Silica chloride nano particle catalyzed ring opening of epoxides by aromatic amines

Article abstract of DOI:10.1002/cjoc.201190195

Silica chloride nano particle (nano SiO₂-Cl), has been found to be heterogeneous catalyst for facile, simple and mild ring opening of epoxides with aromatic amines to afford β-amino alcohols in dry CH ₂Cl₂ at room temperature.

Full text of DOI:10.1002/cjoc.201190195

FULL PAPER
Silica Chloride Nano Particle Catalyzed Ring Opening of
Epoxides by Aromatic Amines
Karimian, Ramina
Piri, Farideh*,a
Karimi, Babakb
Moghimi, Abolghasemc
a Department of Chemistry, Faculty of Science, Zanjan University, P.O. Box 45195-313, Zanjan, I.R. Iran
b Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), P.O. Box 45195-1159,
Gava Zang, Zanjan, Iran
c Department of Chemistry, Imam Hossein University, P.O. Box 16575-347, Tehran, Iran
Silica chloride nano particle (nano SiO2-Cl), has been found to be heterogeneous catalyst for facile, simple and
mild ring opening of epoxides with aromatic amines to afford β-amino alcohols in dry CH2Cl2 at room temperature.
Keywords silica chloride, nano particle, epoxides, catalyzed, ring opening
Introduction
Solid acid catalysts such as amberlyst-15,21 monodis-
persed silica nanoparticles,22 zeolites,23 montmorillonite
K1024 and ionic liquids,25 functionalized alumina or
Epoxides are versatile intermediates in organic syn-
thesis and a large variety of reagents are known for the
ring opening of these compounds.1,2 β-Amino alcohols
are among the most important precursor for a wide
range of biologically active natural and synthetic prod-
ucts,3-5 unnatural amino acids6,7 and chiral auxiliaries.8
The practical route for synthesis of β-amino alcohols is
direct aminolysis of epoxides in presence of surplus
amine at elevated temperature. However, this method-
ology suffers from one or more disadvantages such as
high toxicity and corrosiveness of the acids employed,
moisture sensitivity of catalyst systems, high tempera-
ture, hazardous organic solvent, extended time and the
use of catalyst in a stoichiometric amount or inconven-
ient handling procedures.9-11 Therefore, continuous ef-
forts have been made to develop catalyst-free metohd12
and various catalysts such as sulfamic acid,13 metal tri-
flates,14 metal alkoxides,15 metal halides,16 transition
metal salts,17 heteropolymolybdate or tungstate,18 for the
synthesis of β-amino alcohols. Other limitations such as
low yields, failure of deactivated amines and sterically
demanding aromatic amines are associated with most of
the literature methods. Therefore, the introduction of
new and efficient methods is still in demand. The use of
heterogeneous catalysts provides a perfect solution to
overcome the above limitations. In recent years, the use
of reagents and catalysts on solid supports has made
significant progress.19 Nano silica gel is one of the ex-
tensively used surface material supports for different
chemical transformations in organic chemistry. One of
such modified nano silica is nano silica chloride (nano
SiO2-Cl), which at the first time we reported to be an
efficient catalyst for the synthesis of many organic
compounds such as the amorphous silica chloride.20
26
supported ferric chloride or copper sulfate, Yb(OTf)3
and TS-127 have revealed great promise in this area.
We modified nano silica gel surface by using thionyl
chloride, which acts as a mild and efficient catalyst, and
can be a useful and cheap catalyst for the synthesis of
β-amino alcohols. Our studies have shown that thionyl
chloride is a satisfactory chlorinating agent for nano
silica and amorphous silica, if used undiluted. The ex-
tent of reaction with thionyl chloride gives values for
active silanols per unit area of silica surface, compara-
ble to other method, for determining available activities.
Nano silica chloride was prepared by the readily avail-
able material and can also be easily removed from the
reaction mixture.
Results and discussion
In this paper, a simple and effective catalytic route
for the synthesis of β-amino alcohols under aerobic
conditions is described. 30 mg of amorphous silicon
dioxide, nano silicon dioxide, amorphous silica chloride
and nano silica chloride, catalyzed ring opening of ep-
oxy glycidyl phenyl ether. In order to show the applica-
bility and efficiency of this method, our results have
been compared with some of the same catalysts on the
aminolysis of epoxy glycidyl phenyl ether. As you can
see in Table 1, nano silica chloride is superior to the
other catalysts.
The reaction of an aromatic amine with an epoxide
in the presence of nano silica chloride as catalyst, leads
to the formation of the corresponding β-amino alcohols
2 (Eq. 1).
* E-mail: farideh_piri@yahoo.com
Received August 12, 2010; revised December 10, 2010; accepted January 26, 2011.
Chin. J. Chem. 2011, 29, 955— 958 © 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
955

