1-(1-Alkylsulfonic)-3-methylimidazolium chloride as a reusable Br?nsted acid catalyst for the regioselective azidolysis of epoxides under solvent-free conditions

Article abstract of DOI:10.1016/j.cclet.2016.02.015

In this study, 1-(1-alkylsulfonic)-3-methylimidazolium chloride as a new, green, and reusable Br?nsted acid catalyst was prepared. In this protocol, we used for the regioselective ring-opening reactions of various epoxiodes with sodium azide to afford the

Full text of DOI:10.1016/j.cclet.2016.02.015

Accepted Manuscript
Title: 1-(1-Alkylsulfonic)-3-methylimidazolium chloride as a
reusable Brønsted acid catalyst for the regioselective
azidolysis of epoxides under solvent-free conditions
Author: Sobhan Rezayati Eshagh Rezaee Nezhad Rahimeh
Hajinasiri
PII:
S1001-8417(16)30002-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2016.02.015
CCLET 3602
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
11-12-2015
11-1-2016
2-2-2016
Please cite this article as: S. Rezayati, E.R. Nezhad, R. Hajinasiri, 1-(1-Alkylsulfonic)-
3-methylimidazolium chloride as a reusable Bronsted acid catalyst for the regioselective
azidolysis of epoxides under solvent-free conditions, Chinese Chemical Letters (2016),
http://dx.doi.org/10.1016/j.cclet.2016.02.015
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Graphical Abstract
1-(1-Alkylsulfonic)-3-methylimidazolium chloride as a reusable Brønsted acid catalyst for the regioselective azidolysis of
epoxides under solvent-free conditions
Sobhan Rezayati a,*, Eshagh Rezaee Nezhad a, Rahimeh Hajinasiri b
aDepartment of Chemistry, Payame Noor University, Tehran, P.O. Box 19395-4697, Iran
bChemistry Department, Qaemshahr Branch, Islamic Azad University, P.O. Box 163, Qaemshahr, Iran
A simple, efficient and highly regioselective method for the synthesis of β-azido alcohols by the direct opening of various
epoxiodes with sodium azide under solvent-free conditions is described. This new method appears to be competitive and
alternative to the other methods previously described.
Page 1 of 6

Original article
1-(1-Alkylsulfonic)-3-methylimidazolium chloride as a reusable Brønsted acid catalyst
for the regioselective azidolysis of epoxides under solvent-free conditions
Sobhan Rezayati a,*, Eshagh Rezaee Nezhad a, Rahimeh Hajinasiri b
a Department of Chemistry, Payame Noor University, Tehran, P.O. Box 19395-4697, Iran
b Chemistry Department, Qaemshahr Branch, Islamic Azad University, P.O. Box 163, Qaemshahr, Iran
ARTICLE INFO
ABSTRACT
In this study, 1-(1-alkylsulfonic)-3-methylimidazolium chloride as a new, green, and
reusable Brønsted acid catalyst was prepared. In this protocol, we used for the regioselective
ring-opening reactions of various epoxiodes with sodium azide to afford the corresponding β-
azido alcohols in excellent yields and short reaction time under mild and neutral reaction
conditions. This method offers several advantages including excellent regioselectivity, clean
reactions, simple work-up procedure, a recyclable catalyst, and use of an eco-friendly catalyst.
