Silica chloride catalyzed efficient route to novel 1-amidoalkyl-2- naphthylamines under sonic condition in water

Article abstract of DOI:10.1016/j.ultsonch.2012.06.008

A one-pot three-component condensation of an aldehyde, 2-naphthylamine, and acetamide has been achieved by sonication at 35 kHz. The reaction is catalysed by silica chloride in aqueous medium. This protocol afforded corresponding 1-amidoalkyl-2-naphthylamines in shorter reaction durations, and in high yields. The method involves simple work-up procedure, and avoids use of hazardous reagents.

Full text of DOI:10.1016/j.ultsonch.2012.06.008

Ultrasonics Sonochemistry 20 (2013) 303–307
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Silica chloride catalyzed efficient route to novel 1-amidoalkyl-2-naphthylamines
under sonic condition in water
⇑
Bandita Datta, M.A. Pasha
Department of Studies in Chemistry, Bangalore University, Central College Campus, Bengaluru, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A one-pot three-component condensation of an aldehyde, 2-naphthylamine, and acetamide has been
achieved by sonication at 35 kHz. The reaction is catalysed by silica chloride in aqueous medium. This
protocol afforded corresponding 1-amidoalkyl-2-naphthylamines in shorter reaction durations, and in
high yields. The method involves simple work-up procedure, and avoids use of hazardous reagents.
Ó 2012 Elsevier B.V. All rights reserved.
Received 30 January 2012
Received in revised form 15 June 2012
Accepted 19 June 2012
Available online 28 June 2012
Keywords:
Aldehydes
2-Naphthylamine
Acetamide
Silica chloride
Water
Ultrasound
1. Introduction
tions like Ugi [6] and Passerini reactions [7]. Furthermore, the
scope of this pharmacophore has been increased by the identifica-
Multicomponent reactions (MCRs) have drawn high efforts in
recent years owing to exceptional synthetic efficiency, intrinsic
atom economy, high selectivity, and procedural simplicity [1].
These reactions constitute a valuable approach for the creation of
large libraries of structurally related, drug-like compounds, there-
by enabling identification and leading to optimization in drug dis-
covery [2]. In a true sense, MCRs represent environment friendly
processes by reducing the number of steps, energy consumption
and waste production.
The application of ultrasound in organic synthesis has been
increasing because of its advantages including shorter reaction
times, milder reaction conditions and higher yields in comparison
to classical methods [3]. Since in this technique the reaction is car-
ried out normally at lower external temperature relative to the
usually thermal methods, the possibility of occurrence of unde-
sired reactions is reduced, and as a result of cleaner reaction the
workup is easier [4].
tion of these molecules as the precursors of aminoamides which
find application in the synthesis of dendrimers [8]. Aminoamides
can also be used in the synthesis of metal complexes [9] and could
be employed as adjuvents for drugs [10]. Derivatives of aminoa-
mide have also been shown to have antioxidant and anti-inflam-
matory properties [11]. In view of this we have synthesized some
novel amidoalkyl-2-naphthylamine derivatives from aromatic
aldehydes, 2-naphthylamine and acetamide.
The need to reduce the amount of toxic waste and byproduct
arising from chemical process requires increasing emphasis on
the use of less toxic and environmentally compatible materials in
the design of new synthetic methods [12]. One of the most prom-
ising approaches is use of water as a reaction medium. Breslow,
who showed that hydrophobic effects and polarity effect could
strongly enhance the rate of several organic reactions, rediscovered
the use of water as a solvent in organic chemistry in the 1980s [13].
There has been growing recognition that water is an attractive
medium for many organic reactions [14] and many MCRs in aque-
ous medium have been reported [15]. However, to the best of our
knowledge, we are the first ones to report the present synthesis of
amidoalkyl-2-naphthylamine derivatives under aqueous sonic
condition. As a consequence of our interest in the aqueous medium
organic synthesis [16a] and our continual work on the synthesis of
biologically important molecules [16b,c]. We investigated a first
three-component one-pot synthesis of 1-amidoalkyl-2-naphthyl-
amines from 2-naphthylamine in the presence of silica-chloride
The amide group is an essential building block for numerous
natural products, synthetic pharmaceuticals, and a wide variety
of biologically active compounds [5]. As a consequence; the devel-
opment of general methods for the synthesis of amide derivatives
has been the subject of considerable synthetic efforts and still re-
quires attention. Amide moiety has been involved in many reac-
⇑
Corresponding author. Tel.: +91 80 22961337; fax: +91 80 22961331.
