Rapid synthesis of 1-amidoalkyl-2-naphthols over sulfonic acid functionalized imidazolium salts

Article abstract of DOI:10.1016/j.apcata.2011.04.013

Novel sulfonic acid functionalized imidazolium salts including 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl} (an ionic liquid), 1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} (an ionic liquid) and 3-methyl-1-sulfonic acid imidazolium tetra

Full text of DOI:10.1016/j.apcata.2011.04.013

Applied Catalysis A: General 400 (2011) 70–81
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Rapid synthesis of 1-amidoalkyl-2-naphthols over sulfonic acid functionalized
imidazolium salts
Mohammad Ali Zolfigola,∗, Ardeshir Khazaeia,∗, Ahmad Reza Moosavi-Zarea, Abdolkarim Zareb,
Vahid Khakyzadeha
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
b Department of Chemistry, Payame Noor University (PNU), Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel sulfonic acid functionalized imidazolium salts including 3-methyl-1-sulfonic acid imidazolium
chloride {[Msim]Cl} (an ionic liquid), 1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} (an ionic
liquid) and 3-methyl-1-sulfonic acid imidazolium tetrachloroaluminate {[Msim]AlCl4} (a solid) effi-
ciently catalyze one-pot multi-component condensation of ␤-naphthol with aromatic aldehydes and
amide derivatives under solvent-free conditions to afford 1-amidoalkyl-2-naphthols in excellent yields
(81–96%) and in very short reaction times (1–40 min).
Received 18 December 2010
Received in revised form 8 April 2011
Accepted 11 April 2011
Available online 16 April 2011
Keywords:
Ionic liquid
© 2011 Elsevier B.V. All rights reserved.
Sulfonic acid functionalized imidazolium
salts
␤-Naphthol
1-Amidoalkyl-2-naphthol
Solvent-free
1. Introduction
amidoalkyl-2-naphthols from ␤-naphthol, aromatic aldehydes and
amide derivatives can be efficiently performed in the presence of
Ionic liquids (based imidazolium or other organic cations) have
received considerable interest as eco-friendly solvents, catalysts
and reagents in green synthesis because of their unique proper-
ties, such as low volatility, nonflammability, high thermal stability,
negligible vapor pressure and ability to dissolve a wide range of
materials [1–9]. Among them, Brønsted acidic ionic liquids have
designed to replace solid acids and traditional mineral liquid acids
like sulfuric acid and hydrochloric acid in chemical procedures
[10–14].
As mentioned imidazolium salts having a Brønsted acidic group
are of importance, and they have been successfully utilized as
catalyst in organic synthesis. These subjects encouraged us to
synthesize some functionalized imidazolium salts, with Brønsted
acidic property, including ionic liquid 3-methyl-1-sulfonic acid imi-
dazolium chloride {[Msim]Cl} [10–12], ionic liquid 1,3-disulfonic
acid imidazolium chloride {[Dsim]Cl} and 3-methyl-1-sulfonic
acid imidazolium tetrachloroaluminate {[Msim]AlCl4} (as a solid)
(Fig. 1). We wish to use them as catalysts for different organic
transformations. Herein, we have found that the synthesis of 1-
these imidazolium salts.
1-Amidoalkyl-2-naphthol derivatives are of importance as
they can be easily converted to biologically active compounds,
1-aminoalkyl-2-naphthols, by amide hydrolysis reaction. Hypoten-
sive and bradycardiac properties have been reported for this
class of compounds [15–17]. 1-Amidoalkyl-2-naphthols can be
also converted to 1,3-oxazine derivatives [18]. 1,3-Oxazines
have potentially different biological activities including antibi-
otic [19], antitumor [20], analgesic [21], anticonvulsant [22],
antipsychotic [23], antimalarial [24], antianginal [25], antihy-
pertensive [26], and antirheumatic properties [27]. One-pot
multi-component condensation of ␤-naphthol with aromatic alde-
hydes and amide derivatives or acetonitrile has been used
as a practical synthetic route toward 1-amidoalkyl-2-naphthols
[28–43]. Several Lewis and Brønsted acids have been applied
to catalyze this transformation, such as Ce(SO4)2 [28], p-
toluenesulfonic acid [29], iodine [30], cation-exchanged resins [31],
Fe(HSO4)3 [32], sulfamic acid/ultrasound [33], HClO4/SiO2 [34],
wet cyanuric chloride [35], trityl chloride [36], H3PW12O40 [37],
P2O5 [38], 4-(1-imidazolium)butane sulfonate [39], N-(4-sulfonic
acid)butyl triethylammonium hydrogensulfate [40], 1-butyl-3-
methylimidazolium hydrogen sulphate [41], Cu1.5PW12O40 [42],
and silica sulfuric acid [43]. Nevertheless, many of the reported
methods are associated with one or more of the following draw-
∗
Corresponding authors. Fax: +98 811 8272404.
E-mail addresses: mzolfigol@yahoo.com, zolfi@basu.ac.ir (M.A. Zolfigol),
Khazaei 1326@yahoo.com (A. Khazaei).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.04.013

