Synthesis and application of silica phenyl sulfonic acid as a solid acid heterogeneous catalyst for one-pot synthesis of 2-aryl-1-arylmethyl-1H-1,3- benzimidazoles and bis(indolyl)methanes in water

Article abstract of DOI:10.1002/jhet.765

Silica phenyl sulfonic acid (SPSA) was prepared and effectively used in the one-pot synthesis of 2-aryl-1-arylmethyl-1H-1,3-benzimidazoles from o-phenylenediamine with aldehydes in water in the presence of tetrabutyl ammonium bromide with good to high yield. Also, SPSA was used as a catalyst for the synthesis of bis(indolyl)methanes in water. Copyright

Full text of DOI:10.1002/jhet.765

1448
Synthesis and Application of Silica Phenyl Sulfonic Acid as a
Solid Acid Heterogeneous Catalyst for One-Pot Synthesis of
2-Aryl-1-arylmethyl-1H-1,3-benzimidazoles and
Bis(indolyl)methanes in Water
Vol 48
Hojat Veisi,a* Alireza Sedrpoushan,b,c Mohammad Ali Zolfigol,b* and
Farajollah Mohanazadehc
aDepartment of Chemistry, Payame Noor University (PNU), Iran
bFaculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
cChemical Industries Department, Iranian Research Organization for Science and Technology
(IROST), Tehran, Iran
*E-mail: hojatveisi@yahoo.com
Received August 30, 2010
DOI 10.1002/jhet.765
Published online 23 August 2011 in Wiley Online Library (wileyonlinelibrary.com).
Silica phenyl sulfonic acid (SPSA) was prepared and effectively used in the one-pot synthesis of
2-aryl-1-arylmethyl-1H-1,3-benzimidazoles from o-phenylenediamine with aldehydes in water in the
presence of tetrabutyl ammonium bromide with good to high yield. Also, SPSA was used as a catalyst
for the synthesis of bis(indolyl)methanes in water.
J. Heterocyclic Chem., 48, 1448 (2011).
INTRODUCTION
1,2-disubstituted benzimidazoles can also be accessed
by direct one-step condensation of 1,2-phenylenedi-
amines with aryl aldehydes under the influence of a va-
riety of acid catalysts [9]. However, the last protocol is
currently most popular, probably because of the ease of
accessibility of substituted aryl aldehydes.
Benzimidazole derivatives have versatile pharmaco-
logical properties [1] based on their presence in both
clinical medicines [2] and compounds with broad ranges
of biological functions [3]. The most prominent benzim-
idazole compound in nature is N-ribosyl-dimethylbenzi-
midazole, which serves as an axial ligand for cobalt in
vitamin B12[4]. Thus, synthesis of this heterocyclic nu-
cleus is, therefore, of continuing interest, but few meth-
ods are available for the synthesis of 1,2-disubstituted
benzimidazoles. The more important ones include: N-al-
kylation of 2-substituted benzimidazole in the presence
of a strong base [5], N-alkylation of o-nitroanilides
followed by reductive cyclization [6], cyclocondensation
of N-substituted o-aminoanilides [7], and condensation
of N-substituted phenylenediamines with the sodium
salt of a-hydroxybenzylsulfonic acid [8]. In addition,
The development of bis(indolyl)alkane synthesis has
been of considerable interest in organic synthesis
because of their wide occurrence in various natural
products possessing biological activity and usefulness
for drug design [10]. Bis(indolyl)methanes are found in
cruciferous plants and are known to promote beneficial
estrogen metabolism [11] and induce apoptosis in
human cancer cell. Thus, the development of facile and
environmentally friendly synthetic methods for the prep-
aration of these compounds constitutes an active area of
investigation in pharmaceutical and organic synthesis
C
V
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November 2011 Synthesis and Application of Silica Phenyl Sulfonic Acid as a Solid Acid
Heterogeneous Catalyst for One-Pot Synthesis of 2-Aryl-1-arylmethyl-1H-1,3-benzimidazoles
1449
Scheme 1
Scheme 2
liquid [27], HClO4-SiO2 [28], InCl3 [29], MW/Lewis
acids (FeCl3, BiCl3, InCl3, ZnCl2, and CoCl2) [30],
NaHSO4 and Amberlyst-15 [31], sulfated zirconia [32],
ZrOCl2/SiO2 [33], silica sulfuric acid (SSA) [34], TiO2
[35], (NH4)2HPO4 [36], acidic ionic liquid [37], NaBF4
[38], metal hydrogen sulfates [39], tetrabutylammonium
tribromide [40], superacid SO24ꢀ/TiO2 [41], NaHSO4/
ionic liquid [42], NBS [43], Ph3CCl [44], H3PW12O40
[45], LiClO4 [46], Zr(DS)4 [47] and Bi(NO3)3.5H2O
[48], (CO2H)2.2H2O [49], and N-chloro sulfonamides
[50]. However, most of the existing methods involve
toxic metal ions and solvent, high cost, and cumbersome
work-up procedures. Consequently, new procedures that
address these drawbacks are desirable.
