Cu(ii) immobilized on aminated epichlorohydrin activated silica (CAES): As a new, green and efficient nanocatalyst for preparation of 5-substituted-1H-tetrazoles

Article abstract of DOI:10.1039/c4ra15148h

Cu(ii) immobilized on aminated epichlorohydrin activated silica (CAES) is a novel and efficient heterogeneous nanocatalyst in the [3 + 2] cycloaddition reactions of various organic nitriles with sodium azide. The protocol can provide a series of 5-substituted-1H-tetrazoles under mild conditions in DMSO. Efficient transformation, mild reaction conditions, easy product isolation and the potential reusability of the catalyst are attractive features. The catalyst (CAES) was characterized by FT-IR, TGA, TEM, BET, SEM-EDS, CHN and ICP techniques.

Full text of DOI:10.1039/c4ra15148h

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: N. Razavi and B.
Akhlaghinia, RSC Adv., 2015, DOI: 10.1039/C4RA15148H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
Cu(II) immobilized on aminated epichlorohydrin activated silica
(CAES): as a new, green and efficient nanocatalyst for preparation of
5-substituted-1H-tetrazoles
Nasrin Razavi, Batool Akhlaghinia*
Abstract
Cu(II) immobilized on aminated epichlorohydrin activated silica (CAES) is a novel
and efficient heterogeneous nanocatalyst in the [3+2] cycloaddition reactions of
various organic nitriles with sodium azide. The protocol can provide a series of 5ꢀ
substitutedꢀ1Hꢀtetrazoles under mild conditions in DMSO. Efficient transformation,
mild reaction conditions, easy product isolation and the potential reusability of the
catalyst are attractive features. The catalyst (CAES) was characterized by FTꢀIR,
TGA, TEM, BET, SEMꢀEDS, CHN and ICP techniques.
Keywords:
Cu(II) immobilized on aminated epichlorohydrin activated silica (CAES),
nanocatalyst, 5ꢀSubstitutedꢀ1Hꢀtetrazole, arylnitriles, alkylnitriles, sodium azide,
cycloaddition reaction.
Introduction
Recently, catalytic synthesis of tetrazoles which represent an important class of
heterocycles, has acquired immense attention, due to their wide ranging applications.
Tetrazoles are used in materials as specialty explosives and information recording
systems, in pharmaceuticals as lipophilic spacers and carboxylic acid surrogates, in
coordination chemistry as ligands and also used as precursors in a variety of nitrogen
containing heterocycles.1 The proton acidꢀcatalyzed cycloaddition between hydrazoic
acid and nitriles has long been one of the main routes to 5ꢀSubstitutedꢀ1Hꢀ
1

RSC Advances
Page 2 of 35
View Article Online
DOI: 10.1039/C4RA15148H
tetrazoles.This method suffers from explosion of a large amounts of harmful
hydrazoic acid.2 As, it is necessary to overcome the above mentioned drawback and to
improve the synthetic methods of obtaining 5ꢀsubstitutedꢀ1Hꢀtetrazoles, a number of
new catalysts have also been investigated till date. Most of them which are based on
[3+2] cycloaddition reaction between azide ion and organic nitriles are imidazoleꢀ
based zwitterionicꢀtype molten salts,3 βꢀcyclodextrin,4 copper triflates,5 CdCl2,6
Fe(OAc)2,7 Zn(II) salts,8ꢀ10 AgNO3, Et3N·HCl,12 Lewis acids such as B(C6F5)3,
11
13
AlCl3,14 BF3·OEt2,15 FeCl3,16 TBAF,17 InCl3,18 I2,19 (CH3)2SnO,20 and Bronsted acid
catalyst.21 Also, the reactions were carried out by using some heterogeneous catalysts
such as chitosan derived magnetic ionic liquid,22 tungstates,23 NaHSO4.SiO2,19 FeCl3ꢀ
SiO2,16 COY zeolites,24 mesoporous ZnS nanospheres,25 Zn/Al hydrotalcite,26
nanocrystalline ZnO,27 ZnO/Co3O4,28 ZnꢀCu alloy,29 Zn hydroxyapatite,30 Pd(PPh3)4,31
Cu2O,32 AgNPs,33 WAlPOꢀ5 microspheres,34 Fe3O4@SiO2/Salen of Cu(II)35 and
CuFe2O4 nano particles.36
Unfortunately, with very few exceptions, earlier synthetic methods suffered from
various disadvantages including the use of expensive and toxic metals, expensive
reagents, strong Lewis acids, long reaction times (several hours to days) in
combination with high reaction temperatures, low yield, harsh reaction conditions,
tedious workꢀups and difficulty in the separation and the recovery of the catalyst. In
addition to this in some cases, formation of highly volatile and toxic hydrazoic acid as
by product warrant the safety of the method.37 As, the increasing demands of
environmental legislation promotes the chemical industries to minimize waste
production in chemical manufacture,38 a growing interest has been witnessed in the
use of heterogeneous catalyst, in different areas of organic synthesis. Organic–
2

Page 3 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
inorganic hybrid catalysts, such as organosilane39 having a covalently anchored
organic spacer as a class of tethered heterogeneous catalysts have been widely applied
due to their environmental compatibility combined with good yield , selectivity and
easy separation.40
In the present study, we would like to report a new silicaꢀsupported catalyst based on
Cu(II) immobilized on aminated epichlorohydrin. Designing and the application of
this heterogeneous, more convenient and reusable catalyst in the [3+2] cycloaddition
reactions of various organic nitriles with sodium azide were investigated. At first, the
silica surface was activated by refluxing hydrochloric acid solution (37%) to increase
the terminal silanol–OH groups (I).41 Then the support was heated at reflux with an
aqueous solution of NaOH ( 0.04 M) to change the terminal silanol–OH groups into
negatively charged silanol–O– groups to produce the desired activated silica (II).The
activated silica was suspended to pure epichrorohydrin at 60 oC with vigorous stirring
and then the resulting epoxy activated silica (III) reacted with ammonia solution. The
aminated epichlorohydrin activated silica (IV) was used as the support and ligand for
entrapment of Cu(II) by the reaction of (IV) with a solution of Cu(OAc)2.H2O.The
resulting complex contains Cu(II) immobilized on aminated epichlorohydrin activated
silica (CAES) (V) (Scheme 1).
3

RSC Advances
Page 4 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Scheme 1 Preparation of Cu(II) immobilized on aminated epichlorohydrin activated
silica (CAES).
Results and Discussion
After preparation and characterization of CAES and in continuation of our recent
studies on the application of CuSO4.5H2O,42, 43 in organic reactions, the catalytic
activity of CAES as a new nanocatalyst was evaluated in [3+2] cycloaddition
reactions of various organic nitriles with sodium azide to produce a library of 5ꢀ
substitutedꢀ1Hꢀtetrazoles (Scheme 2).
R
N
N
Cat. (1 mol%)
DMSO, 130 °C
R
CN
N
N
N Na
N
HN
1-17
R= Ph, 4ꢀBrC6H4, 4ꢀClC6H4, 4ꢀCNC6H4, 4ꢀNO2C6H4, 2ꢀNH2 5ꢀNO2C6H3, 4ꢀEtOC6H4,
3,5ꢀMeOC6H3, 3ꢀMeC6H4, 4ꢀOHC6H4, 9ꢀPhenanthrene, 2ꢀthiophene, 4ꢀpyridine, 2ꢀ
pyridine, PhCH2, (CH3)2CHCH2, (CH3)2CH(CH2)2
O
O
O
NH2
NH2
cat.
Cu
O
CAES
Scheme 2 Synthesis of different structurally 5ꢀsubstitutedꢀ1Hꢀtetrazoles in the
presence of CAES in DMSO.
4

