Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as effective solid acid catalyst

Article abstract of DOI:10.1007/s00706-019-02418-2

Abstract: Multiwalled carbon nanotubes (MWCNTs) were modified with sulfonic acid groups through a new method. In the first step, MWCNTs’ surfaces were hydroxylated using KMNO₄ as oxidating agent and a surfactant (TPABr). Second, SiO₂

Full text of DOI:10.1007/s00706-019-02418-2

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-019-02418-2
ORIGINAL PAPER
Solvent‑free synthesis of amidoalkyl naphthols in the presence
of MWCNTs@SiO2/SO3H as efective solid acid catalyst
Masoumeh Ahmadi1 · Leila Moradi1 · Masoud Sadeghzadeh2
Received: 12 July 2018 / Accepted: 1 April 2019
© Springer-Verlag GmbH Austria, part of Springer Nature 2019
Abstract
Multiwalled carbon nanotubes (MWCNTs) were modifed with sulfonic acid groups through a new method. In the frst step,
MWCNTs’ surfaces were hydroxylated using KMNO4 as oxidating agent and a surfactant (TPABr). Second, SiO2-coated
MWCNTs were prepared through the reaction of hydroxylated CNTs with tetraethyl orthosilicate, and in last step, MWC-
NTs@SiO2/SO3H was prepared using the reaction of MWCNTs@SiO2 with ClSO3H. Obtained catalyst was used as efcient
solid acid catalyst for one-pot three-component condensation reaction of 2-naphthol, benzaldehyde, and amide derivatives
to aford the corresponding amidoalkyl naphthols. The reaction was performed under solvent-free conditions and products
were obtained in high to excellent yields (80–98%). Prepared solid acid catalyst was characterized using FT-IR, BET, TGA,
SEM, and EDX techniques. Presented methodology has several advantages such as simple procedure, excellent yields of
products, efective reusable solid acid catalyst, and eco-friendly reaction conditions.
Graphical abstract
O
H
R2
O
OH
R1 NH2
OH
Si
O
HO3SO
HO
OSO3
H
O
catalyst
O
Solvent free
O
Si
H
OSO3
OSO3
H
OH
Catalyst
OSO3
H
O
R1
NH
OH
R2
Keywords MWCNTs@SiO2/SO3H · Amidoalkyl naphthols · Multicomponent reaction · Solvent-free · Green protocol ·
Solid acid catalyst
Introduction
Multicomponent reactions (MCRs) can be considered as an
important method for the synthesis of complex and diverse
organic compounds through the formation of carbon–carbon
and carbon–heteroatom bonds [1–4].
Ortho-quinone methides (o-QMs) are interesting mol-
* Leila Moradi
ecules due to their toxicological properties against cancer-
ous cells and also proposed intermediary in the formation
of many biologically important polymers [5] and antitumor
agents [6]. Tandem reaction involves the in situ prepara-
tion of o-QMs, and then, reaction with amides is one of the
preparation methods of amidoalkyl naphthols [7, 8].
L_moradi@kashanu.ac.ir
1
Department of Organic Chemistry, Faculty of Chemistry,
University of Kashan, P.O. Box 8731753153, Kashan,
Islamic Republic of Iran
2
School of Chemistry, College of Science,
University of Tehran, PO Box 141556455, Tehran,
Islamic Republic of Iran
Vol.:(0123456789)
1 3

M. Ahmadi et al.
A variety of natural products containing 1,3-amino-
oxygenated functional groups exist in biologically sig-
nifcant natural products and efective drugs including
antitumor [9, 10], antibiotics [11], antianginal [12–14],
antimalarial [15, 16], and HIV protease inhibitors [17–19].