Developing environmentally benign and economical
syntheses are an area of research that is being vigo-
rously pursued and avoiding the use of harmful organic
solvents is a fundamental strategy to achieving this. One
of the most attractive alternatives to organic solvents is
water, which has witnessed increasing popularity due to
being inexpensive, readily available, and environmen-
tally benign. In addition, reactions in aqueous media
illustrate unique reactivities and selectivities that are not
usually observed in organic media [51].
[12–14]. Very recently, we have published a comprehen-
sive review related to the synthesis and applications of
bisindolylmethanes and trisindolylmethanes [15a].
Synthetically, the reaction of 1H-indole with alde-
hydes or ketones produces azafulvenium salts that react
further with a second 1H-indole molecule to form
bis(indol-3-yl)methanes [15b]. In recent years, synthesis
of this class of molecules under mild conditions have
been reported, with promoters such as montmorillonite
clay K-10 [16], trichloro-1,3,5-triazine [17], AlPW12O40
[18], sodium dodecyl sulfate (SDS) [19], ZrCl4 [20],
H2NSO3H [21], I2 [22], zeolites [23], bentonite [24],
In(OTf)3/ionic liquid [25], CuBr2 [26], Dy(OTf)3/ionic
RESULTS AND DISCUSSION
In continuation of our studies on the synthesis [52] and
application of SSA [52] as a solid acid heterogeneous
Figure 1. FTIR spectrum silica phenyl sulfonic acid (SPSA).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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H. Veisi, A. Sedrpoushan, M. A. Zolfigol, and F. Mohanazadeh
Vol 48
Table 1
Synthesis of 2-aryl-1-arylmethyl-1H-1,3-benzimidazoles catalyzed by SPSA in the presence of TBAB in water.
Entries
R
Time (min)
Yield (%)a
Mp (ꢁC) (lit.)
Refs.
1
2
C6H5
4-MeC6H5
4-MeOC6H5
2-MeOC6H5
4-ClC6H5
10
12
98
95
90
95
96
95
90
90
88
90
85
0
131–132 (132)
127–129 (128–130)
128–130 (129–130)
124–125 (125–126)
134–136 (136)
157–158 (158–159)
222–223 (222)
303–305 (306–308)
253–255 (255)
210–212 (212–213)
94–95 (94)
[9d]
[9i]
[9d]
[9d]
[9g]
[53c]
[53b]
[54]
[9i]
[9d]
[9d]
–
3
4
15
12
5
15
15
10
15
10
10
12
6
7
2-ClC6H5
4-OHC6H5
4-NO2C6H5
4-(Me2N)C6H5
C6H5ACH¼CH
2-Furyl
8
9
10
11
12
13
CH3(CH2)2
CH3(CH2)8
300
300
–
0
–
–
a Products were characterized from their physical properties, comparison with authentic samples, and by spectroscopic methods.
catalyst, we reported the synthesis of silica phenyl sul-
fonic acid (SPSA) as a new type of silica in organic reac-
tion. Although our first report of SSA has been widely
used [52a] but also we think that SPSA is superior due to
its more stability in the presence of moisture. SPSA is
easily prepared from the silanization of activated silica
gel with diphenyldichlorosilane (DPCS) followed by add-
ing chlorosulfonic acid at room temperature, and washed
with water (Scheme 1). FTIR spectrum SPSA was shown
in Figure 1.
organic substrates (Scheme 2). However, this process is
green, environmentally friendly, clean, and could be car-
ried out easily at room temperature without undesirable
side reactions.
We started this synthesis by examining the reaction of
1,2-phenylenediamine (1 mmol) with benzaldehyde (2
mmol) as a model reaction. We found that the use of
SPSA (50 mg) and 10 mol % TBAB allowed the direct
conversion of 1,2-phenylenediamine into the correspond-
ing 1,2-disubstituted benzimidazole in a yield of 98% in
water (5 mL) at 40ꢁC (Table 1, entry 4). The use of
more than 50 mg of SPSA did not enhance chemical
yield.
The first synthesis of sulfobenzylsilicas has reported
by Saunders et al. [53a] in 1974. The preparation
involved the chlorination of reactive silanol groups, the
reaction of this product with benzyllithium, and finally
sulfonation. We believe that this method is not very
easy, and they have to use organolithium reagent to
achieved sulfobenzylsilicas. But our method is a short-
cut way to synthesis of these types of compounds with-
out using of any organolithium reagent.