Page 5 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
To obtain the best conditions for the synthesis of titled compounds, the reaction of
benzonitrile and sodium azide was selected as a model reaction and was studied in the
presence of CAES by applying different molar ratios of reactants as well as solvents
at different temperatures. The obtained results are summarized in Table 1.
At first we used DMSO as solvent for the reaction between 1:1 molar ratio of
benzonitrile:sodium azide at 130 ºC in the absence of any catalyst. After 24 h, 5ꢀ
phenylꢀ1Hꢀtetrazole was afforded in 35% isolated yield (Table 1, entry 1). The same
result was obtained when the reaction was performed in the presence of aminated
epichlorohydrin activated silica (IV) (Table 1, entry 2).This means that IV has not
any catalytic activity in [3+2] cycloaddition. Applying Cu(II) immobilized on
aminated epichlorohydrin activated silica (CAES) (0.0400g, 1 mol% contains 0.0006
g, 0.01mmol of Cu) as catalyst in cycloaddition reaction produced the desired product
in high yield after 1h (Table 1, entry 3). The presence of CAES has great influence on
reaction time as well as yield (Table 1, entry 3). To investigate the effect of
temperature on the reaction rate, [3+2] cycloaddition was performed at different
temperatures (Table 1, entries 4ꢀ6). Lower temperatures reduced the rate of reaction
considerably while higher temperature (140 ºC) as well as higher catalyst loading
(0.0800 g, 2 mol% contains 0.0012 g, 0.02 mmol of Cu, entry 7) has not any influence
on the reaction rate. In an effort to develop better reaction conditions, solvent free
condition and different solvents were screened for the preparation of 5ꢀphenylꢀ1Hꢀ
tetrazole in the presence of 0.0400 g, 1 mol% of CAES at 130 ºC (Table 1, entries 8ꢀ
12). As can be seen, the catalytic activity of CAES was decreased efficiently in
solvent free condition as well as DMF, CH3CN, H2O and 1,4ꢀdioxane. Further
increase in reaction time has no significant effect on yields. The solvent is known to
significantly affect the reaction rate. The use of aqueous solvent was ineffective (entry
5

RSC Advances
Page 6 of 35
View Article Online
DOI: 10.1039/C4RA15148H
11), however, DMSO was found to be successful, although the superior effect of
DMSO remains uncertain in comparison with the other polar solvents. To improve the
yield of reaction, the effect of different molar ratios of reactants was examined (Table
1, entry 13). According to this study, the increase in amount of NaN3 from 1 to 1.5
mmol was found to have no effect on the yield. In order to ascertain the major role of
CAES as a catalyst in the [3+2] cycloaddition, the model reaction was studied in the
presence of the same amount of Cu (0.01mmol, 0.0006 g) using 0.0018 g, 0.9 mol%
of Cu(OAc)2.H2O. After appropriate reaction time (1h), the reaction was proceeded
with only 50% isolated yield and no additional conversion was obtained even after
longer reaction time. Therefore, we may conclude that the catalytic activity of Cu(II)
in cycloaddition reaction was improved by immobilization on aminated
epichlorohydrin activated silica matrix (IV) (Table 1, entry 14).
Table 1 Synthesis of 5ꢀphenylꢀ1Hꢀtetrazole in the presence of different mol% of
CAES in various solvents, different molar ratios of benzonitrile:NaN3 and different
temperatures.
Entry
Molar
ratio(Nitrile:
NaN3)
Catalyst (g)
Solvent
Temperature
(ºC)
Time (h)
Isolated
Yield (%)
1
1:1
ꢀ
DMSO
130
24
35
2a
3
4
5
6
7
8
1:1
1:1
1:1
1:1
1:1
1:1
1:1
0.04
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
ꢀ
130
130
120
80
24
1
35
95
70
50
95
95
20
0.04 (1 mol%)
0.04 (1 mol%)
0.04 (1 mol%)
0.04 (1 mol%)
0.08 (2 mol%)
0.04 (1 mol%)
1
4
140
140
130
1
1
1
9
1:1
0.04 (1 mol%)
DMF
130
1
60
6

Page 7 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
20
10
11
12
1:1
1:1
1:1
0.04 (1 mol%)
0.04 (1 mol%)
0.04 (1 mol%)
CH3CN
H2O
130
130
130
1
1
trace
5
1,4ꢀ
1
dioxane
13
1:1.5
1:1
0.04 (1 mol%)
DMSO
DMSO
130
130
1
1
95
50
14b
0.0018 (0.9
mol%)
a The reaction was performed in the presence of IV.
b The reaction was performed in the presence of Cu(OAC)2.H2O.
A variety of structurally divergent nitriles possessing a wide range of functional
groups (Scheme 2) selected to explore the generality and scope of [3+2] cycloaddition
reaction catalysed by CAES. The obtained results are summarized in Table 2. The
optimized reaction conditions (1:1 molar ratio of nitrile:sodium azide, 0.0400 g, 1
mol% of catalyst, in DMSO at 130 ºC) were used for all organic nitriles and the
corresponding 5ꢀsubstitutedꢀ1Hꢀtetrazoles were prepared within 1ꢀ7 h with good to
excellent yields. Aromatic nitriles containing both electron withdrawing and electron
donating groups underwent the conversion smoothly. The aromatic nitriles having
electron donating substituents require longer reaction time (compare entries 1ꢀ6 with
entries 7ꢀ10) as donating substituent on aromatic ring decreases the electrophilic
character of nitrile. Cycloaddition reactions of aliphathic nitriles proceeded more
slowly than cycloaddition reactions of aromatic nitriles because of deactivation of
nitriles by electron donating alkyl groups, in other words, aromatic rings can facilitate
the attack of azide anion to the cyano groups and stabilize the corresponding
intermediates (Table 2, entries 15ꢀ17). It is noteworthy that aryl dicyano derivatives
such as terephthalonitrile also reacted smoothly with sodium azide and gave only
mono adduct even by using 1:2 molar ratio of terephthalonitrile:sodium azide and 1
mol% of catalyst (Table 2, entry 4).
7

