Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo): an efficient green catalyst for multicomponent synthesis of amidoalkyl naphthols

Article abstract of DOI:10.1007/s11164-018-3321-4

Abstract: Magnetite (Fe₃O₄)-supported molybdenum oxide (MoO₃) was synthesized from simple starting precursors in aqueous medium. The synthesized nanocat-Fe-Mo was analyzed using several techniques such as X-ray diffraction

Full text of DOI:10.1007/s11164-018-3321-4

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3321-4
Nanomagnetite-supported molybdenum oxide
(nanocat-Fe-Mo): an efficient green catalyst
for multicomponent synthesis of amidoalkyl naphthols
Swapnil R. Bankar1
Sharad N. Shelke1
•
Received: 29 November 2017 / Accepted: 2 February 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Magnetite (Fe3O4)-supported molybdenum oxide (MoO3) was synthesized
from simple starting precursors in aqueous medium. The synthesized nanocat-Fe-Mo
was analyzed using several techniques such as X-ray diffraction (XRD) analysis, X-ray
photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission
electron microscopy (TEM), and vibrating-sample magnetometry (VSM). The catalytic
activity of the synthesized nanocat-Fe-Mo was studied in a benign one-pot multicom-
ponent transformation for synthesis of amidoalkyl naphthol derivatives under solvent-
free condition using both conventional and microwave irradiation methods. Nanocat-Fe-
Mo was found to be highly active and could be reused seven times without notable loss
in catalytic activity. The proposed method offers advantages such as good reaction yield
(80–95%), short process time, simple workup, and recycling of the catalyst, representing
important green chemistry principles.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3321-4) contains supplementary material, which is available to authorized users.
&
Sharad N. Shelke
snshelke@yahoo.co.in
1
P. G. and Research Centre, Department of Chemistry, S.S.G.M. College,
Kopargaon, Ahmednagar, MS 423601, India
123

S. R. Bankar, S. N. Shelke
Graphical Abstract
Keywords MNPs Á Nanocat-Fe-Mo Á Multicomponent reaction Á Amidoalkyl
naphthols Á Benign media Á Green transformation
List of symbols
Ar
Aryl
CCD
DMF
DMSO
EDS
Charge coupled device
Dimethyl formamide
Dimethylsulfoxide
Energy dispersive spectroscopy
Ferrite-molybdenum
Fe-Mo
FT-IR
FWHM
HIV
Fourier-transform infrared
Full width at half maximum
Human immunodeficiency virus
ICP-AES Inductively coupled plasma-atomic emission spectroscopy
LFD
MNPs
MP
Large field detector
Magnetic nanoparticles
Melting point
MW
NMR
NP
Microwave
Nuclear magnetic resonance
Nanoparticle
Phenyl
Ph
ppm
RBF
RF
Parts per million
Round-bottomed flask
Radiofrequency
RT
SEM
Room temperature
Scanning electron microscopy
123

Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
TEM
TLC
TMS
UV
Transmission electron microscopy
Thin-layer chromatography
Tetramethylsilane
Ultraviolet
Vibrating-sample magnetometry
X-ray diffraction
VSM
XRD
Introduction
Working towards sustainability, researchers have made significant advances in
organic transformations by using nanoparticle materials, attracting great attention in
areas such as drug discovery [1, 2], electronic field devices [3], as well as
heterogeneous catalysis [4, 5]. Over the past few decades, ecofriendly heteroge-
neous catalysts have played a vital role in organic transformations [6]. Application
of NPs in heterogeneous catalysis has become an important focus, including
nanosupported metal catalysts, solid-supported inert platforms such as silica, and
iron oxides in biological transformations. Iron-oxide-based NPs have been widely
used as an important support for functionalization of metals, organocatalysts, chiral
catalysts, and N-heterocyclic carbenes [7].
During the last decade, nanocatalysts, especially supported on noble metals such
as Au, Ru, Mo, Pt, and Pd, have introduced a fertile area of selective organic
methodologies as well as catalytic reactions [8, 9]. Immobilization of molybdenum
on solid supports has mainly been applied in a number of important organic
reactions, including A3 coupling, hydrogenation, and hydration, as well as oxidation
of benzyl alcohol [10–12]. In such organic transformations, supported catalysts offer
the advantage of bypassing problems related to inefficient heating and use of
activation methods such as mechanochemical grinding or ultrasonic and microwave
(MW) irradiation for such syntheses [13–17]. Among these processes for rapid
organic synthesis using faster and cleaner approaches, MW heating has also
emerged as an important energy source [18–21]. In addition, solvent-free
approaches for chemical reactions also represent a growing trend from the point
of view of green chemistry with respect to future resources and chemical waste [22].
In recent years, multicomponent reactions have attracted particular attention from
researchers, being considered a special field of combinatorial chemistry because of
their capacity for synthesis of complex compounds in one pot [23]. MCRs offer key
features of green chemistry, since many reagents are added in a single step to form a
novel molecule without any intermediates. The advantages of such reactions include
atom economy, reduced processing time, simple workup method, as well as
enabling environmentally friendly synthesis [24–26].
Literature survey reveals that 1-amidoalkyl-2-naphthols and their derivatives
including, e.g., [1,3]oxazine nucleus represent important compounds for synthesis
of many natural products, antibiotics, nucleosides, and human immunodeficiency
virus (HIV) protease inhibitors such as ritonavir and lopinavir [27, 28]. By amide
123

S. R. Bankar, S. N. Shelke
hydrolysis reaction, 1-amidoalkyl-2-naphthols can be converted to 1-aminomethyl-
2-naphthol derivatives, which have important bioactivity and exhibit bradycardia
and depressor effects in humans [29, 30].
Research has been carried out on synthesis of amidoalkyl naphthols by
combination of aldehydes, 2-naphthols, and amides via various multicomponent
pathways, e.g., in presence of catalysts such as iodine [31, 32], ionic liquids [33],
montmorillonite clay, MgSO4, ZnO nanoparticles, HClO4–SiO2, various Lewis and
Brønsted acids [34–39], and K5CoW12O40Á3H2O [39]. However, some of these
reported methods suffer from certain disadvantages such as use of harmful solvents,
longer reaction time, expensive catalyst, low yield, and harsh reaction conditions
such as high temperature. In view of these drawbacks of previous methods and to
attain sustainability, it is important to develop ecofriendly clean procedures with
good catalytic activity for preparation of 1-amidoalkyl-2-naphthols.
Considering these problems, we present herein a simple, green, sustainable
protocol for one-pot MCR of amidoalkyl naphthols using a highly active magnetite-
supported molybdenum oxide nanocatalyst. Our researcher group previously
reported [10] Mo-functionalized magnetite, active in oxidation and reduction
processes, as well as MCR and coupling chemistries. The advantages of using such
Mo-based Fe catalysts include recyclability and facile handling [10]. MNPs were
prepared by simple wet impregnation methods in benign medium. In continuation of
our research on development of greener techniques and novel methodologies [40],
we have developed here a novel and simple scheme for functionalization of ferrite
MNPs with molybdenum oxide as Lewis acid site for one-pot MCRs. To the best of
the authors’ knowledge and as revealed by literature survey, no earlier reports are
available on use of such Mo-based magnetite catalysts for synthesis of amidoalkyl
naphthols.
Experimental
Resources and reagents
For the current investigation, all commercial chemicals were obtained from Sigma-
Aldrich and used as received. All reactions were carried out using a laboratory
microwave oven (RAGA’S Scientific Microwave System-700 W). All reported
melting points were determined using a model KI-11 (MP-D) melting point
apparatus (Kumar Sales Corporation, Mumbai, India) and are uncorrected. Reaction
progress was monitored with the help of preparative TLC on precoated silica gel
glass plates (Kieselgel 60 mit Fluoreszens-Indicator UV- 254, E. Merck, Germany).
Spots were visualized using ultraviolet (UV) light.
Characterization techniques
XRD analysis was carried out on the newly synthesized Mo-ferrite nanocatalyst.
The X-ray powder diffraction pattern was obtained using a conventional powder
diffractometer (MiniFlexTM II benchtop X-ray diffractometer, Rigaku) with Cu Ka
123

Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
radiation X-ray tube (30 kV/15 mA) operating in Bragg–Brentano (h–2h) geometry.
Samples were prepared by grinding when needed and compressed in the sample
holder with a flat glass. The sample area in the sample holder was about 2 cm2.
XPS measurements were performed on a VSW XPS system with class 100
energy analyzer, being part of an experimental setup assembled for surface
investigation [41]. Spectra were measured in fixed analyzer transmission mode with
FAT 22 mode (energy step 0.1 eV, acquisition time 24 s). Nanoparticle powder was
prepared for XPS by pressing on indium (In) plate as matrix to provide mechanical
support and reduce charging problems. For energy axis calibration, Ag (110) and
polycrystalline Au samples (previously cleaned by ion sputtering) were used.
TEM experiments were performed on a Hitachi H8100 microscope using a
ThermoNoran light-elements energy-dispersive X-ray spectroscopy (EDS) detector
and charge-coupled device (CCD) camera for image acquisition. The nanocat-Fe-
Mo fine powder was placed on a carbon stub, and images were recorded at 5–15 kV
using a large-field detector (LFD) under low vacuum. SEM images were acquired
using a JEOL JSM7001F FEG-SEM. Elemental analysis was performed using a
light-elements EDS detector from Oxford. Nanocat-Fe3O4-MoO3 powder was
spread on double-sided carbon tape and analyzed at acceleration voltage of 25 kV.
Elemental analysis was carried out by inductively coupled plasma-atomic
emission spectrometry (ICP-AES, Ultima; Horiba Jobin–Yvon, France) equipped
with a 40.68 MHz radiofrequency (RF) generator, Czerny–Turner monochromator
with 1.00 m (sequential), AS500 autosampler, and concomitant metals analyzer
(CMA). The magnetic properties of the Fe3O4 materials were analyzed by vibrating-
sample magnetometry (VSM, Lakeshore 7404) at room temperature. FT-IR spectra
were scanned on a PerkinElmer Spectrum version 10.4.2. NMR spectra were
recorded on a Bruker 300 MHz (1H NMR) and 75 MHz (13C NMR) instrument with
CDCl3 or DMSO as solvent and TMS as internal standard; chemical shifts (d) are
stated in ppm, and coupling constants (J) in Hertz. Signal splitting is denoted by
s (singlet), d (doublet), t (triplet), dd (double doublet), and m (multiplet).
Preparation of ferrite MNPs [40–42]
FeCl3Á6H2O (5.4 g) and urea (3.6 g) were dissolved in water (200 mL) for 2 h at
85–90 °C. The solution color became brown. To this brown reaction mixture cooled
at room temperature was added FeSO4Á7H2O (2.8 g), and then NaOH (0.1 M) until
the pH became 10. In this case, the molar ratio of Fe(III) to Fe(II) is nearly 2.00. The
resultant hydroxide was treated by ultrasonication in sealed flasks at 30–35 °C for
30 min. After aging for 5 h, the resulting black powder (Fe3O4) was purified and
dried under vacuum.
Preparation of nanocat-Fe-Mo MNPs [10–12]
Ferrite MNPs, Fe3O4 (2 g), and ammonium molybdate (NH4)6Mo7O24Á4H2O
(0.147 mg to get 1–2% Mo) were stirred at room temperature in aqueous medium
(50 mL) for 1 h. After impregnation, the suspension pH was adjusted to 12 by
adding sodium hydroxide (1.0 M), followed by stirring for 20 h. The resultant solid
123

