Multi-wall carbon nanotube supported Co (II) Schiff base complex: an efficient and highly reusable catalyst for synthesis of 1-amidoalkyl-2-naphthol and tetrahydrobenzo[b]pyran derivatives

Article abstract of DOI:10.1002/aoc.3560

An immobilized Co (II) Schiff base complex supported on multi-wall carbon nanotubes was synthesized and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, the

Full text of DOI:10.1002/aoc.3560

Received: 18 May 2016
DOI 10.1002/aoc.3560
Revised: 26 June 2016
Accepted: 27 June 2016
F U L L PA P E R
Multi‐wall carbon nanotube supported Co (II) Schiff base
complex: an efficient and highly reusable catalyst for synthesis of
1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b]pyran
derivatives
*
Jamshid Rakhtshah | Sadegh Salehzadeh
Faculty of Chemistry, Bu‐Ali Sina University,
Hamedan 6517838683, Iran
An immobilized Co (II) Schiff base complex supported on multi‐wall carbon
nanotubes was synthesized and characterized using Fourier transform infrared
spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive
X‐ray spectroscopy, thermogravimetric analysis and inductively coupled plasma
mass spectrometry. It was shown that the supported complex is a facile, eco‐
friendly, recyclable, reusable and green catalyst for three‐component condensation
of 2‐naphthol and acetamide with various aldehydes for the synthesis of 1‐
amidoalkyl‐2‐naphthol derivatives under solvent‐free conditions. Also, in a further
study, the catalytic application was studied in the synthesis of tetrahydrobenzo[b]
pyran derivatives via the condensation reaction of malononitrile and dimedone
with several aromatic aldehydes. The procedures suggested here for the synthesis
of 1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b]pyran derivatives offer several
advantages, such as stability, recyclability and eco‐friendliness of the catalyst,
simple experimental conditions, short reaction times, high to excellent yields
and easy work‐up.
Correspondence
Sadegh Salehzadeh, Faculty of Chemistry, Bu‐Ali
Sina University, Hamedan 6517838683, Iran.
Email: saleh@basu.ac.ir; ssalehzadeh@gmail.com
KEYWORDS
immobilized Co (II) Schiff base complex supported on MWCNTs, 1‐amidoalkyl‐2‐
naphthol derivatives, tetrahydrobenzo[b]pyrans, solvent‐free
1
|
INTRODUCTION
carbon nanotubes as supports have attracted much
consideration.[7]
Multicomponent reactions (MCRs) represent an eco-
nomic way in one‐pot systems to synthesize highly function-
alized and complex molecules in a single synthetic operation
from simple and readily available starting materials. Thus,
MCRs offer high selectivity, high yield and synthetic simplic-
ity due to the formation of carbon–carbon and carbon–hetero-
atom bonds in a single step.[11–13] Our target compounds from
MCRs were amidoalkylnaphthols, which can be prepared by
multicomponent condensation of aldehydes, 2‐naphthols and
acetonitrile or different amides in the presence of various cat-
alysts.[14–20] Several heterogeneous catalyst have been
reported to catalyse this transformation, such as silica gel‐
supported ─SO3H‐functionalized benzimidazolium,[21]
Many soluble Schiff base complexes show high valuable
catalytic activity in chemical reactions,[1–3] and also these
compounds are efficient catalysts in both homogeneous
and heterogeneous systems. Over the past few years, there
have been many reports of their applications in
homogeneous and heterogeneous catalysis.[4–8] Immobiliza-
tion of transition metal complexes on solid supports can
be used to prepare catalysts which are easy to be separated
from, and reused in, a reaction system and which may pos-
sibly exhibit improved activities because of the support
environment. Various supports have been reported for the
synthesis of a variety of heterogeneous catalysts.[9,10] Due
to good stabilities in both acid and alkaline conditions,
Appl. Organometal. Chem. 2016; 1–9
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
RAKHTSHAH AND SALEHZADEH
cation‐exchanged resins,[22] silica‐supported perchloric
acid,[23] heteropolyacids,[24] silica gel‐supported dual acidic
ionic liquid,[25] sulfanilic acid@MNPs,[26] FeCl3@SiO2,[27]
alumina sulfuric acid[28] and K5CoW12O40⋅3H2O.[29] 1‐
Amidoalkyl‐2‐naphthol derivatives are important intermedi-
ates as an important class of compounds which can be easily
converted to biologically and pharmacologically active deriv-
atives by an amide hydrolysis reaction. Also, the depressor
and bradycardia effects of these compounds have been evalu-
ated.[30,31] MCRs are also suitable for the preparation of 4H‐
benzo[b]pyrans through three‐component condensations
including the use of SO42−@MCM‐41,[32] KF‐alumina[33]
and Fe3O4@MWCNTs[34] as heterogeneous catalysts.