RSC Advances
Page 8 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Table 2 Synthesis of different structurally 5ꢀsubstitutedꢀ1Hꢀtetrazoles in the presence
of CAES in DMSO.
Entry
Substrate
Product
Time(h)
1
Isolated
Yield(%)
N
N
CN
95
90
N
N
1
2
H
N
N
3
2
1
CN
CN
N
N
H
Br
Cl
Br
Cl
N
N
92
96
N
N
N
3
4
5
H
N
N
CN
CN
N
H
NC
NC
N
N
N
1
90
N
H
O2N
O2N
N
N
NH2
NO2
NH2
CN
N
N
H
6
7
3
4
90
85
NO2
N
N
CN
N
N
N
H
EtO
EtO
N
N
N
MeO
CN
MeO
N
8
9
7
5
83
80
H
OMe
CN
OMe
N
N
N
N
H
Me
Me
N
N
CN
N
10
11
7
6
80
85
H
HO
HO
N
HN
N
CN
N
8

Page 9 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
HN
N
S
S
12
13
3
3
5
80
95
80
N
CN
N
N
N
N
CN
N
H
N
N
N
N
CN
N
14
15
N
H
N
N
H
N
N
N
CN
5
7
75
75
N
N
HN
N
16
17
CN
N
H
N
CN
N
5
82
N
N
All synthesized compounds have been characterized by its melting points and FTꢀIR
spectroscopy. The selected compounds were further identified by 1H NMR, 13C NMR
spectroscopy and mass spectroscopy which compared with literature data. The
disappearance of one strong and sharp absorption band (CN stretching band) and the
appearance of an NH stretching band in the FTꢀIR spectra were evidence for the
formation of 5ꢀsubstitutedꢀ1Hꢀtetrazoles. Also, the FTꢀIR spectra of all products show
absorption bands at 1293ꢀ1233 cmꢀ1 due to NꢀN=Nꢀ, 1041ꢀ1106 cmꢀ1 and 1189ꢀ1110
cmꢀ1 due to tetrazole ring. In 1HNMR and 13C NMR spectra, a signal at 16.9 and 161ꢀ
155 ppm are assigned to the NH and quaternary carbon NHꢀC=N respectively.
The catalytic activity of CAES in [3+2] cycloaddition reactions of various organic
nitriles with sodium azide is established by the fact that a long reaction time and
comparatively lower yield of product was observed (Table 1, entry 1) when similar
reaction was carried out in the absence of CAES. The catalytic activity of CAES
could be attributed to the Lewis acidity of the Cu(II) complex. By analogy with
previous reports,43 a plausible mechanism for the reaction methodology under current
development is shown in Scheme 3. Initially, interaction of nitrogen atom of nitrile
9

RSC Advances
Page 10 of 35
View Article Online
DOI: 10.1039/C4RA15148H
compound with Cu(II) forms I which accelerates the cyclization step. The [3+2]
cycloaddition between the C≡N bond of nitrile compound and azide ion takes place
readily to form the intermediate II. Acidic workꢀup, affords III and IV. The
equilibrium leads to formation of the more stable tautomer IV (5ꢀsubstitutedꢀ1Hꢀ
tetrazole). Nevertheless, at this time there is no experimental evidence for the [3+2]
cycloaddition reaction proceeds in this manner, and further studies to elucidate the
details of the mechanism are ongoing.
R
C
N
N
O
N
N Na
O
NH2
NH2
O
O
NH2
NH2
O
O
SiO2
Cu
SiO2
Cu
O
O
R
C
N
N
N
N
Na
I
O
N
N
R
R
NH2
NH2
O
NH
N
H
SiO2
Cu
O
N
N
HN
N
O
IV
III
N
R
N
Na
N
N
II
Scheme 3 Proposed mechanism for the synthesis of 5ꢀsubstitutedꢀ1Hꢀtetrazoles in the
presence of CAES.
A further advantage of this solid catalytic system is its reusability. Catalyst reꢀ
usability was assessed in the cycloaddition reaction of benzonitrile and sodium azide.
To this end, the reaction was stopped after completion and the catalyst retrieved from
the reaction mixture by centrifugation. For each successive use, the catalyst was
washed with ethanol and acetone several times to remove the products, followed dried
at 100 ºC. Table 3 shows the results obtained after five reꢀuse cycles. These results by
10

Page 11 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
themselves suggest that the catalyst efficiency was remained after five using. The
copper content of freshly prepared CAES which was obtained by inductively coupled
plasma (ICP) was 1.6092 wt%, 0.0158 g, 0.25 mmol of Cu per 1.000 g of CAES,
whilst inductively coupled plasma (ICP) shows that the 5th reused CAES contains
1.2452 wt%, 0.0120 g, 0.19 mmol of Cu per 1.000g of 5th reused CAES. It means
that, in spite of some leaching of Cu(II) during recovery process of the catalyst, no
significant loss of activity of the catalyst was observed and the catalytic activity
maintained effectively after five reusing of CAES. In other words, the above results
lead us to conclude that the amount of leached metals from the catalyst is very low.
Table 3 [3+2] cycloaddition reactions of benzonitrile with sodium azide in the
presence of 0.0100 g of reused CAES.
Entry
Run
Time (h)
Isolated
Yield(%)
1
2
3
4
5
1
2
3
4
5
1
1
1
1
1
95
95
90
90
87
To show the advantage of CAES over some of the reported catalysts in the literature,
the catalytic role of CAES in [3+2] cycloaddition reaction of benzonitrile with sodium
azide was compared with various reported catalyst (Table 4). In comparison, some of
these methods, in addition using environmentally hazardous catalysts and tedious
purification of products, require long reaction times to achieve reasonable yields.
11

RSC Advances
Page 12 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Table 4 Comparison of various catalysts in the synthesis of 5ꢀphenylꢀ1Hꢀtetrazole
Entry
1
Catalyst
Solvent Temperature
(°C)
Time
(h)
Yield(%)
Reference
chitosan derived
magnetic ionic liquid
ꢀ
ꢀ
70
7
87
84
22
3
2
imidazoleꢀbased
zwitterionicꢀtype
molten salts
120
12
3
4
mesoporous ZnS
DMF
DMF
120
36
5
96
88
25
silica
reflux
21c
sulfuric acid
5
6
AgNPs
DMF
DMF
120
120
8
7
92
90
33
35
Fe3O4@SiO2/
Salen Cu(II)
7
8
9
B(C6F5)3
AgNO3
CAES
DMF
DMF
120
120
130
8
5
1
94
83
95
13
11
ꢀ
DMSO
Experimental
The purity determinations of the products were accomplished by TLC on silica gel
polygram STL G/UV 254 plates. The melting points of products were determined
with an Electrothermal Type 9100 melting point apparatus. The FTꢀIR spectra were
recorded on an Avatar 370 FTꢀIR Therma Nicolet spectrometer. The NMR spectra
were provided on Brucker Avance 100 and 400 MHz instruments in acetoneꢀd6,
DMSOꢀd6 and CD3CN. Elemental analyses were performed using aThermo Finnegan
Flash EA 1112 Series instrument. Mass spectra were recorded with Agilent
Technologies (HP) 5973 Network Mass Selective Detector and Shimadzu GCꢀMSꢀ
QP5050 instruments at 70 eV. Thermogravimetric analysis (TGA) was performed on
a Shimadzu Thermogavimetric Analyzer (TGꢀ50) under air atmosphere. BET surface
12