Karimian et al.
FULL PAPER
Table 1 Comparison of results for the aminolysis of epoxy
glycidyl phenyl ether catalyzed by some of the silicon catalysts at
the same conditions
even after 1 d at reflux. Inspection of the TEM images
of a sample catalyst from the ring opening of epoxides
indicates the involvement of silica chloride nanoparti-
cles with a size distribution of 15—35 nm (average≈20
nm) (Figure 1). A number of different solvents such as
THF, Et2O, n-hexane, toluene, CH3CN and CH2Cl2
were also investigated and it turned out that CH2Cl2 was
the best suited one as solvent for this purpose.
Entry
Catalyst
Time/h
16
Yield/%
97
1
2
Amorphous SiO2
Nano SiO2
Amorphous
SiO2-Cl
4.15
95
3
4
9.20
1.55
92
95
Nano SiO2-Cl
The ring opening of epoxides can be explained by
the mechanism presented in Scheme 1. Typically, 1.2
mmol of the amine were reacted with 1 mmol of the
epoxide in dichloromethane at room temperature under
the air. The nucleophilic addition is catalyzed by the
presence of 30 mg of nano silica chloride which is very
easy to handle. Several aromatic amines and epoxides
were employed and the results are reported in Table 2.
Eight aminolyses of styrene oxide even led to total con-
versions (Entries 1—9). At this point, it should be men-
tioned that no reaction was observed between aniline
and styrene oxide in the absence of nano silica chloride.
The reactions of aliphatic epoxides were slightly slower
than those of styrene oxide. Furthermore, aliphatic ep-
oxides such as glycidyl phenyl ether and glycidyl iso-
propyl ether and cyclohexene oxide (Table 2, Entries
10—36) reacted with aromatic amines to give the ex-
pected products in satisfactory yields. Sterically more
hindered anilines such as N-methylaniline and
2,4,6-trimethylaniline led to the alcohols still in excel-
lent yields. Electron deficient amines like 3-nitroaniline
and 4-nitroaniline also led to the corresponding β-amino
alcohol in high yields. An interesting feature of this
method is that the aliphatic amines such as diethyl
amine, benzylamine and cyclohexylamine failed to af-
fect the ring opening under the same reaction conditions
Figure 1 TEM image of silica chloride nano particle.
The nano silica chloride was recovered using simple
centrifugation, filtration and readily used in subsequent
reactions (1st＝95%, 2nd＝83%, 3rd＝68% yield) and
exhibited consistent catalytic activity for the ring open-
ing of epoxides without further purification. However,
owing to extensive agglomeration, the activity of the
catalyst dramatically decreased after the second run.
The chlorine content of the SiO2Cl nanoparticle was
also determined with the use of back-titration of the re-
sulting HCl upon the treatment of the material with de-
ionized water for 10 h. This value was 2.99 mmol•g－
1
for SiO2Cl nanoparticle. SiO2Cl nanoparticle was pre-
heated at 180 ℃, before performing hydrolysis and
titration experiments. These results clearly excluded any
interference that might result from physically adsorbed
HCl in the calculation of total chlorine content.
Conclusion
A mild, efficient and simple method for the synthesis
of β-amino alcohols has been described using nano sil-
ica chloride as a heterogeneous catalyst. The main ad-
vantage of this method is that it requires mild reaction
conditions, short reaction times, takes place at room
temperature with operational simplicity and with excel-
lent yields.
Scheme 1 Mechanism of the ring opening of epoxides
Experimental
Preparation of nano silica chloride
To an oven-dried (120 ℃) nano silica gel (5 g) in a
round bottomed flask (250 mL) equipped with a con-
denser and a drying tube, was added thionyl chloride
956
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Chin. J. Chem. 2011, 29, 955— 958

Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides
Table 2 Silica chloride nano particle catalyzed ring opening of epoxides with aromatic amines produced via Eq. 1
Entry
Epoxide
ArNH2
Time
68 min
60 min
75 min
150 min
45 min
40 min
20 min
20 min
120 min
Conversion (Selectivity)b,c/%
100 (93)a,b,c
100 (97)b,c
Product
1
2
3
4
5
6
7
8
9
PhNH2
PhNHMe
3-NO2PhNH2
4-NO2PhNH2
4-FPhNH2
100 (91)b,c
100 (91)b,c
100 (86)b,c
100 (93)b,c
100 (95)b,c
100 (93)b,c
100 (99)b,c
4-BrPhNH2
4-MePhNH2
4-MeOPhNH2
2,4,6-tri-MePhNH2
10
11
12
13
14
15
16
17
18
PhNH2
1.50 h
2 h
95 (90)a,b,c
100 (93)b,c
85 (79)b,c
85 (90)b,c
100 (90)b,c
95 (93)b,c
97 (90)b,c
98 (85)b,c
92 (95)b,c
PhNHMe
3-NO2PhNH2
4-NO2PhNH2
4-FPhNH2
6 h
6 h
5 h
4-BrPhNH2
4-MePhNH2
4-MeOPhNH2
2,4,6-tri-MePhNH2
5 h
1 h
1 h
6 h
19
20
21
22
23
24
25
26
27
PhNH2
3 h
3.10 h
9 h
90 (72)a,b,c
80 (82)b,c
53 (68)b,c
68 (71)b,c
80 (71)b,c
75 (71)b,c
88 (86)b,c
70 (65)b,c
87 (89)b,c
PhNHMe
3-NO2PhNH2
4-NO2PhNH2
4-FPhNH2
9 h
9 h
4-BrPhNH2
4-MePhNH2
4-MeOPhNH2
2,4,6-tri-MePhNH2
6.25 h
2.40 h
1.45 h
12 h
28
29
30
31
32
33
34
35
36
PhNH2
1.30 h
1.30 h
7 h
95a,b,d
100b,d
71b,d
75b,d
85b,d
100b,d
97b,d
98b
PhNHMe
3-NO2PhNH2
4-NO2PhNH2
4-FPhNH2
9 h
3.50 h
4.50 h
1 h
4-BrPhNH2
4-MePhNH2
4-MeOPhNH2
2,4,6-tri-MePhNH2
0.50 h
2.50 h
95b
a Yields refer to crude product (isolated product). b All products were identified by comparison of their physical and spectral data with
those of authentic samples. c Sectivity. d Only yield.
Typical experimental procedure
(toxic and should be used with caution) (100 mL) and
refluxed for one week. The excess thionyl chloride was
distilled off. The resulting white-grayish powder was
flame-dried and stored in a tightly capped bottle.
To a mixture of epoxide (1 mmol) and aromatic
amine (1.2 mmol) in CH2Cl2 (5 mL) was added nano
silica chloride (30 mg) at room temperature. The mix-
Chin. J. Chem. 2011, 29, 955— 958
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957

Karimian et al.
FULL PAPER
ture was stirred for a specified period (Table 2). The
progress of the reaction was monitored by TLC. After
complete conversion of the starting material as indicated
by TLC, the reaction mixture was filtered and diluted
with methylenedichloride (25 mL) and washed with
water followed by brine solution. The organic layer was
dried over MgSO4 and concentrated under reduced
pressure to obtain the crude product, which was purified
by column chromatography (silica gel 60—120 mesh)
using ether and petroleum ether (V∶V＝3∶7) to afford
pure β-amino alcohol. β-Amino alcohols were charac-
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© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 955— 958