These compounds have attracted much attention and con-
siderable interests toward medical application, since they
can be converted into hypotensive and bradycardiac activi-
ties by amide hydrolysis reactions [20, 21]. Various cata-
lysts have been applied for the synthesis of amidoalkyl
naphthols, such as montmorillonite K10 [22], p-TSA [7],
K5CoW12O40·3H2O [23], HClO4–SiO2 [24], Fe(HSO4)3
[25], FeCl3–SiO2 [26], BrØnsted acidic ionic liquid [27],
imidazolium salt [28], P2O5 [14], cyanuric chloride [29],
thiamine hydrochloride [30], trityl chloride [31], [Fem-
SILP] l-prolinate [32], silica sulfuric acid [33, 34], 1-hex-
anesulfonic acid sodium salt [35], and zwitterionic-type
molten salt [36]. The efciency of some reported proce-
dures comes down with long reaction times [7, 37], low
yields of products [22, 38], high temperatures [7, 22, 37,
38], use of toxic reagents, and tedious workup procedures
[7, 39, 40]. Therefore, development of catalytic systems
for the synthesis of 1-amidoalkyl naphthols is still one of
the main interest felds for researchers.
in various felds of industry, catalyst, drug delivery, and so
on [44–50].
In continuation of our studies to develop the mild and
facile procedures for functionalization of MWCNTs and
their applications as heterogeneous catalyst [51, 52], herein,
we report an efcient and rapid method for the synthesis
of 1-amidoalkyl naphthols using MWCNTs@SiO2/SO3H
as a mild, reusable, and efective solid acid catalyst under
solvent-free conditions (Scheme 1).
Results and discussion
Preparation of catalyst was started from the attachment of
hydroxy groups on MWCNTs surfaces using KMnO4 with
the aid of tetrapropylammonium bromide (TPABr). In the
second step, silica-coated MWCNT was successfully pre-
pared by deposition of silica onto nanoparticles surface
using tetraethyl orthosilicate (TEOS). Finally, MWCNTs@
SiO2 was used as support for the immobilization of SO3H
groups by simple mixing of silica-coated MWCNTs and
chlorosulfonic acid in CH2Cl2 (Scheme 2).
Figure 1 shows FT-IR spectra of raw and modifed MWC-
NTs. For raw sample, the weak band around 1630 cm−1 is
from the graphitic structure of MWCNT. Hydroxylated
MWCNT shows O–H-stretching vibration at 3428 cm−1 also,
and C–O-stretching vibration appeared between 1000 and
1100 cm−1 (Fig. 1b). In FT-IR spectrum of MWCNTs@SiO2
and catalyst, peaks at 455, 576, and 884 cm−1 are from the
asymmetric stretching, symmetric stretching, and bending
vibration of Si–O–Si groups, respectively. The strong and
wide peak at about 3383 cm−1 demonstrates that there are
Si–OH groups in the MWCNTs@SiO2 and catalyst struc-
ture (Fig. 1c, d). The presence of sulfonyl groups in catalyst
is authenticated by 1172 and 1071 cm−1 bands that were
covered by a stronger absorption of Si–C and Si–O bonds.
In addition, the increase in the intensities of the band at
2800–3700 cm−1 suggests that there are more OH groups on
the catalyst surfaces after the sulfonation. All of these obser-
vations demonstrate that the –SO3H groups have chemically
attached to the surfaces of MWCNTs.
Sulfuric acid is an essential and efcient catalyst for the
production of industrial important chemicals. Large amounts
of sulfuric acid are consumed annually as homogeneous and
unrecyclable catalyst which need to costly and inefective
separation processes [41]. Application of reusable solid
acids in organic reactions is often considered to follow the
green chemistry principle that catalyzed processes must con-
sume a minimum of energy and reagents or auxiliaries and
minimize waste [42].
Since the discovery of carbon nanotubes (CNTs) in 1991
by Iijima [43], CNTs have an essential role in various felds
of science and technology. Because of their supernatural and
unique properties, CNTs have attracted considerable atten-
tions in wide felds of industry and academic society.