Page 13 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
area and pore size distribution were measured on a Belsorp mini II system at −196 ◦C
using N2 as adsorbate. Transmission electron microscopy (TEM) examination was
performed with a TEM microscope Leo 912 AB120 kV Zeiss Germany. Inductively
coupled plasma (ICP) was carried out on a Varian, VISTAꢀPRO, CCD, Australia.
Elemental compositions were determined with a Leo 1450 VP scanning electron
microscope equipped with an SC7620 energy dispersive spectrometer (SEMꢀEDS)
presenting a 133 eV resolution at 20 kV. All of the products were known compounds
and characterized by the FTꢀIR spectroscopy and comparison of their melting points
with known compounds. The structure of selected products was further confirmed by
1HNMR, 13CNMR spectroscopy, and mass spectrometry.
Preparation of activated silica (II)
Silica (5.00 g, Merck grade 60) was heated at reflux with hydrochloric acid solution
(37%, 30 mL). After 8 h the white suspension was filtered and the precipitate was
thoroughly washed with deionized water until the pH of the eluent reached 6. The
dried activated silica (I) was then treated with refluxing aqueous solution of NaOH
(0.04 M, 30 mL) for 8 h. Then the suspension was filtered and washed with deionized
water until a constant pH= 8 to afford a white solid powder (activated silica II) that
was dried at 110 °C in an oven overnight under vacuum.
Preparation of epoxy activated silica (III)
o
Activated silica (II) (2 g) was suspended to pure epichrorohydrin (10 mL) at 60 C
with vigorous stirring. After 24 h the resulting suspension was cooled to room
temperature and centrifuged. The white precipitate was washed with methanol (4×15)
until removing additional amount of epichlorohydrin. The epoxy activated silica (III)
was then dried at 100 oC under vacuum for 8 h.
13

RSC Advances
Page 14 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Preparation of aminated epichlorohydrin activated silica (IV)
The epoxy activated silica (III) (2 g) was suspended in ammonia solution (25%, 20
o
mL) at 50 C with stirring. After 72 h, the resulting suspension was cooled to room
temperature and centrifuged. The resulting white powder was washed in turn with
methanol (3×5) and water (4×15) until neutralizing the filtrate. The aminated
epichlorohydrin activated silica (IV) was dried under vacuum at 100 o C for 10 h.
Preparation of Cu(II) immobilized on aminated epichlorohydrin silica (CAES)
To a solution of Cu(OAc)2.H2O (0.6 mmol, 0.11 g) in absolute EtOH (5 mL),
aminated epichlorohydrin activated silica (IV) (1 g) was added at room temperature.
The reaction mixture was stirred under Ar atmosphere for 4 h. The resulting
suspension was centrifuged and the blue precipitate was washed in turn with acetone
(4×5), ethanol (4×5) and then dried under vacuum at ambient temperature for 16 h.
Preparation of CAES
As can be seen in Scheme 1, the catalyst was prepared in three steps. Initially, the
surface of silica was activated by refluxing HCl (37%). Hydrochloric acid increased
the terminal SiꢀOH (I, Scheme 1).44 The resulting precipitate was then treated with
boiling NaOH solution which converted the SiꢀOH to negatively charged SiꢀOꢀ groups
to produce the desired activated silica (II, Scheme 1).44 The epoxy activated silica
o
(III, Scheme 1) was obtained upon treatment of II with epichlorohydrin at 60 C
which under treatment with ammonia produced aminated epichlorohydrin activated
silica (IV).The aminated epichlorohydrin activated silica was used as the support and
ligand for entrapment of Cu(II) by the reaction of IV with a solution of
Cu(OAc)2.H2O. The resulting complex contains Cu(II) immobilized on aminated
epichlorohydrin activated silica matrix (CAES).
14

Page 15 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
Characterization of CAES
The catalyst was characterized by a battery of techniques including techniques: FTꢀIR
spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy
(TEM), scanning electron microscopy (SEMꢀEDS), BET analysis, Elemental analysis
(CHN) and inductively coupled plasma (ICP).
The catalyst structure was defined by FTꢀIR spectroscopy. Infrared data are useful
only to confirm the existence of the bonded species. Figure 1 illustrates the FTꢀIR
spectra of activated silica with HCl (I), activated silica with NaOH (II), epoxy
activated silica (III), aminated epichlorohydrin activated silica (IV) and Cu(II)
immobilized on aminated epichlorohydrin activated silica (CAES). The principal
bands for activated silica with HCl were observed at 1064, 808 and 469 cmꢀ1 which
are presumably due to asymmetric, symmetric and bending vibrations of SiꢀOꢀSi
respectively. Also, strong and broad absorption band around 3475 cmꢀ1 confirmed the
presence of the hydrogen bonded SiꢀOH groups and adsorbed water which was
disappeared in the FTꢀIR spectrum of activated silica with NaOH (II).
Due to the low concentration of the organic part of modifier on the surface of silica (
see FTꢀIR spectrum of III), the intensity of the new bands attesting the presence of
organic groups is weak.45 The epoxy rings which are attached to the silicon
framework are identified by the methylene CꢀH stretching bands46 at roughly 3050
cmꢀ1 and CꢀOꢀC vibrational stretching at 1260ꢀ1240 cmꢀ1.The latter vibration
frequency was covered by the broad characteristic band of asymmetric vibration of Siꢀ
OꢀSi. Consequently, the asymmetric vibration band of SiꢀOꢀSi was appeared as a
more broadened absorption band. The results showed that the silica surface has been
immobilized by covalent bonded organic epoxy rings. Ring opening of epoxy ring
15

RSC Advances
Page 16 of 35
View Article Online
DOI: 10.1039/C4RA15148H
with ammonia was confirmed by appearance of a broad absorption band around 3670ꢀ
2900 cmꢀ1 attributed to ꢀOH and –NH2 stretching frequencies and furthermore, other
absorption bands at 1644, 1245 and 1100 cmꢀ1 due to ꢀNH bending vibration, CꢀN and
CꢀO stretching vibrations respectively. The two latter absorption bands were covered
by asymmetric vibration band of SiꢀOꢀSi.
Figure 2 shows the expanded FTꢀIR spectrum of Cu(II) immobilized on aminated
epichlorohydrin activated silica (CAES). Absorption bands at 428, and 450 cmꢀ1
corroborate the coordination of Cu(II) on aminated epichlorohydrin activated silica
which is attributed to CuꢀN and CuꢀO vibrations respectively. The latter absorption
band was covered by bending vibration frequency of SiꢀOꢀSi. Upon coordination of
Cu(II), the intensities of –NH2 stretching frequencies (3624 and 3251 cmꢀ1) were
decreased drastically. The ꢀNH bending absorption band was also shifted to lower
frequency upon coordination with Cu(II).
Figure 1 FTꢀIR spectrum of (a) activated silica with HCl (I); (b) activated silica with
NaOH solution (II); (c) epoxy activated silica (III); (d) aminated epichlorohydrin
activated silica (IV); (e) Cu(II) immobilized on aminated epichlorohydrin activated
silica (CAES).
16

