Synthesis and characterization of a novel nanomagnetic phase-transfer catalyst and its application to regioselective synthesis of β-azido and β-nitro alcohols in water

Article abstract of DOI:10.1134/S1070428017060069

Immobilization of polyethylene glycol-substituted 1-methylimidazolium bromide on the surface of magnetic Fe₃O₄ nanoparticles through hexane-1,6-diyldicarbamate linker afforded a powerful and reusable heterogeneous phase-transfer cata

Full text of DOI:10.1134/S1070428017060069

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2017, Vol. 53, No. 6, pp. 846–852. © Pleiades Publishing, Ltd., 2017.
Synthesis and Characterization of a Novel Nanomagnetic
Phase-Transfer Catalyst and Its Application to Regioselective
Synthesis of β-Azido and β-Nitro Alcohols in Water1
N. Ayashia, M. Fallah-Mehrjardib, c, and A. R. Kiasata*
a Chemistry Department, Collage of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran
*e-mail: m.fallahmehrjardi@yahoo.com
b Department of Chemistry, Payame Noor University (PNU), Tehran, 19395-3697, Iran
c Research Center of Environmental Chemistry, Payame Noor University, Ardakan, Yazd, Iran
Received March 23, 2017
Abstract—Immobilization of polyethylene glycol-substituted 1-methylimidazolium bromide on the surface of
magnetic Fe3O4 nanoparticles through hexane-1,6-diyldicarbamate linker afforded a powerful and reusable
heterogeneous phase-transfer catalysis which was successfully used for regioselective ring opening of epoxides
with azide and nitrite anions in aqueous medium. The new catalyst can readily be recovered by simple
magnetic decantation and recycled several times without appreciable loss of catalytic activity.
DOI: 10.1134/S1070428017060069
In recent decades, interest in nanoscale materials
for various applications has considerably increased.
Nanoparticles are submicron moieties made of
inorganic or organic materials, which have many novel
properties compared with the bulk materials [1].
Nanomaterials have attracted attention because of their
physical, electronic, and magnetic properties. Magnetic
nanoparticles (MNPs) have many unique properties
such as superparamagnetism, low Curie temperature,
high magnetic susceptibility, etc. [2] and are of great
interest for researchers from a broad range of dis-
ciplines, including magnetic fluids [3], data storage
[4], magnetic energy storage [5], biomedicine [6], and
catalysis [7].
Magnetic iron oxide nanoparticles, especially mag-
netite (Fe3O4) and maghemite (γ-Fe2O3), have attracted
much attention because of their unique properties and
potential applications in different fields. Moreover,
MNPs are good supports for immobilization of homo-
geneous catalysts [10]. Therefore, catalytic systems
with MNP supports have been successfully used to
catalyze a broad series of chemical reactions [11–13].
Based on our earlier success in the preparation of
supported MNPs and the use of them as catalysts
[14–16], in continuation of our research on the syn-
thesis of new catalysts [17–19] in this study we per-
formed for the first time functionalization of magnetic
Fe3O4 nanoparticles with polyethylene glycol-substi-
tuted 1-methylimidazolium bromide to obtain the new
catalyst Fe3O4-PEG-ImBr. This novel nanomagnetic
recyclable catalysis was characterized with several
techniques, and its catalytic activity was tested in the
synthesis of β-azido and β-nitro alcohols via regio-
selective ring opening of epoxides with azide and
nitrite anions under aqueous conditions.
Nanoparticles have an exceptionally large surface
area to volume ratio which is responsible for their
widespread advantageous use in catalysis. Nanomag-
netic catalysts have emerged as one of the most useful
heterogeneous catalysts due to their numerous applica-
tions in organic synthesis [8]. These catalysts have
been studied in various significant protocols in organic
chemistry because they are robust, inexpensive, and
readily available. Also, they can be easily prepared
from available metal salts and, most importantly, can
be recycled for several runs without considerable loss
of selectivity and activity [9].
The catalyst was synthesized as shown in
Scheme 1. Naked Fe3O4 magnetic nanoparticles were
prepared by coprecipitation of ferrous and ferric ions
in a basic aqueous solution, followed by thermal
treatment [20]. Hexamethylene diisocyanate (HMDI)
is a widely used linker for the fabrication of drug
1
The text was submitted by the authors in English.
846

SYNTHESIS AND CHARACTERIZATION OF A NOVEL NANOMAGNETIC
847
Scheme 1.