To overcome the agglomeration of CNTs resulted from
strong van der Waals force between the nano tubes struc-
tures, chemical modifcation of CNT surfaces is thought to
be an efective way. Functionalization of CNT surfaces with
organic, organometallic, and polymer matrixes improved
the application and superior properties of these materials
Figure 2 shows SEM images of the raw and sulfonated
MWCNTs. It can be seen that the pristine MWCNTs are
tangled together (Fig. 2a). Most of the MWCNTs are not
Scheme 1
1 3

Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as…
Scheme 2
OH
HO3SO
Si
HO
OSO3H
O
O
O
O
Si
OSO3H
OSO3H
OH
HO3SO
TPABr , KMnO4
HO
Dry CH2Cl2
ClSO3H
OH
Si
HO
HO
HO
HO
HO
OH
O
O
TEOS, NH3
EtOH, H2O
OH
OH
O
OH
O
OH
Si
OH
OH
OH
HO
The components of the MWCNT@SO3H were analyzed
by energy-dispersive X-ray spectroscopy (EDX) technique.
Figure 3 shows the presence of C, O, Si, and S atoms in
catalyst structure and confrms the successful preparation
of solid acid catalyst.
Thermogravimetric analysis (TGA) provided further evi-
dence for evaluation and characterization of catalyst. TGA
measurements carried out in air at a rate of 5 °C/min from
50 to 800 °C. As can be seen in Fig. 4a, there is no signif-
cant weight loss in raw MWCNTs between 50 and 800 °C.
TGA graph of the MWCNTs@SiO2/SO3H was divided into
several regions corresponding to diferent mass loss ranges
(Fig. 4b). The frst region, which occurred below 200 °C,
shows a mass loss that was from the removing of adsorbed
water from the catalyst. The weight loss at higher tempera-
ture (250–600 °C) could be mainly attributed to decompo-
sition of –SO3H and –SiOH groups. Obtained results show
that catalyst is contains about 30% of functional groups
and demonstrated that attachment of SO3H groups on CNT
surfaces was occurred successfully through the mentioned
process.
Fig. 1 FT-IR spectrum of a raw MWCNTs, b MWCNTs-OH, c
MWCNTs@SiO2, and d MWCNTs@SiO2/SO3H
Results from BET analysis (Table 1) indicate that func-
tionalization process increases specifc surface area of
MWCNTs. In fact, functionalization treatment opens up
the tube end caps and generate defects on the sidewall of
nanotubes [17, 18], as well as debundling of CNTs. As a
result, surface area has been increased after modifcation
straight due to some defects and show a few local kinks and
bends. SEM image of catalyst (Fig. 2b) indicated that CNT
surfaces were functionalized and no damage occurred on
CNT structures after chemical treatments.
1 3

M. Ahmadi et al.
Fig. 2 SEM image of a raw MWCNTs and b MWCNTs@SiO2/SO3H
Fig. 3 EDX of MWCNTs@
SiO2/SO3H
Table 1 BET surface area of pristine and functionalized CNTs
Entry
Sample
Surface area/m2/g
1
2
Raw MWCNT
MWCNTs@SiO2/SO3H
42.74
74.42
and accessed into the CNT surfaces, and defects and cavity
of the nanotubes can be achieved.
The XRD profles of raw and functionalized MWCNTs
are presented in Fig. 5. It is clear that, the XRD pattern of
sulfonated MWCNTs is as the same of raw sample with 2θ
of 25.8° and 43.42° correspond to 002 and 01 refection
of polyaromatic structure of CNTs and interlayer spac-
ing between adjacent graphite layers. XRD profles are in
good agreement with the reported values [53]. It is clear
that modifed CNTs have the same interplanar spacing and
cylinder wall structure after the sulfonation process. In
Fig. 4 TGA curve of a raw MWCNTs, and b MWCNTs@SiO2/SO3H
1 3

Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as…
carrying out the reaction using 13 mg of MWCNTs@SiO2/
SO3H at 100 °C under solvent-free conditions (Table 2, entry
4). Furthermore, no reaction was occurred when the mix-
ture was heated to 100 °C for 8 h in the absence of catalyst
(Table 2, entry 9).