Page 17 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
Figure 2 FTꢀIR spectrum (expanded) of Cu(II) immobilized on aminated
epichlorohydrin activated silica (CAES).
The TGA of aminated epichlorohydrin activated silica (IV) (Figure 3) shows two
o
main weight losses. The first one (2%, 27ꢀ300 C) is accounted for physically and
hydrogen bonded water in the structure of IV. The second one which is occurred at
300ꢀ560 oC (11%) is related to the decomposition of organic segment anchored to the
silica surface. This part of the thermogram reveals the amounts of aminated
epichlorohydrin on silica which is estimated to be 11% (w/w). So, the elevated
temperature for pendent organic group removal, indicates the high thermal stability of
IV. Thus, the high thermal stability of IV confirms the covalent bonding of the
aminated epichlorohydrin groups on the surface of silica.
In addition to structural confirmation and thermogravimetric analysis, quantitative
determination of covalently bonded epoxy ring and aminated epoxy ring onto the
surface of silica (III, IV) was performed by elemental analysis. The elemental
analysis of III showed the carbon content to be 4.316%. Also, the results of elemental
analysis of IV which are in good agreement with those of the results of
17

RSC Advances
Page 18 of 35
View Article Online
DOI: 10.1039/C4RA15148H
thermogravimetric analysis, showed that carbon and nitrogen contents of IV were
found to be 4.316% and 0.35% respectively which revealed that 1.15 mmol of
aminated epichlorohydrin was incorporated into the 1.000 g of IV.
The copper content of CAES was obtained by inductively coupled plasma (ICP) to be
16092 ppm, 0.0158 g, 0.25 mmol of Cu per 1.000 g of CAES.
Figure 3 TGA Thermogram of aminated epichlorohydrin activated silica (IV).
The TEM micrographs and size distributions (40 and 32 nm) of nanocatalyst Cu(II)
immobilized on aminated epichlorohydrin activated silica (CAES) is shown in Figure
4. TEM images indicated that the most of the prepared nanoparticles are spherical
shaped and have sized 10ꢀ20 nm.
18

Page 19 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
Figure 4 TEM micrographs of Cu(II) immobilized on aminated epichlorohydrin
activated silica (CAES).
Scanning electron microscopy (SEM) revealed that the nanocatalyst presented the
uniform particles with spherical morphology (Figure 5) which are in good agreement
with the results of TEM. Also, it could be seen that the nanocatalyst has not been
destroyed during the modifications. The energy dispersive spectrum (EDS) indicated
the presence of C, O, Si and Cu elements (Figure 6).This analysis confirms that Cu(II)
is supported on aminated epichlorohydrin activated silica (IV).
Figure 5 SEM micrographs of Cu(II) immobilized on aminated epichlorohydrin
activated silica (CAES).
19

RSC Advances
Page 20 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Figure 6 The EDS spectrum of Cu(II) immobilized on aminated epichlorohydrin
activated silica (CAES).
Table 5 gives the specific surface area and the mean pore diameter data of the
activated silica with HCl (I), aminated epichlorohydrin activated silica (IV) and
Cu(II) immobilized on aminated epichlorohydrin activated silica (CAES). From the
nitrogen adsorptionꢀdesorption isotherms and BET analysis (see supporting
information) the specific surface area of I, IV and CAES were calculated as 362, 346
and 329 m2gꢀ1 respectively. Then, we can conclude that all modified samples
exhibited similar isotherm shape which suggested no obvious change of structure after
modification. As can be seen from the data obtained from Table 5, functionalization
of activated silica by aminated epichlorohydrin and immobilization of Cu(II) on
aminated epichlorohydrin activated silica decreased the specific surface area.
20

Page 21 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
Table 5 BET surface area and the mean pore diameter of the activated silica with HCl
(I); aminated epichlorohydrin activated silica (IV) and Cu(II) immobilized on
aminated epichlorohydrin activated silica (CAES).
Sample
SBET (m2gꢀ1)
Mean pore diameter
(nm)
ICP (wt%)
362
346
329
7.139
8.403
8.57
ꢀ
ꢀ
I
IV
1.6092
CAES
Typical procedure for the preparation of 5-phenyl-1H-tetrazole
Sodium azide (0.0650 g, 1mmol) and CAES (0.0400 g, 1 mol%), were added to a
solution of benzonitrile (0.1031 g, 1 mmol) in DMSO (2 mL) with stirring at room
temperature. The reaction temperature was raised up to 130 °С for 1 h. The progress
of the reaction was monitored by TLC. After completion of reaction, the reaction
mixture was cooled and centrifuged. The filterate was treated with HCl (4 N, 10 mL)
and then EtOAc (10 mL). The resultant organic layer was separated, washed with
distilled water (2×10), dried over anhydrous sodium sulfate, and concentrated to give
the crude solid 5ꢀphenylꢀ1Hꢀtetrazole. The crude product was recrystallized from nꢀ
hexane/ethylacetate (1:1) obtaining 0.1386 g of colourless crystals (95% yield).
5-Phenyl-1H-tetrazole (Table 2, Entry 1). white solid; mp 214ꢀ216 ºC ( Lit. 47 214ꢀ
216 ºC); FTꢀIR (KBr): νmax/cmꢀ1 3125, 3043, 2982, 2913, 2835, 2765, 2692, 2606,
2557, 2488, 1613, 1563, 1485, 1465, 1409, 1163, 1056, 726, 703, 687; 1H NMR (400
MHz, DMSOꢀd6, ppm) δ 7.61 (s, 3 H, Ph), 8.05 (s, 2 H, Ph); 13C NMR (100 MHz,
DMSOꢀd6, ppm) δ 124.6, 127.4, 129.9, 131.7, 155.7.
5-(4-Boromophenyl)-1H-tetrazole (Table 2, Entry 2). white solid, mp 264ꢀ265 ºC
(Lit.48 265 ºC); FTꢀIR (KBr): νmax/cmꢀ1 3089, 3063, 2996, 2900, 2844, 2761, 2729,
2633, 1652, 1604, 1560, 1482, 1431, 1405, 1157, 1076, 1054, 1018, 829, 744, 502; 1H
21

