Clay-supported 2-phenyl-1H-imidazole derivatives for heterogeneous catalysis of Henry reaction

Article abstract of DOI:10.1002/jhet.669

Figure represented. Six derivatives (1-6) of 2-phenyl-1H-imidazole were tested as catalysts of Henry reaction. Three new (4-6) 2-phenyl-1H-imidazole derivatives, differently substituted (thio)ureas, were synthesized and determined by ¹H NMR and

Full text of DOI:10.1002/jhet.669

July 2011
Clay-Supported 2-Phenyl-1H-Imidazole Derivatives for
Heterogeneous Catalysis of Henry Reaction
907
a
Sylva Holesova, * Patrik Parık, and Miroslav Ludwig
b
b
ˇ
´
ˇ´
a
ˇ
Nanotechnology Centre, VSB-TU Ostrava, Nanotechnology centre,
708 33 Ostrava-Poruba, Czech Republic
bInstitute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of
Pardubice, 532 10 Pardubice, Czech Republic
*E-mail: sylva.holesova@vsb.cz
Received June 18, 2010
DOI 10.1002/jhet.669
Published online 19 April 2011 in Wiley Online Library (wileyonlinelibrary.com).
Six derivatives (1–6) of 2-phenyl-1H-imidazole were tested as catalysts of Henry reaction. Three new
(4–6) 2-phenyl-1H-imidazole derivatives, differently substituted (thio)ureas, were synthesized and deter-
mined by H NMR and IR spectroscopy and elemental analysis. Two types of catalysis, homogeneous
1
and heterogeneous, were examined and compared. Clay minerals Ca-MMT and Cu-MMT were used as
solid supports for heterogeneous catalysis. The best results were obtained using compound 2 under con-
ditions of heterogeneous method D from the point of view of yield and reaction time.
J. Heterocyclic Chem., 48, 907 (2011).
C-nucleophile generated from nitroalkane reacts with an
electrophilic carbonyl carbon which gives versatile syn-
thetic intermediate b-nitroalcohol. Several efficient cata-
lytic methods for performing mainly enantioselective
version of this reaction have been described in recent
years. First pioneers Shibasaki and coworkers reported a
series of bimetallic catalysts [6]. Trost and Yeh showed
new generation of dinuclear zinc complexes yielding
high enantioselectivity [7]. One of the classes of com-
pounds that could be used as ligands for Cu catalysts
are five-membered heterocycles, for example bis(oxazo-
lines) [8], bis(thiazolines) [9], and/or imidazole deriva-
tives [10,11]. Henry reaction was catalyzed without
INTRODUCTION
Heterocyclic compounds including the imidazole ring,
which is part of biologically significant compounds histi-
dine (essential amino acid) and his derivative histamine,
have many important properties. They act as nucleophile
or proton-transfer agent in biological systems [1], they
play significant role in the binding of metallic ions to pro-
teins during enzyme reactions [2], they have antibacterial
and/or antifungal effects [3,4], and last but not least they
are applied as catalysts in quite of few organic reactions.
The nitroaldol (Henry) reaction is one of the classical
reactions forming CAC bonds in organic synthesis [5].
C
V
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S. Holesova, P. Parık, and M. Ludwig
908
Vol 48
presence of metals with the aid of derivatives of follow-
ing compounds, guanidine [12], (thio)ureas [13], or gua-
nidine-thiourea bifunctional catalysts [14], too.
ously described in literature [22,23] and three novel
derivatives of 2-phenyl-1H-imidazole (4–6). All deriva-
tives have substituted ortho position on the benzene
ring.
The development of new heterogeneous catalysts to
promote organic reactions is field of growing interest [15–
18], because of their advantages over homogeneous cata-
lysts, such as simplification of the work-up, easy separa-
tion, and recyclability of catalyst. Recently, mesoporous
silica and/or similar materials were used as solid support
for catalysis of the Henry reaction under heterogeneous
conditions. Abdi and coworkers anchored chiral BINOL
ligand on silica and mesoporous MCM-41 [19]. Several
Cu(II) diamine complexes have been anchored on amine
functionalized silica, Cu-exchanged zeolite and on nano-
porous carbon and used for Henry reaction [20].
2-(2-hydroxyphenyl)-1H-imidazole (1) and 2-(2-pro-
poxyphenyl)-1H-imidazole (2) were synthesized follow-
´
ing the method of Parık et al. [22].
