Nano Al2O3: An efficient and recyclable nanocatalyst for the one-pot preparation of 1-amidoalkyl-2-naphthols under solvent-free conditions

Article abstract of DOI:10.1007/s11164-015-2062-x

A direct approach for the one-pot preparation of 1-amidoalkyl-2-naphthols via three-component reaction of β-naphthol, aromatic aldehydes, and acetamide in the presence of nano-structured Al₂O₃ under solvent-free conditions has been d

Full text of DOI:10.1007/s11164-015-2062-x

Res Chem Intermed
DOI 10.1007/s11164-015-2062-x
Nano Al O : an efficient and recyclable nanocatalyst
2
3
for the one-pot preparation of 1-amidoalkyl-2-
naphthols under solvent-free conditions
1
1
•
Ali Reza Kiasat
Seyyed Jafar Saghanezhad
•
Lida Hemat-Alian
2
Received: 25 December 2014 / Accepted: 16 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A direct approach for the one-pot preparation of 1-amidoalkyl-2-naph-
thols via three-component reaction of b-naphthol, aromatic aldehydes, and ac-
etamide in the presence of nano-structured Al O under solvent-free conditions has
2
3
been developed. Some benefits of this procedure are: recyclability of the catalyst,
short reaction time, high yield of the products, environmentally benign procedure,
and facile work-up.
Keywords Nano alumina Á 1-Aminoalkyl-2-naphthols Á Multi-component reaction
(
MCR) Á Solvent-free conditions
Introduction
One-pot multicomponent reactions (MCRs) have attracted interest due to their
simplicity and ability to produce highly functionalized organic molecules and
pharmacologically important heterocyclic compounds [1]. Some examples of MCRs
are Bigenilli, Mannich, Ugi, and Strecker reactions [2–5].
Due to the importance of 1-amidoalkyl-2-naphthols and the capability of their
conversion into important biologically active aminoalkyl naphthol derivatives by an
amide hydrolysis reaction, their synthesis is of great importance [6]. Although
several catalysts have been reported for the synthesis of 1-amidoalkyl-2-naphthols,
such as K CoW O Á3H O [7], sulfamic acid [8], HClO –SiO [9], P O [10],
5
12 40
2
4
2
2 5
zwitterionic-type molten salt [11], functionalized imidazolium salts [12], Fe(HSO )
4
3
[
13], FeCl -SiO [14], nano-sulfated zirconia [15], and silica chloride [16],
3
2
&
Ali Reza Kiasat
akiasat@scu.ac.ir
1
2
Chemistry Department, College of Science, Shahid Chamran University,
61357-4-3169 Ahvaz, Iran
ACECR-Production Technology Research Institute, Ahvaz, Iran
123

A. R. Kiasat et al.
however, some of these protocols suffer from drawbacks, such as the use of toxic,
highly acidic and/or expensive catalysts, low yields, or prolonged reaction times.
Thus, new catalysts with high ability to overcome some of these disadvantages are
still needed. Thakur and coworkers [17] have stated that certain nanoparticles can
enhance some organic reactions, which they have named ‘‘nanoparticle-catalyzed
organic synthesis enhancement (NOSE)’’.
With this notion in mind, and in continuation of our effort in the synthesis of
novel catalysts and their application in organic synthesis [18, 19], nano-structured
Al O has been utilized as a heterogeneous catalyst for the one-pot preparation of
2
3
1-amidoalkyl-2-naphthols through the three-component reaction of b-naphthol,
aromatic aldehydes, and acetamide under solvent-free conditions (Scheme 1).
Results and discussion
To find the optimum quantity of nano-structured Al O (Fig. 1), the reaction of
3
2
benzaldehyde (1 mmol), b-naphthol (1 mmol), and acetamide (1.4 mmol) was
carried out under solvent-free conditions using different quantities of catalyst at
1
to give the product in minimum time. To verify the nano Al O dimensions, we took
10 °C (Table 1). It was found out that 0.07 g (68.7 mol%) of the catalyst is enough
2
3
its SEM image (Fig. 1). The Al O nanoparticles are about 50 nm.
2
3
In the next step, we decided to perform the reaction in some organic solvents to
evaluate the efficiency of this procedure. It was found out that performing the
reaction under solvent-free conditions is worthwhile according to reaction time and
also yield of the product (Table 2).
Optimization of the temperature and amount of acetamide for this reaction under
solvent-free conditions was performed. It was found out that conducting the reaction
at 110 °C and 1.4 mmol of acetamide gives a higher yield of the desired product in a
shorter reaction time (Table 3).
Accordingly, with optimum ratio of the reactants in hand, 1:1:1.4 of aromatic
aldehyde, b-naphthol, and acetamide and 68.7 mol% of nano alumina as the
catalyst, at 110 °C, we decided to evaluate the catalytic activity of the catalyst in the
preparation of 1-amidoalkyl-2-naphthol derivatives. This procedure is simple, mild,
and effective, which leads to good-to-excellent yield of the products. A wide variety
CHO
OH
Ar
o
Solvent-Free, 110 C
OH
O
+
Nano-Al O (68.7 mol%)
2
3
Ar
NH
O
H C
NH2
H C
3
3
Scheme1 Three-component synthesis of 1-amidoalkyl-2-naphthols
1
23

