Ultrasound mediation for one-pot multi-component synthesis of amidoalkyl naphthols using new magnetic nanoparticles modified by ionic liquids

Article abstract of DOI:10.1016/j.ultsonch.2013.10.024

The ionic liquid 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium acetate was immobilized on the Fe₃O₄ nanoparticles (MNPs-IL-OAc) and used as an efficient new heterogeneous nanocatalyst for the one-pot multi-component synthesis of 1

Full text of DOI:10.1016/j.ultsonch.2013.10.024

Ultrasonics Sonochemistry 21 (2014) 1132–1139
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Ultrasound mediation for one-pot multi-component synthesis
of amidoalkyl naphthols using new magnetic nanoparticles modified by
ionic liquids
⇑
Javad Safari , Zohre Zarnegar
Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, P.O. Box: 87317-51167, Kashan, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 August 2013
Received in revised form 23 October 2013
Accepted 28 October 2013
Available online 13 November 2013
The ionic liquid 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium acetate was immobilized on
the Fe O nanoparticles (MNPs-IL-OAc) and used as an efficient new heterogeneous nanocatalyst for
3 4
the one-pot multi-component synthesis of 1-amidoalkyl-2-naphthols under ultrasound irradiation. The
advantages of present combined method are the use of a low scale catalyst, easier work-up procedure,
waste-free, green and efficient synthetic entry to excellent yield of products in a high reusability and a
short reaction time.
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Amidoalkyl naphthols
Ultrasound irradiation
Magnetic nanoparticles
Multi-component reaction
Supported ionic liquids
1
. Introduction
heating or sonication conditions using various catalysts such as
montmorillonite K10 clay [21], Ce(SO
[24], Sulfamic acid [25] and cation-exchange resins [26], Ferric(III)
hydrogensulfate [27], SiO –HClO [28], and silica sulfuric acid [29].
4 2
) [22], Iodine [23], p-TSA
One-pot multicomponent reactions (MCRs) are of increasing
importance in organic synthesis in recent years [1–5] as they can
produce target products in a single operation without isolating
the intermediates and therefore reducing the reaction times and
energy input [6,7]. Particularly, in the last three decades a number
of three and four-component MCRs have been developed, specially
the Bignelli [8], Passerini [9], Ugi [10] and Mannich [11] reactions,
which have further led to renaissance of MCRs. Therefore, great ef-
forts have been and still are being made to find and develop new
MCRs.
One of the classic MCRs is the synthesis of 1-aminoalkyl-2-
naphthol derivatives as they can be easily converted into biologi-
cally active derivatives by amide hydrolysis [12,13]. Also, these
useful compounds can be also converted into 1,3-oxazines [14]
with potentially different biological activities such as antibiotic
2
4
However, some of these methods are not environmentally
friendly and suffer from one or more limitations, such as prolonged
reaction times, high reaction temperature, lower yield of the desire
product, tedious work-up, toxicity and recovery and reusability of
the catalyst. Therefore, the development of the cleaning processes
and utilizing eco-friendly and green catalysts is still challenging to
develop a safe alternate method for the synthesis of amidoalkyl
naphthols. The demand for environmentally benign procedure
with heterogeneous and reusable catalyst, promoted us to develop
a safe alternate method for the preparation of amidoalkyl naph-
thols [30].
In recent years, ionic liquids (ILs) based heterogeneous catalysis
has attracted a considerable attention under the heading of ‘‘green
chemistry’’ as they permit mutual advantages of both homoge-
neous as well as heterogeneous catalysts in organic synthesis
[31–34]. In comparison to pure Lewis acidic ILs, Imidazolium-
based ILs as heterogeneous catalyst offers more advantage like
decrease in the amount of ILs used with ease of separation and effi-
cient catalyst recovery [35,36]. Therefore, magnetic nanoparticles
(MNPs), silica and polymer-supported ILs have been tested as cat-
alysts in organic synthesis with variable results regarding activity
and recycling [37–39]. Additionally, recent studies show that MNPs
are excellent supports for ILs [39]. The supported catalysts proved
[
15], analgesic [16], antitumor [17], anticonvulsant [18], antihyper-
tensive [19], and antirheumatic properties [20]. Owing to the
biological and medicinal as well the pharmacological importance
of 1-amidoalkyl-2-naphthols, efforts have been made by various
researchers in developing MCRs for the preparation of 1-amid-
oalkyl-2-naphthols from aldehydes, b-naphthols or b-naphthyl-
amine, and amides/carbamates and/or urea under thermal and/or
⇑
Corresponding author. Tel.: +98 361 591 2320; fax: +98 361 5912397.