Article history:
Received 11 December 2015
Received in revised form 11 January 2016
Accepted 2 February 2016
Available online
Keywords:
Ionic liquids (ILs)
β-Azido alcohols
Ring opening
Regioselective
Brønsted acid
1. Introduction
Ionic liquids (ILs), known as molten salts (consisting only of
cations and anions) with melting point under 100-150 °C or room
temperature, have attracted an increasing attentions in the context
of green synthesis in recent years. ILs were introduced as an
alternative green media for their unique properties, such as low
vapour pressure being non-volatile, high thermal stability (up to
about 300 °C), wide liquid temperature range, low volatility,
highly polar, non flammability, large electrochemical window,
miscible with certain organic solvents and/or water and good
solubility of organic and inorganic materials, chemically inert,
etc. [1-4]. In addition, the ionic liquids are readily recycled and
tunable to specific chemical tasks. One type is Brønsted-acidic
task-specific ionic liquids (BAILs). Also, ILs in the recent years
have become more attractive in other fields such as formation of
metal nanostructures [5], bioanalytical chemistry [6], catalysis
[7], in basic electrochemical studies of organic compounds and
inorganic compounds [8], analytical chemistry [9], sensors [10],
and for electrochemical biosensors [11]. β-Azido alcohols are
compounds of interest in organic synthesis, because they are
precursors of vicinal amino alcohols or in the chemistry of
carbohydrates, nucleosides, lactames, and oxazolines [12]. Also,
β-azido alcohols are versatile intermediates in organic synthesis
and increasingly important in drugs and pharmaceutics [13-14].
A common method for the synthesis of a β-azido alcohols
involves the regioselective ring opening of epoxide with sodium
azide under various reaction conditions. If the epoxide is
unsymmetrical, azidolysis occurs via a bimolecular reaction at
the least substituted carbon atom [15]. Several catalysts have
sodium azide, including NaN3/3D‐network polymer based on
calix[4]resorcinarene [16], NaN3/CAN [17], NaN3/halohydrin
dehalogenase
[18],
NaN3/(TBA)4PFeW11O39.3H2O
[19],
NaN3/[bmim]BF4/H2O [20], NaN3/SiO2-OPEG(300) [21],
NaN3/PVA or PAA, poly(vinylamine) or poly(allylamine) [22],
NaN3/CeCl3 [23], and NaN3/oxone [24]. It is worth mentioning
some of these methods suffer from disadvantages such as long
reaction times, difficulty in work-up and isolation of products,
require high temperatures, using expensive catalysts and
difficulty in preparation of catalysts, and low regioselectivity.
Therefore, it seems that there is still a need for development of
newer methods that proceed under green and ecofriendly
conditions and economically appropriate conditions. In this
study, the Brønsted acidic ionic liquids 1a and 1b were prepared
by condensation of methyl imidazole with 1,3-propane or 1,4-
butane sultone and acidification of the zwitterion with
concentrated HCl as shown in Scheme 1 [25].
In continuation of our ongoing program to develop
environmentally benign methods using ionic liquids as new
promoters [26-31], we report herein an efficient and simple
method for the ring opening of epoxide with sodium azide and
consequently the corresponding β-azido alcohols under solvent-
free conditions using 1-(1-alkylsulfonic)-3-methylimidazolium
chloride as a reusable Brønsted acid catalyst (Scheme 2).
2. Experimental
Products were separated and purified by different
chromatographic techniques and were identified by the
comparison of their IR, NMR, and Melting point with those
been used to promote azidolysis of epoxides in the presence of
———
* Corresponding author.
Email address: sobhan.rezayati@yahoo.com
Page 2 of 6

1
reported for the authentic samples. H NMR (400 MHz) and 13C
1.50-1.53 (m, 2H), 3.14 (s, 1H), 3.30-3.32 (m, 2H), 3.39-3.44 (m,
4H), 3.87 (m, 1H); 13C NMR (100 MHz, CDCl3): δ 13.78, 19.16,
30.74, 53.52, 69.74, 70.59, 70.71.
NMR (100 MHz) spectra were recorded on a Bruker Avance
(400 MHz) spectrometer using CDCl3 as the solvent and TMS as
an internal standard. All chemical shifts are given as δ value with
reference to Tetra methyl silane (TMS) as an internal standard.
IR spectra were recorded on a Frontier Fourier transform infrared
(FTIR) (Perkin Elmer) spectrometer using a KBr disk. Melting
Points were taken on an Electrothermal capillary melting point
apparatus and are uncorrected. The progress of reaction was
followed with thin-layer chromatography (TLC) using silica gel
SILG/UV 254 and 365 plate. All the solvents and reagents were
purchased from Aldrich and Merck with high-grade quality and
used without any purification.