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
71
+
+
+
Cl
N
N
N
N
Cl
N
N
AlCl4
SO3H
HO3S
SO3H
SO3H
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Fig. 1. Structures of 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl}, 1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} and 3-methyl-1-sulfonic acid imida-
zolium tetrachloroaluminate {[Msim]AlCl4}.
backs: (i) low yields, (ii) long reaction times, (iii) the use of large
amount of catalyst, (iv) the use of toxic or expensive catalysts, (v)
inefficiency of method when aromatic amides or urea are used in
the reaction, and (vi) no agreement with the green chemistry proto-
cols. Thus, search for finding an efficient, general and nonpolluting
method for the synthesis of 1-aminoalkyl-2-naphthols is still of
practical importance.
In this paper, we report our results on the efficient and rapid
synthesis of 1-amidoalkyl-2-naphthols from ␤-naphthol, aryl alde-
hydes and amides/urea in the presence of catalytic amounts
of the functionalized imidazolium salts, [Msim]Cl, [Dsim]Cl or
[Msim]AlCl4, under solvent-free conditions (Scheme 1). Interest-
ingly, this method for the preparation of 1-amidoalkyl-2-naphthol
derivatives has none of the above-mentioned drawbacks at all.
residue was washed with dry CH2Cl2 (3 × 50 mL) and dried under
vacuum to give [Dsim]Cl as a viscous pale yellow oil in 95% yield,
1.257 g.
2.2.1. Spectral data of [Dsim]Cl
Pale yellow oil; 1H NMR (300 MHz, DMSO-d6): ı (ppm) 7.34 (s,
2H), 8.67 (s, 1H), 13.34 (s, 2H); 13C NMR (75 MHz, DMSO-d6): ı
(ppm) 119.5, 134.3; MS: m/z = 265 (M++1), 264 (M+), 229 (M+–Cl),
148 (M+–ClSO3H), 67 (M+–2ClSO3H).
2.3. Procedure for the preparation of [Msim]AlCl4 (Fig. 1)
A round-bottomed flask (50 mL) was charged with 3-methyl-
1-sulfonic acid imidazolium chloride (0.9931 g, 5 mmol), and then
AlCl3 (0.6667 g, 5 mmol) was added over a period of 5 min at 50 ◦C.
Afterward, the reaction mixture was stirred for 30 min at 50 ◦C to
give [Msim]AlCl4 as a white powder in 98% yield, 1.623 g.
2. Experimental
All chemicals were purchased from Merck or Fluka Chemical
Companies. The known products were identified by comparison of
their melting points and spectral data with those reported in the
literature. Progress of the reactions was monitored by TLC using
silica gel SIL G/UV 254 plates. The reaction conversions were mea-
sured by GC on a Shimadzu model GC-16A instrument using a 25 m
CBPI-S25 (0.32 mm ID, 0.5 ␮m coating) capillary column. The 1H
NMR (250 or 300 MHz) and 13C NMR (62.5 or 75 MHz) were run on
a Bruker Avance DPX-250 FT-NMR spectrometer (ı in ppm). Micro-
analyses were performed on a Perkin-Elmer 240-B microanalyzer.
Melting points were recorded on a Büchi B-545 apparatus in open
capillary tubes.
2.3.1. Spectral data of [Msim]AlCl4
White powder, mp 391 ◦C (dec.); 1H NMR (300 MHz, DMSO-d6):
ı (ppm) 3.83 (s, 3H, CH3), 7.57 (s, 1H), 7.63 (s, 1H), 9.02 (s, 1H),
12.24 (s, 1H); 13C NMR (75 MHz, DMSO-d6): ı (ppm) 35.8, 120.1,
123.5, 136.3; MS: m/z = 332 (M++1), 331 (M+), 316 (M+–CH3), 168
(M+–C4H7N2O3S), 163 (M+–AlCl4), 82 (M+–SO3HAlCl4).
2.4. General procedure for the synthesis of
1-amidoalkyl-2-naphthols 1a–t
To a well-ground mixture of ␤-naphthol (0.288 g, 2 mmol),
aldehyde (2 mmol) and amide derivative (2.4 mmol) in a 10 mL
round-bottomed flask connected to a reflux condenser, was added
the catalyst (0.2 mmol), and the resulting mixture was stirred in
an oil-bath (120 ◦C). After completion of the reaction, as monitored
with TLC, the reaction mixture was cooled to room temperature,
and was added to a column chromatography on silica gel, and eluted
with EtOAc/n-hexane (1/1) to give the pure product.
2.1. General procedure for the preparation of ionic liquid
[Msim]Cl (Fig. 1)
A
round-bottomed flask (100 mL) was charged with 1-
methylimidazole (0.410 g, 5 mmol) in dry CH2Cl2 (50 mL), and then
chlorosulfonic acid (0.605 g, 5.2 mmol) was added dropwise over a
period of 5 min at room temperature. After the addition was com-
pleted, the reaction mixture was stirred for 20 min, stand for 5 min,
and the CH2Cl2 was decanted. The residue was washed with dry
CH2Cl2 (3 × 50 mL) and dried under vacuum to give [Msim]Cl as a
viscous colorless oil in 92% yield, 0.912 g [10–12].
Note: When liquid aldehydes were applied in the reaction, at
first, ␤-naphthol and amide derivative were ground, and subse-
quently aldehyde and the catalyst were added.
2.5. Selected spectral data of the products 1a–t
2.1.1. Spectral data of [Msim]Cl
2.5.1.
Viscous colorless oil (lit. [10–12] viscous colorless oil); 1H NMR
(300 MHz, DMSO-d6): ı (ppm) 3.77 (s, 3H, CH3), 7.46 (s, 1H), 7.51
(s, 1H), 8.84 (s, 1H), 13.96 (s, 1H); 13C NMR (75 MHz, DMSO-d6):
ı (ppm) 36.5, 120.6, 124.2, 136.6; MS: m/z = 199 (M++1), 198 (M+),
183 (M+–CH3), 163 (M+–Cl), 82 (M+–ClSO3H), 67 (M+–CH4ClSO3).
N-[(2-hydroxynaphthalen-1-yl)(phenyl)methyl)]acetamide (1a)
White solid; mp 238–240 ◦C (lit. [28] mp 241–243 ◦C); 1H NMR
(250 MHz, DMSO-d6): ı (ppm) 2.06 (s, 3H), 7.01–7.20 (m, 9H),
7.65–7.73 (m, 3H), 8.11 (d, J = 7.7 Hz, 1H), 9.69 (s, 1H); 13C NMR
(62.5 MHz, DMSO-d6): ı (ppm) 23.5, 41.3, 118.8, 120.2, 122.0, 123.9,
124.9, 125.7, 127.6, 128.1, 128.3, 128.5, 128.6, 134.2, 144.0, 152.6,
169.6.
2.2. Procedure for the preparation of ionic liquid [Dsim]Cl (Fig. 1)
To a round-bottomed flask (100 mL) containing imidazole
(0.340 g, 5 mmol) in dry CH2Cl2 (50 mL), was added chlorosulfonic
acid (1.1885 g, 10.2 mmol) dropwise over a period of 20 min at room
temperature. After the addition was completed, the reaction mix-
ture was stirred for 12 h under pressure of nitrogen (to remove the
produced HCl), stand for 5 min, and the CH2Cl2 was decanted. The
2.5.2. N-[(2-hydroxynaphthalen-1-yl)(3-
nitrophenyl)methyl)]acetamide
(1g)
Pale yellow solid; mp 238–240 ◦C (lit. [33] mp 236–237 ◦C); 1
H
NMR (250 MHz, DMSO-d6): ı (ppm) 2.06 (s, 3H), 7.15–7.49 (m, 6H),
7.78–8.04 (m, 5H), 8.54 (d, J = 8.1 Hz, 1H), 10.12 (s, 1H); 13C NMR

