An easy one-step photocatalytic synthesis of 1-aryl-2-alkylbenzimidazoles by platinum loaded TiO2 nanoparticles under UV and solar light

Article abstract of DOI:10.1016/j.tetlet.2011.04.090

One-pot synthesis of disubstituted benzimidazoles from N-substituted 2-nitroanilines or 1,2-diamines with 3-12 nm-sized platinum particles loaded on the TiO₂ using solar and UV-A light is described. 1-Aryl-2-alkylbenzimidazoles from 2-nitrodiphenylamines are formed by combined redox photocatalytic reaction, condensation and catalytic dehydrogenation on Pt-TiO₂. In case of diamines, this reaction is proceeded by Pt-TiO₂ assisted photocatalytic oxidation of an alcohol and a catalytic dehydrogenation of the intermediate on the surface of platinum nanoparticles. In both cases product formation was achieved by tandem photocatalytic and catalytic reactions on Pt-TiO₂.

Full text of DOI:10.1016/j.tetlet.2011.04.090

Tetrahedron Letters 52 (2011) 3386–3392
Contents lists available at ScienceDirect
Tetrahedron Letters
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An easy one-step photocatalytic synthesis of 1-aryl-2-alkylbenzimidazoles
by platinum loaded TiO2 nanoparticles under UV and solar light
⇑
K. Selvam, M. Swaminathan
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
One-pot synthesis of disubstituted benzimidazoles from N-substituted 2-nitroanilines or 1,2-diamines
with 3–12 nm-sized platinum particles loaded on the TiO2 using solar and UV-A light is described. 1-
Aryl-2-alkylbenzimidazoles from 2-nitrodiphenylamines are formed by combined redox photocatalytic
reaction, condensation and catalytic dehydrogenation on Pt-TiO2. In case of diamines, this reaction is pro-
ceeded by Pt-TiO2 assisted photocatalytic oxidation of an alcohol and a catalytic dehydrogenation of the
intermediate on the surface of platinum nanoparticles. In both cases product formation was achieved by
tandem photocatalytic and catalytic reactions on Pt-TiO2.
Received 7 November 2010
Revised 21 April 2011
Accepted 23 April 2011
Available online 30 April 2011
Keywords:
Pt-TiO2
Combined redox reaction
Photocatalysis
Ó 2011 Elsevier Ltd. All rights reserved.
1-Aryl-2-alkylbenzimidazoles
Tandem reaction
Benzimidazoles play a vital role in the synthesis of pharmaceu-
ticals.1 2-Substituted benzimidazoles are used as anthelmintics in
veterinary medicine2 and display significant anticancer, antiviral,
antiallergic, antiulcer, and anticoagulant properties in human ther-
apeutics.3 Methods of benzimidazole synthesis include the conden-
sation of o-aryldiamines and aldehyde in refluxing nitrobenzene,4,5
the condensation of o-aryldiamines with carboxylic acids or their
derivatives in the presence of strong acids such as polyphosphoric
acid6 or mineral acids7 and the thermal or acid promoted cycliza-
tion of N-(N-arylbenzimidoyl)-1,4-benzoquinoneimines.8 Direct
condensation of o-aryldiamines and aldehydes is not a good syn-
thetic reaction, as it is well known to yield a complex mixture of
1,2-disubstituted benzimidazoles, the bis anil and dihydrobenzim-
idazoles.9 However, in this reaction, the addition of a transition me-
tal, namely copper(II) acetate,10 mercury oxide11 or lead
tetracetate12 allows a partial selective synthesis of benzimidazoles.
Unfortunately, many of these processes suffer some limitations,
such as drastic reaction conditions, low yields, tedious work-up
procedures and co-occurrence of several side reactions. This way,
the development of clean, general, and selective routes to benzim-
idazoles, including the use of new catalysts, renewable starting
materials, and non-classical energy sources continues to attract
the interest of synthetic organic chemists.
sis of 1-aryl-2-alkylbenzimidazoles. Photocatalysts such as TiO2,
Pt-TiO2 and others have been reported for the synthesis of benzim-
idazoles.13–15 Pt-TiO2 is able to promote two different transforma-
tions in one-pot by employing both photocatalytic and catalytic
actions: the conversion of nitro to amino group and alcohols into
aldehydes through a platinum-assisted photocatalytic redox reac-
tion on the Pt-TiO2 surface,15 and the catalytic dehydrogenation
of benzimidazoline intermediates generated by the condensation
of ortho-arylenediamines and aldehydes on the platinum particle
surface.