2 3
Nano Al O : an efficient and recyclable nanocatalyst for…
2 3
Fig. 1 SEM image of nano-structured Al O
2 3
Table 1 Optimization of the quantity of nano-structured Al O in the reaction of benzaldehyde (1 m-
mol), b-naphthol (1 mmol), and acetamide (1.4 mmol) under solvent-free conditions at 110 °C
Entry
Catalyst (mol%)
Time (min)
Yield (%)
1
2
3
4
5
19.6
39.2
49
60
30
30
15
15
65
76
82
94
92
68.7
78.5
Table 2 Reaction of benzaldehyde (1 mmol), b-naphthol (1 mmol), and acetamide (1.4 mmol) to obtain
amidoalkyl-2-naphthols in the presence of nano alumina in different solvents and under solvent-free
conditions
Entry
Solvent
Condition of reaction
Time (h)
Yield (%)
1
2
3
4
EtOH
Reflux
Reflux
Reflux
110 °C
12
68
78
75
94
Water
12
DMF
12
Solvent-free
0.25
of aromatic aldehydes, containing both electron-withdrawing and -donating
substitutes gave the corresponding products (Table 4).
As it is evident from Table 4, nano-structured Al O gives products in short
2
3
reaction time and high yield. A mechanistic rationale for this procedure is shown in
Scheme 2. It is postulated that the nanocatalyst activates the carbonyl group of
123

A. R. Kiasat et al.
Table 3 Optimization temperature and amount of acetamide in the synthesis of 1-amidoalkyl-b-
naphthols
Entry
Temperature (°C)
Acetamide (mmol)
Time (min)
Yield (%)
1
2
3
4
5
25
60
1
120
80
40
15
15
52
64
81
88
94
1.2
1.2
1.2
1.4
80
110
110
aldehyde, so that the nucleophilic attack of b-naphthol is promoted. After
Knoevenagel condensation, acetamide is added with Michael addition, which is
also promoted with the nanocatalyst. Afterwards, with hydrogen transfer, the
product is formed.
With the increasing respect for environmental aspects of chemical processes, the
recyclability of the catalyst was assessed. It was found out that a small decrease in
catalyst activity was observed after four runs (Fig. 2).
To show the merit of the present work in comparison with reported results in the
9
literature, we compared the reactions of nano-Al O with HClO . SiO
2
,
2
3
15
4
1
1
14,
16
zwitterionic salt , SiO ÁFeCl nano-sulfated zirconia , and silica chloride in
2
3
the synthesis of 1-amidomethyl-2- naphthol derivatives. As shown in Table 5, some
of the reported catalysts are Brønsted or Lewis acids (entries 1, 2, 5) or need high
loading of the catalyst (entry 3) or give low yield of the product (entry 4). These
results clearly confirm that nano alumina is an equally or more efficient catalyst for
this reaction.
It is also noteworthy that to elucidate nano alumina as the catalyst, we decided to
perform a comparative reaction with alumina to see if being nano for the catalyst is
important or not. The result demonstrates that nano alumina gives the product in a
shorter reaction time (Table 6).
Experimental
General
All commercially available chemicals were purchased from Fluka and Merck
companies and used without further purification. Products were characterized by
their physical constant and comparison with authentic samples. Reaction monitoring
was accomplished by TLC on silica gel POLYGRAM SILG/UV 254 plates. The IR
spectra were recorded on a BOMEM MB-Series 1998 FT-IR spectrophotometer
-
1
using KBr pellets for the samples and the catalyst in the range of 4000–400 cm
1
.
H and C NMR spectra were recorded in CDCl and DMSO-d on a Bruker
13
3
6
Avance DPX 400-MHz spectrometer using TMS as the internal standard. The SEM
1
23