Using the optimized reaction conditions, the reaction
was extended to substituted aromatic aldehydes, which was
reacted with benzamide (or acetamide) and β-naphthol. As
evident from the results (Table 3), it was shown that aro-
matic aldehydes with electron-withdrawing groups reacted
faster (with higher yields) than those with electron-releas-
ing groups and also sterically hindered aromatic aldehydes
required longer reaction times (entry 3). Obtained results
show the high activity and efciency of solid acid catalyst.
In a plausible mechanism (Scheme 3) which is sup-
ported by the literature [27], aromatic aldehyde is activated
by acidic group of catalyst to produce I. Then, 2-naphthol
attacks to the carbonyl group of the activated aldehyde and
gives intermediate II. Then, by removing H2O from II,
ortho-quinone methide (o-QM, III) was prepared. Again,
MWCNTs@SiO2/SO3H activates intermediate III as a
Michael acceptor. Afterward, Michael addition of amide to
intermediate IV afords the expected amidoalkyl naphthol.
According to proposed mechanism, the aromatic aldehydes
with electron-withdrawing groups reacted faster than those
having electron-donating groups.
Fig. 5 XRD pattern of a raw and b MWCNTs@SiO2/SO3H
Table 2 Optimization of the catalyst amount and the reaction temper-
ature for the preparation of amidoalkyl naphthols
Entry
Catalyst/mg
Temperature/°C
Yielda/%
A comparison between the efcacy of MWCNTs@SiO2/
SO3H catalyst for the preparation of N-[phenyl-(2-hydrox-
ynapthalen-1-yl)-methyl]benzamide (4a) with some of those
reported in the literatures is presented in Table 4. Although
all of reaction conditions have considerable advantageous,
but as can be seen, MWCNTs@SiO2/SO3H is one of the
high-efcient catalysts with respect to reaction times and
yield of products. On the other hand, the advantageous of
prepared catalyst in compared to zinc benzenesulfonate
(with shorter time and higher yield, entry 14) is that MWC-
NTs@SiO2/SO3H is a heterogeneous reusable catalyst and
its recycling is simpler than ZBS. In fact, catalysts based on
CNTs provided high-efcient, selective, and green condi-
tions for organic synthesis reactions [49, 51, 52]. Further-
more, in presented method, low amount of catalyst (13 mg)
with high yield of products provided a sufcient method for
preparation of amidoalkyl naphthols and also can be used
for other acid catalyzed organic reactions.
1
2
3
4
5
6
7
8
9
5
8
100
100
100
100
100
100
90
78
82
85
90
90
90
86
90
–
10
13
15
18
13
13
–
110
100
Reaction conditions: benzaldehyde (1 mmol), 2-naphthol (1 mmol),
and benzamide (1.2 mmol); time 15 min
aIsolated yield
fact, CNT structure was stable without any changes after
the treatment (Fig. 5).
After the characterization of the solid acid catalyst, the
catalyst activity of prepared solid acid catalyst has been
tested in the preparation of amidoalkyl naphthol derivatives.
In a typical experimental manner, a mixture of aldehyde
(1 mmol), β-naphthol (1 mmol), benzamide (1.2 mmol), and
CNT@SiO2/SO3H (13 mg) as a model study was taken in
round-bottom fask and stirred for a certain period of time
as required to complete the reaction (indicated by TLC) at
100°C. As shown in Table 1, the best result was obtained by
We observed that the catalyst can be easily recovered
by simple fltration after the reaction. The reusability of
the catalyst was studied by the reaction of benzaldehyde,
2-naphthol, and benzamide. After completion of reaction,
the catalyst was separated, washed with acetone and dried
at 80 °C, and then reused for the next cycle. As shown in
Fig. 6, the yield of the product decreased from the frst run
to ffth run (90–79%). Obtained results show the good ef-
ciency of prepared solid acid catalyst. On the other hand,
1 3

M. Ahmadi et al.
Table 3 Solvent-free synthesis
of amidoalkyl naphthols in the
presence of MWCNTs@SiO2/
SO3H
Entry
Product
R1
R2
Time/min
Yielda/%
M.p./°C [Refs.]