S. R. Bankar, S. N. Shelke
was washed with distilled water (five times, 10 mL). The obtained metal precursors
were reduced by adding 0.2 M NaBH4 water solution dropwise under gentle stirring
in ice–water bath for 30 min until no bubbles were obtained in the solution. The
resulting nanocat-Fe-Mo MNPs were kept under ultrasonication for 10 min then
washed with distilled water and subsequently with ethanol and dried under vacuum
at 60 °C for 24 h. The Mo content in the nanocatalyst was determined to be
0.42 wt% by ICP-AES analysis.
One-pot synthesis of amidoalkyl naphthols using nanocat-Fe-Mo
For synthesis of amidoalkyl naphthol analogs, a combination of 2-naphthol
(10 mmol), substituted aromatic aldehyde (10 mmol), urea (12 mmol), and nanocat-
Fe-Mo (10 mol%) was added. The reaction was performed conventionally at 120 °C
for 30 min under solvent-free conditions. The same reaction mixture was also
carried out in the microwave oven at 350 W in benign medium, for comparison. The
microwave oven was adjusted to boost the internal reaction temperature to 120 °C
within 1 min, and then continue with appropriate irradiation (0–700 W) at the same
temperature, for the suitable time. Reaction monitoring was carried out with the
help of TLC. It was observed that, compared with the conventional oil bath heating
process, the nonconventional MW technique was superior and clean.
After completion, the reaction content was cooled to room temperature, then the
solid mixture was dissolved in boiling ethanol and stirred for 2 min. The solution
was then filtered by magnetic decantation technique. The solid obtained on cooling
the solution to room temperature was purified by column chromatography technique
on silica bed using n-hexane and ethyl acetate as eluent, and the final solid obtained
Table 1 Ferrite-Mo-catalyzed synthesis of amidoalkyl naphthol analogs (4a–l): yields and melting
points
4
R
R1
M.p. (°C)
Method A
Time (min)/yield (%)
Method B
Time (min)/yield (%)
4a
4b
4c
4d
4e
4f
H
CH3
NH2
CH3
NH2
CH3
NH2
CH3
NH2
CH3
NH2
CH3
NH2
240
170
216
172
228
165
210
190
248
172
224
178
3/94
3/92
3.5/95
4/89
4/92
4/86
5/92
3/90
4/92
4/87
4/90
4/93
30/94
40/91
35/86
30/93
30/94
35/86
45/81
40/92
30/90
35/86
35/90
30/80
H
4-CH3
4-CH3
4-Cl
4-Cl
4g
4h
4i
4-OCH3
4-OCH3
4-Br
4j
4-Br
4k
4l
4-NO2
4-NO2
Method A, microwave technique; method B, oil bath
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Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
was analyzed by melting point measurements and TLC Rf values. Catalyst was
recovered by evaporation of organic solvents under reduced pressure and drying
well using vacuum. Nanocat-Fe-Mo was used again without loss of activity.
Different analogs were obtained by following the same experimental process. The
compounds synthesized using the above-described procedure are summarized in
Table 1 together with their characterization data. All known compounds were
reported earlier in literature and were characterized by comparison with NMR
spectra of authentic samples.
The method using the presented Fe-Mo catalyst was also compared with other
inorganic and organic catalysts reported in literature for synthesis of amidoalkyl
naphthol derivatives (Table 2), clearly showing that the present nanocat-Fe-Mo
catalyst was more efficient compared with reported procedures.
Results and discussion
Magnetic nanocat-Fe-Mo characterization
Magnetically recyclable nanocat-Fe-Mo was prepared from ferrite NPs and
ammonium molybdate by simple wet impregnation method in benign medium
(Scheme 1) and characterized using various techniques including X-ray diffraction
(XRD) analysis, inductively coupled plasma-atomic emission spectroscopy (ICP-
Table 2 Comparison of synthesis of amidoalkyl naphthol using nanocat Fe-Mo with other catalysts
reported in literature
No. Catalyst
Conditions
Yield (%) References
1
2
3
Ce(SO4)2
Iodine
CH3CN reflux, 36 h
66–78
71–84
70–78
[31]
[32]
[37]
Solvent free, 125 °C, 5 h
Solvent free, 125 °C, 1.5 h
Montmorillonite
K10
4
5
MgSO4
Solvent free, 100 °C, 1 h
Solvent free, (a) 130 °C, 30 min (b) MW,
6 min
72–90
81–94
[36]
[34]
ZnO NPs
6
Imidazolium salt
H4SiW12O40
Trityl chloride
p-TSA
Solvent free, 120 °C, 40 min
Solvent free, 110 °C
Room temp., 1–4 h
81–95
78–94
83–94
83–93
81–94
75–94
84–96
[46]
[47]
[48]
[49]
[50]
[51]
7
7
8
Solvent free, 125 °C, 4–8 h
Solvent free, 120 °C, 40 min
Solvent free, 120 °C, 60 min
Solvent free, 120 °C, 30 min
9
MNPs-PhSO3H
MSNs-HPZ-SO3H
Ferrite-Mo
10
11
Present
work
12
Ferrite-Mo
Solvent free, MW, 3 min
86–94
Present
work
123