Some of the modified semiconductor photocatalysts developed
in our laboratory have been used for several organic transforma-
tions.16–18 Recently we reported the synthesis of 2-alkylbenzimi-
dazoles by combined redox reaction of 2-nitrophenyl azides in
alcohols using Pt-TiO2 catalyst.19 In the present study, we report
a new strategy for the acid- and oxidant-free synthesis of 1-aryl-
2-alkylbenzimidazoles using 2-nitrodiphenylamines or 2-aminodi-
phenylamines and alcohols at room temperature under UV and
solar light. To the best our knowledge this is the first report on
the semiconductor mediated one-pot photocatalytic synthesis of
1-aryl-2-alkylbenzimidazoles with good yield under mild condi-
tions. The reaction mechanism and steps taken to validate the
mechanism are discussed.
In the context of developing eco-friendly green chemical pro-
cess, we decided to look at the use of photocatalysts for the synthe-
Pt-TiO2, prepared by photodeposition method,20 was character-
ized by X-ray diffraction (XRD), high resolution transmission elec-
tron microscopy (HR-TEM), X-ray photoelectron spectroscopy
(XPS), BET surface area and diffuse reflectance spectroscopy
(DRS) techniques (see Supplementary data, Figs. S1–S4). The
X-ray diffraction patterns of the Pt-TiO2 [Fig. S1(b)] samples match
⇑
Corresponding author. Tel.: +91 4144 225072, mobile: +91 9842381967; fax:
+914144 238145.
E-mail address: chemres50@gmail.com (M. Swaminathan).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.090

K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
3387
that of the undoped TiO2 and are identical with the JCPDS pattern
of anatase. This reveals that photodeposition of the platinum does
not modify the basic crystal structure of the TiO2 used. The high-
resolution transmission electron microscopy (HR-TEM) image of
Pt (1.5%)-TiO2 (Fig. S2) shows non-spherical platinum particles
with an average diameter of 3–12 nm. The electronic state of Pt
in the catalysts was verified by XPS. The XPS survey spectrum
(see Supplementary data, Fig. S3) of the Pt-TiO2 indicates the peaks
of elements Ti, O, C and Pt (trace). High-resolution XPS spectrum
(inset Fig. S3) from 80 to 90 eV confirms the existence of Pt.
Figure S3 shows the binding energies of Pt4f7/2 (70.3 eV) and
Pt4f5/2 (74.0 eV) and the splitting of the 4f doublet (3.7 eV). These
binding energies indicate that platinum is present in metallic state.
The diffuse reflectance spectrum of 1.5% Pt-doped TiO2 is shown in
Figure S4. Pt-TiO2 has higher absorption in the visible region.
Initial experiments were carried out with ethanolic solution of
2-nitrodiphenylamine (1) containing TiO2 nanoparticles under dif-
ferent conditions. Irradiation of 2-nitrodiphenylamine with TiO2 in
ethanol using UV light produced cyclized product of 2-methyl-1-
phenylbenzimidazole (2).21 Either the irradiation of ethanolic
solution of 2-nitrodiphenylamine alone or the solution of 2-nitro-
diphenylamine and the catalyst without light did not give any
product of our interest. This indicates that both light and TiO2
are essential for the formation of 2-methyl-1-phenylbenzimida-
zole. With pure TiO2 (Table 1, entry 1), 8 h photoirradiation was re-
quired to obtain 75% of product 2 in addition to small amounts of
other reduction products (12%). The structure of product 2 was
confirmed by GC–MS and NMR.22 The percentage yield was deter-
mined by comparison with the retention times of authentic sam-
ples and by co-injection with the authentic compounds. The
main product identified was 2-methyl-1-phenylbenzimidazole. In
contrast, Pt (1.5%)-TiO2 promoted the rapid and selective produc-
tion by achieving 92% yield of product 2 with 4 h irradiation (Ta-
ble 1, entry 4). Higher yield (92%) by Pt-TiO2 with half the time
required for TiO2 reveals the efficiency and selectivity of Pt-TiO2
in this reaction. Best results were obtained with 50 mg of the cat-
alyst. Lower loading resulted in lower yields, while higher loading
did not increase product yields significantly. The percentage yields
of the product with 0.5 and 1 wt % of platinum content are 72.0 and
83.0%, respectively (Table 1, entries 2 and 3). The same reaction
when performed without catalyst for 4 h gave no product. When
the platinum content was increased to 2 wt %, the product yield
decreased to 87.0% (Table 1, entry 5). Hence 1.5 wt % of platinum
was found to be the optimum level. Encouraged by this initial
result, we set out to examine the scope and limitations of this
procedure.