To the best of our knowledge, the synthesis of 1‐
amidoalkyl‐2‐naphthols in the presence of transition metal
Schiff base complexes has not yet been reported. Herein we
report the synthesis and characterization of a Co (II) Schiff
base complex immobilized on the surface of multi‐wall car-
bon nanotubes (MWCNTs) through a silicon linker. We
report the efficient, rapid and green synthesis of 1‐
amidoalkyl‐2‐naphthols in the presence of catalytic amounts
of this catalyst under solvent‐free conditions (Scheme 1). In
addition, the synthesized catalyst was efficaciously engaged
in the synthesis of numerous tetrahydrobenzo[b]pyran deriv-
atives via the condensation reaction of dimedone and
malononitrile with several aromatic aldehydes, under sol-
vent‐free condition (Scheme 2).
SCHEME
2
Synthesis of tetrahydrobenzo[b]pyran derivatives using
immobilized Co (II) Schiff base complex supported on MWCNTs
2
| RESULTS AND DISCUSSION
Scheme 3 summarizes the reactions that lead to the Co.(II) Schiff
base complex supported on MWCNT nanomaterials. This syn-
thesis was carried out as detailed in the experimental section.
2.1 | Characterization of Immobilized Cobalt(II) Schiff
Base Complex Supported on MWCNTs as Heterogeneous
Catalyst
The structure of the immobilized cobalt(II) Schiff base com-
plex supported on MWCNTs as a heterogeneous catalyst was
SCHEME 3 Sequence of events in the preparation of MWCNTs@Schiff
base and its Co (II) complex
studied, considered and identified using Fourier transform
infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD),
scanning electron microscopy (SEM), energy‐dispersive X‐
ray spectroscopy (EDX), and inductively coupled plasma
mass spectrometry (ICP).
In order to confirm the surface modification of
MWCNTs, the FT‐IR spectra of the prepared materials were
SCHEME
1
Synthesis of 1‐amidoalkyl‐2‐naphthol derivatives using
immobilized Co (II) Schiff base complex supported on MWCNTs

RAKHTSHAH AND SALEHZADEH
3
obtained and are shown in Figure 1. The FT‐IR spectrum of
MWCNTs@COOH (Figure 1(a)) shows a strong band at
1710 cm−1 and a weaker band at 1228 cm−1 attributed to
C═O and C─OH groups in oxidized MWCNTs, respectively,
as well as a broad band at about 3420–3480 cm−1 assigned to
O─H stretching vibrations which are not observed in the
spectrum of pristine MWCNTs. Comparison studies of
MWCNTs@COOH and MWCNTs@APTMS reveal an addi-
tional strong band at 1000–1100 cm−1 corresponding to char-
acteristic absorption of Si─O bonds formed through the
silylation process. The presence of anchored propyl chain
was confirmed by C─H stretching vibrations appearing at
about 2923 cm−1. The presence of these bands suggests that
during the anchoring of APTMS, a condensation reaction
occurs between the OH surface groups of the oxidized
MWCNTs and methoxy groups of APTMS to form the stable
covalent Si─O─C linkage, leading to the attachment of
aminopropyl groups on the surface of MWCNTs. Also, the
band in the spectral region of 1629 cm−1 can be assigned to
the azomethine peak of the attached salicylaldehyde on the
MWCNTs modified with APTMS. In the FT‐IR spectrum
of the MWCNTs@Co (II) Schiff base, a considerable shift
to lower energy (1616 cm−l) is observed in the strong sharp
C═N stretching frequency upon complexation with cobalt
which suggests the imine nitrogen atoms are coordinated
(Figure. 1(d)).
