Photocatalytic synthesis of anilides from nitrobenzenes under visible light irradiation: 2 in 1 reaction

Article abstract of DOI:10.1016/j.jphotobiol.2015.02.010

An efficient method has been developed for the synthesis of a series of anilides via a two in one reaction of nitrobenzenes with anhydride in the presence of TiO₂ as a nanocatalyst and photocatalyst under sunlight or blue LED irradiation. In this method simultaneously, nitrobenzenes convert to the corresponding anilines via photocatalytic reduction on the TiO₂ surface, and a condensation of aniline with the anhydride performed on the Lewis acid site of the TiO₂ surface. Interestingly amidation step leads to the promotion of better reaction and good selectivity in reduction of nitrocompounds. This method is simple, rapid, high yield, and green.

Full text of DOI:10.1016/j.jphotobiol.2015.02.010

Accepted Manuscript
Photocatalytic Synthesis of Anilides from Nitrobenzenes under Visible Light
Irradiation: 2 in 1 Reaction
Zahra Zand, Foad Kazemi, Adel Partovi
PII:
S1011-1344(15)00047-0
DOI:
http://dx.doi.org/10.1016/j.jphotobiol.2015.02.010
JPB 9947
Reference:
Journal of Photochemistry and Photobiology B: Bi-
ology
To appear in:
Received Date:
Revised Date:
Accepted Date:
3 January 2015
5 February 2015
10 February 2015
Please cite this article as: Z. Zand, F. Kazemi, A. Partovi, Photocatalytic Synthesis of Anilides from Nitrobenzenes
under Visible Light Irradiation: 2 in 1 Reaction, Journal of Photochemistry and Photobiology B: Biology (2015),
doi: http://dx.doi.org/10.1016/j.jphotobiol.2015.02.010
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Photocatalytic Synthesis of Anilides from Nitrobenzenes under Visible Light
Irradiation: 2 in 1 Reaction
Zahra Zand,a Foad Kazemi, a, b * Adel Partovi a
a Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava
Zang, Zanjan, 45137-66731, Iran.
b Center for Climate and Global Warming (CCGW), Institute for Advanced Studies in Basic
Sciences (IASBS), Gava Zang, Zanjan, 45137-66731, Iran.
*Corresponding Author:
E-mail: kazemi_f@iasbs.ac.ir; Phone: +98 24 3315-3219; Fax: +98 24 3315-3232.

Abstract:
An efficient method has been developed for the synthesis of a series of anilides via a two in one
reaction of nitrobenzenes with anhydride in the presence of TiO2 as a nanocatalyst and
photocatalyst under sunlight or blue LED irradiation. In this method simultaneously,
nitrobenzenes convert to the corresponding anilines via photocatalytic reduction on the TiO2
surface, and a condensation of aniline with the anhydride performed on the Lewis acid site of the
TiO2 surface. Interestingly amidation step leads to the promotion of better reaction and good
selectivity in reduction of nitrocompounds. This method is simple, rapid, high yield, and green.
Keywords: Two in one reaction, Photocatalysis, Anilide. Visible light
Introduction

Anilide and its derivatives occupy pivotal positions in organic synthesis and synthesis of
biologically and pharmaceutically active compounds [1-4]. Generally, the amides are produced
through the reaction of a carboxylic acid or ester with an amine. Lately, one-pot reaction has
become one of hot topics in green chemistry because it eliminates isolation of unstable
intermediates and reduces waste production [5-8]. The conversion of nitroarenes to their
corresponding acetanilides in a one-pot reaction is an important transformation in organic
chemistry. As nitrobenzenes are readily available industrial chemicals, it is more efficient to start
directly from the nitrocompound rather than to start from the corresponding amine or isocyanate
[9]. In general, direct conversion of nitroarenes to acetanilides are carried out by iron powder
with acetic acid [10], Pt nanoparticle ZrO2 and acetic anhydride [11], molybdenum
hexacarbonyl/acetic acid [12], and also anilides have been obtained either via nickel [13] or
rhodium [14] or platinum [15] catalyzed carbonylation of nitroarenes. However, 50 to 100 atm
CO required in each case.
In the last decades, the increasingly serious energy crisis has led to an aggressive search for
conversion of light energy into chemical energy by photocatalysis processes. [16-25] The Design
of heterogeneous photocatalysis systems that encourage efficient one-pot synthesis is currently
the focus of attention [26]. Photocatalyst TiO2 is able to promote two different transformations in
one-pot by employing both photocatalytic and catalytic actions.
Lately, some successful examples of photocatalytic reduction of nitro compounds have been
reported. TiO2 [27-29], and N-doped TiO2 [30], have been investigated for the reduction of
nitrobenzenes to their corresponding anilines under UV light irradiation. On the other hand,
CdS/Graphene [31-32], dye-sensitized TiO2 P25 [33-34], and PbBiO2X [35] have been employed
to reduce these molecules by visible light irradiation. Shiraishi et al. reported one-pot synthesis