To test the generality of this reaction, a series of aro-
matic aldehydes was subjected to the optimal reaction
conditions (Table 1). By using water as solvent at 40ꢁC,
1,2-disubstituted benzimidazoles with various functional
groups were obtained in excellent yields. Among the
reactions of different aromatic aldehydes, no significant
distinction on the yields of target products was
observed. Even the sensitive substrate furfuraldehyde
(Table 1, entry 11) produced the corresponding 1,2-dis-
ubstituted benzimidazole without any difficulty. All sub-
strates gave their corresponding 1,2-disubstituted benzi-
midazoles exclusively as a single product. However,
butyraldehyde and octanal (Table 1, entries 12, 13)
failed to react under the present reaction conditions.
In continuation of our recent interest in the synthesis
of heterocyclic compounds [52], we, herein, developed a
green and selective reaction to synthesis of 2-aryl-1-
arylmethyl-1H-1,3-benzimidazoles through the reactions
of 1,2-phenylenediamine with aryl aldehydes in aqueous
media, in the presence of SPSA as a solid acid heteroge-
neous catalyst, and tetrabutyl ammonium bromide
(TBAB) as a surfactant to assist in solubilizing the
Scheme 3
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2011 Synthesis and Application of Silica Phenyl Sulfonic Acid as a Solid Acid
Heterogeneous Catalyst for One-Pot Synthesis of 2-Aryl-1-arylmethyl-1H-1,3-benzimidazoles
1451
A possible mechanism for the reaction consists of a
two-step sequence involving the acid catalyst-promoted
formation of the N,N-dibenzylidene-1,2-phenylenedi-
amine derivative followed by ring closure. Aromatiza-
tion then takes place by a deprotonation–reprotonation
process [9j].
The scope of this system has been successfully
extended to the synthesis of bis(indolyl)methanes in water
(Scheme 3). The optimum conditions were indole (2
mmol) and aldehyde (1 mmol), in the presence of SPSA
(200 mg) and TBAB (10 mol %) in water at 25ꢁC (Fig. 2).
Figure 2. Photographs of the reaction of indole with benzaldehyde in
the presence of SPSA and TBAB in H2O at 25ꢁC: (left side) at the
start of the reaction; and (right side) at the end of the reaction.
Table 2
Synthesis of Bis(indolyl)methanes catalyzed by SPSA in the presence of TBAB in water.
Entries
R1
R2
Time (min)
Yield (%)a
Mp (ꢁC) (lit.)
Refs.
1
2
C6H5
4-MeC6H5
H
H
10
12
5
96
95
98
98
96
98
90
92
80
85
90
90
92
95
80
75
80
85
70
90
85
85
124–125 (124–125)
94–95 (93–94)
[55]
[19]
[55]
[48]
[55]
[19]
[47]
[56]
[19]
[57]
[48]
[19]
[19]
[19]
[47]
[47]
[58a]
[50]
[58b]
[47]
[47]
[48]
3
4
4-MeOC6H5
2-MeOC6H5
4-ClC6H5
2-ClC6H5
4-BrC6H5
4-OHC6H5
H
H
190–192 (192–193)
134–136 (133–135)
76–78 (78–80)
5
5
6
H
H
5
5
70–72 (70–71)
7
8
H
H
10
15
25
25
20
25
15
12
30
30
30
20
30
20
25
20
110–112 (112–113)
123–125 (123–125)
218–220 (217–220)
258–260 (260–261)
224–226 (225–226)
98–100 (98–99)
9
4-NO2C6H5
3-NO2C6H5
4-(Me2N)C6H5
C6H5ACH¼CH
2-Furyl
H
10
11
12
13
14
15
16
17
18
19
20
21
22
H
H
H
H
>300 (>300)
2-Thienyl
H
H
151–154 (150–153)
121–123 (122–124)
190–182 (181–182)
255–257 (256–258)
194–195 (194–195)
>300 (>300)
165–167 (166–168)
190–192 (190–191)
115–116 (114–116)
CH3(CH2)2
CH3(CH2)8
Indol-3-carbaldehyde
Terephthaldialdehyde
Isatin
H
–
–
–
C6H5
4-NO2C6H5
Cyclohexanone
CH3
CH3
–
a Products were characterized from their physical properties, comparison with authentic samples and by spectroscopic methods.
Scheme 4
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1452
H. Veisi, A. Sedrpoushan, M. A. Zolfigol, and F. Mohanazadeh
Vol 48
Scheme 5
These results promoted us to investigate the scope, and
efficiency, mild reaction conditions, easy work up, sim-
plicity, and chemoselectivity of this protocol provide a
fast, green, and low-cost procedure for the synthesis of
these compounds.
the generality of this new protocol for various aldehydes
and ketones under optimized conditions. As shown in
Table 2, a series of aromatic, aliphatic, and heterocyclic
aldehydes underwent electrophilic substitution reaction
with indole smoothly to afford a wide range of substi-
tuted bis(indolyl)methanes in good to excellent yields
(Table 2, entries 1–22). Ketones required longer reaction
times, which is most probably due to the electron-donat-
ing and steric effects of the methyl group.