FIGURE 2 XRD patterns: (a) MWCNTs; (b) MWCNTs@Schiff base; (c)
MWCNTs@Co (II) Schiff base complex
Figure 2 displays the XRD patterns of parent MWCNTs,
MWCNTs@Schiff base and MWCNTs@Co (II) Schiff base
complex. The XRD patterns of MWCNTs bearing cobalt(II)
complex and Schiff base are somewhat similar to that of
MWCNTs. This indicates that the crystallinity and morphol-
ogy of MWCNTs are preserved during the grafting process.
Figure 2 shows the XRD pattern of MWCNTs, which is sim-
ilar to that of highly oriented pyrolytic graphite.[35] The
MWCNTs show typical peaks of (002), (110) and (400) at
2θ = 26°, 43° and 53°, respectively.
FIGURE 3 Field‐emission SEM image of MWCNTs@Co (II) Schiff base
complex
FIGURE
1
FT‐IR
spectra:
(a)
MWCNTs@COOH;
(b)
MWCNTs@APTMS; (c) MWCNTs@Schiff base; (d) MWCNTs@Co (II)
Schiff base complex
FIGURE 4 EDX diagram of MWCNTs@Co (II) Schiff base complex

4
RAKHTSHAH AND SALEHZADEH
The functionalization process of the MWCNTs with the
Schiff‐base and the formation of its complex were also con-
firmed from the EDX pattern of the product. The presence
of Co atoms in the Co.(II) Schiff base complex supported
on MWCNTs as nanocatalyst is confirmed by the EDX
results which also show the presence of C, O, N, Cl and Si
atoms in Figure 4. The Co. content of the immobilized com-
plex supported on MWCNTs was also measured by ICP, the
value of which is about 0.623 mmol g−1
.
From the thermogravimetric analysis (TGA) curve of Co
(II) Schiff base complex supported on MWCNTs (Figure 5),
a total weight loss of ca 20% is observed on heating to 700 °
C. These studies have been made in the temperature range
50–1000 °C in nitrogen atmosphere. Degassing and solvent
evaporation at low temperatures account for approximately
1% of the loss. The majority of the weight loss occurs at tem-
peratures >450 °C. However, for the corresponding
supported complex, 3 and 8% weight losses appear at temper-
atures of 209 and 368 °C, respectively.
FIGURE 5 TGA curve of MWCNTs@Co (II) Schiff base complex
The structure and morphology of the nanomaterial was
analysed using field‐emission SEM. The SEM image of
immobilized complex supported on MWCNTs is shown in
Figure 3. From the micrograph it can be concluded that the
nanotubes are aggregated and have retained their nanotube
nature. This indicates that the sonication condition used in
current study is important and the integrity of the tubes is
not destroyed during the treatment. The smooth surface of
nanotubes has been altered to a rough surface after the immo-
bilization process, which can be associated with the complex
moieties attached to the nanotube surfaces.
2.2 | Application of Immobilized Co (II) Schiff base
Complex Supported on MWCNTs as Heterogeneous
Catalyst
At first, screening trials were performed to optimize various
reaction parameters, including catalyst amount, solvent and
TABLE 1 Effect of amount of catalyst and temperature on condensation reaction of biphenyl‐4‐carbaldehyde, β‐naphthol and acetamide under solvent‐free
conditionsa
Entry
Amount of
Catalyst (g)
Reaction
temperature
(°C)
Reaction
time
(min)
Yield
(%)b
1
2
—
r.t.
100
r.t.
120
120
120
120
120
120
60
—
—
5
—
3
0.001
0.001
0.002
0.002
0.005
0.005
0.01
0.01
0.01
0.01
0.01
0.02
0.02
4
100
r.t.
38
7
5
6
100
r.t.
51
10
65
15
63
93
93
93
15
93
7
8
100
r.t.
60
9
60
10
11
12
13
14
15
50
60
75
25
100
125
r.t.
25
25
60
100
25
aReaction conditions: biphenyl‐4‐carbaldehyde (1 mmol), β‐naphthol (1 mmol), acetamide (1.2 mmol).
bIsolated yield.