SOCl2, pyridine
toluene, reflux, 6 h
NaBr, 120°C
O
O
O
HO
OH
HO
Cl
HO
Br
n
n
n
Polyethylene glycol (PEG)
Polyethylene glycol
Polyethylene glycol
monobromide (HO-PEG-Br)
monochloride (HO-PEG-Cl)
OH
HO
OH
NH3/H2O, N2
80°C, 1 h
OCN(CH2)6CNO
CH2Cl2, r.t., 3 h
H
FeCl3·6H2O
+
FeCl2·4H2O
Fe3O4
OH
Fe3O4
HO
HO
OH
OH
O
N
N
NCO
( )6
O
O
(1)
, CH2Cl2, reflux, 3 h
HO
Br
n
(2) 1-Methyl-1H-imidazole, reflux, 12 h
H
H
N
Me
Fe3O4
O
N
N
O
( )6
O
n
Br–
O
O
Fe3O4-PEG-ImBr
delivery vehicles with reportedly a very low degree of
toxicity. It was used in the present work to bind
polyethylene glycol monobromide to the surface of
magnetite nanoparticles. For this purpose, Fe3O4 nano-
particles were preliminarily treated with HMDI which
reacted with hydroxy groups present on the nano-
particle surface. The surface was then modified with
polyethylene glycol monobromide to obtain function-
alized Fe3O4 nanoparticles (Fe3O4-PEG-Br). Finally,
1-methylimidazole was immobilized onto the modified
MNPs, yielding the nanomagnetic phase-transfer
catalyst (Fe3O4-PEG-ImBr).
Fe–O bonds. Due to the presence of polyethylene
glycol-substituted 1-methylimidazolium bromide moi-
ety bound to the Fe3O4 surface, C–H stretching and
bending bands were observed at 2850–2950 and 1400–
1500 cm–1, respectively. In addition, bands at 1619 and
1567 cm–1 were present, which were assigned to vibra-
tions of the imidazole C=N bond and imidazole ring.
The morphologies of Fe3O4 and Fe3O4-PEG-ImBr
were characterized by scanning electron microscopy
(SEM). As shown in Figure 2, the size of Fe3O4 and
Fe3O4-PEG-ImBr nanoparticles was about 48 and
63 nm, respectively. Moreover, the nanoparticles have
spherical shape.
The catalyst has been characterized by various
techniques, including FT-IR, SEM, and TGA. The
FT-IR spectrum of Fe3O4-PEG-ImBr is shown in
Fig. 1. The spectrum displayed an absorption band at
~3300 cm–1 which was assigned to stretching vibra-
tions of the surface O–H bonds. The low-frequency
band at ~580 cm–1 belongs to vibrations of iron oxide
The thermal decomposition behavior of Fe3O4-
PEG-ImBr in air was investigated by thermal gravi-
metric analysis (TGA) by raising the temperature at
a rate of 10 deg/min up to 500°C (Fig. 3). Two main
stages of weight loss were observed. The first small
weight loss below 220°C was assigned to removal of
physically adsorbed water and dehydration of the
surface OH groups, and the second weight loss (14%)
in the region of 225–300°C is probably due to decom-
position of organic groups grafted on the magnetite
surface.
After successful characterization of Fe3O4-PEG-
ImBr, its catalytic activity was estimated in phase-
transfer ring opening of epoxides. The ring-opening
reactions of epoxides with azide anion afford the
corresponding β-azido alcohols. In order to optimize
the conditions, the reaction of 2,3-epoxypropyl phenyl
ether (1 mmol) with sodium azide (2 mmol) in water at
90°C was chosen as model. The best result was
4000
3000
2000
ν, cm–1
1000
Fig. 1. FT-IR spectrum of Fe3O4-PEG-ImBr.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 6 2017

AYASHI et al.
(a)
848
(b)
Fig. 2. SEM images of (a) Fe3O4 and (b) Fe3O4-PEG-ImBr.
Scheme 2.
NaN3, H2O, 90°C
5–60 min
N3
OH
OH
or
OH
N3
R
R
R
O
Fe3O4-PEG-ImBr
R
NaNO2, H2O, 90°C
20–90 min
NO2
or
OH
NO2
R
R = Ph, PhOCH2, CH2=CHCH2OCH2, i-PrOCH2, BuOCH2 (see Table 1).
obtained using 0.05 g of Fe3O4-PEG-ImBr; in this
case, 1-azido-3-phenoxypropan-2-ol was isolated in
nearly quantitative yield (98%; Table 1). Under the
optimal conditions, the catalyst Fe3O4-PEG-ImBr was
then used to synthesize β-azido alcohols from different
epoxides with electron-donating and electron-with-
drawing groups. The results are given in Table 1.
more substituted carbon atom of epoxides is strongly
favored (α-attack). In contrast, steric factor predomi-
nates for epoxides with electron-withdrawing groups,
and nucleophilic attack of anions is directed at the less
substituted carbon atom (β-attack).