The syntheses of novel 1-subst.-3-[2-(1H-imidazol-2-
yl)phenyl](thio)ureas (4–6) started from 2-(2-amino-
phenyl)-1H-imidazole (3), which was prepared accord-
ing following two-step synthesis. 2-Nitrobezaldehyde
reacted with glyoxal trimer dihydrate and ammonium
acetate in acetic acid to form 2-(2-nitrophenyl)-1H-imid-
azole as intermediate in quite low yield 19%, but oppo-
site literature [23], it was more than double yield. This
compound was then hydrogenated using Pd/C as catalyst
in high yield 91%.
Clay minerals have continuously attracted attention also
for the possibility of modifying their layered structure by
intercalation, thus creating new materials such catalysts [21].
The clay mineral montmorillonite, a member of dioctahedral
smectite group, is the most important smectite used in cata-
lytic applications. Smectites have a layered structure formed
by two tetrahedral sheets linked with an octahedral sheet. The
octahedral sites of montmorillonite are occupied mainly by
Al3þ cations which are to some extent replaced by Fe3þ and/
or Mg2þ ions. The tetrahedron contains as the central atoms
mostly Si4þ, partially substituted by Al3þ. Nonequivalent
substitution of the central atoms in the octahedron and/or tet-
rahedron generates a negative charge on the layers, which is
balanced by hydrated exchangeable cations in the interlayers,
most frequently Ca2þ, Mg2þ, and Naþ in natural samples.
We focused on comparison of homogeneous versus
heterogeneous catalysis using our catalytic systems in
Henry reaction between 4-nitrobenzaldehyde and nitro-
methane as model reaction. Two types of clay minerals,
natural Ca(II)-montmorillonite (Ca-MMT) and modified
Cu(II)-montmorillonite (Cu-MMT), were used as solid
supports for heterogeneous catalysis. Cu-MMT was cho-
sen on the basis of studies deal with catalysis of Henry
reaction by Cu(II) complexes of five-membered hetero-
cycles, which are good catalysts, and Ca-MMT was cho-
sen as starting material for comparison. Three previously
prepared 2-(2-hydroxyphenyl)-1H-imidazole (1), 2-(2-
propoxyphenyl)-1H-imidazole (2) [22], and 2-(2-amino-
phenyl)-1H-imidazole (3) [23], and three novel prepared
derivatives of 1-subst.-3-[2-(1H-imidazol-2-yl)phenyl]
(thio)ureas (4–6) were chosen as catalysts. Syntheses of
mentioned (thio)ureas started from 2-(2-aminophenyl)-
1H-imidazole with appropriate iso(thio)cyanate.
1-(subst.phenyl)-3-[2-(1H-imidazol-2-yl)phenyl]ureas
(4, 6) were synthesized from 2-(2-aminophenyl)-1H-im-
idazole (3) by reactions with appropriate isocyanates. It
was important to find an appropriate solvent for the suc-
cessful accomplishment of reaction; acetonitrile ap-
peared to be the best option. First urea derivative 1-(4-
nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]urea (4) was
obtained in average yield 49%; on the other hand, sec-
ond urea derivative 1-[3,5-bis(trifluoromethyl)phenyl]-3-
[2-(1H-imidazol-2-yl)phenyl]urea (6) was obtained in
very high yield 95%.
1-(4-nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]th-
iourea (5) was synthesized from 2-(2-aminophenyl)-
1H-imidazole (3) by reaction with appropriate isothio-
cyanate, but in contrast with structurally similar urea
derivative, it had to use milder reaction conditions
and dichloromethane was used as solvent. We
obtained product (5) in quite low yield 33%.
The purity and structure of prepared novel compounds
1
(4–6) were determined by the H NMR spectroscopy, IR
spectroscopy, and elemental analysis. Figures 1–3 show
1H NMR spectra of novel prepared compounds (4–6).
For detailed data see Experimental section.
The prepared compounds (1–6) and their modifica-
tions were examined as catalysts for Henry nitroaldol
condensation. We focused on comparison of two types
of catalysis, homogeneous versus heterogeneous. In the
first case two subtypes, method A and B, were used.
Reaction was catalyzed either by derivatives 1–6
(method A) or these derivatives acted as ligands in reac-
tion with metal precursor copper(II)acetate (method B)
in ratio ligand/Cu(II) (1:1). In the case of heterogeneous
catalysis, two subtypes were examined, because we used
two clay minerals as solid supports, Ca-MMT (method
C) and Cu-MMT (method D).