RAKHTSHAH AND SALEHZADEH
5
TABLE 2 Effect of solvent on reaction of biphenyl‐4‐carbaldehyde, β‐
the catalyst in the synthesis of amidoalkylnaphthol deriva-
tives. Thus the solvent‐free condensation of biphenyl‐4‐
carbaldehyde, β‐naphthol and acetamide (model reaction)
was examined in the presence of catalyst in the temperature
range 25–120 °C (Table 1). We also examined the influence
of catalyst loading (Table 1). The model condensation reac-
tion was tested in the presence of various amounts of Co
(II) complex supported on MWCNTs under similar condi-
tions. For the optimized amount of catalyst, we found that
0.01 g of nanocatalyst effectively catalyses the reaction for
the synthesis of the desired product. The same reaction with-
out nanocatalyst does not lead to product (Table 1, entries 1
and 2). Thus the catalytic efficiency of this catalyst was
definitely identified. In view of environmentally friendly
methodologies, we have discovered that this reaction
proceeds very efficiently by stirring a mixture of neat
reactants at 75 °C for only 25 min, under solvent‐free
conditions, and produces amidoalkylnaphthol derivatives in
high yields (Table 1, entry 11).
naphthol and acetamidea
Entry
Solvent
Solvent‐free
H2O
Reaction time (min)
Yield (%)b
1
2
3
4
5
6
7
8
25
120
60
93
—
31
57
60
—
18
—
C2H5OH
CH3CN
45
CH2Cl2
45
Toluene
120
120
120
CH3CO2Et
n‐Hexane
aReaction conditions: biphenyl‐4‐carbaldehyde (1 mmol), β‐naphthol (1 mmol),
acetamide (1.2 mmol), 75 °C, catalyst (0.01 g).
bIsolated yield.
In the next step, in order to check the effect of solvents in
the model reaction, various solvents were used. As evident
from Table 2, the reaction proceeds most readily to give the
highest yield of the desired product under solvent‐free
conditions.
temperature, with the results being summarized in Tables 1
and 2. After the synthesis, characterization and identification
of the heterogeneous catalyst, we considered the efficacy of
TABLE 3 Three‐component synthesis of amidoalkylnaphthol derivatives using 0.01 g of nanocatalysta
Entry
1
R
4‐NO2
R′
Time (min)
Yield (%)b
95
M.p. (°C) (colour)
245–247 (yellow)[36]
254–256 (white)[36]
201–203 (yellow)[36]
261–263 (white)[36]
208–210 (pink)[36]
163–165 (white)[36]
283–285 (white)[36]
274–276 (pink)[39]
209–211 (yellow)[39]
263–265 (white)[39]
291–293 (white)[39]
199–201 (cream)[36]
253–255 (pink)[37]
266–268 (pink)[39]
140–142 (white)[36]
142–154 (white)[36]
230–232 (yellow)[38]
201–203 (yellow)[39]
245–247 (white)[39]
285–287 (white)[39]
─CH3
─Ph
20
25
30
25
30
35
30
35
40
25
30
35
25
30
30
30
20
20
25
30
2
4‐NO2
93
3
4‐NO2
─NH2
─CH3
─Ph
90
4
4‐Cl
93
5
4‐Cl
91
6
4‐Cl
─NH2
─CH3
─Ph
88
7
2,5‐Dimethoxy
2,5‐Dimethoxy
2,5‐Dimethoxy
1‐Naphthyl
1‐Naphthyl
1‐Naphthyl
2‐Naphthyl
2‐Naphthyl
2‐Furyl
90
8
89
9
─NH2
─CH3
─Ph
87
10
11
12
13
14
15
16
17
18
19
20
92
90
─NH2
─CH3
─Ph
88
92
90
─NH2
─NH2
─CH3
─Ph
89
2‐Thienyl
4‐Cinnamyl
4‐Cinnamyl
4‐Ph
89
90
90
─CH3
─Ph
93
4‐Ph
91
aReaction conditions: aldehyde (1 mmol), β‐naphthol (1 mmol), amide derivatives (1.2 mmol), 75 °C, solvent‐free.
bIsolated yield.

6
RAKHTSHAH AND SALEHZADEH
After optimization of the reaction conditions, we studied
the generality of these conditions with a series of aromatic
aldehydes under the optimized conditions (Table 1, entry 11;
Table 2, entry 1), and the results are summarized in Table 3.