E-mail addresses: Safari@kashanu.ac.ir, safari_jav@yahoo.com (J. Safari).
1
350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2013.10.024

J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
1133
to be effective and easily separated from the reaction media by
2.2. Preparation of catalyst
applying an external magnetic field [39].
On the other hand, greener process involves mainly clean sol-
vents, ultrasound irradiation and microwave irradiation. Ultra-
sound has increasingly been used in synthetic organic chemistry,
because of its advantages including shorter reaction times, milder
reaction conditions, higher yields, improved selectivity and clean
reaction in comparison to classical methods [40–42]. Since in this
green technique the reaction is carried out at lower external tem-
perature relative to the usually thermal methods, the possibility of
occurrence of undesired reactions is reduced, and as a result of
cleaner reaction the workup is easier [43].
With the aim to develop a more efficient synthetic process, we
herein describe a practical and effective method for the prepara-
tion 1-amidoalkyl-2-naphthol via the one-pot reaction of b-naph-
thol, aldehydes derivatives, amides or urea in the presence of
magnetically MNPs-IL-OAc catalyst under ultrasound irradiation
and ambient conditions (Scheme 1). To the best of our knowledge,
there are no examples of the use magnetically heterogeneous nan-
ocatalyst for the ultrasound assisted synthesis of amidoalkyl
naphthols.
2.2.1. Synthesis of 1-methyl-3-(3-trimethoxysilylpropyl)-1H-imidazol-
3-ium Chloride (IL-Cl)
1-Methylimidazole (13.6 mL, 0.17 mol) and (3-chloropropyl)
trimethoxysilane (31 mL, 0.17 mol) were refluxed at 80 °C for
3 days without solvent under Ar atmosphere. The unreacted mate-
rials were washed by diethyl ether (3 Â 8 mL). The residue was
evaporated under reduced pressure, to yield a yellowish viscous li-
quid isolated yield was 97% [44].
À1
1
FT-IR (KBr, cm ): 1656, 1612, 1584. H NMR (400 MHz, CDCl
(ppm): 10.22 (broad, 1H, Are-H), 7.59 (1H, dd, J = 7.89 and
2.86 Hz, Are-H), 7.26 (1H, dd, J = 7.89 and 2.79 Hz, Are-H), 4.06
3
):
d
H
(2H, t, J = 7.25 Hz, –NCH
OCH
SiCH
2
), 3.86 (3H, s, –NCH
), 0.37 (2H, t, J = 7.09 Hz,
, TMS): d = 138.13, 123.34,
3
), 3.30 (9H, s,
3
), 1.74 (2H, tt, J = 7.14 Hz, –CH
2
1
3
2
).
C NMR (100 MHz, CDCl
3
C
121.58, 58.53, 51.66, 36.51, 24.32, 18.2, 7.03. Anal. Calcd.: C,
48.45; H, 8.39; N, 8.69. Found: C, 48.35; H, 8.32; N, 8.79.
2
.2.2. Modification of magnetic nanoparticles with IL-Cl to obtain
MNPs-IL-Cl
Fe -MNPs were prepared using chemical coprecipitation de-
scribed in the literature [39] and subsequently freshly prepared
Fe nanoparticles (2 g) were suspended in ethanol (95%,
50 mL), and sonicated for 30 min. The resulted suspension was
mechanically stirred, followed by addition of a solution of ethanol
95%, 100 mL) containing IL (6 g, 18.5 mmol) and concentrated
ammonia (28%, 1 mL). Stirring under Ar was continued for 36 h.
The modified Fe nanoparticles were magnetically separated
3 4
O
2
. Experimental
3 4
O
2
2.1. Chemicals and apparatus
(
Chemical reagents in high purity were purchased from Merck
and Aldrich and were used without further purification. Melting
3 4
O
points were determined in open capillaries using an Electrother-
mal Mk3 apparatus and are uncorrected. 1H NMR and 13C NMR
and washed three times with ethanol (95%, 50 mL) and then dis-
solved in methanol (200 mL) and stirred mechanically for 30 min.