E-mail address: mafpasha@gmail.com (M.A. Pasha).
1350-4177/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2012.06.008

304
B. Datta, M.A. Pasha / Ultrasonics Sonochemistry 20 (2013) 303–307
1
1H NMR (DMSO–d6, 400 MHz) d: 1.94 (s, 3H); 3.67 (s, 3H);
2
O
6.28 (s, 1H); 6.80 (s, 1H); 7.05 (d, J = 8 Hz, 3H); 7.18–7.26
(m, 2H); 7.34 (t, J = 8 Hz, 1H); 7.73 (d, J = 8 Hz, 1H); 7.78
(d, J = 8 Hz, 1H); 7.83 (d, J = 8 Hz, 1H); 8.38 (s, 2H); 9.92 (s,
1H) ppm;
O
O
O
R
Si Cl
H2N
HN
H
H2N
+
O
)))), 28 ºC
H2O
R
13C NMR (DMSO–d6, 100 MHz) d: 22.65, 47.42, 54.95,
118.55, 118.95, 122.29, 122.56, 125.92, 126.03, 126.18,
127.20, 127.47, 128.41, 128.45, 129.02, 153.00, 155.23,
157.63, 168.99 ppm;
NH2
O
4
3
HRMS (M + Na): 344.1504.
Scheme 1. Synthesis of 1-amidoalkyl-2-naphthylamines.
(3) N-[(2’-aminonaphthalen-1-yl)(4-hydroxy-3-methoxyphenyl)-
methyl]acetamide, 4c:IR (KBr) v: 3502, 3423, 3199, 1643,
1517, 1438, 1371, 1033, 987, 945, 850, 813, 750 cmÀ1
;
1H NMR (DMSO–d6, 400 MHz) d: 2.00 (s, 3H); 3.28 (s, 3H);
3.60 (s, 1H); 6.314 (s, 1H); 7.16 (d, J = 8 Hz, 1H); 7.20 (d,
J = 8 Hz, 1H); 7.28 (t, J = 8 Hz, 1H); 7.40 (t, J = 8 Hz, 1H);
7.52–7.58 (m, 2H); 7.80 (t, J = 8 Hz, 2H); 7.85 (d, J = 8 Hz,
1H); 7.99 (s, 1H); 8.02–8.05 (m, 1H); 8.58 (s, 1H) ppm;
13C NMR (DMSO–d6, 100 MHz) d: 22.66, 47.81, 55.66, 118.56,
118.88, 119.13, 122.30, 123.57, 127.48, 127.69, 128.47,
128.91, 129.23, 132.31, 134.25, 152.97, 153.02, 155.24,
157.65, 168.89 ppm;
as a catalyst under aqueous sonic condition as shown in the
Scheme 1.
2. Methods
2.1. Materials and instruments
All starting materials were commercial products, and were used
without further purification, except liquid aldehydes which were
distilled before use. Yields refer to yield of the isolated products.
Melting points were measured on a RAAGA, Indian make melting
point apparatus. Nuclear magnetic resonance spectra were ob-
tained on a 400 MHz Bruker AMX instrument in DMSO-d6 using
TMS as a standard. LC–mass spectra were performed on an Agilent
Technologies 1200 series instrument. HRMS analyses were carried
out using ESI-Q TOF instrument. Infrared spectra were recorded
using Shimadzu FT-IR-8400s spectrophotometer as KBr pellets.
All the reactions were studied using SIDILU, Indian make sonic
bath working at 35 kHz (constant frequency, 120 W) maintained
at 28 °C without mechanical stirring. Silica chloride was prepared
using the reported method [17].
HRMS (M + Na): 360.1453.