RSC Advances
Page 22 of 35
View Article Online
DOI: 10.1039/C4RA15148H
NMR (100 MHz, DMSOꢀd6, ppm) δ 8.00 (q, 4 H, Ph); MS, m/z (%): 226 [M++2], 224
[M+], 198 [(M++2)ꢀN2], 196 (100) [M+ꢀN2], 185 [(M++2)ꢀN3], 183 [M+ꢀN3].
5-(4-Chlorophenyl)-1H-tetrazole (Table 2, Entry 3). white solid, mp 261ꢀ262 ºC
(Lit. 49 261ꢀ263 ºC); FTꢀIR (KBr): νmax/cmꢀ1 3092, 3060, 3007, 2978, 2907, 2851, 2725,
2622, 2537, 2471, 1609, 1564, 1486, 1435, 1160, 1096, 1053, 1020, 990, 833, 745, 508;
1H NMR (400 MHz, DMSOꢀd6, ppm) δ 7.68 (d, J= 8.4 Hz, 2H, Ph), 8.05 (d, J= 8.8 Hz,
2H, Ph); 13C NMR (100 MHz, DMSOꢀd6, ppm) δ 123.5, 129.2, 130.0, 136.4, 155.3.
4-(1H-tetrazol-5-yl)benzonitrile (Table 2, Entry 4). white solid, mp 190ꢀ191 ºC
(Lit.50 192 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3150, 3092, 3013, 2928, 2861, 2758, 2610,
1
2231, 1585, 1560, 1494, 1433, 1279, 1153, 1014, 976, 944, 850, 749, 554; H NMR
(100 MHz, CD3CN, ppm) δ 7.90 (d, J= 7.5 Hz, 2H, Ph), 8.20 (d, J= 7.5 Hz, 2H, Ph);
13C NMR (400 MHz, DMSOꢀd6, ppm) δ 113.8, 118.6, 128.0, 129.1, 133.7, 155.6; MS,
m/z (%): 171 [M+], 142 (100) [M+ꢀN2], 114 (M+ꢀ2N2).
5-(4-Nitrophenyl)-1H-tetrazole (Table 2, Entry 5). Yellow solid, mp 218ꢀ219 ºC
(Lit.32 219ꢀ220 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3448, 3334, 3235, 3109, 3080, 2974, 2900,
2819, 2659, 1562, 1532, 1488, 1357, 1340, 1315, 1143, 1106, 995, 867, 853, 730, 710.
1H NMR (400 MHz, DMSOꢀd6, ppm) δ 8.31 (d, J= 8.4 Hz, 2H, Ph), 8.46 (d, J= 8.8 Hz,
2H, Ph); 13C NMR (100 MHz, DMSOꢀd6, ppm) δ 125.1, 128.6, 131.0, 149.2, 155.9.
4-Nitro-2-(1H-tetrazol-5-yl)benzenamine (Table 2, Entry 6). white solid, mp 268ꢀ
270 ºC (Lit.51 270ꢀ271 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3411, 3321, 3199, 3084, 2937,
1
1645, 1616, 1572, 1477, 1325, 1278, 1141, 1041, 910, 831, 751, 722; H NMR (400
MHz, DMSOꢀd6, ppm) δ 7.00 (d, J= 9.2 Hz, 1H, Ph), 7.94 (1H,br s, NH), 8.10 (dd, J=
9.2, J= 2,4 Hz, 1H, Ph), 8.81 (d, J= 2.4 Hz, 1H, Ph); 13C NMR (100 MHz, DMSOꢀd6,
ppm) δ 104.4, 116.3, 126.1, 127.6, 136.3, 153.0, 154.4.
22

Page 23 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
5-(4-Ethoxyphenyl)-1H-tetrazole (Table 2, Entry 7). white solid, mp 234ꢀ235 ºC
(Lit.43 234ꢀ235 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3145, 3101, 3060, 2986, 2921, 2868,
2737, 2647, 1613, 1505, 1470, 1394, 1293, 1262, 1189, 1056, 1041, 923, 827, 751,
653, 522; 1H NMR (100 MHz, acetoeꢀd6, ppm) δ 1.40 (t, J= 5 Hz, 3H, ꢀOEt), 4.20 (q,
2H, ꢀOEt), 7.15 (d, J= 9.5 Hz, 2H, Ph), 8.07 (d, J= 9.5 Hz, 2H, Ph).
5-(3,5-Dimethoxyphenyl)-1H-tetrazole (Table 2, Entry 8). white solid, mp 204ꢀ205
ºC (Lit. 36 204ꢀ206 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3129, 3064, 3011, 2975, 2941, 2843,
2757, 2712, 2634, 1605, 1562, 1480, 1430, 1287, 1208, 1162, 1167, 1054, 827, 747;
1H NMR (400 MHz, DMSOꢀd6, ppm) δ 3.84 (s, 6H, ꢀOMe), 6.73 (t, J= 2 Hz, 1H, Ph),
7.21 (d, J= 2 Hz, 2H, Ph), 16.91(1H, br s, NH); 13C NMR (100 MHz, DMSOꢀd6,
ppm) δ 56.0, 103.4, 105.3, 125.7, 156.3, 161.5; MS, m/z (%): 207 [M+H], 149 (100)
[M+ꢀ2N2].
5-m-Tolyl-1H-tetrazole (Table 2, Entry 9). white solid, mp 149.5ꢀ150 ºC (Lit.52151ꢀ
152 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3120, 3061, 2979, 2917, 2871, 2746, 2611, 2490,
1
1728, 1605, 1565, 1486, 1463, 1150, 1060, 1038, 802, 741, 705, 687; H NMR (100
MHz, CD3CN, ppm) δ 2.43 (s, 3H, CH3), 7.40ꢀ7.90 (m, 4H, Ph).
4-(1H-tetrazol-5-yl)phenol (Table 2, Entry 10). white solid, mp 233ꢀ234 ºC ( Lit. 32
234ꢀ235 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3252, 3101, 3066, 3019, 3000ꢀ2200, 1615, 1599,
1
1511, 1466, 1413, 1282, 832, 752, 514; H NMR (400 MHz, d6 DMSOꢀd6, ppm) δ
6.97 (d, J= 8.4 Hz, 2H, Ph), 7.87 (d, J= 8.8 Hz, 2H, Ph), 10.20 (2H, br s, OH); 13C
NMR (100 MHz, DMSOꢀd6, ppm) δ 115.0, 116.6, 129.2, 155.2, 160.5.
5-(Phenanthren-9-yl)-1H-tetrazole (Table 2, Entry 11). white solid, mp 241ꢀ242 ºC
(Lit.53 243ꢀ244 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3105, 3076, 3016, 2978, 2878, 2830,
2724, 2686, 2622, 2590, 2520, 2478, 1612, 1565, 1450, 1399, 1246, 1112, 1053,
1038, 992, 934, 771, 737, 721, 424; 1H NMR (100 MHz, DMSOꢀd6, ppm) δ 7.79ꢀ7.82
23