Tables 2 and 3 compare the catalytic efficiencies of
Fe3O4-PEG-ImBr and some reported catalysts in the
ring opening reaction of styrene oxide with azide and
We also examined the catalytic activity of Fe3O4-
PEG-ImBr in the synthesis of β-nitro alcohols via
reaction of epoxides (1 mmol) with sodium nitrite
(5 mmol) in the presence of 0.05 g of Fe3O4-PEG-
ImBr in water at 90°C. All epoxides reacted efficiently
to afford the corresponding β-nitro alcohols in high to
excellent yields (Table 1).
Weight, %
100
95
90
85
80
75
In all cases, the ring opening of epoxides in the
presence of Fe3O4-PEG-ImBr was highly regioselec-
tive, and only one isomer was obtained. The reactions
with epoxides derived from cyclic olefins afforded
exclusively trans isomers (Scheme 3). Obviously, the
regioselectivity of this reaction is largely determined
by its mechanism, specifically by steric and electronic
factors. As shown in Table 1, for epoxides bearing
electron-donating groups, the electronic factor pre-
dominates, and nucleophilic attack of anions on the
0
100
200
300
400
500
Temperature, °C
Fig. 3. TGA curve of Fe3O4-PEG-ImBr.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 6 2017

SYNTHESIS AND CHARACTERIZATION OF A NOVEL NANOMAGNETIC
849
Scheme 3.
Scheme 4.
NaX, Fe3O4-PEG-ImBr
H2O, 90°C
OH
X
O
H
H
Fe3O4
O
O
N
N
O
O
Na+
O
O
( )n
( )n
( )6
n = 1, 3, 5; X = N3, NO2 (see Table 1).
O
O
O
H
nitrite anions to produce β-azido alcohols and β-nitro
alcohols, respectively. These data indicated that our
procedure is advantageous due to high regioselectivity
and stereoselectivity, high yield, and mild conditions.
O
O
Me
Nu–
N
N
O
A possible mechanism explaining the role of Fe3O4-
PEG-ImBr in the regioselective ring opening of
epoxides is outlined in Scheme 4. This catalyst con-
tains three different units linked together, and each unit
is believed to play a special role in the ring opening of
epoxides by anions. Presumably, polyethylene glycol
moiety encapsulates alkali metal cation much like
crown ethers, and this complex favors activation of the
anion. The 1-methylimidazolium moiety endows the
catalyst with ionic liquid properties. In addition, hy-
droxy groups on the surface of magnetic nanoparticles
facilitate epoxide ring opening via hydrogen bonding
with the epoxide oxygen atom. Due to extremely small
size of nanoparticles, the surface area is maximized,
and the number of polymers attached thereto increases,
Table 1. Preparation of β-azido and β-nitro alcohols from epoxides in the presence of Fe3O4-PEG-ImBr in water at 90°C
Reaction with sodium azide
Reaction with sodium nitrite
reaction yield,b
reaction yield,b
Substrate
producta
producta
time, min
%
time, min
%
O
N3
NO2
15
90
30
85
OH
OH
Ph
Ph
Ph
Ph
Ph
Ph
O
O
OH
OH
O
10
10
98
87
45
20
95
90
O
O
N3
OH
O
NO2
OH
O
O
N3
NO2
H2C
Me
H2C
Me
H2C
Me
O
OH
OH
O
O
N3
O
NO2
5
83
60
85
Me
Me
Me
OH
OH
O
15
45
85
84
90
20
93
87
Me
O
Me
O
N3
Me
O
NO2
OH
OH
O
NO2
OH
N3
OH
O
60
45
84
90
60
45
91
92
N3
NO2
OH
OH
N3
O
NO2
a
The products were identified by comparison of their physical and spectral data with those of authentic samples.
Isolated yield.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 6 2017

AYASHI et al.