72
M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
O
O
Imidazolium salt (10 mol%)
OH
NH
+
+
Solvent-free, 120 °C
1-40 min
R'
NH2
R
H
R
OH
R'
1a-t
Isolated yield: 81-96%
O
R = Ph, Aryl R' = CH3, Ph, NH2, 3-Pyridyl
Imidazolium salt: [Msim]Cl, [Dsim]Cl or [Msim]AlCl4
Scheme 1. The synthesis of 1-amidoalkyl-2-naphthols from ␤-naphthol, aromatic aldehydes and amide derivatives.
(62.5 MHz, DMSO-d6): ı (ppm) 23.3, 48.1, 118.1, 118.7, 120.5, 122.3,
123.8, 125.7, 127.3, 128.4, 129.1, 129.6, 130.8, 133.1, 134.1, 144.5,
148.7, 152.9, 169.8.
2.6. General procedure for the preparation of
1-amidoalkyl-2-naphthol derivatives 2a, 3a and 3b
To a well-ground mixture of ␤-naphthol (0.576 g, 4 mmol),
terephthalaldehyde (0.268 g, 2 mmol) and acetamide (0.284 g,
4.8 mmol) in a 10 mL round-bottomed flask connected to a reflux
condenser, was added the catalyst (0.3 mmol, 15 mol%), and the
resulting mixture was stirred in an oil-bath (120 ◦C) for the appro-
priate time (Schemes 2 and 3). Afterward, the reaction mixture
was cooled to room temperature, and warm aqueous ethanol
(15%, 30 mL) containing triethylamine (0.2 mL) were added to
it, and stirred for 5 min (1-amidoalkyl-2-naphthol is soluble in
warm aqueous ethanol, however, bis-1-amidoalkyl-2-naphthol
is insoluble in this solvent). During this time, the crude 1-
amidoalkyl-2-naphthol was dissolved in the ethanol, and pure
bis-1-amidoalkyl-2-naphthol was remained; thus, two products
were easily separated by filtration. Then, the solvent of the fil-
trate was evaporated and the crude 1-amidoalkyl-2-naphthol was
purified by column chromatography on silica gel eluted with
EtOAc/n-hexane (1/1).
2.5.3. N-[(2-hydroxynaphthalen-1-yl)(4-
chlorophenyl)methyl)]acetamide
(1h)
Pale yellow solid; mp 220–222 ◦C (lit. [28] mp 224–227 ◦C); 1
H
NMR (250 MHz, DMSO-d6): ı (ppm) 2.07 (s, 3H), 7.06 (m, 2H),
7.14–7.24 (m, 5H), 7.68–7.77 (m, 3H), 7.98 (d, J = 7.4 Hz, 1H), 8.16
(d, J = 7.1 Hz, 1H), 9.90 (s, 1H); 13C NMR (62.5 MHz, DMSO-d6): ı
(ppm) 23.2, 47.6, 118.8, 119.8, 122.1, 123.7, 125.8, 126.9, 127.4,
128.3, 128.6, 129.3, 129.9, 134.0, 143.4, 152.5, 169.8.
2.5.4. N-[(4-chloro-phenyl)-(2-hydroxy-naphthalen-1-yl)-
methyl]nicotinamide
(1t)
White solid; mp 206–209 ◦C; IR (KBr): 3408, 3234, 3065, 1645,
1581, 1514, 1273 cm−1 1H NMR (300 MHz, DMSO-d6): ı (ppm)
;
7.27–7.50 (m, 9H), 7.83 (d, J = 8.7 Hz, 2H), 8.10 (d, J = 8.4 Hz, 1H),
8.27 (d, J = 7.8 Hz, 1H), 8.71 (d, J = 4.4 Hz, 1H), 9.12 (s, 1H), 9.35 (d,
J = 7.6 Hz, 1H), 10.38 (s, 1H); 13C NMR (75 MHz, DMSO-d6): ı (ppm)
49.4, 118.2, 119.1, 123.1, 123.5, 123.9, 127.2, 128.6, 128.9, 129.2,
130.1, 130.4, 131.7, 132.8, 135.8, 141.2, 149.1, 152.4, 153.9, 165.4;
MS: m/z = 388.3 (M+); Anal. Calcd. for C23H17ClN2O2: C, 71.04; H,
4.41; N, 7.20. Found: C, 70.78; H, 4.30; N, 7.35.
2.7. Selected spectral data of the products 2a, 3a and 3b
2.7.1. N-[(4-diethoxymethyl-phenyl)-(2-hydroxy-naphthalen-1-
yl)-methyl]acetamide
(2a)
Pale yellow solid; mp 173–175 ◦C (lit. [36] mp 173–175 ◦C); 1
H
NMR (300 MHz, DMSO-d6): ı 1.17 (t, J = 6.9 Hz, 6H), 2.02 (s, 3H),
OH
CHO
MeCONH2
NHCOMe
OH
+
+
MeOCHN
HO
Catalyst (15 mol%)
OH
NHCOMe
Solvent-free
EtO
120 °C
EtO
OEt
OEt
2a
3a
3a
Yielda (%)
2a
Catalyst
Molar ratio of β-naphthol/aldehyde/amide
Time (min)
[Msim]Cl
[Msim]Cl
[Dsim]Cl
[Dsim]Cl
1/1/1.2
2/1/2.4
5
6
25
6
31
78
34
81
1/1/1.2
2/1/2.4
1/1/1.2
2/1/2.4
4
6
27
8
[Msim]AlCl4
[Msim]AlCl4
7
9
30
22
5
73
aIsolated yield.
Scheme 2. The condensation of ␤-naphthol with 4-(diethoxymethyl)benzaldehyde and acetamide.