RSC Advances
Page 24 of 35
View Article Online
DOI: 10.1039/C4RA15148H
(m, 4H, Ph), 8.08ꢀ8.20 (m, 1H, Ph), 8.40ꢀ8.52 (m, 2H, Ph), 8.92ꢀ9.10 (m, 2H, Ph);
MS, m/z (%): 246 [M+], 218 (100) [M+ꢀN2], 190 (M+ꢀ2N2).
5-(Thiophen-2-yl)-1H-tetrazole (Table 2, Entry 12). white solid, mp 205ꢀ207 ºC
(Lit.54 205ꢀ207 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3109, 3074, 2974, 2891, 2780, 2722,
2628, 2569, 2500, 2456, 1830, 1595, 1503, 1411, 1233, 1139, 1046, 962, 853, 740,
719; 1H NMR (100 MHz, CD3CN, ppm) δ 7.20ꢀ7.30 (m, 1H, Tiophen), 7.67ꢀ7.80 (m,
2H, Tiophen); MS, m/z (%): 152 [M+], 124 (100) [M+ꢀN2], 97 [M+ꢀ2N2].
4-(1H-tetrazol-5-yl)pyridine (Table 2, Entry 13). white solid, mp 255ꢀ258 ºC (Lit.47
255ꢀ258 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3485, 3264, 3099, 3035, 2966, 1624, 1529,
1435, 1388, 1123, 1096, 1042, 1022, 845, 730, 674, 593, 465.
2-(1H-tetrazol-5-yl)pyridine (Table 2, Entry 14). white solid, mp 211ꢀ213 ºC (Lit.
49
210ꢀ213 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3088, 3060, 2959, 2929, 2864, 2737, 2692,
2622, 2582, 1728, 1602, 1557, 1483, 1449, 1405, 1284, 1158, 1068, 1024, 955, 795,
1
743, 726, 703, 637, 496; H NMR (400 MHz, DMSOꢀd6, ppm) δ 7.65 (s, 1H, Py),
8.10 (s, 1H, Py), 8.24 (d, J= 6.4 Hz, 1H, Py), 8.81 (s, 1H, Py); 13C NMR (100 MHz,
DMSOꢀd6, ppm) δ 123.1, 126.7, 138.7, 144.0, 150.6, 155.3.
5-Benzyl-1H-tetrazole (Table 2, Entry 15). white solid, mp 117ꢀ119 ºC ( Lit. 55 118ꢀ
120 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3109, 3031, 2984, 2945, 2863, 2778, 2704, 2594,
1
1768, 1707, 1638, 1549, 1533, 1494, 1457, 1241, 1108, 1074, 772, 734, 695; H
NMR (100 MHz, CD3CN, ppm) δ 4.30 (s, 2H, ꢀCH2ꢀ), 7.31 (s, 5H, Ph).
5-Isobutyl-1H-tetrazole (Table 2, Entry 16). white solid, mp 52ꢀ54 ºC (Lit. 56 53.5ꢀ
54 ºC). FTꢀIR (KBr): νmax/cmꢀ1 3089, 3063, 2971, 2901, 2845, 2765, 2729, 2633,
1605, 1482, 1454, 1430, 1156, 1075, 1053, 1017, 990, 829, 772, 743, 502.
5-Isopentyl-1H-tetrazole (Table 2, Entry 17). white solid, mp 94 ºC (Lit.56 95ꢀ96
ºC). FTꢀIR (KBr): νmax/cmꢀ1 2962, 2931, 2874, 2709, 2618, 2482, 1867, 1583, 1553,
24

Page 25 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
1
1469, 1404, 1110, 1048, 772; H NMR (100 MHz, CDCl3, ppm) δ 1.00 (d, J= 5 Hz,
6H, 2 CH3), 1.40ꢀ2.05 (m, 3H, ꢀCHꢀ, ꢀCH2ꢀ), 3.10 (t, J= 6 Hz, 2H, ꢀCH2ꢀ).
Conclusion
In conclusion, a simple and effective method for the synthesis of 5ꢀsubstitutedꢀ1Hꢀ
tetrazoles from nitriles and sodium azide has been developed using nanocatalyst
Cu(II) immobilized on aminated epichlorohydrin activated silica (CAES). This nano
sized heterogeneous catalyst is easily prepared and stable to air which shows excellent
catalytic performance for various nitriles. Also, the nanocatalyst could be separated
easily from the reaction mixture which offers simple workꢀup and high yields.The
catalytic activity of the catalyst remains unaltered after five consecutive cycles. The
given methodology is efficient and environmentally benign.
Acknowledgements
The authors gratefully acknowledge the partial support of this study by Ferdowsi
University of Mashhad Research Council (Grant no. p/3/32111).
Notes and references
Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad
9177948974, Iran.
* Corresponding author: Phone: +98-51-3880-5527, Fax: +98-51-3879-5457,
E-mail: akhlaghinia@um.ac.ir
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here].
1. (a) R. N. Butler, in Comprehensive Heterocyclic Chemistry, A. R. Katritzky,
C.W. Rees, E. F.V. Scriven, Eds, vol. 4; Pergamon: Oxford, UK, 1996. pp:674;
(b) H. Singh, A. S. Chala, V. K. Kapoor, D. Paul, R. K. Malhotra, Prog. Med.
Chem., 1980, 17, 151; (c) V. A. Ostrovskii, M. S. Pevzner, T. P. Kofmna, M. B.
25

RSC Advances
Page 26 of 35
View Article Online
DOI: 10.1039/C4RA15148H
Sheherbinin, I. V. Tselinskii, Targets Heterocycl. Syst., 1999, 3, 467; (d) M.
Hiskey, D. E. Chavez, D. L. Naud, S. F. Son, H. L. Berghout, C. A. Bome,
Proc. Int. Pyrotech. Semin., 2000, 27, 3.
2. D. M. Zimmerman, R. A. Olofson, Tetrahedron Lett., 1969, 10, 5081.
3. M. Rahman, A. Roy, M. Ghosh, Sh. Mitra, A. Majee, A, Hajra, RSC Adv., 2014,
4, 6116.
4. D. R. Patil, Y. B. Wagh, P. G. Ingole, K. Singh, D. S. Dalal, New J. Chem.,
2013, 37, 3261.
5. L. Bosch, J. Vilarrasa, J. Angew. Chem., 2007, 46, 3926.
6. G. Venkateshwarlu, A. Premalatha, K. C. Rajanna, P. K. Saiprakash, Synth.
Commun., 2009, 39, 4479.
7. J. Bonnamour, C. Bolm, Chem. Eur. J., 2009, 15, 4543.
8. D. J. Carini, J. V. Duncia, P. E. Aldrich, A. T. Chiu, A. L. Johnson, M. E.
Pierce, W. A. Price, J. B. Santella, G. J. Wells, J. Med. Chem., 1991, 34, 2525.
9. Z. P. Demko, K. B. Sharpless, J. Org. Chem., 2001, 66, 7945.
10. (a) Z. P.Demko, K. B. Sharpless, Org. Lett., 2002, 4, 2525; (b) F. Himo, Z. P.
Demko, L. Noodleman, K. B. Sharpless, J. Am. Chem. Soc., 2002, 124, 12210;
(c) F. Himo, Z. P. Demko, L. Noodleman, K. B. Sharpless, J. Am. Chem. Soc.,
2003, 125, 9983.
11. P. Mani, A. K. Singh, S. K. Awasthi, Tetrahedron Lett., 2014, 55, 1879.
12. (a) J. Roh, T. V. Atramonova, K. Vavrova, G. I. Koldobskii, A. Hrabalek,
Synthesis, 2009, 2175. (b) K. Koguro, T. Oga, S. Mitsui, R. Orita, Synthesis,
1998, 910.
13. S. K. Prajapti, A. Nagarsenkar, B. N. Babu, Tetrahedron Lett., 2014, 55, 3507.
14. D. P. Matthews, J. E. Green, A. J. Shuker, J. Comb. Chem., 2000, 2, 19.
15. A. Kumar, R. Narayanan, H. Shechter, J. Org. Chem., 1996, 61, 4462.
16. M. Nasrollahzadeh, Y. Bayat, D. Habibi, S. Moshaee, Tetrahedron Lett., 2009,
50, 4435.
17. D. Amantini, R. Beleggia, F. Fringuelli, F. Pizzo, L. Vaccaro, J. Org. Chem.,
2004, 69, 2896.
18. V. S. Patil, K. P. Nandre, A. U. Borse, S. V. Bhosale, E. J. Chem., 2012, 9,
1145.
19. B. Das, C. R. Reddy, D. N. Kumar, M. Krishnaiah, R. Narender, Synlett, 2010,
391.
26