850
Table 2. Azidation of styrene oxide by different methods
Regioselectivity, %
Reagents and conditions
Time, h
Yield, % Reference
α-attack
β-attack
LiClO4/NaN3/MeCN /80°C
05
05
82
81
18
19
21
22
09
12
20
05
10
00
00
92
90
94
65
95
96
85
85
85
98
90
[16]
[16]
NH4Cl/NaN3/MeOH–H2O/reflux
LiN3/MeCN/80°C
20
79
[16]
Zr(OTf)4/TMGAa/MeCN/room temperature
Polymeric PTCb/NaN3/H2O/room temperature
CeCl3/NaN3/MeCN–H2O/reflux
(TBA)4PFeW11O39 ·3H2O/NaN3/MeCN–H2O/80°C
MPTCc/NaN3/H2O/90°C
42
78
[17]
06
91
[18]
03
88
[19]
0.04.5
0.00.5
0.01.5
0.00.5
00.00.25
80
[20]
95
[21]
NaN3/PEG-300/60°C
90
[22]
SiO2-PEG-ImBr/NaN3/H2O/90°C
Fe3O4-PEG-ImBr/NaN3/H2O/90°C
100
100
[23]
This work
a
TMGA is 1,1,3,3-tetramethylguanidinium azide.
Polymeric PTC is poly[N-(2-aminoethyl)acrylamido]trimethylammonium iodide.
MPTC is a multi-site phase transfer catalyst.
b
c
Table 3. Nitration of styrene oxide by different methods
Regioselectivity, %
Reagents and conditions
Time, h
Yield, % Reference
α-attack β-attack
MgSO4/NaNO2/MeOH/65°C
3.5
2.0
1.0
8.0
1.5
1.0
0.5
000
040
091
089
089
100
100
100
60
09
11
11
00
00
75
80
93
89
90
80
85
[24]
[25]
Amberlite IRA-400, NO2–/EtOH/50°C
QPAa/NaNO2/MeCN/room temperature
LaCl3 ·7H2O/Bu4NBr/NaNO2/Et2O–H2O/room temperature
PNBAb/NaNO2/H2O/room temperature
SiO2-PEG-ImBr/NaNO2/H2O/90°C
[26]
[27]
[28]
[29]
Fe3O4-PEG-ImBr/NaNO2/H2O/90°C
This work
a
QPA is poly[N-(2-aminoethyl)acrylamido]trimethylammonium chloride resin.
PNBA is poly(N-bromoacrylamide).
b
which leads to dramatic increase in the catalyst
efficiency.
To examine the reusability, the catalyst was ex-
1-methylimidazolium bromide onto the surface of
Fe3O4 magnetic nanoparticles. The catalyst has been
characterized by FT-IR, SEM, and TGA data, and its
catalytic efficiency in the regioselective preparation of
β-azido alcohols and β-nitro alcohols from epoxides in
aqueous medium has been demonstrated. This novel
catalytic method offers several advantages, including
environmental friendliness, high yield, short reaction
time, mild reaction conditions, simple work-up proce-
dure, ease of separation, and recyclability of the mag-
netic catalyst. The catalyst could be easily recovered
by magnetic decantation and reused at least five times
without noticeable loss of activity. We believe that the
proposed procedure could be a new and useful addition
to the present methodologies in this area.
tracted by an external magnet from the reaction mix-
ture in the azidolysis of styrene oxide, washed with
methanol or acetone, dried in the air, and reused as
such in subsequent experiments (up to five cycles)
under similar reaction conditions. The yields of the
product remained comparable in all experiments (90,
89, 85, 88, and 86% in cycles 1–5, respectively),
indicating that the catalyst can be recycled for at least
five times without significant loss of activity.
In conclusion, we have synthesized and charac-
terized a novel green phase-transfer catalyst via im-
mobilization of polyethylene glycol-substituted
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SYNTHESIS AND CHARACTERIZATION OF A NOVEL NANOMAGNETIC
851
EXPERIMENTAL
pyridine (7.9 g, 0.1 mol) in 500 mL of toluene. The
mixture was refluxed for about 6 h and cooled, the
precipitate of pyridine hydrochloride was filtered off,
and the solvent was removed from the filtrate under
reduced pressure. The residue was dissolved in
methylene chloride and treated with activated alumina,
and the process was repeated twice. The solution was
filtered and evaporated to dryness to obtain 28 g (90%)
of polyethylene glycol monochloride (HO-PEG-Cl).
A mixture of HO-PEG-Cl (28 g, 45 mmol) and sodium
bromide (15.5 g, 150 mmol) was heated in an oil bath
at 120°C overnight. After cooling, methylene chloride
(20 mL) was added, the solution was filtered, and the
solvent was removed to obtain polyethylene glycol
monobromide. Yield 26 g (87%).