S. R. Bankar, S. N. Shelke
Scheme 1 Synthesis of nanocat-Fe-Mo (1)
Fig. 1 XRD pattern of nano-Fe-Mo catalyst with reference to magnetite
AES), X-ray photoelectron microscopy (XPS), transmission electron microscopy
(TEM), field-emission-gun scanning electron microscopy with energy-dispersive
spectrometry (FEG-SEM–EDS), and vibrating-sample magnetometry (VSM). The
Mo content in the nanocatalyst was determined to be 0.40 wt% by ICP-AES
analysis.
The crystallite size of the Fe-Mo MNPs was determined using the Debye–
Scherrer equation. The XRD spectra of the ferrite and nanocat-Fe-Mo nanoparticles
(Fig. 1) showed that the crystallite size of the nanocat-Fe-Mo MNPs was 30.1 nm,
similar to the TEM result indicating size distribution between 20 and 40 nm. Due to
the low percentage (0.42 wt%) of Mo, no diffraction lines corresponding to the Mo
oxides observed by XPS method could be detected by XRD.
To confirm the oxidation state and nature of the Mo species in the nanocatalyst,
the nanocat magnetite-Mo was analyzed by X-ray photoelectron spectroscopy
(XPS). The surface composition of the MNP powder was determined from the
intensities of the characteristic XPS peaks of C, O, Fe, and Mo, viz. C 1s, O 1s, Fe
2p, and Mo 3d, respectively. In the final nanocatalyst, oxygen appeared to be the
most abundant element (51.2%), followed by carbon (34.1%), iron (10.3%), and
molybdenum (0.4%). The Mo content obtained from XPS was found to be in
agreement with that measured by ICP-AES technique, revealing that the Mo was
123

Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
Fig. 2 Mo 3d XPS spectrum of Mo-Fe3O4 nanocatalyst
Fig. 3 a TEM image of nanocat-Fe-Mo at 200 nm. b Histogram of nanocat-Fe-Mo
present on the surface of the nanoferrite in the final nanocatalyst. The main
characteristic peaks of molybdenum (Mo 3d) are shown in Fig. 2. The two peaks
(3d5/2 and 3d3/2) have intensity ratio of 62:38 (close to the theoretical ratio of
60:40), with full-width at half-maximum (FWHM) of about 1.68 eV. The 3d5/2 line
appeared at 232.7 eV, perfectly matching with the MoO3 state in literature [43, 44].
TEM of nanocat-ferrite-Mo (Fig. 3) revealed that the synthesized MNPs
exhibited uniform size with somewhat spherical morphology. The diameter of the
NPs ranged from 20 to 40 nm (average 20 nm), consistent with the XRD results.
FEG-SEM analysis of the nanomagnetite-Mo sample was carried out at
acceleration voltage of 25 kV, revealing nanoparticles of uniform size and
somewhat spherical morphology with woolly cloud-like clusters (Fig. 4).
After characterization, the catalytic activity of nanocat-Fe-Mo was investigated
in a series of reactions to confirm its versatility due to the contained Mo.
123

S. R. Bankar, S. N. Shelke
Fig. 4 SEM images of nanocat-Fe-Mo nanoparticles
Fig. 5 SEM images of
recovered catalyst after seventh
cycle
Fig. 6 VSM curve of
synthesized Fe3O4 and Fe-Mo-
coated nanomaterial
After the seventh cycle, recovered catalyst was characterized by SEM, showing
almost the same results as for freshly synthesized catalyst with no significant
changes (Fig. 5). Meanwhile, it is important to stress that reactions carried out using
nonfunctionalized ferrite (without Mo) delivered no/low yield in the studied
reactions.
123

Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
To study the magnetic properties of the synthesized ferrite nanomaterial, the
magnetization curve of Fe3O4 material obtained by VSM at room temperature is
shown in Fig. 6. The saturation magnetization of the Fe3O4 nanoparticles was found
to be 88.69 emu g-1, not far from the actual magnetization of Fe3O4 of 92 emu g-1
[45]. After application of molybdenum on the ferrite, the magnetic moment of the
sample dropped to 22.46 emu g-1, clearly confirming the coating of molybdenum
on the ferrite material.
Nanocat-Fe-Mo-catalyzed multicomponent synthesis of amidoalkyl
naphthols
To confirm the efficacy and scope of the synthesized and characterized nanocat
Fe3O4-Mo in MCRs, aromatic aldehydes and amides were subjected to one-pot
condensation with 2-naphthol in presence of catalytic amount of nanocat-Fe-Mo to
obtain 1-amidoalkyl 2-naphthol analogs. All reactions proceeded smoothly when
using the conventional method (120 °C, 30 min) or under microwave irradiation at
350 W for 3–6 min. The reaction progressed well under MW in solvent-free
conditions and benign medium with good product yield (Scheme 2).
Another possibility is quantitative formation of 14-aryl-14H-dibenzo[a,j]xan-
thenes when b-naphthol is used with aldehyde in 2:1 molar ratio. However, use of
1:1 mol ratio of b-naphthol and aldehyde with urea in presence of nanocat-Fe-Mo
exclusively resulted in amidoalkyl naphthols. To optimize the reaction conditions,
we selected as model reaction that of aromatic aldehyde with 2-naphthol, urea, and
nanocat-Fe-Mo under solvent-free condition at 120–130 °C (Table 3).
In further study, condensation of b-naphthol, aromatic aldehyde, and urea was
examined in presence of different quantities of nanocat-Fe-Mo at reaction
temperature (Table 4). As indicated in Table 4, reasonable results were obtained
when the reaction was performed using 10 mol% nanocat-Fe-Mo (entry 2), with no
improvement observed on increasing the amount of nanocatalyst (entries 3, 4).
CHO
OH
O
Nanocat Fe-MO
OH
NH
R1
NH2
Solvent free, Method 1 & 2
R
R1
O
R
4
2
3
1
Method 1- Microwave
Method 2- Conventional
Scheme 2 Nanocat-Fe-Mo-catalyzed synthesis of amidoalkyl naphthols under solvent-free condition
123

S. R. Bankar, S. N. Shelke
Table 3 Optimization of reaction conditiona
S. no.
Catalyst
Solvent
Time (min)
Temp.
Yieldb
1
2
3
4
5
6
7
8
No catalyst
–
1440 min
1440 min
60 min
RT
NR
Trace
Trace
35
No catalyst
–
100 °C
RT
Nanocat-Fe-Mo
Nanocat-Fe-Mo
Nanocat-Fe-Mo
Nanocat-Fe-Mo
Nanocat-Fe-Mo
Nanocat-Fe-Mo
–
–
1440 min
30 min
RT
–
120 °C
120 °C
120 °C
120 °C
91
–
3–6 min (MW)
30–40 min
120 min
94
H2O
EtOH
80
78
aReaction condition: 2-naphthol (10 mmol), aromatic aldehyde (10 mmol), urea (12 mmol), nanocat-Fe-
Mo (10 mol%), temperature 120–130 °C, heating in sealed RBF; NR (no reaction)
bIsolated yield of pure product
Table 4 Effect of amount of
catalyst on reaction yield
Entry
Catalyst amount (mol%)
Time (h)
Yielda (%)
1
2
3
4
5
10
15
20
3
1
1
1
80
94
94
94
aIsolated yield
Recycle of Nanocat-Fe-Mo
100%
95%
90%
85%
80%
75%
Fresh
2
3
4
5
6
7
Number of Runs
Fig. 7 Reusability of nanocat-Fe3O4-MoO3
In addition to the applicability and advantages of the synthesized nanocat-Fe-Mo
in the studied reaction, its stability was also checked by recycling. After each cycle,
the catalyst was separated magnetically, washed with ethanol, and finally dried at
60 °C under vacuum to remove residual solvent. The nanocat was utilized for other
analogs of the same series under the same reaction condition. The results after
various cycles with reaction yield are shown in Fig. 7. The catalyst could be used up
to seven times without considerable loss of its initial catalytic activity. In absence of
123