We extended our study using MWCNTs@Co (II) Schiff base
complex (0.01 g) in the absence of solvent with various aro-
matic aldehydes to prepare a series of 1‐amidoalkyl‐2‐naph-
thol derivatives. A variety of differently substituted aromatic
aldehydes possessing electron‐donating and electron‐with-
drawing groups give good yields (87–95%) and the reactions
are completed within 20–40 min under solvent‐free condi-
tions. Several aromatic aldehydes containing electron‐releas-
ing substituents, electron‐withdrawing substituents and
halogens on their aromatic ring were utilized in the reaction,
and give the corresponding products in high yields and in short
reaction times. As evident from Table 3, the ease of the reac-
tion is directly related to the substituents attached to the ben-
zene ring. The electron‐withdrawing groups (such as nitro
and halide) are found to activate the aldehyde towards nucleo-
philic attack and increase the reaction rate (entries 1–6).
Scheme 4 shows a possible mechanism[40] for the synthe-
sis of 1‐amidoalkyl‐2‐naphthol derivatives in the presence of
MWCNTs@Co (II) Schiff base complex as catalyst. The
mechanism begins with the activation of the carbonyl group
of the aldehyde with the immobilized catalyst and ends with
the reaction of o‐quinone methides (o‐QMs) with amides or
urea to form the 1‐amidoalkyl‐2‐naphthol derivatives.
SCHEME 4 Proposed mechanism for the synthesis of 1‐amidoalkyl‐2‐
naphthol using immobilized cobalt(II) Schiff base complex supported on
MWCNTs as a heterogeneous catalyst
The results are summarized in Table 4. Tetrahydrobenzo[b]
pyran derivatives containing electron‐withdrawing groups
such as nitro and halide groups or electron‐donating groups
such as hydroxyl and alkoxy groups are formed in a short reac-
tion time (15–35 min) with excellent yields (90–95%).
The reusability of the catalyst was investigated in the con-
densation of biphenyl‐4‐carbaldehyde, β‐naphthol and acet-
amide. At the end of the reaction, ethyl acetate was added
to the reaction mixture and heated to extract the product from
the catalyst (the product is soluble in hot ethyl acetate and the
catalyst is insoluble). As shown in Figure 6, the recovered
catalyst was reused for seven successive runs without signif-
icant loss of its catalytic activity. The general methods to
determine the presence or absence of leached soluble cobalt
in the reaction solution are a hot filtration test or elemental
analysis of the recovered catalyst. The heterogeneity of the
In another study, in order to establish the general applica-
tion of our catalyst, we extended the scope of the reaction to
the synthesis of various tetrahydrobenzo[b]pyran derivatives.
We used the above‐mentioned optimized condition to evaluate
the condensation reaction of malononitrile and dimedone with
a series of aromatic aldehydes under solvent‐free conditions.
TABLE 4 Three‐component synthesis of tetrahydrobenzo[b]pyran derivatives using 0.01 g of nanocatalysta
Entry
R
Time (min)
Yield (%)b
M.p. (°C) (colour)
164–166 (white)[32]
231–233 (yellow)[32]
230–232 (yellow)[41]
284–286 (yellow)[42]
245–247 (yellow)[43]
275–277 (yellow)[42]
224–226 (white)[44]
216–218 (white)[32]
196–198 (white)[45]
221–223(yellow)[34]
1
2
4‐NO2
15
20
20
20
35
20
20
30
30
20
95
93
93
93
91
93
93
92
90
91
4‐Cl
3
1‐Naphthyl
2‐Naphthyl
4‐Hydroxy
4‐Ph
4
5
6
7
3‐NO2
8
4‐Methoxy
2‐Methoxy
2,4‐Dichloro
9
10
aReaction conditions: aldehyde (1 mmol), dimedone (1 mmol), malononitrile (1 mmol), 75 °C, solvent‐free.
bIsolated yield.

RAKHTSHAH AND SALEHZADEH
7
FIGURE 6 Study of cobalt(II) Schiff base complex supported on MWCNTs after seven catalytic cycles: (a) SEM image; (b) FT‐IR spectrum; (c) EDX pattern;
(d) XRD pattern
nanocatalyst in solvent‐free condition is obvious and in such
condition hot filtration is useful. ICP analysis of the product
after isolation of catalyst shows no loss of metal (cobalt) dur-
ing the catalytic reaction, indicating that no metal leaching
occurs. It is also observed from spectral studies (Figure 7)
that there is no change in the nature of the catalyst even after
seven cycles. The SEM images of catalyst before (Figure 3)
and after (Figure 7(a)) the reactions show identical shapes.