(4) N-[(2’-aminonaphthalen-1-yl)(3-nitrophenyl)methyl]acetam-
ide, 4d: IR (KBr) v: 3374, 3226, 1647, 1533, 1436, 1350, 1110,
991, 923, 804, 734, 713, 675, 622, 584, 491 cmÀ1
;
1H NMR (DMSO–d6, 400 MHz) d: 1.97 (s, 3H); 6.53 (s, 1H);
7.10–7.16 (m, 2H); 7.21 (t, J = 8 Hz, 2H); 7.26–7.29 (m, 2H),
7.31–7.36 (m, 1H); 7.75 (d, J = 8 Hz, 1H); 7.79 (dd, J = 8 Hz,
8 Hz, 1H); 7.83 (d, J = 8 Hz, 1H); 8.40 (s, 2H); 9.6 (s, 1H) ppm;
13C NMR (DMSO–d6, 100 MHz) d: 22.50, 47.58, 117.74, 118.42,
120.37, 121.18, 122.55, 122.71, 126.71, 128.34, 128.64,
129.52, 129.83, 132.11, 132.80, 145.37, 147.69, 153.35,
169.62 ppm;
HRMS (M + Na): 359.1250.
2.2. General procedure for the synthesis of 1-amidoalkyl-2-
naphthylamines
(5) N-[(2’-aminonaphthalen-1-yl)(4-nitrophenyl)methyl]acetam-
ide, 4e: IR (KBr) v: 3307, 3210, 2850, 2451, 1967, 1622, 1596,
1510, 1467, 1394, 1342, 1294, 1209, 1161, 1070, 985,
823 cmÀ1
;
Aromatic aldehyde (5 mmol), 2-naphthylamine (5 mmol), acet-
amide (5 mmol) and silica chloride (100 mg) was added to water
(5 mL) in a 25 mL RB flask and irradiated in an ultrasonic bath.
After completion of the reaction ethyl acetate (10 mL) was added
and the catalyst was filtered, washed with warm ethanol and dried
for reuse. The filtrate after distilling the solvent was dried under
vacuum to afford the crude product. The pure product was ob-
tained after silica gel column chromatography (30% EtOAc). All
the products were characterized by the IR, 1H NMR, 13C NMR and
HRMS analysis.
1H NMR (DMSO–d6, 400 MHz) d: 2.07 (s, 3H); 6.61 (s, 1H);
7.17 (d, J = 8 Hz, 1H); 7.21 (d, J = 8 Hz, 1H); 7.26–7.30 (m,
1H); 7.40 (t, J = 8 Hz, 1H); 7.54 (m, 2H); 7.80 (m, 2H); 7.86
(d, J = 8 Hz, 1H); 8.00–8.05 (m, 1H); 8.59 (s, 2H); 9.32 (s,
1H) ppm;
13C NMR (DMSO–d6, 100 MHz) d: 22.50, 47.58, 118.42, 118.74,
123.37, 124.48, 125.55, 126.33, 126.71, 127.77, 128.73,
129.12, 129.85, 141.81, 143.50, 148.85, 168.81 ppm;
HRMS (M + Na): 359.1244.
The spectral data of the products:
(6) N-[(2’-aminonaphthalen-1-yl)(thiophen-2-yl)methyl]acetam-
ide, 4f: IR (KBr) v: 3292, 3161, 2923, 2513, 2110, 1170, 1108,
1045, 945, 813 cmÀ1
;
(1) N-[(2’-aminonaphthalen-1-yl)(phenyl)methyl]acetamide, 4a:
IR (KBr) v: 3409, 3372, 3172, 2887, 2796, 2646, 2312,
1585, 1419, 1340, 1274, 1147, 1093, 983, 813, 746, 698 cmÀ1
1H NMR (DMSO–d6, 400 MHz) d: 2.07 (s, 3H); 5.83 (s, 1H);
6.42 (d, J = 8 Hz, 5H); 6.55 (t, J = 8 Hz, 1H); 6.67 (d, J = 8 Hz,
1H); 6.94 (d, J = 8 Hz, 1H); 7.12 (s, 1H); 7.37–7.41 (m, 2H);
8.42 (s, 2H), 9.83 (s, 1H) ppm;
1H NMR (DMSO–d6, 400 MHz) d: 1.73 (s, 3H); 5.71 (s, 1H);
6.41 (s, 2H); 6.70 (d, J = 8 Hz, 1H); 7.10–7.30 (m, H); 7.67
(dd, J = 8 Hz, 8 Hz, 1H); 8.12 (s, 2H); 9.76 (s, 1H) ppm;
13C NMR (DMSO–d6, 100 MHz) d: 22.85, 45.18, 119.26, 120.76,
122.54, 123.95, 124.16, 124.97, 126.19, 126.40, 128.76,
128.93, 129.13, 134.00, 148.95, 152.97, 172.11 ppm;
HRMS (M + Na): 320.0963.