3. Results and discussion
Herein we wish to report an extremely convenient and
efficient method for regioselective ring opening of various
epoxides
using
1-(1-alkylsulfonic)-3-methylimidazolium
chloride as a new, efficient and recyclable catalyst under solvent-
free conditions at 80 °C. The molecular structure of the Brønsted
acidic ionic liquids 1a and 1b were characterized via FT-IR
analysis (Fig. 1). All the data of characterization are in
accordance with the expected compositions and structures. The
O=S=O asymmetric and symmetric stretching modes of the
sulfonic acid functional groups were found in the ranges 1227-
1235 cm–1. Also, respectively one absorption is visible at 1400
cm–1 for C=C and 1637 for C=N cm–1 group. Also showed a
broad OH stretching absorption around 3448 cm–1.
2.1. Preparation of 1-(1-alkylsulfonic)-3-methylimidazolium
chloride
1-(1-Propylsulfonic)-3-methylimidazolium
chloride
was
prepared via the condensation of 1-methylimidazole with 1,3-
propanesultone and acidification of the resulting salt with
concentrated HCl, according to the literature procedure [25]. To
approximate the Brønsted acidity of the ILs, UV–Vis
spectroscopic measurement was used to determine the Hammett
acidity.
After
characterization
of
1-(1-propylsulfonic)-3-
methylimidazolium chloride [PSMIM]Cl 1a, as a model reaction,
the reaction of phenyl glycidyl ether (1 mmol) with NaN3 (1.1
mmol) was tested using different amounts of [PSMIM]Cl at
range of 70–100 °C in the absence of solvent. The results are
summarised in Table 1, where it can be seen that this reaction
was strongly influenced by the amount of catalyst. No product
was obtained in the absence of the catalyst even after 24 h (Table
1, entry 1) indicating that the catalyst is necessary for the
reaction. The best results were obtained when amount of the
catalyst was 5 mol% at 80 °C, and give the product in excellent
yield and in short reaction time (Table 1, entry 3). Moreover, the
product yield was not changed by increasing the amount of the
catalyst (Table 1, entries 4 and 5). On the other hand increasing
the reaction temperature did not improve the results (Table 2,
entries 7 and 8).
To improve the yield of the target product versus the solvent-
free procedure, the reaction between phenyl glycidyl ether (1
mmol) with NaN3 (1.1 mmol) using [PSMIM]Cl (5 mol%) was
checked in various solvents (5 mL) at 80 °C and the results are
presented in Table 2. As can be seen from Table 2, low yields of
the product were obtained in solution conditions even after
elongated reaction times.
After optimisation of the reaction conditions, various aromatic
and aliphatic epoxides (1 mmol) reacted smoothly with sodium
azide (1.1 mmol) in the presence of BAIL 1a and 1b at 80 °C
under similar reaction conditions to produce the corresponding β-
azido alcohols in excellent yields and short reaction time (Table
3). In general, Table 3 shows the results that clarify the fact that
the reaction proceeds very efficiently in all cases. Various
epoxides underwent ring opening easily in the presence of BAIL
1a and 1b at 80 °C. Bicyclic epoxides such as cyclopentene,
cyclohexene and cyclooctene epoxides also underwent cleavage
with sodium azide to produced β-azido alcohols in high yields.
The products were formed in high yields (85-95%) in short
reaction time (12-35 min) for BAIL 1a and high yield (85-95 %)
in short reaction time (15-35 min) for BAIL 1b. Environmental-
friendly ionic liquid afforded a valuable alternative to promote
2.2. Reactions of epoxides with NaN3 catalyzed Brønsted acidic
ionic liquids 1a and 1b
To a mixture of various epoxides (1 mmol) in NaN3 (1.1
mmol), BAIL 1a or 1b (5 mol%) was added; these were placed
in a round bottom flask and stirred under solvent-free conditions
at 80 °C. After complete consumption of epoxide monitored by
TLC (using n-hexane/ethylacetate (5:1) as eluent), the catalyst
was recovered for reuse by simple filtration, and the product was
extracted with ethyl acetate (3×5 mL). The extract was dried over
anhydrous Na2SO4, and concentrated under vacuum to obtain
β‐hydroxyazide in 85%-95% isolated yields. For styrene oxide,
further purification was achieved by preparative TLC or by silica
gel column chromatography. The spectral data of all the products
were identical with those of the authentic samples. The spectral
data (1H NMR, 13C NMR and IR) of some representative
compounds are given below, and the spectra are deposited in
Supporting information.
