on the resin, 0.5 g
of the each resins, Dowex-SO
with methanol, dried and mixed with 20 mL of 0.5 M NaOH for
h. Then, the solutions were titrated with 0.5 M HCl. The degree
3
H and Dowex-b-CD, were washed
1
of immobilization of b-CD units on the main backbone of the resin
was 0.9 mmol/g resin.
It has been reported that CDs affected the reduction of epox-
ide with sodium borohydride [23]. But, to our knowledge, there
Table 1
Effect of Dowex- b-CD on the ring-opening reaction of 2, 3-epoxypropyl phenyl ether.
O
OH
Dowex-β−CD
(1.0 mmol)
+
NaBH (4.0 mmol)
PhO
+
PhO
OH
PhO
4
CH3
H O, Mix
2
1
1
a
1b
Entry
Catalyst
Time (h)
Conversion (%)
Isolated yields (%)
1
2
3
4
Dowex-b-CD
Dowex
8
8
48
12
100
40
10
40 (1a), 55 (1b)
12 (1b and some diol was isolated)
5 (1b)
–
*
Dowex-b-CD
100
70 (1a), 15 (1b)
*
Inactivated sites resins.

4
86
A.R. Kiasat, S. Sayyahi / Catalysis Communications 11 (2010) 484–486
Table 2
Results of the treatment of epoxides with NaBH
4
catalyzed by Dowex-b-CD.
Entry
Epoxide
Product(s)a
Time
Yield
(%)
b
(
h)
1
8
40(55)c
40(50)c
85
O
OH
CH3
PhO
Ph
OH
PhO
Ph
PhO
2
3
6
8
O
OH
OH
CH3
Ph
OH
O
H
4
5
12
24
75
10
OH
O
O
OH
CH
O
O
3
a
b
c
Products were identified by comparison of their physical and spectral data with those of authentic samples.
Isolated yields.
According to GLC analysis.
SO3H
SO3H
SO3H
Acknowledgement
SO3H
SO2Cl
SO3H
SO2Cl
SO2-β−CD
SO3H
SOCl2, reflux, N2, 6 h
1- Pyridine, N2, 0.5 h
- β−CD, N2, 24 h
SO3H
The authors gratefully acknowledge the Research Council of
Shahid Chamran University for financial support.
2
SO3H
SO2-β−CD
a
b
c
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[
(
4
. Conclusion
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