TONc
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
CH3
H
4-Cl
2-Cl
15
10
10
6
90
95
93
97
98
84
86
80
84
85
93
88
98
244–246 [54]
186–188 [55]
266–269 [56]
238–240 [57]
234–236 [57]
208–210 [14]
220–224 [58]
220–222 [15]
259–262 [59]
190–191 [27]
240–243 [8]
184–286 [8]
249–251 [8]
11,110
11,730
11,480
11,970
12,100
10,370
10,610
9880
10,370
10,490
11,480
10,860
12,100
4-NO2
3-NO2
4-OCH3
SC4Hb3
4-(CH3)2N
4-CHO
4-CH3
H
6
25
12
26
20
20
15
22
7
4g
4h
4i
9
10
11
12
13
4j
4k
4l
CH3
CH3
4-OCH3
4-NO2
4m
aIsolated yield
b2-thiophenecarbaldehyde was used as aldehyde
cMoles of desired product/moles of catalyst
Scheme 3
H
O
OH
O
H
R2
H
OH
O
H
SO3
H
O
-
H
2O
R2
-H
R2
I
II
R1
NH
OH
O
H2N
R1
R2
R2
R2
H
SO3
O
OH
(o-QMs)
IV
III
because of turn over number (TON=moles of desired prod-
uct/moles of catalyst) which is more crucial than good recy-
cling ability of a catalyst [64], TON values were calculated
for every recycling process. The TON value was in range
of 11,110–9750, which demonstrated the good activity and
stability of heterogeneous acidic catalyst.
short reaction times, easy workup, and inexpensive and
recoverable of the catalyst make the procedure an attractive
route to the existing methods for the synthesis of amidoalkyl
naphthols.
Experimental
Conclusion
Multiwalled carbon nanotubes were prepared from Shen-
zhen Nanotechnology Co., Ltd. (China). The Purity of the
CNTs was about 90–95%, with diameters ranging between
20 and 40 nm and lengths 5–15 μm. All organic materi-
als were purchased commercially from Sigma-Aldrich and
Merck companies. FT-IR spectra were recorded with KBr
In conclusion, we have reported a new method for highly
sulfonated MWCNTs as efcient solid acid catalyst for novel
and eco-friendly synthesis of amidoalkyl naphthols under
solvent-free conditions. Green and mild reaction conditions,
1 3

Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as…
Table 4 Comparison of
Entry
Catalyst
Conditions
Time/min
Yield/%
References
MWCNTs@SiO2/SO3H with
other catalysts reported in the
literature for the synthesis of
compound 4a
1
2
3
4
5
6
7
8
Montmorillonite K10
p-TSA
MNPs-SO3H
K5CoW12O40·3H2O
H4SiW12O40
P2O5
0.1 g, 125 °C
90
900
10
120
20
10
120
10
5
6
95
7
120
15
15
78
89
82
80
88
85
80
90
82
88
84
82
87
92
90
[22]
[7]
10 mol%; 125 °C
0.02 g, 100 °C
1 mol%, 125 °C
5 mol%, 110 °C
10 mol%, 60 °C
10 mol%, 80 °C
10 mol%, 100 °C
50 mg, 100 °C
0.02 mmol, 100 °C
10 mg, 120 °C
80 mg, 100 °C
0.075 mmol, 125 °C
2 mol%, 80 °C
13 mg, 100 °C
[60]
[38]
[61]
[15]
[36]
[39]
[32]
[62]
[63]
[8]
Zwitterionic salt
Cyanuric chloride
SILPa
9
10
11
12
13
14
15
β-CD-BSAb
MSNs-HPZ-SO3Hc
SILCd
HClO4-Ce
[37]
[40]
This work
ZBSf
MWCNTs@SiO2/SO3H
aFerrocene-labeled supported ionic liquid phase
bβ-Cyclodextrin-butanesulfonic acid
cMesoporous silica nanoparticles functionalized with homopiperazine sulfamic acid
dSilica gel-supported –SO3H
eGraphite-supported perchloric acid
fZinc benzenesulfonate (as homogeneous catalyst)
Fig. 6 Recyclability of MWC-
NTs@SiO2/SO3H
disk using a Magna-IR, spectrometer 550 Nicolet. NMR
spectra were recorded using a Bruker 400 MHz spectrom-
eter with TMS as an internal standard and DMSO-d6 as
solvent. The thermogravimetric analysis (TGA) curves
were carried out using a V5.1A DUPONT 2000. To inves-
tigate the morphology of the MWCNTs, FE-SEM images
and EDX analysis were used by a Sigma ZEISS, Oxford
Instruments Field Emission Scanning Electron Micro-
scope. Brunauer–Emmett–Teller (BET) analysis was used
to characterize the functionalized surfaces of CNTs by
MicrotracBEL Corp instrument.