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
73
OH
CHO
CHO
MeCONH2
NHCOMe
OH
+
+
MeOCHN
HO
Catalyst (15 mol%)
Solvent-free
120 °C
OH
NHCOMe
OHC
3a
Time (min)
3b
Yielda (%)
3a
Catalyst
Molar ratio of β-naphthol/aldehyde/amide
3b
[Msim]Cl
[Msim]Cl
1/1/1.2
2/1/2.4
5
6
29
82
34
14
32
12
[Dsim]Cl
1/1/1.2
2/1/2.4
1/1/1.2
2/1/2.4
4
5
38
84
[Dsim]Cl
[Msim]AlCl4
[Msim]AlCl4
6
9
33
12
27
78
aIsolated yield.
Scheme 3. The condensation of ␤-naphthol with terephthaldehyde and acetamide.
3.58 (q, J = 6.9 Hz, 4H), 6.96–7.46 (m, 9H), 7.73–7.85 (m, 3H), 8.26 (d,
J = 8.5 Hz, 1H), 10.22 (s, 1H); 13C NMR (75 MHz, DMSO-d6): ı (ppm)
19.1, 23.2, 48.5, 56.7, 111.8, 119.1, 119.6, 120.9, 122.7, 124.5, 126.2,
128.5, 129.1, 129.7, 132.9, 134.8, 139.7, 142.4, 153.3, 169.9.
material) or another possible product formed from the reac-
tion of 1-methylimidazole with ClSO3H (i.e. 1-methylimidazolium
chlorosulfonate), we also run the 1H NMR spectra of ClSO3H and 1-
methylimidazolium chloride in DMSO-d6 (the acidic hydrogens of
1-methylimidazolium chlorosulfonate and 1-methylimidazolium
chloride are same). In these spectra, the peaks of the acidic hydro-
gens of [Msim]Cl, ClSO3H and 1-methylimidazolium chloride were
observed in 13.96, 13.45 and 8.46 ppm, respectively. The difference
between the peaks of the acidic hydrogens in [Msim]Cl, ClSO3H and
1-methylimidazolium chloride confirmed that the peak observed in
13.96 ppm of the 1H NMR spectra of [Msim]Cl is correctly related
to the SO3H group of this compound.
In order to prove that the sulfonic acid functionalized with imi-
dazolium salts was correctly synthesized, and this is responsible
of the catalytic results, as a model, the solvent-free condensa-
tion of ␤-naphthol with 4-chlorobenzaldehyde and acetamide was
examined in the presence of 10 mol% of the starting materials
used for the preparation of the catalysts (i.e. 1-methylimidazole
and ClSO3H) as well as a possible product formed from the reac-
tion of 1-methylimidazole with ClSO3H (this possible product is
1-methylimidazolium chlorosulfonate; however, there was not this
compound in the Chemical Companies catalogs. Moreover, the
acidic hydrogen of 1-methylimidazolium chlorosulfonate catalyzes
the reaction. Thus, we used 1-methylimidazolim chloride instead of
it). The reaction was carried out at 120 ◦C and the catalytic results
are presented in Table 1. It can be seen that 1-methylimidazole
and 1-methylimidazolium chloride afforded lower yield of reac-
tion products to those achieved over the catalysts. Only in the case
of ClSO3H, it has been observed a relatively moderate yield. The
reaction was also performed in the presence of imidazole as well
as imidazolium chloride in which the product was obtained in low
or moderate yields after long reaction times (Table 1, entries 8 and
9). However, when the reaction was carried out in the presence
of [Msim]Cl, [Dsim]Cl or [Msim]AlCl4, we observed high yields at
very short reaction times. These results also confirmed that the
functionalized sulfonic acid imidazolium salts have been correctly
synthesized.
2.7.2.
N-[{4-[acetylamino-(2-hydroxy-naphthalen-1-yl)-methyl]-
phenyl}-(2-hydroxy-naphthalen-1-yl)-methyl]acetamide
(3a)
White solid; mp 277–279 ◦C (lit. [36] mp 277–279 ◦C); 1H NMR
(300 MHz, DMSO-d6): ı (ppm) 2.01 (s, 6H), 7.17–7.39 (m, 12H),
7.77–7.93 (m, 6H), 8.53 (d, J = 8.2 Hz, 2H), 10.09 (s, 2H); 13C NMR
(75 MHz, DMSO-d6): ı (ppm) 23.1, 48.2, 118.9, 119.2, 122.8, 126.3,
126.8, 128.9, 129.0, 129.6, 132.7, 140.8, 140.9, 153.6, 169.7.
2.7.3. N-[(4-formylphenyl)(2-hydroxynaphthalen-1-
yl)methyl]acetamide
(3b)
Pale yellow solid; mp 237–240 ◦C (lit. [36] mp 237–240 ◦C); 1
H
NMR (300 MHz, DMSO-d6): ı (ppm) 2.02 (s, 3H), 6.91–7.39 (m, 6H),
7.79–7.82 (m, 4H), 8.41 (d, J = 6.6 Hz, 1H), 8.56 (d, J = 7.6 Hz, 1H), 9.93
(s, 1H), 10.10 (s, 1H); 13C NMR (75 MHz, DMSO-d6): ı (ppm) 23.0,
48.4, 118.6, 118.8, 122.9, 123.5, 126.3, 127.1, 128.9, 129.1, 129.9,
130.1, 132.7, 134.9, 150.6, 153.7, 170.1, 193.1.
3. Results and discussion
3.1. Studies to confirm the structures of the imidazolium salts
The structures of the sulfonic acid functionalized imidazolium
salts were identified by 1H and 13C NMR as well as mass spectra. The
corresponding spectral data have been reported in Section 2. More-
over, the graphical 1H and 13C NMR spectra of the imidazolium salts
are presented in Figs. 2 and 3. Here, we study 1H NMR data of ionic
liquid 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl}.
The important peak of 1H NMR spectra of [Msim]Cl is related to the
acidic hydrogen (SO3H) which observed in 13.96 ppm. To confirm
that this peak (13.96 ppm) is really related to the hydrogen of SO3H
in the compound, not hydrogen of ClSO3H (its unreacted starting
The other case for the mixing of 1-methylimidazole with ClSO3H
in CH2Cl2, is formation of a separate phase, “ClSO3H dissolved in