Having completed this optimization study, we proceeded to
investigate the reaction with different alcohols using 2-nitrodiphe-
nylamine (Table 2). Moderate to good yields (40–96%) of 2-substi-
tuted phenylbenzimidazoles were obtained from methanol,
ethanol, propanol and butanol (entries 1–4) under the same condi-
tions. Except in isopropanol, corresponding benzimidazoles were
formed in other alcohols. The yield of benzimidazole in ethanol
was high (96%), whereas the yield of benzimidazole in methanol
was low (40%). The yield decreased from ethanol to butanol (96
to 75%) gradually. Spectral and GC–MS data of the products formed
22
from methanol, ethanol, propanol and butanol are given in Ref.
In case of isopropanol, acetone is formed and it is less likely to un-
dergo condensation with 1,2-diamine due to steric effect.13 Hence
only the reduction of nitro group to amine was observed. This reac-
tion was very slow with aromatic alcohols such as benzyl alcohol
and the product formed was less than 5% even for 8 h irradiation.
With the same reaction conditions, we screened a series of
N-arylnitroanilines and N-alkylnitroanilines with alcohols, which
resulted in the formation of either N-arylbenzimidazoles or
N-alkylbenzimidazoles (Table 3). Both 1-aryl- and 1- alkyl -substi-
tuted benzimidazoles were successfully produced in very good
yields. These reactions were carried out with this catalyst under
direct solar light and the results are compared with UV process.
The trend observed in solar light is similar to the one in UV light
(Table 3), but the efficiency is found to be more in UV light than
in solar light.
Semiconductor oxide provides a microheterogeneous center for
oxidation and reduction and so simultaneous oxidation of alcohol
to aldehyde and reduction of nitro to amine group take place. This
is followed by the condensation of amine and aldehyde leading to a
cyclized product. A mechanism for the formation of 2-methyl-1-
phenylbenzimidazole from 2-nitrodiphenylamine in ethanol is
proposed in Scheme 1. TiO2 on irradiation produces electron and
hole (h+) pair. The h+ oxidizes ethanol to acetaldehyde while the
electron reduces the nitro compound 1 to amino compound 2 on
the surface. Oxidation of alcohol and reduction of nitro group by
semiconductor photocatalyst has been well established.13
Compound 2 undergoes spontaneous condensation with aldehyde
producing a mono imine intermediate 3. Cyclization of this inter-
mediate gives 2-methyl-N-phenylbenzimidazoline 4, which on
Table 1
Table 2
Comparison of catalytic efficiencies for the photocatalytic synthesis of 2-methyl-1-
phenylbenzimidazole from 2-nitrodiphenylamine
Results obtained on 4h irradiation (365 nm) of 2-nitrodiphenylamine with 1.5% wt
Pt-TiO2 nanoparticles in different alcohols
Conversiona
(%)
Entry Alcohols
Products yield (%)
By
Conversiona
Entry Catalyst
Time Products yield (%)
(h)
By
product
(%)
product (%)
(%)
1
2
3
4
5
Prepared
TiO2
8
4
4
4
4
2-Methyl-1-
phenylbenzimidazole
(75)
2-Methyl-1-
phenylbenzimidazole
(72)
2-Methyl-1-
phenylbenzimidazole
(83)
2-Methyl-1-
phenylbenzimidazole
(92)
12
87.0
80.0
88.0
96.0
92.0
1
2
3
4
5
2-
2-Methyl-1-
4
9
5
6
4
96
99
80
46
99
Nitrodiphenylamine/ phenylbenzimidazole
ethanol
2-
Nitrodiphenylamine/ phenylbenzimidazole
propanol
2-
Nitrodiphenylamine/ phenylbenzimidazole
butanol
2-
Nitrodiphenylamine/ Phenylbenzimidazole
methanol
2-
(92)
2-Ethyl-1-
Pt (0.5%)
TiO2
8
(90)
2-Propyl-1-
Pt (1.0%)
TiO2
5
(75)
1-
Pt (1.5%)
TiO2
4
(40)
2-
Pt (2.0%)
TiO2
2-Methyl-1-
phenylbenzimidazole
(87)
5
Nitrodiphenylamine/ Aminodiphenylamine
isopropanol (95)
All reactions were performed with a 25 mM ethanolic a reactant 50 mg of catalyst
All reactions were performed with a 25 mM alcoholic solution of a reactant 50 mg
suspension, I = 1.381 Â 10À6 einstein LÀ1 sÀ1
.