of benzimidazoles and imines by simultaneous photocatalytic and catalytic reactions on Pt@TiO2
nanoparticles [26, 36]. Also, Sa et al. reported one-pot photo-reductive N-alkylation of aniline
and nitroarene derivatives with primary alcohols over Au–TiO2 [37]. Considering that the solar
energy is an endless resource, recently significant progresses have been seen in heterogeneous
photocatalysis for the synthesis of organic compounds using sunlight. Swaminathan et al.
reported one-pot photocatalytic syntheses of benzimidazoles and indazole by Pt-TiO2, Ag-TiO2,
and TiO2-P25 nanoparticles under UV and sunlight [38-39]. Lately our group have reported on
activated amorphous TiO2 coated into periodic mesoporous organosilicas (PMOs) [40], TiO2-N
Doped [41], β-Cyclodextrin / TiO2 [42], and CdS [43-44] as efficient photocatalysts for synthesis
of selective organic transformation under visible light. Moreover, we have reported that TiO2-
P25 showed selectivity of over 80% for reduction of a series of nitrobenzens under sunlight and
LED irradiation [45]. TiO2-P25, which is frequently used as a standard in heterogeneous
photocatalysis, consists of a mixture of anatase (75%) and rutile (25%) phases. The junction
between anatase and rutile phases in TiO2-P25 exhibit high rate of the charge separation in
comparison to pure phases. Also, the rutile phase for TiO2–P25 acts as an antenna to extend the
photoactivity into visible wavelengths [45].
Experimental
Photocatalytic synthesis of anilide. Photocatalytic reactions were carried out in a round bottom
Pyrex flask and irradiated using four high power blue light LEDs 3 W lamp or by solar light
under magnetic stirring at room temperature. Reaction conditions with solar light: the aromatic
nitro compounds (0.05 mmol) and anhydride (0.052 mmol) were carried out in the presence of
TiO2-P25 (0.03 g) in EtOH (10 mL) and irradiated under sunlight for 1-4 h. Reaction conditions
with blue LED irradiation: aromatic nitro compounds (0.002 mmol) and anhydride (0.0025

mmol) were carried out in the presence of TiO2-P25 (0.08 g) in EtOH (4 mL), and irradiated by
four high power blue light LEDs 3 W lamp for 30 hours. While stirring, the mixture became
heterogeneous as the reaction progressed. The product yields were determined by gas
chromatography monitoring. The structure of products were confirmed by NMR (see ESI†).
Results and Discussion
In continuation of our work on visible light photoreduction of nitroaromatic compounds using
sunlight and blue LED irradiation [45], in order to develop and improve this method, we present
a strategy for one-pot synthesis of anilides using nitrobenzens and anhydride as the reactants and
TiO2-P25 nanoparticles as a heterogeneous catalyst at room temperature under visible
photoirradiation. According to the best of our knowledge, the photoamidation of nitro
compounds and anhydride under blue LED lamp irradiation using TiO2-P25 has not been
addressed before.
Initially, the photosynthesis of N-phenylacetamide using TiO2-P25 was investigated as a model
reaction, and the results are shown in Table 1. The results of this experiment showed that by
employing an ethanol solution containing nitrobenzene (0.02, 0.05, and 0.1 mmol) and acetic
anhydride (0.022, 0.052, and 0.12 mmol) with TiO2-P25 (0.01, 0.03, and 0.05 g) under argon and
irradiation sunlight, N-phenylacetamide is obtained at 100% yield in a full conversion (Table 1,
entries 1-3). The results have shown that N-phenylacetamid can be synthesized efficiently
without the addition of a base or an additive [47]. Under the same reaction conditions, we found
that the reduction of nitrobenzene in the absence of acetic anhydride gives selectivity with 55%
yield, while in its presence it shows 100% yield (Table 1, entries 2 and 6). This result suggested
that one-pot reaction causes a promotion of photoreduction of nitrobenzene with amidation step.