Preparation of catalyst
Hydroxylation of MWCNTs surfaces
Raw MWNTs (0.2 g) and 100 cm3 methylene chloride were
added into a 250 cm3 fask and sonicated for 10 min. After
1 3

M. Ahmadi et al.
that, TPABr (1 g dissolved in 10 cm3 H2O), KMnO4 (0.25 g
dissolved in 5 cm3 H2O), and 10 cm3 acetic acid were added.
The mixture was stirred vigorously at 25 °C for 24 h. Then,
the mixture was fltered through a 10-μm pore size polycar-
bonate flter paper and washed with HCl and methanol. After
drying, MWCNTs functionalized with hydroxyl groups
(MWCNTs-OH) were achieved [65].
room temperature and washed with hot water to remove the
remained amide. Then, 10 cm3 acetone were added to the
reaction mixture and fltered of for separation the catalyst.
After that, the fltrate was evaporated for obtaining the crude
product and for further purifcation recrystallized from hot
ethanol.
Acknowledgements Authors are grateful for fnancial support from the
University of Kashan by Grant number of 784946.
Preparation of sulfonated MWCNTs (MWCNTs@SiO2/SO3H)
MWCNTs-OH (0.50 g) were dispersed in 50 cm3 of etha-
nol (using bath sonicator for 10 min) followed by addition
of 1.0 cm3 28 wt% concentrated ammonia aqueous solu-
tion (NH3·3H2O), 9 cm3 deionized water, and 0.50 cm3 of
tetraethyl orthosilicate (TEOS). The mixture was vigorously
stirred at 25°C for 16 h. After that, MWCNTs@SiO2 were
fltered through a 10-μm pore size polycarbonate flter paper
and washed with deionized water, ethanol, and acetone, and,
fnally, dried at 60 °C under vacuum.
References
1. Strecker A, Liebigs A (1850) Ann Chem Pharm 75:27
2. Terret NK, Gardener M, Gordon DW, Kobylecki RJ, Steele J
(1995) Tetrahedron 51:8135
3. Domling A, Ugi L (2000) Angew Chem Int Ed 39:3168
4. Thomson LA, Ellman JA (1996) Chem Rev 96:555
5. Brousmiche D, Wan P (1998) Chem Commun 4:491
6. Song Y, Tian T, Wang P, He H, Liu W, Zhou X, Cao X, Zhang
XL, Zhou X (2006) Org Biomol Chem 4:3358
7. Khosropour AR, Khodaei MM, Moghanian H (2005) Synlett 955
8. Kotadia DA, Soni SS (2012) J Mol Catal A Chem 353–354:44
9. Mulla SAR, Salama TA, Pathan MY, Inamdar SM, Chavan SS
(2013) Tetrahedron Lett 54:672
For sulfonation of MWCNTs@SiO2, a 500 cm3 suction
fask was equipped with a pressure equalizing dropping
funnel-containing chlorosulfonic acid and gas inlet tube
for conducting HCl gas over adsorbing the solution water.