All materials and reagents were purchased from
Fluka and Merck and were used without further
purification. Polyethylene glycol (600) was heated at
80°C in a vacuum for 30 min before use to remove
traces of moisture. Magnetic nanoparticles were syn-
thesized by co-precipitation of FeCl3 · 6 H2O and
FeCl2 ·4H2O in aqueous ammonia according to the
reported procedure [20]. The isolated compounds were
characterized by comparison of their physical data and
IR and H and 13C NMR spectra with those of
1
authentic samples. The NMR spectra were recorded in
CDCl3 on a Bruker Avance DPX 400 MHz spectrom-
eter using tetramethylsilane as internal standard. The
IR spectra were recorded on a BOMEM MB-Series
1998 FT-IR spectrometer. The purity of the products
and reaction progress were monitored by TLC on silica
gel PolyGram SILG/UV 254 plates. The TGA curve of
the Fe3O4-PEG-ImBr was recorded on a BAHR SPA
503 instrument at a heating rate of 10 deg/min in air
atmosphere over the temperature range 25–500°C. The
particle morphology was examined by scanning elec-
tron microscopy using a Philips XL30 microscope.
Fe3O4-PEG-ImBr. Polyethylene glycol mono-
bromide (5 g) was added to a well stirred mixture of
magnetic Fe3O4-urethane nanocomposite and anhy-
drous methylene chloride (50 mL), and the mixture
was stirred under reflux for 3 h. The solid material was
filtered off and washed with anhydrous methylene
chloride (3×30 mL), 1-methylimidazole (3.28 g,
40 mmol) was added, and the mixture was stirred for
12 h under reflux. The magnetic phase-transfer catalyst
was washed with methylene chloride and dried at room
temperature.
Magnetic Fe3O4 nanoparticles [20]. Superpara-
magnetic nanoparticles (MNPs) were prepared via im-
proved chemical co-precipitation method. According
to this method, FeCl2·4H2O (6.37 g, 32 mmol) and
FeCl3·6H2O (15.15 g, 56 mmol) were dissolved in
640 mL of deionized water under nitrogen at 80°C for
1 h, and the solution was added to 25% aqueous
ammonia (80 mL) with vigorous mechanical stirring.
After the color of bulk solution turned black, the mix-
ture was stirred for 1 h under nitrogen. The precipitat-
ed particles were washed five times with hot water and
separated by magnetic decantation. Finally, magnetic
NPs were dried under reduced pressure at 70°C.
General procedure for the preparation of
β-azido alcohols using Fe3O4-PEG-ImBr in water.
The catalyst Fe3O4-PEG-ImBr (0.05 g) was added to
a mixture of epoxide (1 mmol) and sodium azide
(2 mmol) in water (5 mL), and the mixture was stirred
at 90°C. The progress of the reaction was monitored
by TLC using hexane–ethyl acetate (5:1) as eluent.
When the reaction was complete, the catalyst was
recovered by filtration, and the product was extracted
with diethyl ether (3×10 mL). The combined extracts
were dried over CaCl2 and evaporated under reduced
pressure. The yields of β-azido alcohols are given
in Table 1.
Magnetic Fe3O4–urethane nanocomposite. The
MNPs powder prepared as described above (1 g) was
dispersed in anhydrous methylene chloride (50 mL) by
sonication, a solution of hexamethylene diisocyanate
(2.96 g, 17.6 mmol) in 5 mL of anhydrous methylene
chloride was added dropwise, and the mixture was
mechanically stirred on heating under reflux for 3 h.
After cooling, the mixture was filtered, and the solid
residue was washed with anhydrous methylene
chloride (3×50 mL).
General procedure for the preparation of β-nitro
alcohols using Fe3O4-PEG-ImBr in water. The cata-
lyst Fe3O4-PEG-ImBr (0.05 g) was added to a mixture
of epoxide (1 mmol) and sodium nitrite (5 mmol) in
water (5 mL), and the mixture was stirred at 90°C for
a time indicated in Table 2. The progress of the reac-
tion was monitored by TLC using hexane–ethyl acetate
(5:1) as eluent. When the reaction was complete, the
product was extracted with diethyl ether (3×10 mL),
and the combined extracts were dried over CaCl2 and
evaporated under reduced pressure. The yields of
β-nitro alcohols are listed in Table 1.
Polyethylene glycol monobromide (HO-PEG-Br)
[21]. Thionyl chloride (8 g, 0.07 mol) was slowly
added with stirring over a period of 30 min to a solu-
tion of polyethylene glycol 600 (30 g, 0.1 mol OH) and
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AYASHI et al.
852
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University.
2015, vol. 41, p. 2991.
16. Igder, S., Kiasat, A.R., and Shushizadeh, M.R., Res.
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