13C NMR (DMSO–d6, 100 MHz) d: 22.45, 47.43, 118.44, 118.95,
122.32, 123.23, 126.00, 126.24, 128.17, 128.41, 129.23,
132.25, 132.29, 134.37, 134.56, 140.47, 142.57, 153.11,
169.48 ppm;
(7) N-[(2’-aminonaphthalen-1-yl)(pyridin-2-yl)methyl]acetamide,
4g: IR (KBr) v: 3425, 3306, 1649, 1519, 1442, 1375, 1338,
1284, 1263, 1033, 987, 939, 852, 821 cmÀ1
;
1H NMR (DMSO–d6, 400 MHz) d: 1.94 (s, 3H); 5.72 (s, 1H);
6.41 (s, 2H); 7.04 (d, J = 8 Hz, 1H); 7.14 (t, J = 8 Hz, 2H);
7.22 (t, J = 8 Hz, 1H); 7.35 (d, J = 8 Hz, 2H); 7.66–7.76 (m,
3H); 7.95 (d, J = 8 Hz, 1H); 8.38 (s, 2H); 8.50 (t, J = 8 Hz,
1H); 10.05 (s, 1H) ppm;
HRMS (M + Na): 314.1399.
(2) N-[(2’-aminonaphthalen-1-yl)(4-methoxyphenyl)methyl]acet-
amide, 4b: IR (KBr) v: 3330, 3212, 2993, 2960, 2937, 2738,
2322, 1608, 1573, 1444, 1307, 1253, 1168, 1027, 941, 865,
813, 752, 613 cmÀ1
;

B. Datta, M.A. Pasha / Ultrasonics Sonochemistry 20 (2013) 303–307
305
13C NMR (DMSO–d6, 100 MHz) d: 23.01, 50.52, 118.07, 118.96,
119.40, 121.25, 121.92, 122.71, 123.64, 126.63, 128.79,
129.58, 132.98, 136.83, 148.56, 153.58, 161.81, 169.70 ppm;
HRMS (M + Na): 315.1351.
Table 2
Screening of solvents.
Entry Solvent
With sonication time Without sonication
(min)/yielda (%)
time (min)/yielda (%)
1
2
3
4
5
6
7
Ethanol
CH3CN
CHCl3
DCM
DCE
Water
Solvent-free
condition
20/55
/50
60/50
60/55
60/42
60/30
60/36
60/70
60/ND
3. Results and discussion
20/44
20/60
20/80
18/96
60/65
Initially we conducted a catalyst-free reaction of benzaldehyde
(1), 2-naphthylamine (2) and acetamide (3) in water at ambient
temperature and at reflux for 3 h and found that, no condensation
product was formed. Subsequently we tested the reaction of 1, 2
and 3 in water under sonic condition in presence of various heter-
ogeneous catalysts. The results of this study are summarized in Ta-
ble 1. It was found that, when the reaction was carried out without
any additives only trace amount of product was detected (Table 1,
entry 1). Only silica gel could not catalyze this reaction (Table 1,
entry 2). Some other catalysts such as Amberlyst-120, Dowex-50
and acidic alumina were employed and were found to catalyze this
reaction with moderate yields (Table 1, entries 3–5). The best re-
sult was obtained when silica chloride was used, which is evident
from the yield and the reaction duration (Table 1, entry 8). As the
catalysts other than Si–Cl are protic catalysts, removal of –OH
group for the creation of Si+ from Si–OH is probably relatively dif-
ficult when compared to Si–Cl cleavage; hence, there is difference
in the reactivity between silica chloride and other catalysts.