74
M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
Fig. 3. 13C NMR of 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl},
1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} and 3-methyl-1-sulfonic acid
imidazolium tetrachloroaluminate {[Msim]AlCl4}.
Fig. 2. 1H NMR of 3-methyl-1-sulfonic acid imidazolium chloride {[Msim]Cl},
1,3-disulfonic acid imidazolium chloride {[Dsim]Cl} and 3-methyl-1-sulfonic acid
imidazolium tetrachloroaluminate {[Msim]AlCl4}.
As it can be seen, the 1H NMR data of the product are different
with those in 1-methylimidazole and ClSO3H. Thus, the treatment
of 1-methylimidazole with ClSO3H did not afford the separate
phase, “ClSO3H dissolved in 1-methylimidazole”, and really gave
[Msim]Cl. Moreover, 1-methylimidazole and ClSO3H were easily
dissolved in CH2Cl2; however, the product obtained from the mix-
ing of these compounds {[Msim]Cl} was insoluble in CH2Cl2. This
subject also confirmed that the separate phase, “ClSO3H dissolved
in 1-methylimidazole” was not formed.
The above explanations are also applicable for the synthesis of
[Dsim]Cl from imidazole and ClSO3H.
In another study, to prove that the reaction of [Msim]Cl
with AlCl3 leads to [Msim]AlCl4, not [Msim]Cl/AlCl3 mixture,
we achieved carefully the reaction of ␤-naphthol with 4-
1-methylimidazole”. To recognize that this physical phenomenon
cannot be achieved in these conditions, we noticed to the 1H NMR
spectral data of the product obtained from the mixing, with those
in 1-methylimidazole and ClSO3H separately. The 1H NMR spectral
data include:
The product: 1H NMR (300 MHz, DMSO-d6): ı (ppm) 3.77 (s, 3H,
CH3), 7.46 (s, 1H), 7.51 (s, 1H), 8.84 (s, 1H), 13.96 (s, 1H).
1-Methylimidazole: 1H NMR (300 MHz, DMSO-d6): ı (ppm) 3.61
(s, 3H, CH3), 7.02 (s, 1H), 7.11 (s, 1H), 7.64 (s, 1H).
ClSO3H: 1H NMR (300 MHz, DMSO-d6): ı (ppm) 13.45 (s, 1H).