of catalyst suspension, I = 1.381 Â 10À6 einstein LÀ1 sÀ1
.
a
a
Remaining nitroaniline.
Remaining nitroaniline.

3388
K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
Table 3
Results obtained on irradiation (365 nm) of various N-substituted 2-nitroanilines with Pt-TiO2 nanoparticles in different alcohols
Entry
Nitroaniline
Alcohol
OH
Product
UV
92
Solar
82
NO2
NO2
NO2
N
N
H
N
CH3
1
N
N
OH
H
N
C2H5
2
3
90
75
80
71
N
N
OH
H
N
C3H7
N
OH
OH
CH3
N
Cl
Cl
Cl
4
90
70
Cl
NH
NO2
N
C2H5
N
5
6
80
72
63
60
Cl
Cl
NH
NO2
N
N
OH
C3H7
NH
NO2
CH3
N
N
OH
OH
HN
HN
HN
CH3
NO2
7
8
9
96
95
90
91
84
79
CH3
CH3
NO2
N
C2H5
C3H7
CH3
N
CH3
CH3
NO2
N
OH
N
CH3
H
N
N
OH
OH
CH3
CH3
CH3
10
11
12
13
92
88
82
86
90
83
77
86
N
NO2
C2H5
N
H
N
C2H5
N
NO2
C2H5
N
H
N
OH
C3H7
N
NO2
C2H5
N
H
N
OH
CH3
OH
N
H
Cl
Cl
NO2

K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
3389
Table 3 (continued)
Entry
Nitroaniline
Alcohol
OH
Product
UV
80
Solar
H
N
N
C2H5
OH
14
15
71
63
N
H
Cl
Cl
Cl
NO2
H
N
N
OH
C3H7
OH
70
95
N
H
Cl
NO2
NO2
NO2
NO2
N
N
OH
OH
H
N
CH3
16
17
18
87
72
61
Cl
Cl
Cl
Cl
N
H
N
C2H5
N
78
70
Cl
N
OH
H
N
C3H7
N
Cl
oxidation forms 2-methyl-N-phenylbenzimidazole 5. The higher
conversion of 2-nitrodiphenylamine with 1.5% Pt-TiO2 (Table 1, en-
try 4) is due to the trapping of electrons by Pt on the excited TiO2.
The electrons excited from the valence band of TiO2 to the conduc-
tion band are efficiently transferred to Pt due to the charge separa-
tion effect and accumulated therein. The oxidant (alcohol) and the
reductant (N-substituted 2-nitroanilines) are abundantly supplied
to the oxidation (TiO2), and reduction sites (Pt), respectively by a
reasonable delivery effect facilitating a combined redox reaction.
Further platinum, present in Pt-TiO2, catalyzes the oxidation of
benzimidazoline. This catalytic dehydrogenation was reported ear-
lier by Shiraishi et al.15
As the catalyst was used earlier for benzimidazole synthesis
from o-phenylenediamines,15 we extended the use of this catalyst
with N-substitiuted 1,2-diamines. Thus, N-substituted diamines
with alcohols gave the corresponding benzimidazoles in good yield
under both UV and solar light (Table 4). Thermal synthesis of
benzimidazoles from N-substituted diamines was reported to be
unsuccessful.23 Therefore this methodology is ideal for preparing
1-alkylated-2-substituted benzimidazoles from N-substituted
diamines. In case of benzyl alcohol and 4-chlorobenzyl alcohol,
the reaction was slow and the yield was less (Table 4, entries 19
and 20) when compared to other alcohols. When N-hydroxy-
ethyl-1,2-diamine was used with ethanol, propanol and butanol,
the products formed were similar to the products formed with
1,2-diamine (Table 4, entries 13, 14 and 15). This shows that the
hydroxyl ethyl group is eliminated before cyclization due to steric
effect. Since the benzimidazole formation starts from substituted
1,2-diamines, same mechanism proposed in Scheme 1 is followed
in this reaction also.