Ether (50 mL) was added and the modified nanoparticles were
magnetically separated, washed with ether (50 mL) and dried un-
der a vacuum for 24 h and the nanoparticles of immobilized chlo-
ride ionic liquid was prepared [39].
spectra were recorded with a Bruker DRX-400 spectrometer at
4
00 and 100 MHz respectively. FT-IR spectra were obtained with
À1
potassium bromide pellets in the range 400–4000 cm with a Per-
kin–Elmer 550 spectrometer. Nanostructures were characterized
using a Holland Philips Xpert X-ray powder diffraction (XRD) dif-
fractometer (CuK, radiation, k = 0.154056 nm), at a scanning speed
of 2°/min from 10° to 100° (2h). Scanning electron microscope
2
.2.3. Anion exchange in the immobilized chloride ionic liquid (MNPs-
IL-OAc)
Immobilized chloride ionic liquid on MNPs and an excess
(
SEM) was performed on a FEI Quanta 200 SEM operated at a
2
0 kV accelerating voltage. The samples for SEM were prepared
amount of NaOAc were added into the deionized water and stirred
for 24 h at room temperature. NaCl which was prepared during the
exchange of chloride anion with OAc, was removed by washing
by spreading a small drop containing nanoparticles onto a silicon
wafer and being dried almost completely in air at room tempera-
ture for 2 h, and then were transferred onto SEM conductive tapes.
The transferred sample was coated with a thin layer of gold before
measurement. Purity of the compounds synthesized was moni-
tored by TLC, visualizing with ultraviolet light. A multiwave ultra-
sonic generator (Sonicator 3200; Bandelin, MS 73, Germany),
equipped with a converter/transducer and titanium oscillator
with deionized water. Immobilized acetate ionic liquid on Fe
nanoparticles was obtained as brownish black powder
Scheme 2).
3 4
O
a
(
2.3. General procedure for the synthesis of amidoalkyl naphthols
2.3.1. Typical heating method (method A)
A mixture of b-naphthol (5 mmol), aldehyde (5 mmol), amide/
urea (5.5 mmol) and MNPs-IL-OAc (0.04 g) were taken in round
bottom flask and stirred and heated at 100 °C for appropriate times
(monitored by TLC). Then, ethanol (20 mL) was added and the cat-
alyst was separated by an external magnet. The reaction mixture
was evaporated to remove solvent and the crystalline material left
was taken up in ethanol:water (1:3) for recrystallization.
(
horn), 12.5 mm in diameter, operating at 30 kHz with a maximum
power output of 200 W, was used for the ultrasonic irradiation. The
ultrasonic generator automatically adjusted the power level. A
circulating water bath (DC2006, Shanghai Hengping Apparatus
Factory) with an accuracy of 0.1 K was adopted to keep the reaction
temperature at a constant. The known products were characterized
1
13
by comparison of their spectral ( H NMR and C NMR) and phys-
ical data with those of authentic samples. All yields refer to iso-
lated products after purification.
R1
O
OH
O
3
O
MNPs-IL-OAc
)))), 30°C
2
+
1
R
+
R2
N
H
R
H N
H
2
OH
1
2
4
a-x
Scheme 1. One-pot synthesis of 1-amidoalkyl-2-naphthol catalyzed by MNPs-IL-OAc under ultrasound irradiation at ambient conditions.

1
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J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
3 4
Scheme 2. Preparation steps for fabricating 1-methyl-3-(3-trimethoxysilylpropyl)-1H-imidazol-3-ium acetar-functionalized magnetic Fe O nanoparticles.
2.3.2. Ultrasound irradiation method (method B)
3 4
Fig. 4 presents the magnetization curve for Fe O nanoparticles
A mixture of b-naphthol (5 mmol), a liquid aldehyde (5 mmol),
and MNPs-IL-OAc. Room temperature specific magnetization (M)
an amide/urea (6 mmol), and MNPs-IL-OAc (0.04 g), taken in a flask
50 mL), was sonicated at 30 kHz frequency and 50 W power while
versus applied magnetic field (H) curve measurements of the sam-
À1
(
ple indicate a saturation magnetization value (M
lower than that of bare MNPs (60.6 emu g ) due to the coated
shell [39].
s
) of 52.2 emu g
,
À1
pure argon was continuously purged in the reaction at 30 °C (by
circulating water) for appropriate times. For solid aldehydes,
dichloroethane (10 mL) was added to the mixture. After the TLC
indicates the disappearance of starting materials, ethanol (20 mL)
was added and the catalyst was separated by an external magnet
and reused as such for the next experiment. The reaction mixture
was concentrated on a rotary evaporator under reduced pressure
and the crude residue was purified by crystallization in etha-
nol:water (1:3) to afford pure amidoalkyl naphthol.