1-Azido-3-phenoxy-2-propanol (Table 3, entry 1): IR νmax/cm-
1: 3420, 3067, 3036, 2930, 2878, 2103, 1599, 1496, 1291, 1244,
1045; H NMR (400 MHz, CDCl3): δ 3.45–3.54 (m, 2H), 3.89
(m, 1H), 3.97–4.03 (m, 2H), 4.18 (s, 1H), 6.95–7.00 (m, 2H),
7.02–7.06 (m, 1H), 7.27–7.36 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ 53.5, 69.2, 69.3, 114.3, 121.1, 129.4, 158.3.
2-Azido-2-phenyl-1-ethanol (Table 3, entry 2): IR νmax/cm-1:
1
1
3373, 3051, 3025, 2926, 2102, 1453, 1070; H NMR (400 MHz,
CDCl3): δ 3.37 (1H, s), 3.74 (2H, m), 4.65-4.69 (1H, m), 7.34-
7.44 (5H, m); 13C NMR (100 MHz, CDCl3): δ 66.37, 68.03,
127.49, 128.46, 128.61, 136.47.
1-Azido-3-butoxy-2-propanol (Table 3, entry 11): IR νmax/cm-
1: 3445, 2960, 2932, 2872, 2102, 1459, 1121; H NMR (400
1
MHz, CDCl3): δ 0.87 (t, 3H, J = 7.38 Hz), 1.31-1.35 (m, 2H),
Page 3 of 6

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numerous efficient catalytic systems that have already been
proposed for the ring opening of epoxides. The products obtained
were purified by silica gel column chromatography and
characterised by spectroscopic (1H NMR, 13C NMR and IR). The
infrared spectra of the 1-Azido-3-phenoxy-2-propanol exhibit a
band at 3420 cm−1 assigned to O-H and 2103 cm−1 assigned to
N3. The good reusability of a catalyst is important aspect of green
chemistry and environmental points of view. So the potential for
recovery of BAIL 1a and 1b were investigated. The activities of
the recovered catalyst were carefully investigated through the
reaction of phenyl glycidyl ether (1 mmol) with NaN3 (1.1
mmol) using BAIL 1a and 1b at 80 °C. After completion of the
reaction, the product was extracted in to ethyl acetate; catalyst
from aqueous layer was separated by simple filtration, washed
with MeOH, dried and reused. The catalyst was reused for five
times without any significant changes in the yields and the
reaction times. To show the merit of the present work in
comparison with reported results in the literature, we compared
results of BAIL 1a and 2b with (TBA)4PFeW11O39.3H2O [19],
[bmim]BF4/H2O [20], SiO2-OPEG(300) [21], and [Hmim]N3
[32], for the preparation of β-azido alcohols derivatives. As
shown in Table 4, the present methodology offers several
advantages, such as excellent yields, a simple procedure, short
reaction times, easy synthesis, simple work-up and greener
conditions, in contrast with other existing methods.
4. Conclusion
In conclusion, a new 1-(1-alkylsulfonic)-3-methylimidazolium
chloride was synthesized and its application as an efficient,
green, and reusable Brønsted acid catalyst for regioselective ring
opening of epoxides to β-azido alcohols by azide anion under
solvent-free conditions at 80 °C. The advantages of the present
protocol, such as being an environmentally friendly alternative,
the short reaction times, high yield of products, simple work-up
procedure, excellent regioselectivity. Also, the catalyst was
recyclable and has been reused for five successive runs with little
loss of the catalytic activities.
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Acknowledgment
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DOI 10.1007/s11164-015-2168-1
The authors gratefully acknowledge partial support of this
study by the Payame Noor University (PNU) of Ilam, I.R. Iran.