Scheme 1. Photocatalytic and catalytic pathway of Pt-TiO2 on synthesis of N-
substituted benzimidazoles.
In conclusion, Pt-TiO2 enables efficient benzimidazole produc-
tion under photoirradiation conditions. This is promoted by
one-pot multiple catalytic transformations on Pt-TiO2, which in-
volve a platinum-assisted photocatalytic oxidation on TiO2 and a
catalytic dehydrogenation on the surface of the platinum particles.
This process has significant advantages when compared with other
methods: (i) a cheap and stable reactant (alcohol), (ii) it does not
require the use of acids or oxidants and (iii) the reaction proceeds

3390
K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
Table 4
Results obtained on irradiation (365 nm) of various N-substituted 1,2-diamines with Pt-TiO2 nanoparticles in different alcohols
Entry
Diamine
Alcohol
OH
Product
UV
98
Solar
85
NH2
NH2
NH2
N
N
H
N
CH3
1
N
N
OH
H
N
C2H5
2
3
90
75
83
77
N
N
OH
H
N
C3H7
N
OH
OH
CH3
N
Cl
Cl
Cl
4
5
6
95
82
76
86
74
69
Cl
Cl
NH
NH2
N
C2H5
N
NH
NH2
N
OH
C3H7
N
Cl
NH
NH2
CH3
N
N
OH
OH
HN
CH3
NH2
7
8
9
97
87
81
87
79
71
CH3
CH3
N
HN
HN
C2H5
C3H7
CH3
N
NH2
CH3
CH3
NH2
N
OH
N
CH3
N
CH3
CH3
CH3
N
OH
OH
10
11
12
13
92
86
80
92
88
73
75
88
N
NH2
N
C2H5
N
C2H5
N
NH2
N
C2H5
N
OH
C3H7
N
NH2
C2H5
N
H
N
OH
CH3
OH
N
H
Cl
Cl
NH2

K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
3391
Table 4 (continued)
Entry
Diamine
Alcohol
OH
Product
UV
86
Solar
H
N
N
C2H5
C3H7
OH
OH
14
15
73
75
N
H
Cl
Cl
NH2
H
N
N
OH
80
85
N
H
Cl
Cl
NH2
NH2
N
N
OH
OH
H
N
CH3
16
17
18
81
64
62
Cl
Cl
N
NH2
H
N
C2H5
N
72
60
Cl
Cl
Cl
N
NH2
OH
H
N
C3H7
N
Cl
N
NH2
OH
H
N
N
19
20
40
35
31
27
NH2
N
N
OH
H
N
Cl
Cl
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under mild ambient conditions. Therefore, this process has the po-
tential for a sustainable synthesis of 1-aryl-2-alkylbenzimidazole
from N-substituted nitroanilines and 1,2-diamines.
Acknowledgments
Authors thank Professor P.V. Satyam, IOP, Bhubaneswar, India
for HR-TEM measurements. The author (M.S) thanks Council of Sci-
entific and Industrial Research (CSIR), New Delhi, for the financial
support through research grant No.21 (0799)/10/EMR-II. One of
the authors, K.S. is thankful to CSIR, New Delhi, for the award of Se-
nior Research Fellowship.
Supplementary data
Supplementary data (synthesized compounds and characteriza-
tion of Pt–TiO2 by X-ray diffraction (XRD), High resolution trans-
mission electron microscope (HR-TEM), and diffuse reflectance
spectroscopy (DRS)) associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.04.090.
References and notes
19. Selvam, K.; Krishnakumar, B.; Velmurugan, R.; Swaminathan, M. Catal.
Commun. 2009, 11, 280–284.
20. Pt(x)-TiO2 samples, containing different platinum loadings [x (wt % ) = Pt/
1. (a) Boiani, M.; Gonzalez, M. Mini-Rev. Med. Chem. 2005, 5, 409–425; (b) Spasov,
A. A.; Yozhitsa, I. N.; Bugaeva, L. I.; Anisimova, V. A. Pharm. Chem. J. 1999, 33,
232–243.