We also evaluated the amount of silica chloride required for the
present reaction. It was found that, increasing the amount of the
silica chloride from 50 to 100, 150 and 200 mg resulted in 86–
94%, 93%, and 91% yield, respectively (Table 1, entries 6–9). As
can be seen 100 mg of silica chloride in water under sonic condi-
tion is sufficient to push this reaction forward, and more amounts
of the silica chloride did not improve the yields. Hence, all the
other reactions were carried out using 100 mg silica chloride. Fi-
nally, we studied the reaction at different durations and the results
of this study are also presented in Table 1. It can be seen from the
Table 1 that, the reaction was complete within 20 min (Table 1, en-
tries 7, 10, 11) to give the product in very high yield.
ND, not detected.
a
Isolated yield.
Table 3
Synthesis of novel 1-amidoalkyl-2-naphthylamines from aldehydes, 2-naphthylamine
and acetamide under sonic condition.
Entry Aldehyde (R) Product (min) Time (min) Yielda (%) Melting point (°C)
1
2
3
4
5
6
7
H
4a
4b
18
27
36
9
12
20
30
96
91
90
95
97
95
92
218–220
208–210
>300
220–222
178–180
234–236
200–202
4-OCH3
3-OCH3, 4-OH 4c
3-NO2
4-NO2
Pyridine
Thiophene
4d
4e
4f
4g
a
Isolated yield.
Subsequently, this study was extended to a one-pot three-com-
ponent synthesis of diverse 1-amidoalkyl-2-naphthylamines by
condensing aromatic aldehydes, 2-naphthylamine, acetamide, in
water as a solvent in a sonic bath (35 kHz) maintained at 28 °C
by continuously circulating water. We demonstrate that this proto-
col accepts different aromatic aldehydes and produces respective
1-amidoalkyl-2-naphthylamines in excellent yields and the results
are presented in Table 3. As shown in Table 3, aromatic aldehydes
with electron-donating or electron-withdrawing groups reacted
successfully and gave the products in high yields. It was also ob-
served that, the aromatic aldehydes with electron-withdrawing
groups react faster than the aromatic aldehyde with electron-
donating groups. Heteroaromatic aldehydes also underwent the
transformation conveniently (Table 3, entries 6 and 7). All the pre-
pared products were characterized by the IR, 1HNMR, 13CNMR and
HRMS analysis.
The choice of an appropriate reaction medium is crucial for a
successful synthesis. We examined the same reaction under simi-
lar conditions in different solvents as shown in Table 2, and water
was found to be the best solvent in terms of reaction time and yield
of the product. As cavitation in water is most effective compared to
other solvents, the ultrasonic intensity in aqueous solutions is
higher because of the low sound absorption coefficient [18], hence,
the effect of nature of solvent on the reactivity is predominant in
the present reaction. We also conducted the reaction of liquid alde-
hydes under solvent-free condition but the product was formed in
low yield.
Next, we investigated the reusability and recycling of silica
chloride. At first, we took a mixture of benzaldehyde (5 mmol),
2-naphthylamine (5 mmol), acetamide (5 mmol), water (10 mL)
Table 1
Effect of catalyst on the synthesis of 1-amidoalkyl-2-naphthylamine.a
Entry
Catalyst
Quantity (mg)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
None
Silica gel
Amberlyst-120
Dowex-50
Acidic alumina
Silica chloride
Silica chloride
Silica chloride
Silica chloride
Silica chloride
Silica chloride
20
90
20
20
20
60
20
18
20
20
30
10
Trace
15
53
69
36
86
96
93
91
100
100
100
100
50
100
150
200
100
100
9
10
11
93
82
a
Reaction condition: Benzaldehyde (5 mmol), 2-naphthylamine (5 mmol), acet-
amide (5 mmol) and water (10 mL) under sonic condition (35 kHz).
b
Isolated yield.
Fig. 1. Reusability of silica chloride.

306
B. Datta, M.A. Pasha / Ultrasonics Sonochemistry 20 (2013) 303–307
Table 4
the results of this study are presented in Table 4. It is clear from
this table that, the desired product could form only in moderate
yield at reflux temperature of the solvent.
Comparative study on the synthesis of 1-amidoalkyl-2-naphthylamines under
different conditions.