Page 27 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
20. S. J. Wittenberger, B. G. Donner, J. Org. Chem., 1993, 58, 4139.
21. (a) S. H. Watterson, Z. Xiao, D. S. Dodd, D. R. Tortolani, W. Vaccaro, D.
Potin, M. Launay, D. K. Stetsko, S. Skala, P. M. Davis, J. Med. Chem., 2010,
53, 3814; (b) S. Takale, S. Manave, K. Phatangare, V. Padalkar, N. Darvatkar,
A. Chaskar, Synth. Commun., 2012, 42, 2375; (c) Zh. Du, Ch. Si, Y. Li, Y.
Wang, J. Lu, Int. J. Mol. Sci., 2012, 13, 4696.
22. A. KhalafiꢀNezhad, S. Mohammadi, RSC Adv., 2013, 3, 4362.
23. J. He, B. Li, F. Chen, Zh. Xu, G. Yin, J. Mol. Catal. A: Chem., 2009, 304,
135.
24. J. Braun, W. Keller, Ber. Dtsch. Chem. Ges., 1932, 65, 1677.
25. (a) L. Lang, B. Li, W. Liu, L. Jiang, Z. Xu, G.Yin, Chem. Commun., 2010, 46,
448; (b) L. Lang, H. Zhou, M. Xue, X. Wang, Zh. Xu, Mater. Lett., 2013, 106,
443.
26. M. L. Kantam, K. B. Shiva Kumar, K. Phani Raja, J. Mol. Catal. A Chem.,
2006, 247, 186.
27. M. Lakshmi Kantam, K. B. S. Kumar, C. Sridhar, Adv. Synth. Catal., 2005,
347, 1212.
28. S. M. Agawane and J. M. Nagarkar, Catal. Sci. Technol., 2012, 2, 1324.
29. G. Aridoss, K. K. Laali, Eur. J. Org. Chem., 2011, 2011, 6343.
30. M. L. Kantam, V. Balasubrahmanyam, K. B. Shiva Kumar, Synth. Commun.,
2006, 36, 1809.
31. Y. S. Gyoung, J. ꢀG. Shim, Y. Yamamoto, Tetrahedron Lett., 2000, 41, 4193.
32. T. Jin, F. Kitahara, S. Kamijo, Y. Yamamoto, Tetrahedron Lett., 2008, 49,
2824.
33. P. Mani, Ch. Sharma, S. Kumar, S. K. Awasthi, J. Mol. Catal. A: Chem.,
2014, 392, 150.
34. D. Kong, Y. Liu, J. Zhang, H. Li, X. Wang, G. Liu, B. Li, Zh. Xu, New J.
Chem., 2014, 38, 3078.
35. F. Dehghani, A. R. Sardarian, M. Esmaeilpour, J. Organomet. Chem., 2013,
743, 87.
36. B. Sreedhar, A. S. Kumar, D. Yadav, Tetrahedron Lett., 2011, 52, 3565.
37. (a) D. P. Curran, S. Hadida, S. Y. Kim, Tetrahedron, 1999, 55, 8997; (b) R.
Shelkar, A. Singh, J. Nagarkar, Tetrahedron Lett., 2013, 54, 106.
27

RSC Advances
Page 28 of 35
View Article Online
DOI: 10.1039/C4RA15148H
38. B. Franca, C. Luca, M. Raimondo, S. Giovanni, J. Org. Chem., 1999, 64,
1033.
39. S. Shanmuganathana, L. Greiner, P. D. de Maríaa, Tetrahedron Lett., 2010,
51, 6670.
40. (a) M. H. Valkenberg, W. F. Holderich, Catal. Rev., 2002, 44, 321; (b) E. L.
Margelefsky, R. K. Zeidan, M. E. Davis, Chem. Soc. Rev., 2008, 37, 1118; (c)
J. C. Hicks, R. Dabestani, A. C. Buchanan, C. W. Jones, Chem. Mater., 2006,
18, 5022; (d) J. C. Hicks, R. Dabestani, A. C. Buchanan, C. W. Jones, Inorg.
Chim. Acta., 2008, 361, 3024; (e) M. W. McKittrick, C. W. Jones, J. Am.
Chem. Soc., 2004, 126, 3052; (f) K. Q. Yu, M. W. McKittrick, C. W. Jones,
Organometallics, 2004, 23, 4089.
41. J. F. Fritz, J. N. King, Anal. Chem., 1976, 48, 570.
42. B. Akhlaghinia, S. Tavakoli, Synthesis, 2005, 1775.
43. B. Akhlaghinia, S. Rezazadeh, J. Braz. Chem. Soc., 2012, 23, 2197.
44. H. Sharghi, M. H. Beyzavi, M. M. Doroodmand, Eur. J. Org. Chem., 2008,
24, 4126.
45. V. Coman, R. Grecu, J. Wegmann, S. Bachmann, K. Albert, Stud. Univ.
Babes- Bolyai, Phys., 2001, Special Issue.
46. F. Adam, K. M. Hello, H. Osman, Chin. J. Chem., 2010, 28, 2383.
47. V. Aureggi, G. Sedelmeier, Angew. Chem. Int. Ed., 2007, 46, 8440.
48. S. Lossen, Justus Liebigs Ann. Chem., 1897, 298, 102.
49. V. Rama, K. Kanagaraj, K. Pitchumani, J. Org. Chem., 2011, 76, 9090.
50. A. Köennecke, R. Döme, E. Kleinpeter, Lippmann, E. Tetrahedron, 1997, 35,
1957.
51. F. Ek, L.G. Wistrand, T. Frejd, J. Org. Chem., 2003, 68, 1911.
52. Z. Yizhong, R. Yiming, C. Chun, Helv. Chim. Acta., 2009, 92, 171.
53. G. Satzinger, Justus Liebigs Ann. Chem., 1960, 638, 159.
54. A. Najafi Chermahini, A. Teimouri, A. Moaddeli, Heteroat. Chem., 2011, 22,
168.
55. A. R. Katritzky, B. E. M. ElꢀGendy, B. Hall, C. D. Draghici, P. J. Steel, J.
Org. Chem., 2010, 75, 6468.
56. M. Herbst, J. Org. Chem., 1950, 15, 1082.
28

Page 29 of 35
RSC Advances
View Article Online
DOI: 10.1039/C4RA15148H
29