3.2. Evaluation of the catalytic activity of MNPs-ILs through the
synthesis of amidoalkyl naphthols
The concept of supported ionic liquid catalysis (SILC) was first
developed by Mehnert’s group in 2002 [46,47]. SILC, especially
MNPs supported ILs, have emerged as a new class of pseudo-homo-
geneous–heterogeneous nanocatalyst. An important feature of
these nanocatalysts is simple separation of them using an external
magnet without filtration. Also, they have high catalytic activity
owing to a uniform distribution of catalytic active species within.
Therefore, we are reporting here an efficient MNPs-IL-OAc cata-
lyzed and ultrasound induced much improved modification to syn-
thesis of 1-aminoalkyl-2-naphthol derivatives. Moreover, the
ultrasound technique represented a better procedure in terms of
the higher yield, milder reaction conditions.
In order to consider the effects of this nanocatalyst under ultra-
sound irradiation; catalytic activity of same types of magnetic nan-
ocatalyst such as MNPs, MNP-IL-Cl and MNP-IL-OAc were
compared in the reaction of aldehyde, b-naphthol and acetamide
as the model substrates at 30 °C (Scheme 3). Obtain results were
indicated that in absence of catalyst, trace amount of product
was generated but in presence of MNP-IL-OAc nanoparticles the
reaction proceeds in high yield. Thereafter, the reaction was evalu-
ated by varying the concentrations of catalyst (0.01–0.04 g). The
resulting of Scheme 3 shows the optimum amount of the catalyst
was (0.04) of MNP-IL-OAc nanoparticles which increasing of this
amount did not show any significant change in yield.
3
. Results and discussion
3.1. Characterization of MNPs-IL-OAc as catalyst
The magnetite nanoparticles of 20 nm were prepared by copre-
cipitation of iron(II) and iron(III) ions in basic solution at 85 °C
using the method described by Massart [45]. For the surface mod-
ification, the MNPs coated with N-methyl-3-(3-trimethoxysilylpro-
pyl) imidazolium acetate (Scheme 2).
Fig. 1 shows the Fourier transform infrared (FTIR) spectra of
À1
MNPs. The Fe–O stretching vibration near 580 cm , O–H stretch-
À1
ing vibration near 3432 cm and O–H deformed vibration near
À1
1
625 cm were observed for both in Fig. 1(a) and (b). The signifi-
cant features observed for Fig. 1(b) are the appearance of the peaks
À1
À1
at 1010 cm (Si–O stretching), 2800 cm (–CH
2
stretching) and
À
at 1575 (COO stretching). These results provided the evidences
that ILs were successfully attached to the surface of Fe
nanoparticles.
3 4
O
Fig. 2 presents the XRD-diffraction patterns of MNPs and MNPs-
IL-OAc. The position and relative intensities of all peaks confirm
well with standard XRD pattern of Fe
417) indicating retention of the crystalline cubic spinel structure
during functionalization of Fe nanoparticles by imidazolium io-
nic liquid [39]. It is implied that the resultant nanoparticles are
pure Fe with a spinel structure and that the grafting process
did not induced any phase change of Fe
The SEM image shows that magnetite nanoparticles have a
mean diameter of about 20 nm and a nearly spherical shape in
Fig. 3(a) and (b) shows that MNPs-IL-OAc nanoparticles still keep
3
O
4
(JCPDS card No. 79-
Next, we carried out the reaction in presence of various solvents
and the results are presented in Table 1. It was found that dichlo-
roethane accelerated the reaction and therefore high yields were
obtained for all solid aromatic aldehydes including 3-nitrobenzal-
dehyde. These solvents differ with respect to polarity and have sig-
nificant cavitational intensity. Dichloroethane (DCE) was found to
be the best solvent (Cav. Int. 39%) [25]. Different molar ratios of re-
agents were examined and the best result was obtained with
1:1:1.2:0.008 ratios of b-naphthol, aldehyde, amide/urea and
MNP-IL-OAc.
0
3 4
O
3 4
O
3 4
O .
the morphological properties of Fe
particle size and smoother surface, which silica are uniform coated
on the Fe nanoparticles to form MNPs supported ILs.