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Scheme 1. Synthesis of Brønsted acidic ionic liquids (1a, b).
Scheme 2. Regioselective azidolysis of epoxides using Brønsted acidic ionic liquid (1a, b).
Fig. 1. The IR spectrum of Brønsted acidic ionic liquids 1a and 1b.
Table 1
Effect of the catalyst amount and temperature on the reaction between phenyl glycidyl ether (1 mmol) with NaN3 (1.1 mmol).
Entry
Catalyst amount
Temp.(°C)
Time (min)
Yield
(%)a
Trace
82
95
95
91
90
91
89
(mol%)
None
1
2
3
4
5
6
7
8
25
80
80
80
80
70
90
100
24 h
30
12
12
12
15
20
20
1
5
7
10
5
5
5
a Yield of isolated products.
Table 2
Effect of various solvents on the reaction of phenyl glycidyl ether (1 mmol) with NaN3 (1.1 mmol) in the presence of [PSMIM]Cl (5 mol%).
Entry
Solvent
Time (min)
Yield (%)a
1
2
3
4
5
EtOH
60
60
60
60
60
51
35
40
30
30
CH2Cl2
EtOAc
CHCl3
H2O
a Yield of isolated products.
Table 3
Synthesis of β-azido alcohols using Brønsted acidic ionic liquids 1a and 1b.
Page 5 of 6

Entry
1
Product(s)
BAIL 1a
Time (min)
12
BAIL 1b
Time (min)
15
Yield (%)
95
Yield (%)
94
OH
N3
O
N3
Ph
N3
2
3
OH
17
91(11:89)
20
92(11:89)
OH
Ph
Ph
OH
25
27
90
94
25
25
91
95
O
N3
OH
4
O
N3
O
5
6
20
25
25
90
88
95
20
25
25
88
90
93
OH
Me
Cl
N3
N3
OH
N3
7
8
OH
N3
30
35
30
92
88
88
30
35
35
90
88
85
OH
N3
9
OH
OH
10
O
N3
OH
N3
11
12
25
25
90
85
35
35
89
88
O
N3
OH
Table 4
The reusability of BAIL 1a and 1b for the preparation of 1-Azido-3-phenoxy-2-propanol.
BAIL
Yield (%)
cycle 1
cycle 2
cycle 3
cycle 4
cycle 5
95
94
94
94
94
93
93
91
91
90
1a
1b
Table 5
Comparison of β-azido alcohols of some epoxides with different catalysts.
Entry
Product
Catalyst
Conditions
Time (min)
Yield (%)
94
1
(TBA)4PFeW11O39.3H2O
γ-Fe2O3@HAP-Ni+2
[Hmim]N3
CH3CN:H2O, 80 °C
H2O, 80 °C
3 h
20
55
2 h
12
15
2 h
35
65
1.5 h
25
25
3 h
30
70
2 h
25
35
OH
90
94
83
95
94
93
92
83
83
95
93
83
90
89
87
90
O
N3
CH3CN, 60 °C
H2O/ reflux
Ph
SiO2-OPEG(300)
BAIL 1a
BAIL 1b
Solvent-free, 80 °C
Solvent-free, 80 °C
CH3CN:H2O, 80 °C
H2O, 80 °C
2
3
N3
(TBA)4PFeW11O39.3H2O
γ-Fe2O3@HAP-Ni+2
[Hmim]N3
SiO2-OPEG(300)
BAIL 1a
CH3CN, 60 °C
H2O/ reflux
OH
Solvent-free, 80 °C
Solvent-free, 80 °C
CH3CN:H2O, 80 °C
H2O, 80 °C
BAIL 1b
OH
(TBA)4PFeW11O39.3H2O
γ-Fe2O3@HAP-Ni+2
[Hmim]N3
O
N3
CH3CN, 60 °C
H2O/ reflux
SiO2-OPEG(300)
BAIL 1a
BAIL 1b
Solvent-free, 80 °C
Solvent-free, 80 °C
89
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