MWCNT@SiO2 (500 mg) was debundled in dry CH2Cl2
using bath sonicator for 10 min, and then, chlorosulfonic
acid (0.4 cm3 in dry CH2Cl2) was added dropwise over a
30 min period. After the addition of ClSO3H, the mixture
was fltered through 10-μm pore size polycarbonate flter
paper and MWCNTs@SiO2/SO3H as a black solid was sepa-
rated and washed with methanol before being dried in an
oven at 70 °C.
10. Remillard S, Rebhun LI, Howie GA, Kupchan SM (1975) Science
189:1002
11. Kusakabe Y, Nagatsu J, Shibuya M, Kawaguchi O, Hirose C, Shi-
rato S (1972) J Antibiot 25:44
12. Benedini F, Bertolini G, Cereda R, Dona G, Gromo G, Levi S,
Mizrahi J, Sala A (1995) J Med Chem 38:130
13. Clark RD, Caroon JM, Kluge AF, Repke DB, Roszkowski AP,
Strosberg AM, Baker S, Bitter SM, Okada MD (1983) J Med
Chem 26:657
14. Nandi GC, Samai S, Kumar R, Singh MS (2009) Tetrahedron Lett
50:7220
15. Ren H, Grady S, Gamenara D, Helnzen H, Moyna P, Crott S,
Kendrick H, Yardey V, Moyna G (2001) Med Chem Lett 11:1851
16. Muskawar PN, Kumar SS, Bhagat PR (2013) J Mol Catal A Chem
380:112
Determination the acidity of catalyst
The acidity of prepared catalyst was quantitatively ana-
lyzed by back titration method. In a common route, 0.1 g
of MWCNTs@SiO2/SO3H was dispersed in 15 cm3 of a
0.1 N NaOH using a bath sonicator (20 min) and then stirred
overnight. After that, the mixture was fltered and the fl-
trate was titrated with a 0.1 N HCl solution to determine
the excess NaOH. Obtained result shows that the concen-
tration of SO3H groups on prepared solid acid surfaces was
6.2 mmol g−1. Accordingly, the acidity of 13 mg of catalyst
in synthesis of amidoalkyl naphthols was 0.081 mmol.
17. Seebach D, Matthews JL (1997) Chem Commun 21:2015
18. Knapp S (1995) Chem Rev 95:1859
19. Juaristi E (1977) In: enantioselective synthesis of β-aminoacids.
Wiley, New York
20. Dingermann T, Steinhilber D, Folkers G (2004) Molecular biology
in medicinal chemistry. Wiley-VCH, Weinheim
21. Shen AY, Tsai CT, Chen CL (1999) Eur J Med Chem 34:877
22. Kantevari S, Vuppalapati SVN, Nagarapu L (2007) Catal Commun
8:1857
23. Nagarapu L, Baseeruddin M, Apuri S, Kantevari S (2007) Catal
Commun 8:1729
24. Shaterian HR, Yarahmadi H, Ghashang M (2008) Tetrahedron
64:1263
General procedure for the synthesis of amidoalkyl
naphthols
25. Shaterian HR, Yarahmadi H, Ghashang M (2008) Bioorg Med
Chem Lett 18:788
26. Shaterian HR, Yarahmadi H (2008) Tetrahedron Lett 49:1297
27. Zolfgol MA, Khazaei A, Moosavi-Zare AR, Zare A, Khakyzadeh
V (2011) Appl Catal A 400:70
A mixture of arylaldehyde (1 mmol), β-naphthol (1 mmol),
amide (1.2 mmol), and MWCNTs@SiO2/SO3H (13 mg)
were taken in a round-bottom fask and stirred and heated
in an oil bath (100 °C). After the reaction was completed
(monitored by TLC), the reaction mixture was cooled to
28. Hajipour AR, Ghayeb Y, Sheikhan N, Ruoho AE (2009) Tetrahe-