3 4
O except for a slightly larger
After optimizing the reaction conditions, we have extended the
procedure using different kinds of aldehyde carrying either
3 4
O

J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
1135
Fig. 1. The comparative FT-IR spectra for (a) MNPs, (b) MNP-IL-OAc.
Fig. 2. XRD patterns of (a) MNPs, (b) MNP-IL-OAc.

1
136
J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
Fig. 3. The SEM image of (a) MNPs (b) MNPs-IL-OAc.
Fig. 4. Magnetization curves for the prepared MNPs and MNPs-IL-OAc at room temperature.
Scheme 3. Optimization of the model reaction using magnetic catalysts under ultrasonic irradiation.

J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
1137
Table 1
Reaction of 3-nitrobenzaldehyde (5 mmol), b-naphthol (5 mmol) and acetamide
6 mmol) to obtain in the presence of MNP-IL-OAc in different solvents and under
solvent-free condition.
98
96
(
9
8
Entry
Solvent
Yielda (%)
Time (min)
9
4
9
6
1
2
3
4
5
6
7
8
CH
3
CH
3
CH
3
CH
OH
CN
2
OH
60
53
45
70
85
98
20
20
20
20
20
20
60
60
9
5
95
92
93
9
2
92
CHCl
CH Cl
Cl
3
9
8
0
8
2
2
C
2
H
4
2
n-Hexane
Solvent-free condition
No reaction
65
1
2
3
4
5
6
7
a
Run
Isolated yield.
Fig. 5. Reusability and recycling of nanocatalyst for synthesis of 4a under
ultrasound irradiation.
electron-donating or -withdrawing substituents. In all cases, aro-
matic aldehydes with substituent carrying either electron-donat-
ing or electron withdrawing groups reacted successfully and gave
the products in excellent yields.
The study was extended to prepare various amidoalkyl naph-
thols using MNP-IL-OAc nanoparticles. For explain the efficiency
and scope of the present process and to delineate the role of ultra-
sound, reactions were compared at heating conditions (method A)
and ultrasonic irradiation (method B) in ambient conditions at
30 °C in the presence of MNP-IL-OAc 0.04 g (Table 2). As illustrated
in Table 2, method B in comparison with method A is better in both
yields and especially in the reaction times. Once more, ultrasound
enhanced the rate of a reaction and, consequently, reduced energy
consumption. The driving force for the increased efficiency of for-
mation of amidoalkyl naphthols by ultrasound is because of the in-
crease in the temperature due to the formation of hot spots; and
Table 2
a
One-pot synthesis of amidoalkyl naphthols in the presence of MNPs-IL-OAc under heating conditions and sonication (method A and B).
Entry
R1
R2
Product
Method B
Method A
Mp (lit. mp) [Ref.]
Time (min)/yieldb (%)
Time (min)/Yieldb (%)
1
2
3
4
5
6
7
8
9
C
6
H
5
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
3
3
3
3
3
4a
4b
4c
4d
4e
4g
4i
10/95
20/91
30/93
20/92
20/98
20/93
20/94
15/95
20/93
20/92
20/90
15/95
25/97
25/92
10/90
15/92
90/90
242–244 [245–246] [7]
223–224 [222–223] [7]
120–122 [123–125] [7]
184–186 [183–185] [7]
253–254 [256–258] [51]
202–203 [201–203] [7]
214–216 [213–215] [7]
217–219 [218–219] [50]
231–233 [231–233] [51]
229–230 [229–230] [51]
222–223 [224–226] [52]
238–240 [237–238] [52]
230–233 [232–234] [52]
209–211 [208–210] [52]
177–178 [177–179] [52]
190–192 [193] [48]
4-CH
4-N(CH
4-CH OC
3-NO
2,4-Cl
2-ClC
2-NO
2,3-(CH
C
CH
C
3-NO
4-CH
C
3
C
6
H
4
150/87
180/85
190/85
60/97
180/93
100/88
80/92
180/90
150/90
150/87
100/85
90/92
3
)
2
C
6
H
4
3
6
H
4
2 6 4
C H
2
C
6
H
3
6 4
H
2
C
6
H
4
4j
4l
3
O)
2
C
6
H
3
10
11
12
13
14
15
16
10
H
7
4m
4n
4o
4p
4q
4r
4s
3
CH
2
CH
2
6
H
5
C
C
C
6
H
6
H
6
H
5
5
5
2 6 4
C H
3
OC
6
H
4
210/80
90/82
85/88
6
H
5
NH
NH
2
3-NO
2
C
6
H
4
2
a
Reaction conditions: b-naphthol 5 mmol, aldehyde 5 mmol, amide 6 mmol and MNPs-IL-OAc 0.04 g.