RESULTS AND DISCUSSION
The synthetic part of our work includes syntheses of
three derivatives of 2-phenyl-1H-imidazole (1–3) previ-
Clay-supported catalysts were characterized by XRD
analysis and IR spectroscopy. The Figure 4(a) shows
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

July 2011
Clay-Supported 2-Phenyl-1H-Imidazole Derivatives for Heterogeneous
Catalysis of Henry Reaction
909
Figure 1. 1H NMR spectrum of 1-(4-nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]urea (4).
XRD patterns of original Ca-MMT (d001 ¼ 1.56 nm)
and its modified forms by compounds 1–6. The changes
of basal spacing reflect the intercalation stages of com-
pounds 1 (d001 ¼ 1.84 nm), 2 (d001 ¼ 1.76 nm) and 3
(d001 ¼ 1.64 nm) into interlayer spaces of Ca-MMT.
Other compounds 4–6 were probably anchored on clay
surface. Figure 4(b) shows XRD patterns of Cu-MMT
(d001 ¼ 1.36 nm) and its modified forms by compounds
1–6. In comparison with starting material Ca-MMT, the
XRD patterns of Cu-MMT shows decrease of basal
spacing caused by difference in ionic radius of Cu2þ
ion, which is smaller than Ca2þ ion.
Broad band in the Ca-MMT spectrum is attributed to
stretching vibrations of structural OAH groups (3631
cmꢀ1) and water molecules (3423 cmꢀ1). The most
intense band due to the SiAOASi stretching mode is
observed at 1040 cmꢀ1. The presence of IR bands about
2930 cmꢀ1 and 2860 cmꢀ1 (Fig. 5) were attributed to
asymmetric and symmetric CAH stretching bands of ar-
omatic skeleton of compounds 1–6 supported by clay
matrix. Compared to the Ca-MMT, the Cu-MMT [Fig.
5(b)] has additional band appearing at 3365 cmꢀ1 which
can be attributed to the OAH stretching vibration in
dimerized Cu2þ ions bridging two hydroxyls [24].
The mid-IR spectra of Ca-MMT and its modified
forms by compounds 1–6 are shown on Figure 5(a).
Catalysis of Henry reaction was assessed from point
of view of yield and reaction time (see Table 1).
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S. Holesova, P. Parık, and M. Ludwig
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Vol 48
Figure 2. 1H NMR spectrum of 1-(4-nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]thiourea (5).
Primarily, reaction was accomplished without applica-
tion of catalyst for further comparison; in this case, the
reaction time was 24 h and yield 58%. Second, reaction
was accomplished in presence of solid supports Ca-
MMT and Cu-MMT. In both cases, reaction times are
comparable with reaction time of reaction without cata-
lyst, but yields are evidently higher (see Table 1). So,
from the point of view of yield, chosen solid supports
are catalytically active.
pounds create stable complexes with Cu2þ counterion.
Generally, the lowest yields and longest reaction times
were achieved by homogeneous method B, which is
conventionally used [10,11]. Very good yields were
obtained by homogeneous method A, but reaction times
were comparable with reaction without application of
catalyst, except catalysis by compound 3.
EXPERIMENTAL
The best results were obtained using compound 2
under conditions of heterogeneous method D. On the
other hand, heterogeneous method C did not provide
such a good results. This difference could be caused by
type of clay counterion. There is a possibility that com-
Instrumentation, analysis and starting materials. The pu-
rity of novel prepared (thio)urea derivatives 4–6 was checked
by elemental analysis using an automatic analyser EA 1108
1
(Fisons). H NMR spectra were measured at 25ꢁC using 5%
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July 2011
Clay-Supported 2-Phenyl-1H-Imidazole Derivatives for Heterogeneous
Catalysis of Henry Reaction
911
Figure 3. 1H NMR spectrum of 1-[3,5-bis(trifluoromethyl)phenyl]-3-[2-(1H-imidazol-2-yl)phenyl]urea (6).