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
75
Table 1
ent quantities of the functionalized imidazolium salts, [Msim]Cl,
[Dsim]Cl or [Msim]AlCl4, at range of 90–130 ◦C under solvent-free
conditions (Scheme 1). The results are summarized in Table 3.
Interestingly, the three imidazolium salts were highly efficient and
10 mol% of them was sufficient to afford the product in excellent
yields and in very short reaction times at 120 ◦C (Table 3, entry 3).
No improvement in the reaction results was observed by increasing
the amount of the catalysts and the temperature. The solvent-free
condensation was also tested at 120 ◦C without catalyst in which
the reaction was not progressed even after long reaction time (12 h).
In another study, the solvent-free reaction of ␤-naphthol with
4-chlorobenzaldehyde and acetamide was checked using the cat-
alysts at 120 ◦C, and conversion percents as well as yields of the
reactions were measured in different reaction times (each 15 s). The
corresponding curves (variation of conversion or yield with time)
are presented in Fig. 5. As it can be seen in Fig. 5, the catalytic activ-
ity of [Dsim]Cl was higher than [Msim]Cl and [Msim]AlCl4. This can
be attributed to more number of SO3H groups in [Dsim]Cl; this cat-
alyst has two SO3H groups, but [Msim]Cl and [Msim]AlCl4 have one
SO3H group. Moreover, [Msim]Cl and [Msim]AlCl4 showed almost
similar catalytic activity in this reaction.
After optimization of the reaction conditions, the condensation
of ␤-naphthol with various aryl aldehydes and amides/urea was
examined in the presence of [Msim]Cl, [Dsim]Cl or [Msim]AlCl4 at
120 ◦C in the absence of solvent, in order to assess the scope and the
generality of the catalysts. The results are displayed in Table 4 . As
it is shown in Table 4, aryl aldehydes possessing electron-releasing
substituents, electron-withdrawing substituents and halogens on
their aromatic rings were utilized successfully in the reaction, and
gave the desired products in high yields and in very short reaction
times. Moreover, the imidazolium salts efficiently catalyzed the
reaction when benzamide, urea or nicotinamide were used instead
of acetamide. Thus, all catalysts were general and highly efficient.
The condensation of ␤-naphthol with 4-chlorobenzaldehyde and acetamide using
1-methylimidazole, chlorosulfonic acid, 1-methylimidazolium chloride, imidazole
and imidazolium chloride.
Entrya
Catalystb
Time (min)
Yieldc/Conv.d (%)
1
2
3
4
5
6
7
8
9
–
12 h
2
2
2
150
5
120
150
120
No reaction
96/99
96/99
95/98
29/34
73/77
51/56
34/39
57/61
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
1-Methylimidazole
Chlorosulfonic acid
1-Methylimidazolium chloride
Imidazole
Imidazolium chloride
a
All reactions were carried out at 120 ◦C.
The amount of the catalysts was 10 mol%.
Isolated yield.
b
c
d
Conversion.
chlorobenzaldehyde and acetamide, as well as with benzaldehyde
and urea in the presence of 10 mol% of [Msim]Cl/AlCl3 mixture
(1/0.5 to 1/1 molar ratio) as well as AlCl3 at 120 ◦C (Table 2).
As Table 2 shows, when the reactions were carried out using
[Msim]Cl/AlCl3 mixture, the yields were similar to those obtained
using [Msim]Cl, not [Msim]AlCl4. In these cases, the reaction times
were not sufficient to produce [Msim]AlCl4 (the time needed for
the synthesis of this catalyst is 35 min); thus, the results were not
similar to [Msim]AlCl4. AlCl3 also afforded moderate yields of the
products in longer reaction times. Moreover, in the mass spectra
of [Msim]AlCl4, there was a peak in 168 which related to AlCl4.
[Msim]Cl and [Msim]AlCl4 have also different 1H and 13C NMR
spectra (please see Figs. 2 and 3). These observations confirmed
the structure of [Msim]AlCl4.
Study on thermal gravimetric analysis (TGA) of [Msim]Cl and
[Msim]AlCl4 was also confirmed that [Msim]AlCl4 has been syn-
thesized. The corresponding diagrams are shown in Fig. 4. As it can
be seen in Fig. 4, the thermogravimetry (TG) and derivative ther-
mogravimetry (DTG) of the catalysts showed weight losses in one
step; [Msim]Cl and [Msim]AlCl4 were decomposed after 330 and
390 ◦C in one step. This subject confirmed that the catalysts are
one-system, not binary systems. In binary systems, the thermo-
gravimetry (TG) diagrams must be showed weight losses in two
or more steps. Moreover, the TG and DTG diagrams of [Msim]Cl
and [Msim]AlCl4 are different. These results are important to prove
that the reaction of [Msim]Cl with AlCl3 leads to [Msim]AlCl4, not
[Msim]Cl/AlCl3 binary system.
3.3. The synthesis of 1-amidoalkyl-2-naphthols 2a, 3a and 3b
It must be mentioned that the condensation of ␤-naphthol
with 4-(diethoxymethyl)benzaldehyde and acetamide in the pres-
ence of [Msim]Cl, [Dsim]Cl or [Msim]AlCl4 afforded two products
2a and 3a (Scheme 3). When 1 equiv. of ␤-naphthol and 1 equiv.
of the aldehyde were reacted with 1.2 equiv. of acetamide, both
1-amidoalkyl-2-naphthol 2a and bis-1-amidoalkyl-2-naphthol 3a
were obtained in moderate yields. However, the use of 2 equiv.
of ␤-naphthol, 1 equiv. of 4-(diethoxymethyl)benzaldehyde and
2.4 equiv. of acetamide afforded mainly compound 3a.
3.2. The synthesis of 1-amidoalkyl-2-naphthols 1a–t
The condensation of ␤-naphthol with bis-aldehydes (tereph-
thaldehyde) and acetamide, using the imidazolium salts, was also
rapidly performed (Scheme 4). The use 1 equiv. of ␤-naphthol,
1 equiv. of terephthalaldehyde and 1.2 equiv. of acetamide in the
reaction afforded both bis-1-amidoalkyl-2-naphthol 3a and 1-
To optimize the reaction conditions, the condensation of
␤-naphthol (2 mmol) with 4-chlorobenzaldehyde (2 mmol) and
acetamide (2.4 mmol) was examined in the presence of differ-
Table 2
The reaction of ␤-naphthol with 4-chlorobenzaldehyde and acetamide (A) as well as with benzaldehyde and urea (B) using [Msim]Cl/AlCl3 mixture and also AlCl3 (1/0.5 to
1/1, mol/mol).
Entrya
Catalystb
Reaction A
Time (min)
Reaction B
Time (min)
Yieldc/Conv.d (%)
Yieldc/Conv.d (%)
1
2
3
4
5
6
[Msim]Cl
[Msim]AlCl4
AlCl3
[Msim]Cl/AlCl3 (1/0.5)
[Msim]Cl/AlCl3 (1/0.75)
[Msim]Cl/AlCl3 (1/1)
2
2
10
2
2
2
96/99
95/98
82/85
96/99
96/99
96/99
5
6
20
6
6
6
81/86
85/89
70/74
82/86
83/87
83/87
a
The reaction temperature was 120 ◦C.
The amount of the catalysts was 10 mol%.
Isolated yield.
b
c
d
Conversion.