Nanomagnetite-supported molybdenum oxide (nanocat-Fe-Mo)…
Table 5 Solvent effect on
reaction using nanocat-Fe-Mo
Entry
Solventa
Condition
Yieldb (%)
1
2
3
4
EtOH
Reflux, 2 h
Reflux, 3 h
Reflux, 3 h
120 °C, 30 min
78
62
58
96
DMF
n-Hexane
Solvent free
a1 mL solvent
bIsolated yield
Table 6 Effect of temperature
on reaction yield
Entry
Reaction temperature (°C)
Reaction yield (%)
1
2
3
4
70
100
120
150
57
81
94
91
nanocat-Fe-Mo, no fruitful results were obtained under the same reaction conditions
even after 12 h.
To compare the effect of solutions versus the solvent-free condition, we also
carried out the reaction in both presence and absence of solvents such as EtOH,
dimethylformamide (DMF), and n-hexane. Nearly all reactions were less efficient in
presence than absence of solvent, in terms of both reaction time and yield (Table 5).
To study the effect of temperature, the three-component reaction was carried out
at four different temperatures of 70, 100, 120, and 150 °C. Notably, the best results
were obtained at 120 °C (Table 6, entry 3). With further increase of the
temperature, no considerable increase in yield was observed (Table 6, entry 4).
Therefore, all other reactions were carried out at 120 °C.
Initially, for comparison with the reactions performed using MNPs (Tables 1, 2),
compounds 4a–h were also obtained using the conventional, refluxing method,
obtaining low yields (Tables 1, 2). In contrast, when carrying out the same reactions
in presence of MNPs by the microwave irradiation method, very clean products
were obtained in appreciably higher yield. All experiments were carried out three
times to confirm the reliability of the results.
Spectral data of some synthesized compounds
Compound 4b: 1H NMR (300 MHz CDCl3, d, ppm): 6.08 (2H, bs, –NH2),
7.17–7.18 (1H, d, –ArOH), 7.19–7.49 (7H, m, –ArH), 7.62–7.64 (4H, m, –ArH),
7.73–7.78 (1H, t, –ArH), 9.25 (1H, s, –CONH).
13C NMR (75 MHz, CDCl3): 46.31, 116.56, 119.89, 122.97, 127.67, 128.23,
128.59, 128.96, 129.05, 129.38, 131.44, 132.84, 134.32, 138.30, 149.01, 161.56.
Compound 4g: 1H NMR (300 MHz CDCl3, d, ppm): 2.05 (3H, s, –COCH3), 3.42
(3H, s, –OCH3), 5.10 (1H, bs, –CH), 6.00 (1H, bs, –Ar-OH), 7.39–7.72 (10H, m, –
ArH), 9.05 (1H, bs, –CONH).
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S. R. Bankar, S. N. Shelke
13C NMR (75 MHz, CDCl3): 32.07, 40.85, 50.76, 114.82, 115.10, 115.27,
118.83, 124.91, 126.10, 127.39, 129.25, 130.67, 130.83, 130.93, 139.94, 151.33,
160.98, 161.91, 164.24.
Conclusions
The present work provides a simple approach for one-pot MCR for synthesis of
amidoalkyl naphthols in good yield using magnetically reusable nanocat-Fe-Mo as
catalyst. This method offers various benefits such as atom economy and use of less
hazardous chemicals in an economic and environmentally friendly process.
Moreover, use of the microwave irradiation technique for direct heating of the
reaction mixture and the solvent-free mild condition continue our efforts to identify
green routes following sustainable methodologies.
Acknowledgements S.R.B. gratefully thanks the BCUD, Savitribai Phule Pune University, Pune for
granting research stipend. The authors are grateful to the Director of SAIF, Panjab University
(Chandigarh, India) for spectral analysis. S.R.B. thanks Dr. M. B. Gawande for constant inspiration. We
also acknowledge the HOD and Principal, S.S.G.M. College, Kopargaon, Ahmednagar (MH) for
providing research facilities.
Compliance with ethical standards
Conflict of interest The authors declare they have no competing financial interests.
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