solutions of compounds in DMSO-d6 on a NMR AVANCE
400 at 400 MHz; the chemical shifts were referenced to the
solvent signal. Proton numbering for assignment of 1H NMR
shifts shows Figure 6. The mid-infrared spectra were obtained
on a Perkin Elmer 2000 Fourier transform infrared spectrome-
ter. For each sample, 32 scans were recorded in the 4000–400
cmꢀ1 spectral range with a resolution of 4 cmꢀ1 at room tem-
perature using the KBr pressed disc technique (0.8 mg of sam-
ple and 290 mg of KBr). XRD analysis was used for charac-
terization of clay-supported catalysts obtained by the X-ray
diffractometer INEL equipped with a curved position-sensitive
detector CPSD 120 (reflection mode, Ge-monochromatized
CuKa1 radiation) and next infrared spectroscopy with experi-
mental arrangement above mentioned was used for characteri-
zation. Progress of Henry reactions was monitored by thin-
layer chromatography (TLC) using Precoated TLC-sheets
ALUGRAM? SIL G/UV254 and ethyl acetate/hexane (1:4) as
mobile phase. Other chemical materials were purchased from
Aldrich, Fluka and Merck Companies.
2-(2-Hydroxyphenyl)-1H-imidazole (1) and 2-(2-propoxy-
phenyl)-1H-imidazole (2). Compounds 1 and 2 were synthe-
sized following the procedure reported in literature [22].
2-(2-Aminophenyl)-1H-imidazole (3). Compound
3 was
synthesized according the procedure reported in literature [23].
1-(4-Nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]urea (4). To
a mixture of 0.25 g (1.57 mmol) of 2-(2-aminophenyl)-1H-im-
idazole in acetonitrile was added 0.26 g (1.57 mmol) of 4-
nitrophenyl isocyanate. Reaction mixture was refluxed under
stirring for 5 h, following with stirring overnight under labora-
tory temperature. Pale yellow crystals were collected by
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S. Holesova, P. Parık, and M. Ludwig
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Figure 4. XRD patterns of (a) Ca-MMT and its modified forms by compounds 1–6 and (b) Cu-MMT and its modified forms by compounds 1–6.
1
filtration to yield 0.25 g (49%) of 4; mp 198–202ꢁC; H NMR
(DMSO-d6, 400 MHz): d 12.82 (s, 1H, H-8), 12.14 (s, 1H, H-
5), 10.41 (s, 1H, H-9), 8.32 (d, 1H, H-1), 8.25 (d, 2H, H-10),
7.93 (d, 1H, H-4), 7.85 (d, 2H, H-11), 7.36–7.42 (m, 2H, H-3,
H-6[7]), 7.27 (s, 1H, H-6[7]), 7.17 (t, 1H, H-2); IR (KBr):
3215 (NH), 1687 (C¼¼O), 1504 (NO2); Anal. Calcd for
C16H13N5O3: C, 59.44; H, 4.05; N, 21.66. Found: C, 59.26; H,
4.24; N, 21.42.
1-(4-Nitrophenyl)-3-[2-(1H-imidazol-2-yl)phenyl]thiourea (5). A
mixture of 0.1 g (0.628 mmol) of 2-(2-aminophenyl)-1H-imid-
azole in dichloromethane was stirred under argon atmosphere
and cooled in ice. To this mixture was added 0.11 g (0.628
Figure 5. IR spectra of (a) Ca-MMT and its modified forms by compounds 1–6 and (b) Cu-MMT and its modified forms by compounds 1–6.
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Clay-Supported 2-Phenyl-1H-Imidazole Derivatives for Heterogeneous
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913
Table 1
Yields and reaction times of realized Henry reactions.
mmol) of 4-nitrophenyl isothiocyanate and 3 drops of dry trie-
thylamine, reaction mixture was stirred for 30 min. Cooling
bath was then removed and mixture was stirred overnight
under laboratory temperature and argon atmosphere. Yellow
crystals were collected by filtration to yield 0.07 g (33%) of 5;
Reaction
timea (h)
Compound
Method of catalysis
Yield (%)
1
mp: 140–145ꢁC; H NMR (DMSO-d6, 400 MHz): d 12.85 (s,
–
–
–
1
Without catalyst
Ca-MMT
Cu-MMT
58
75
84
63
47
45
60
51
47
42
82
76
46
34
60
72
53
59
56
44
27
39
48
76
32
44
40
24
25
20
26
48
16
6
25
25
22
5
2H, H-5, 8), 11.10 (s, 1H, H-9), 8.48 (d, 1H, H-1), 8.27 (d,
2H, H-10), 7.91 (d, 3H, H-4, 11), 7.40 (t, 1H, H-3), 7.27 (t,
1H, H-2), 7.22 (s, 2H, H-6, 7); IR (KBr): 3180 (NH), 1507
(NO2), 1259 (C¼¼S); Anal. Calcd for C16H13N5O2S: C, 56.36;
H, 3.86; N, 20.64; S, 9.45. Found: C, 55.90; H, 4.24; N,
20.41; S, 9.75.