Isolated yields.
b
MNP-IL-OAc
O
OH
H
R1
OH
R1
.
.
H
O
-
H O
2
O
R1
o-QMs
O
O
N
H
R 2
R1
..
2
2
R1
H N
R
O
OH
o-QMs
Scheme 4. Possible mechanism for the synthesis of amidoalkyl naphthol using MNP-IL-OAc.

1
138
J. Safari, Z. Zarnegar / Ultrasonics Sonochemistry 21 (2014) 1132–1139
Fig. 6. XRD patterns of recovered MNPs-IL-OAc after five recovery.
due to increase in the reactant contact surface area through cavita-
tion phenomenon. Upon irradiation with ultrasound, the forma-
tion, growth, and implosive collapse of bubbles can create
extreme chemical and physical conditions in solid/liquid systems,
leading to short-lived localized hot-spots which produce relatively
high temperature for this one-pot condensation reaction to occur,
and the rate of the reaction got well accelerated under sonic con-
dition [49]. Moreover, when cavitation phenomenon occurs near
the solid catalyst surface, cavity collapse is non-spherical and as
a result of this a liquid jet will be formed which is targeted at
the surface and this effect is equivalent to high-pressure/high-
velocity liquid. These jets activate the heterogeneous catalyst and
increase the mass transfer to the surface by the disruption of the
interfacial boundary layers as well as dislodging the material occu-
pying the inactive sites [49c].
according to the magnetite phase (JCPDS card No. 750449), and so
there is no considerable change in its magnetic phase. Thus, the
magnetite nanocatalyst is stable during synthesis of amidoalkyl
naphthols under ultrasound irradiation.
Compared to other commonly employed methods for the
preparation of amidoalkyl naphthols, the methodology presented
herein also provided a novel, convenient and efficient access to a
wide variety of amidoalkyl-2-naphthols in a one-pot manner under
ultrasound irradiation. Ultrasound process as a synthetic green ap-
proach has gradually been used in this organic synthesis. Combin-
ing the advantages of ultrasonic irradiation and nanotechnology,
this method provides an efficient and much improved modification
of the multi-component synthesis of amidoalkyl naphthols.
4
. Conclusions
A proposed mechanism for this reaction was outlined in
Scheme 4. The MNP-IL-OAc as a Lewis acid participate in the reac-
tion which activate the aldehyde followed by nucleophilic addition
of b-naphthol forming the intermediate ortho-quinone methides
Simultaneously application of the ultrasonic and MNPs sup-
ported ILs as combined catalytic system in preparation of the some
biologically interesting organic molecules via multicomponent
reaction. Undoubtedly, as part of the continuing exploration of
ultrasonic/magnetic nanocatalyst for the green organic reactions,
these methods have great prospects of applications in organic
syntheses, pharmacy and industrial processes that which this
report opens an important field to the use of green strategy in or-
ganic process. At the outset of our studies, there was few literature
precedent for the direct application of magnetically separable
catalyst in combination with ultrasound.
(
o-QMs). On the basis of this mechanism, the implosive collapse
of the cavitations period of the sound waves generates the bubbles
at localized sites in the liquid phase. When these bubbles burst, it
results in high temperature and high pressure which facilitate the
intermediate o-QMs in the presence of solid catalyst. Then o-QMs
reacted with amides or urea via a Michael addition to afford the ex-
pected amidoalkyl naphthols [48]. Ultrasound provides an unusual
mechanism due to the immense temperatures and pressures and
the extraordinary heating rate generated by cavitation bubble col-
lapse. When the catalyst is a solid, the ultrasonic irradiation has
several additional enhancement effects [49]. Since this system is
a heterogeneous catalytic system, it seems that the main effect of
US is due to its mechanical effect. On the other hand, during the
sonication, break-up of the surface structure allows penetration
of reactants and/or release of materials from surface and acceler-
ated motion of suspended particles leads to better mass transfer
Acknowledgments
We gratefully acknowledge the financial support from the
Research Council of the University of Kashan for supporting this
work by Grant NO. 256722/16.
References
[
49].
The possibility of recycling the catalyst was examined after
[
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