dron Lett 50:5649
29. Mahdavinia GH, Bigdeli MA (2009) Chin Chem Lett 20:38330
30. Lei M, Ma L, Hu L (2009) Tetrahedron Lett 50:6393
1 3

Solvent-free synthesis of amidoalkyl naphthols in the presence of MWCNTs@SiO2/SO3H as…
31. Khazaei A, Zolfgol MA, Moosavi-Zare AR, Zare A, Parhami A,
Khalaf-Nezhad A (2010) Appl Catal A Gen 386:179
32. Rashinkar G, Salunkhe RJ (2010) Mol Catal A Chem 316:146
33. Srihari G, Nagaraju M, Murthy MM (2007) Helv Chim Acta
90:1497
51. Mahinpour R, Moradi L, Zahraei Z, Pahlevanzadeh N (2018) J
Saudi Chem Soc 22:876
52. Moradi L, Zare M (2018) Green Chem Lett Rev 11:197
53. Khakde BA, Allouche H, Mahima S, Sathe BR, Pillai VK (2008)
Carbon 46:567
34. Zhang Q, Luo J, Wei Y (2010) Green Chem 12:2246
35. Niralwad KS, Shingate BB, Shingare MS (2011) Chin Chem Lett
22:551
54. Szatmari I, Fulop F (2004) Curr Org Synth 1:155
55. Patil SB, Singh PR, Surpur MP, Samant SD (2007) Ultrason Sono-
chem 14:515
36. Kundu D, Majee A, Hajra A (2010) Catal Commun 11:1157
37. Lei ZK, Xiao L, Lu XQ, Huang H, Liu CJ (2013) Molecules
18:1653
56. Wang M, Liang Y (2011) Monatsh Chem 142:153
57. Ansari SAMK, Sangshetti JN, Kokare ND, Wakte PS, Shinde DB
(2010) Indian J Chem Technol 17:71
38. Nagarapu L, Baseeruddin M, Apuri S, Kantevari S (2007) Catal
Commun 8:1729
58. Adrom B, Hazeri N, Maghsoodlou MT, Mollamohammadi M
(2015) Res Chem Intermed 41:4741
39. Mahdavinia GH, Bigdeli MA (2009) Chin Chem Lett 20:383
40. Wang M, Song ZG, Liang Y (2012) Synth Commun 42:582
41. Koukabi N, Kolvari E, Zolfgol MA, Khazaei A, Shaghasemi BS,
Fasahati B (2012) Adv Synth Catal 354:2001
42. Rostamnia S, Nuri A, Xin H, Pourjavadi A, Hosseini SH (2013)
Tetrahedron Lett 54:3344
59. Zare A, Kaveh H, Merajoddin M, Moosavi-Zare AR, Hasaninejad
A, Zolfgol MA (2013) Phosphorus. Sulfur Silicon Relat Elem
188:573
60. Safari J, Zarnegar ZJ (2013) Mol Catal A Chem 379:269
61. Supale AR, Gokavi GS (2010) J Chem Sci 122:189
62. Gong K, Wang H, Ren X, Wanga Y, Chen J (2015) Green Chem
17:3141
43. Ijima S (1991) Nature 354:56
44. Moradia L, Rezaeei Bina M, Partovi T (2014) Curr Chem Lett
3:147
63. Nasresfahani Z, Kassaee MZ, Eidi E (2016) New J Chem 40:4720
64. Molnár Á, Papp A (2017) Coord Chem Rev 349:1
65. Kim M, Hong CK, Choe S, Shim SE (2007) J Polym Sci A Polym
Chem 45:4413
45. Moradi L, Najaf GR, Saeidiroshan H (2015) Iran J Catal 5:357
46. Moradi L, Etesami I (2016) Fuller Nanotub Carbon Nanostruct
24:213
47. Xia H, Wang Q, Qiu G (2003) Chem Mater 15:3879
48. Park C, Oundaies Z, Watson KA, Crooks RE, Smith J Jr, Lowther
SE, Connell JW, Siochi EJ, Harrison JS, St Clair TL (2002) Chem
Phys Lett 364:303
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
49. Safari J, Zarnegar Z (2014) J Ind Eng Chem 20:2292
50. Moradi L, Mohajeri A, Naeimi H, Rashidi AM (2011) J Nanosci
Nanotech 11:8903
1 3