1-[3,5-Bis(trifluoromethyl)phenyl]-3-[2-(1H-imidazol-2-yl)
phenyl]urea (6). To a mixture of 0.25 g (1.57 mmol) of 2-(2-
aminophenyl)-1H-imidazole in acetonitrile was added 0.271
mL (1.57 mmol) of 3,5-bis(trifluoromethyl)phenyl isocyanate.
Reaction mixture was refluxed under stirring for 5 h, following
with stirring overnight under laboratory temperature. White
crystals were collected by filtration to yield 0.62 g (95%) of 6;
mp 222–230ꢁC; 1H NMR (DMSO-d6, 400 MHz): d 12.83 (s,
1H, H-8), 12.29 (s, 1H, H-5), 10.35 (s, 1H, H-9), 8.38 (d, 1H,
H-1), 8.32 (s, 2H, H-10), 7.94 (d, 1H, H-4), 7.67 (s, 1H, H-
11), 7.35–7.42 (m, 2H, H-3, H-6[7]), 7.27 (s, 1H, H-6[7]),
7.16 (t, 1H, H-2); IR (KBr): 3193 (NH), 1686 (C¼¼O), 1388
(CF); Anal. Calcd for C18H12F6N3O: C, 52.18; H, 2.92; N,
13.52. Found: C, 52.40; H, 3.22; N, 13.73.
A
B
C
D
A
B
C
D
A
B
C
D
A
B
C
D
A
B
C
D
A
B
C
D
2
3
4
5
6
5
48
5
5
25
75
4
7
15
72
8
10
24
72
21
24
General procedure for clay-supported catalyst. The natu-
ral Ca-MMT from a deposit Ivancice in the Czech Republic,
selected as a starting material, was fractionated to less than <45
lm particles. The structural formula of this montmorillonite as
calculated from the chemical analysis is (Al2.52Fe30þ:54Mg0.90Ti0.04
)
a Reaction time corresponds to the disappearance of starting aldehyde
monitored by TLC.
(Si7.96Al0.04) O20(OH)4(Ca0.24K0.06Na0.09Mg0.10). The Cu-MMT
was prepared from 10 g Ca-MMT by cation exchange method
Figure 6. Proton numbering for assignment of 1H NMR shifts.
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S. Holesova, P. Parık, and M. Ludwig
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via addition of 100 mL of 1M CuCl2.2H2O water solution, and
the mixture was stirred and heated at 70ꢁC for 2 h. After centrif-
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and finally dried at 50ꢁC. To prepare clay-supported catalysts
mixture of 0.5 g of Ca-MMT or 0.5 g of Cu-MMT together with
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General procedure for the Henry reaction. A solution of
catalyst (0.1 mmol) (Method A: compounds 1–6; Method B:
compounds 1–6 together with 0.1 mmol of copper(II)acetate;
Method C: compounds 1–6 supported by Ca-MMT; Method
D: compounds 1–6 supported by Cu-MMT) in ethanol (5 mL)
was stirred for 30 min at room temperature in a Teflon coated
flask. It was used 10 wt % of Ca-MMT and/or Cu-MMT for
reactions in presence of only solid support. 4-Nitrobenzalde-
hyde (0.151 g, 1 mmol), triethylamine (14 lL, 0.1 mmol), and
nitromethane (0.55 mL, 10 mmol) were then added under stir-
ring. Conversion of reaction was monitored by TLC (ethyl ac-
etate/hexane 1:4). Only when starting aldehyde was not
observed, ethanol was then evaporated under reduced pressure
and replaced by ether. The precipitate was filtered off through
a plug of silica and washed with ether. The ether extract was
washed with aqueous sodium bisulfite, water and dried with
sodium sulphate. Solvent was again evaporated under reduced
pressure to give product.
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MHz), d 4.66–4.71 (m, 1H, CH(OH)CH2NO2), 4.98–5.02 (dd,
1H, CH(OH)CH2NO2), 5.47–5.50 (dd, 1H, CH(OH)CH2NO2),
6.48 (bs, 1H, CH(OH)CH2NO2), 7.79 (d, 2H, ArH), 8.28 (d,
2H, ArH).
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´
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(project GACR No. 205/08/0869), and the Ministry of Education,
Youth and Sports of the Czech Republic (projects MSM
6198910016 and MSM 0021627501).
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