76
M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
Fig. 4. The TG and DTG diagrams of [Msim]Cl and [Msim]AlCl4.
Table 3
Effect of amounts of the catalysts and temperature on the condensation of ␤-naphthol with 4-chlorobenzaldehyde and acetamide.
Entry
Catalyst amounta (mol%)
Temp. (◦C)
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Time (min)
Time (min)
Yieldb/Conv.c (%)
Time (min)
Yieldb/Conv.c (%)
Yieldb/Conv.c (%)
1
2
3
4
5
6
7
8
5
7.5
10
15
10
10
10
10
120
120
120
120
90
100
110
130
5
3
2
2
15
10
5
87/90
92/95
96/99
96/99
68/73
79/83
86/89
92/99
4
2
2
2
89/91
93/95
96/99
96/99
72/76
84/87
89/93
91/99
6
3
2
2
20
12
6
84/88
90/93
95/98
94/98
59/64
73/78
82/86
90/99
11
8
4
2
2
2
a
The reaction was not proceeded in the absence of catalyst.
Isolated yield.
Conversion.
b
c
Fig. 5. Variation of the reaction conversion and yield with time on the solvent-free condensation of ␤-naphthol with 4-chlorobenzaldehyde and acetamide using the
imidazolium salts at 120 ◦C.
amidoalkyl-2-naphthol 3b in moderate yields. Nevertheless, the
condensation of 2 equiv. of ␤-naphthol with 1 equiv. of the alde-
hyde and 2.4 equiv. of acetamide gave compounds 3b as a main
product.
the synthesis of 1-amidoalkyl-2-naphthols in different terms, for
example in terms of reaction time, yield and turn-over frequency
(TOF). The reaction times were shorter, and the yields and TOFs
were higher when our catalysts were utilized.
3.4. Comparison of the efficiency of the catalysts with the recently
reported catalysts for the synthesis of 1-amidoalkyl-2-naphthols
3.5. Proposed mechanism
In a plausible mechanism (Scheme 5) which is supported by
the literature [29,31,38]; at first, aromatic aldehyde is activated by
acidic group of [Msim]Cl to produce I. Then, ␤-naphthol attacks
to the carbonyl group of the activated aldehyde, and affords inter-
mediate II. Next, by removing H2O from II, orthoquinone methide
(o-QM, III) is prepared. [Msim]Cl again activates intermediate III
to give IV as a Michael acceptor. Afterward, Michael addition
To compare the applicability and the efficiency of our
catalysts with the reported catalysts for the synthesis of 1-
amidoalkyl-2-naphthols, we have tabulated the results of these
catalysts to perform the condensation of ␤-naphthol with 4-
chlorobenzaldehyde and acetamide in Table 5. As it is shown in
Table 5, [Msim]Cl, [Dsim]Cl and [Msim]AlCl4 remarkably improved

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
77
Table 4
The solvent-free synthesis of 1-aminoalkyl-2-naphthols from ␤-naphthol, aromatic aldehydes and amides/urea using the sulfonic acid functionalized imidazolium salts.
Producta
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Time (min)
Mp ◦C (Lit.)
Time (min)
Yieldb/Conv.c (%)
Time (min)
Yieldb/Conv.c (%)
Yieldb/Conv.c (%)
5
5
94/97
1
2
95/98
5
6
95/98
238–240 (241–243) [28]
91/95
94/97
93/97
223–225 (220–230) [37]
5
88/91
3
90/94
5
89/93
197–199 (200–202) [31]
12
15
4
87/91
85/88
95/98
96/99
96/99
7
16
2
90/94
95/97
94/98
95/99
96/99
15
25
4
86/91
89/92
95/98
93/97
95/98
200–202 (203–205) [32]
230–232 (235–236) [32]
246–248 (248–250) [37]
238–240 (236–237) [33]
220–222 (224–227) [28]
3
2
3
2
2
2
3
93/97
2
93/97
3
92/95
197–199 (194–196) [33]

78
M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
Table 4 (Continued)
Producta
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Time (min)
Mp ◦C (Lit.)
Time (min)
Yieldb/Conv.c (%)
Time (min)
Yieldb/Conv.c (%)
Yieldb/Conv.c (%)
3
4
5
4
91/93
2
2
4
3
94/97
3
93/96
226–228 (228–230) [32]
90/94
81/86
83/87
94/97
92/96
94/97
4
6
6
89/93
85/89
84/88
206–208 (203–205) [33]
174–176 (172–174) [33]
183–185 (184–186) [33]
6
5
86/90
90/93
4
3
93/96
94/96
7
5
85/88
88/91
237–239 (234–236) [33]
214–216 (216–217) [33]
4
87/90
3
89/93
5
86/90
225–227 (228–230) [31]
4
5
90/94
87/90
2
3
92/96
90/94
4
6
91/94
89/93
178–180 (177–178) [33]
191–193 (193–194) [33]

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
79
Table 4 (Continued)
Producta
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Time (min)
Mp ◦C (Lit.)
Time (min)
Yieldb/Conv.c (%)
Time (min)
Yieldb/Conv.c (%)
Yieldb/Conv.c (%)
7
86/91
4
91/95
7
85/90
187–189 (192–193) [33]
35
83/87
20
89/94
40
85/89
206–209
a
All products were synthesized at 120 ◦C.
Isolated yield.
Conversion.
b
c
O
S
+
Cl
N
N
O
O
R1
H
OH
O
S
O
O
+
H
Cl
N
N
O
H
O
O
H
H
OH
R1
R1
I
II
O
R2
R1
R1
R1
H2N
O
S
R2
O
+
Cl
N
N
O
NH
OH
O
S
+
Cl
O
N
N
O
O
H
O
OH
III (o-QMs)
IV
1-Amidoalkyl-2-naphtol
Scheme 4. The proposed mechanism for the synthesis of 1-amidoalkyl-2-naphthols.
Table 5
Comparison of the results of the condensation of ␤-naphthol with 4-chlorobenzaldehyde and acetamide catalyzed by our new catalysts with those obtained by the recently
reported catalysts.
Catalyst
Catalyst amount (mol%)
Time (min)
Yield (%)
TOFa (min−1
)
Ref.
c
[Msim]Cl, 120 ◦
C
10
10
10
5
51.5
10
2
2
2
2
96b
96d
95e
90
92
90
88
88
93
96
85
85
93
78
89
4.8
6.4
–
–
–
[Dsim]Cl, 120 ◦
C
c
c
[Msim]AlCl4, 120 ◦
I2, r.t.
C
4.75
0.026
0.015
0.9
0.55
1.7
3.87
1.92
0.07
1.7
0.531
0.433
–
690
120
10
80
45
40
5
120
10
35
90
96
[30]
[33]
[35]
[37]
[32]
[34]
[38]
[39]
[40]
[41]
[42]
[43]
Sulfamic acid, ultrasound, 28-30 ◦C
Cyanuric chloride, 100 ◦C
H3PW12O40, 100 ◦
Fe(HSO4)3, 85 ◦
HClO4/SiO2, 90 ◦
C
C
5
C
0.6
10
10
5
5
2
P2O5, 60 ◦
C
4-(1-Imidazolium)butane sulfonate, 80 ◦C
N-(4-sulfonic acid)butyl triethylammonium hydrogensulfate, 120 ◦C
1-Butyl-3-methylimidazolium hydrogen sulphate, 60 ◦C
Cu1.5PW12O40, 100 ◦
Silica sulfuric acid, r.t.
C
0.02 g
a
Turn-over frequency.
In this reaction, the conversion was 99%.
Our work.
In this reaction, the conversion was 99%.
In this reaction, the conversion was 98%.
b
c
d
e