Entry
R (4)
Product
Time/yield (min)/(%)a
Time/yield (min)/(%)b
A plausible mechanism for the formation of 1-amidoalkyl-2-
naphthylamines is envisaged. Due to high speed jets and shock
waves and in the presence of an aldehyde the Cl of the silica chlo-
ride may get more easily and selectively displaced as ClÀ to give a
cationic center. 2-Naphthylamine may then react with this acti-
vated aromatic aldehyde in the next step, and in one of the sub-
sequent steps the addition of acetamide can take place to give the
final product with the release of silica chloride as shown in
Scheme 2.
1
2
3
H
4a
4b
4c
20/65
30/50
20/75
18/96
27/91
18/95
4-OCH3
3-NO2
a
At reflux [reaction condition: aromatic aldehyde (5 mmol), 2-naphthylamine
(5 mmol), acetamide (5 mmol), silica chloride (100 mg) and water (10 mL) as
solvent].
b
Under sonication [35 kHz, reaction condition: aromatic aldehyde (5 mmol), 2-
naphthylamine (5 mmol), acetamide (5 mmol), silica chloride (100 mg) and water
(10 mL) as solvent].
In all the reactions it was found that, use of ultrasound leads to
faster reaction and higher yields. Symmetrical cavitation and sym-
metrical collapse of bubbles in the liquid medium is very common;
if cavitation bubbles are formed at or near a solid surface the bub-
ble collapse will no longer be symmetrical. The solid surface hin-
ders liquid movement from that side and the major liquid flow
into the collapsing bubble will be from the opposite side. As a re-
sult of this a strong high energy liquid jet will be formed which
is targeted at the surface. These jets can induce mechanical de-
aggregation and dispersion of loosely held clusters, and improve
mass transfer to the surface. In the present reaction, we feel that
the shock waves and high speed jets are responsible for the
enhancement in the rate and yield of the target molecules under
sonic condition.
and 100 mg of silica chloride in a 25 mL RB flask; the mixture was
irradiated in a sonic bath for 18 min. When the reaction was com-
plete, silica chloride was separated by filtration after adding ethyl
acetate (10 mL). The recovered silica chloride was washed with
warm ethanol, dried and reused in subsequent reactions without
significant decrease in activity till fourth run (Fig. 1). In fifth run
the catalytic activity reduced considerably. The reduction of the
observed catalytic activity may be due to catalyst damage by the
shock waves and high speed jets.
To verify the effect of ultrasound on this reaction the synthesis
of 1-amidoalkyl-2-naphthylamines was carried out in water in the
presence of silica chloride under ultrasonication and at reflux and
Si
Si
Cl
O
Si
Si
Cl
H2N
O
Si
Si
Cl
Cl
..
..
O
H
_
H
_
+
+
-Cl
Ar
H
Ar
Ar
H
Cl
NH
Si
Si
NH
Si
Si
Cl
+
Si
Si
N
..
H
H
H
H
O
Cl
H
O
H
Ar
Ar
O
Ar
_
Cl
Si
Si
NH
Ar
Si
Si
Si
Si OH
NH
Ar
NH
H
NH
H
+
+
NH
H
Ar
H
O
OH
OH
O
..
H2N
_
O
Cl
_
Cl
Si
H
Cl
H
+
Cl
Si Cl
Si
NH
..
NH
H2N
H
HN
Cl
Si
Si
H
NH
+
H
NH
Ar
Ar
Si
Ar
OH
OH
H
O
O
_
O
4
Cl
O
O
O
O
O
O
Si
Si
Si
Si
=
Scheme 2. A plausible mechanism.

B. Datta, M.A. Pasha / Ultrasonics Sonochemistry 20 (2013) 303–307
International, J. Chem. Res. 1 (2010) 28;
307
4. Conclusions
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In conclusion, we have described an ultrasound assisted, effi-
cient, one-pot three-component synthesis of novel 1-amidoalkyl-
2-naphthylamines from a variety of aromatic aldehydes, 2-naph-
thylamine and acetamide in the presence of catalytic amounts of
silica chloride in water. This new method has the advantages of
higher yields, mild reaction conditions, and shorter reaction dura-
tion; and is a convenient, energy efficient, environment friendly
procedure.
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