2 3
Nano Al O : an efficient and recyclable nanocatalyst for…
Table 4 Preparation of 1-amidoalkyl-2-naphthol derivatives in the presence of nano alumina as the
catalyst under solvent-free conditions at 110 °C
Entry
Ar
Product
Time (min)
Yield (%)
Melting point (reported) (°C)
1
C
6
H
5
15
94
240–242 (238–240 [12])
OH
NH
H3C
O
2
3
4-Me C
6
H
4
85
40
70
97
213–215 (215–216 [13])
225–227 (223–225 [13])
OH
NH
Me
H3C
O
4-Cl C
6
H
4
OH
NH
H3C
O
Cl
4
5
4-OMe C
6
H
4
190
30
84
95
183–185 (183–185 [13])
249–251 (248–249 [13])
OH
NH
MeO
3
H C
O
3-F C
6
H
4
OH
NH
F
H3C
O
6
7
4-Br C
6
H
4
30
30
85
80
229–231 (230–232 [22])
242–244 (246–248 [12])
OH
NH
Br
H3C
O
2 6 4
4-NO C H
OH
NHCOMe
O2N
8
9
3-OMe C
6
H
3
120
75
202–204 (202 [21])
OH
NH
H3C
OMe
O
2-NO
2
2
C
C
6
H
H
4
90
70
80
92
179–181 (179–182 [13])
241–243 (238–240 [12])
OH
NHCOMe
NO2
1
1
0
1
3-NO
6
4
OH
NHCOMe
NO2
2-OH C
6
H
4
45
85
228–230 (234–236 [20])
OH
NH
HO
H3C
O
analyses were carried out using a LEO 1455VP scanning electron microscope
operating at 1–30 kV. Alumina nanoparticles (Al O , alpha/gamma, 99.9 %,
2
3
5
0 nm) were purchased from US Research Nanomaterials, Inc.
123

A. R. Kiasat et al.
H
HO
(2)
Ar
H
O
HO
H
OH
O-H
OH
-
H O
2
H+
Ar
H
+
-
(1)
H
O
H
O
Ar
2
O
H
N
O
Ar
N
Ar
CH3
O
CH3
OH
H N
CH3
O
2
H+
-
H+
+
(3)
(
4)
(
5)
Scheme 2 Suggested mechanism for the preparation of 1-amidoalkyl-2-naphthols catalyzed by nano-
structured Al
2 3
O
9
4
9
5
9
2
9
1
9
0
88
8
5
1
2
3
4
Run
Fig. 2 Reusability of nano alumina (68.7 mol%) in the synthesis of benzaldehyde, b-naphthol, and
acetamide, under solvent-free conditions
2 3
Table 5 Comparison of nano-Al O with reported catalysts in the reaction of benzaldehyde, b-naphthol,
and acetamide
Entry
Catalyst
Time (min)
Amount
of catalyst (g)
Yield (%)
1
2
3
4
5
6
SiO
SiO
2
ÁHClO
ÁFeCl
4
[9]
40
11
32
20
9
0.012
0.025
0.2
89
86
91
80
95
94
2
3
[14]
Nano-sulfated zirconia [15]
Zwitterionic salt [11]
Silica chloride [16]
0.041
0.1
Nano-Al
2
O
3
15
0.07
General procedure for the preparation of 1-amidoalkyl-2-naphthols
A mixture of benzaldehyde (1 mmol),b –naphthol (1 mmol), acetamide (1.4 mmol),
and 68.7 mol% (0.07 g) nano-structured Al O was heated in an oil bath at 110 °C.
Completion of the reaction was followed by TLC [ethyl acetate/n-hexane (2:5)].
2
3
1
23

2 3
Nano Al O : an efficient and recyclable nanocatalyst for…
Table 6 Comparative study of
nano alumina and bulk alumina
in synthesis of 1-amidoalkyl-2-
naphthols
Entry
Catalyst
Time (min)
1
2
Nano alumina
Alumina
15
105
After completion of the reaction, the insoluble crude product was dissolved in hot
ethanol. Then nano-structured Al O was removed by filtration and the filtrate was
2
3
cooled to 25 °C. At the end, the crude solid was recrystallized from ethanol–water
to afford the pure product.
N-[(2-hydroxy-phenyl)-(2-hydroxy-napthalen-1-yl)- methyl]-acetamide (Table 4,
entry 11)
-
IR (KBr): cm 3399.51, 3225.66, 1634.82, 1538.21, 1460.97; HNMR (400 MHz,
1
1
DMSO-d ): d 1.88 (3H), 7.006 (1H), 7.67 (NH), 6.68-8.35 (Haromat), 9.39 (OH), 9.83
6
1
3
(
OH); CNMR (100 MHz, DMSO-d ): d 23.124, 45.31, 115.49-133.123 (Caromat),
6
1
53.566 (C–OH), 155.057 (C–OH), 168.928 (CO)
Conclusions
In conclusion, we have described a facile and environmentally friendly procedure
for the synthesis of 1-amidoalkyl-2-naphthols in the presence of nano-structured
alumina as an environmentally safe heterogeneous catalyst under solvent-free
conditions. This method offers several advantages including high yields, short
reaction times, easy work-up, recyclable catalyst, and performance of the reaction
under green conditions.
Acknowledgements We gratefully acknowledge the support of this work by Shahid Chamran
University Research Council.
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