80
M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
Table 6
Effect of impurities of water on the condensation of ␤-naphthol with 4-chlorobenzaldehyde and acetamide.
Entrya
Water amount (mmol)
[Msim]Cl
[Dsim]Cl
[Msim]AlCl4
Time (min)
Time (min)
Yieldb/Conv.c (%)
Time (min)
Yieldb/Conv.c (%)
Yieldb/Conv.c (%)
1
2
3
4
5
6
7
8
9
–
2
4
2
2
4
96/99
96/99
96/99
93/96
89/92
83/86
78/82
71/74
65/69
2
2
2
2
3
96/99
96/99
96/99
96/99
96/99
94/97
91/94
84/87
79/82
2
2
3
95/98
95/98
95/98
94/97
93/96
90/93
86/89
78/81
70/74
8
6
5
16
24
30
50
80
15
25
35
60
120
10
20
30
50
120
7
15
40
110
a
The amounts of ␤-naphthol, 4-chlorobenzaldehyde, acetamide and the catalyst in all reactions were 2, 2, 2.4 and 0.2 mmol, respectively, and the reaction temperature
was 120 ◦C.
b
Isolated yield.
Conversion.
c
methylimidazole. The recovered 1-methylimidazole was reacted
with chlorosulfonic acid to give [Msim]Cl. The catalytic activity of
the reproduced [Msim]Cl was as same as the first one. The recov-
ery and reuse cycle of this catalysts are summarized in Scheme 5.
[Dsim]Cl and [Msim]AlCl4 were also reproduced accordingly.
+
Cl
N
N
SO3H
i and ii
3.7. Effect of impurity of water on the catalytic activity of the
imidazolium salts
To study effect of impurity of water on the catalysts activity, the
condensation of ␤-naphthol (2 mmol) with 4-chlorobenzaldehyde
(2 mmol) and acetamide (2.4 mmol) using the imidazolium salts
(0.2 mmol) was examined in the presence of different amounts
of H2O at 120 ◦C (Table 6). As Table 6 indicates, 16 mmol of H2O
did not affect significantly on the catalytic activity of [Msim]Cl
and [Msim]AlCl4; however, more increasing the amount of H2O
decreased their activity. This can be attributed to hydrolysis of these
catalysts to 1-methylimidazole (as monitored on TLC) and H2SO4
in aqueous media. The catalytic activity of [Dsim]Cl retained in the
presence of 30 mmol of H2O. Moreover, the rate of decreasing the
activity of [Dsim]Cl was slower than [Msim]Cl and [Msim]AlCl4.
These subjects are attributed to more number of SO3H groups in
[Dsim]Cl relative to [Msim]Cl and [Msim]AlCl4.
N
N
ClSO3H
i) The synthesis of 1-amidoalkyl-2-naphthol
ii) Addition of NaOH solution
Scheme 5. The recovery and reuse cycle of [Msim]Cl.
of amide to intermediate IV affords the expected 1-amidoalkyl-
2-naphthol. The reaction results, which have been presented in
Table 4, confirm the mechanism. As Table 4 indicates, electron-
releasing substituents slightly decreased the yields and increased
the reaction times (Table 4, compounds 1b–e), and electron-
withdrawing substituents had no significant effects on the yields,
but slightly decreased the reaction times (Table 4, compounds 1f,
1g, 1m and 1o). In fact, electron-releasing substituents deactivate
aldehyde to accept nucleophilic attack of ␤-naphthol; however,
electron-withdrawing groups activate aldehyde. These are in accor-
dance with the proposed mechanism.
4. Conclusions
In summary, we have introduced the novel sulfonic acid func-
tionalized imidazolium salts, [Msim]Cl, [Dsim]Cl and [Msim]AlCl4,
as highly efficient and green catalysts for organic transformations.
For example, in this work, the synthesis of 1-amidoalkyl-2-
naphthols, via the one-pot three-component condensation of
␤-naphthol with various aryl aldehydes and amides/urea, was
efficiently catalyzed by these imidazolium salts. The promising
points for the presented methodology are efficiency, generality,
high yields, very short reaction times, cleaner reaction profile, sim-
plicity, ease of preparation of the catalyst, and compliance with the
green chemistry protocols.
3.6. Recovering and reusing the catalysts (Scheme 5)
As previously showed, [Msim]Cl, [Dsim]Cl and [Msim]AlCl4
were highly efficient and general for the synthesis of 1-amidoalkyl-
2-naphthols. To raise the catalysts worth, recoverability and
reusability of them were studied. For this purpose, the reaction
of ␤-naphthol with 4-chlorobenzaldehyde and acetamide using
[Msim]Cl was carried out several times, and the reaction mix-
tures were combined. Afterward, H2O was added to the combined
reaction mixtures, stirred for 5 min, and filtered {[Msim]Cl is sol-
uble in H2O; however, the reaction mixture is not soluble in
H2O}. In the aqueous media, a quantity of [Msim]Cl hydrolyzed
to 1-methylimidazole (as monitored on TLC) and H2SO4. To
complete hydrolysis of [Msim]Cl, and consequently formation of
1-methylimidazole, a solution of NaOH (10%) was added to the fil-
trate, and stirred for 5 min. The solution was extracted with EtOAc,
washed with H2O and dried. Evaporation of the solvent gave 1-
Acknowledgements
The authors gratefully acknowledge partial support of this work
by the Research Affairs Office of Bu-Ali Sina University (Grant num-
ber 32-1716 entitled development of chemical methods, reagents
and molecules), and Center of Excellence in Development of Chem-
ical Method (CEDCM), Hamedan, I.R. Iran.

M.A. Zolfigol et al. / Applied Catalysis A: General 400 (2011) 70–81
81
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