(TiO2 + Pt)100; x = 0.5, 1.0, 1.5, 2.0] were prepared by
a conventional

3392
K. Selvam, M. Swaminathan / Tetrahedron Letters 52 (2011) 3386–3392
photodeposition method, in which photoirradiation of an aqueous solution
home made TiO2 with hexachloroplatinic acid (HPtCl4Á4H2O) afforded gray
powder of the Pt-TiO2 catalyst.
dichloromethane and methanol (volume ratio: 8:2). For solar experiments, all
reactions have been carried out under similar conditions on sunny days of
different months of 2008–2009 between 10 A.M. and 2 P.M. The intensity of
solar light was measured using a LT Lutron LX-10/A digital Lux meter and it
was found to be 1250 Â 100 ( 100) lux. The intensity was nearly constant
during the experiments.
21. The photocatalytic and catalytic synthesis was carried out using the following
procedure. Appropriate amounts of catalyst and 2-nitrodiphenylamine or 2-
aminodiphenylamine in 25 mL of alcohol were taken in a reaction tube. The
reaction tube was sealed with a rubber septum and purged with nitrogen for
30 min. The reaction mixture was irradiated with UV (365 nm) medium-
22. 2-methyl-1-phenyl benzimidazole: 1H NMR: 2.46, s, 3H, CH3, 7.06–7.75, m, 9H,
Ar-H’s. 13C NMR: 12.21 CH3, 135.99, 136.42, 142.57, 151.53, ipso C’s, 109.98–
129.95, Ar-C’s. GC–MS (m/z): 208 (M+)166, 152, 130, 76, 63, 51, 39.
2-ethyl-1-phenyl benzimidazole: 1H NMR: 1.33, t, 3H, CH3, 2.77, q, 2H, CH2,
7.08–7.78, m, 9H, Ar-H’s. 13C NMR: 14.6 CH3, 21.33 CH2, 136.08, 136.67, 142.59,
156.36, ipso C’s, 110.00–130.00, Ar-C’s. GC–MS (m/z): 222 (M+)166,
152,130,76,63,51,39. IR (KBr) (cmÀ1) = 1613, 1596, 1520, 1499, 1455, 1398,
pressure
mercury
lamp
(Sankyo
Denki,
Japan;
intensity
I = 1.381 Â 10À6 einstein LÀ1 sÀ1)/ solar light at constant stirring. The
temperature of the reaction medium during UV irradiation was 32 °C and it
was nearly constant. With solar light, the temperature of the solution changed
gradually from 32 to 48 °C for all the experiments. The progress of the reaction
was monitored using thin layer chromatography (TLC). Product analysis was
performed by GC analysis, Perkin-Elmer GC-9000 with a capillary column of
DB-5 and flame ionization detector was used. GC–MS analysis was carried out
using Varian 2000 Thermo with the following features: capillary column
VF5MS (5% phenyl–95% methylpolysiloxane), 30 m length, 0.25 mm internal
1275, 1228, 1189, 1070, 1020, 743, 704 cmÀ1
.
1-phenyl-2-propyl benzimidazole: 1H NMR: 0.86, t, 3H, CH3, 2.69, t, 2H, CH2 CH2
CH3, 1.75, m, 2H, CH2CH2 CH3, 6.99–7.74, m, 9H, Ar-H’s. 13C NMR: 13.98 CH3,
21.25 CH2CH2CH3, 29.65 CH2CH2CH3, 136.01, 136.56, 142.61, 155.17 ipso C’s,
110.01–129.96 Ar-C’s. GC–MS (m/z): 236 (M+).
diameter, 0.25
lm
film thickness, temperature of column range from
1-phenyl benzimidazole: 1H NMR: 8.2,s, 1H, 7.93–7.78,m, 1H, 7.77–7.50,m, 6H,
7.45–7.35,m, 2H; 13C NMR: 144.0, 142.3, 136.4, 133.7, 128.1, 124.1, 123.7,
122.8, 120.6, 110.5; GC–MS (m/z): 195.0 [M+H]+.
50À280 °C (10 °C/min) and injector temperature 250 °C, attached with mass
spectrometer model SSQ 7000. The isolation was performed by column
chromatography on
a
silica gel column by eluting with
a
co-solvent of
23. Wilfred, C.; Taylor, R. J. K. Synlett 2010, 1628–1630.