EXPERIMENTAL
Preparation of modified silica sulfuric acid. Fifty grams
of silica gel 1 (SiO2, mesh 35–70, 675 m2/gr, Merk) was
added to 200 mL HCl (0.1M) in a suitable vessel and stirred
for 60 min at room temperature. After 60 min, the solid was
filtrated and washed with deionized water for several times to
get the activated silica gel (2). The activated SiO2 (2) was
dried under vacuum (60 mm/Hg) in 70ꢁC for 3 h.
This reaction was further explored for the synthesis of
tri(bisindolyl)methane (7) and tetra(bisindolyl)methanes
(9) as new triarylmethanes and tetraarylmethanes, by the
condensation of aldehyde (6) with six equivalents indole
and aldehydes (8) with eight equivalents indole under
similar condition in high yields (Schemes 4 and 5).
3-Substituted indole was examined for this reaction
under the above reaction conditions with aldehydes
(Scheme 6). Because the more active site (C-3) in indole
was blocked in this case, electrophilic substitution took
place at C-2 in indole giving the corresponding bis(indo-
lyl)methane in high yield under same conditions.
Activated SiO2 (50 g) was dispersed in dry toluene (70 mL)
under nitrogen condition and then DPCS (25 mL) was added
to the dispersion for 30 min at room temperature and stirred
for 15 h in reflux conditions. After that, filterated and washed
with dry toluene (100 mL) and dry CHCl3 (200 mL) and dried
under vacuum (60 mm/Hg) in 70ꢁC to get the chlorodiphenyl-
silylated silica (3). In the next step, 25 g dry phenyl silica (3)
was suspended in 50 mL of dry chloroform in a three-neck
flask fitted with a motor-driven glass stirrer, gas inlet tube, and
dropping funnel. A solution of 30 g of chlorosulfonic acid in
50 mL of dry chloroform was added dropwise in 10 min. The
sulfonating mixture was stirred 20 h at room temperature. Af-
ter filtering off the sulfonating mixture, the product was
washed with small portions of chloroform totaling 250 mL.
The washing was continued using a total of 200 mL of ace-
tone. Residual acid, color, and chloride ion were removed by
suspending the product in five successive 100-mL portions of
distilled water and allowing water to filter through by gravity
percolation.
CONCLUSION
In summary, a practical and convenient synthetic
method in aqueous media using SPSA as a solid acid het-
erogeneous catalyst, and TBAB as a surfactant has been
developed for the facile synthesis of 1,2-disubstituted
benzimidazoles and bis(indolyl)methanes. In addition,
The product was washed with acetone and chloroform and
dried under vacuum (60 mm/Hg) in 70ꢁC. Final weight recov-
ered was 26.3 g (5).
Scheme 6
General procedure for the synthesis of 2-aryl-1-aryl-
methyl-1H-1,3-benzimidazoles. The aryl aldehyde (2 mmol)
and 1,2-phenylenediamine (1 mmol) were added to a solution
of TBAB (10 mol %, 0.032 g) and SPSA (50 mg) in H2O
Journal of Heterocyclic Chemistry
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November 2011 Synthesis and Application of Silica Phenyl Sulfonic Acid as a Solid Acid
Heterogeneous Catalyst for One-Pot Synthesis of 2-Aryl-1-arylmethyl-1H-1,3-benzimidazoles
1453
(5 mL), and the mixture stirred at 40ꢁC for the time given
(Table 1). The progress of the reaction was monitored by TLC
(eluent: 4:1 n-hexane-acetone). After completion of the reac-
tion, the resulting precipitate of product filtered off. Then etha-
nol (10 mL) was added to the solid, and the catalyst was
removed by filtration. Evaporation of the solvent under
reduced pressure gave the crude products. Finally, the crude
product was recrystallized in ethanol (85–98%).
Synthesis of bis(indolyl)methanes. The aldehyde or ketone
(1 mmol) and indole (2 mmol) were added to a solution of
TBAB (10 mol %, 0.032 g) and SPSA (200 mg) in H2O (5
mL), and the mixture stirred at room temperature for the time
given (Table 1). The progress of the reaction was monitored
by TLC (eluent: 4:1 n-hexane-acetone). After completion of
the reaction, the resulting precipitate of product filtered off.
Then ethanol (10 mL) was added to the solid, and the catalyst
was removed by filtration. Evaporation of the solvent under
reduced pressure gave the crude products. Finally, the crude
product was recrystallized in ethanol–water (70–98%).
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