Likewise, the FT‐IR and powder XRD analyses exhibit iden-
tical peaks for both the fresh and recovered catalyst (Figures 7
(b) and (d)). These experimental results clearly suggest that
the reaction involves a heterogeneous process and there is
no significant change in the catalytic activity of the
nanocatalyst after its catalytic application.
3
| CONCLUSIONS
Immobilized Co (II) Schiff base complex supported on
MWCNTs was synthesized, characterized and used as a
highly efficient and green nanocatalyst for the synthesis of
1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b]pyran deriv-
atives under solvent‐free conditions at 75 °C. We have
described herein a comprehensive methodology for the syn-
thesis of these derivatives using various structurally different
aldehydes in good to excellent isolated yields. Simplicity in
process, short reaction time, avoiding the use of any base or
Lewis acid catalyst, absence of side products, ease of product
isolation and low costs are some of the prominent features of
these reactions with our catalyst.
FIGURE 7 Reusability of immobilized cobalt(II) Schiff base complex
supported on MWCNTs as a heterogeneous catalyst in 25 min

8
RAKHTSHAH AND SALEHZADEH
4
|
EXPERIMENTAL
purified by recrystallization from ethanol. The heterogeneous
nanocatalyst was recycled and reused seven times without
significant loss of its catalytic activity.
4.1 | Immobilized Co.(II) Schiff base complex on
MWCNTs: preparation and purification
4.3 | General Procedure for Synthesis of
Tetrahydrobenzo[b]pyran Derivatives
4.1.1
| MWCNT functionalization and purification
Following careful purification, MWCNTs were oxidized in a
mixture of concentrated sulfuric and nitric acids (3:1, 98 and
70%, respectively) by ultrasonication for 12 h to obtain
oxidized MWCNTs (MWCNTs@COOH).[35] To increase the
reactivityand/or populationofOHsurfacegroups,theresulting
material was further treated with sodium borohydride in meth-
anol and carboxyl groups were reduced to CH2OH groups.
A mixture of aromatic aldehyde (1 mmol), malononitrile
(1 mmol), dimedone (1 mmol) and Co (II) Schiff base com-
plex supported on MWCNTs (0.01 g) was stirred under
solvent‐free conditions for a suitable time at 75 °C. After
completion of the reaction as indicated by TLC (n‐hexane–
ethyl acetate, 5/2), ethyl acetate (10 ml) was added to reaction
mixture, stirred and refluxed for 3 min, and was then filtered
to separate the catalyst from the other materials. The solvent
of the organic layer was evaporated and the crude product
was purified by recrystallization from ethanol.
4.1.2
| Preparation of MWCNTs@NH2
The as‐prepared MWCNTs@OH (1 g) was dispersed in
100 ml of xylene and loaded in a 250 ml round‐bottom flask,
followed by stirring and ultrasonication (25 W, 40 kHz) for
1 h. Subsequently, APTMS (excess) was added dropwise into
the suspension. The mixture was stirred and refluxed for 24 h
under dry nitrogen atmosphere. After cooling to room tem-
perature, the prepared MWCNTs@NH2 was filtered and
washed with absolute ethanol and water three times to
remove the unreacted residue of silylating reagent and then
dried at 80 °C.
ACKNOWLEDGEMENTS
We thank Dr. Saeed Baghery, University of Bu‐Ali Sina,
Hamedan, for useful comments and suggestions. Financial
support from Bu‐Ali Sina University is greatly appreciated.
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Amidoalkylnaphthol Derivatives
To a mixture of aromatic aldehyde (1 mmol), β‐naphthol
(1 mmol) and amide derivative (1 mmol) in a round‐bottom
flask was added the immobilized Co (II) Schiff base complex
supported on MWCNTs as a heterogeneous catalyst (0.01 g).
The resulting mixture was firstly stirred magnetically under
solvent‐free conditions at 100 °C. After completion of the
reaction, as checked via TLC (n‐hexane–ethyl acetate, 5/2),
ethyl acetate (10 ml) was added to the reaction mixture,
stirred and refluxed for 3 min, and was then filtered to sepa-
rate the catalyst from the other materials. The solvent of the
organic layer was evaporated and the crude product was
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How to cite this article: J. Rakhtshah, and S.
Salehzadeh (2016), Multi‐wall carbon nanotube
supported Co (II) Schiff base complex: an efficient
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