The reaction is initiated by photoexcitation of TiO2, producing electron (e-) and positive hole
(h+) pairs under visible light. The (e-) reduces nitrobenzene to aniline and EtOH is oxidized by
the hole. The catalytic condensation of the formed aniline and anhydride on the Lewis acid site
of TiO2 [26, 48] produces N-phenylacetamide (Scheme 1).
Please, insert Scheme 1, here.
The catalytic condensation of aniline with anhydride on the Lewis acid site of TiO2 is confirmed
by the reaction of aniline with acetic anhydride in at 298 K. As results shown, the absence of
catalyst gives N-phenylacetamide with 10% yield, while in the presence of TiO2 shows 80%
yield, indicating that this catalyst promotes condensation (Table 1, entries 4 and 5). Under the
above optimized conditions (Table 1, entry 2), various anilides were synthesized in the
condensation reaction of a series of nitrobenzenes with anhydrides using TiO2-P25 under
sunlight. The obtained results are summarized in Table 2.
Nitrobenzene containing functional groups (CN, OMe, NO2, and COCH3) with acetic anhydride
gave the corresponding N-phenylacetamide in excellent yields (Table 2, entries 3 and 6-10). This
method was also applied to the one-pot synthesis of the N-phenylbenzamide of benzoic
anhydride (Table 2, entries, 2, 5, and 8). It is also possible to carry out this reaction for synthesis
of N-phenyl, 3-methylbenzamide of 3-methylbenzoicanhydride in 100% yield (Table 2, entry 4).
Thus, a series of anilides were synthesized using the conditions reported herein.
Please, insert Table 1, here.
Corresponding to, recently visible light emitting diodes (LED) sensitization with a low power is
an attractive means to initiate photocatalytic reactions. Several advantages are associated with
the use of LED lamps as a light source. For example, high photon efficiency, need low voltage of
electricity, power stability, emit broader spectral wavelength [49].

In continuation, according to our previous report on photoactivity TiO2-P25 under blue LED, we
were encouraged to turn our attention to the use of blue LED for one-pot photosynthesis of
anilides.
Please, insert Table 2, here.
Interestingly, our investigations showed that the photocatalytic conversion of nitrobenzene and
acetic anhydride to N-phenylacetamide could be carried out successfully by using TiO2-P25
under blue LED with high yield (Table 1, entry 7). We also found that high selectivity reduction
of nitrobenzene is observed in the presence of acetic anhydride than photoreduction nitrobenzene
in its absence (Table 1, entries 7 and 9). This result suggested that one- pot reaction led to the
promotion of better reaction and good selectivity (Table 1, entry 7). After optimizing the reaction
conditions a variety of nitrobenzenes and anhydrides were reacted successfully under blue LED.
(Table 2)
Nitrobenzene containing chemical functional groups, which are often prone to either oxidation or
reduction (e.g., carbonyl, cyanide, and methoxy), were found that gave anilide with good
selectivity (Table 2, entries 3, 7, 8, and 10). Comparing these results with our previous report
[45], we saw an increase in selectivity reduction of nitro compound (Table 2 entries 10 and 11).
These results confirm that one-pot reaction forms an efficient and selective condition for
synthesis of anilides.
In summary, the presented results propose that nano TiO2-P25 photocatalyst can be used for the
synthesis of anilides from nitrobenzene and anhydride in one-pot reaction with high yield under
sunlight or blue LED irradiation. Photocatalyst TiO2 is able to promote two different
transformations in one-pot by employing both photocatalytic and catalytic actions on the TiO2

surface. The one-pot reaction leads to both an enhancement of selectivity and yield of products.
According to light emitting diodes (LEDs) with a low electrical power requirement in the visible
spectra offer a promising replacement for conventional light sources in many applications.
Therefore efficient synthesis anilide under blue LED, has the great potential to be used as a
sustainable method for anilide photosynthesis. The reported approach is facile, mild, green, and
high yield.
Acknowledgments
The authors gratefully acknowledge the support provided by the Institute for Advanced Studies
in Basic Sciences (IASBS).
† Electronic Supplementary Information
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Captions
Scheme 1. Synthesis of N-phenylacetamide from nitrobenzene and acetic anhydride using TiO2-P25
under visible light.
Table 1. Photosynthesis of N-phenylacetamid from nitrobenzene and acetic anhydride in the presence of
TiO2- P25 under sunlight and blue LED irradiation.
Table 2. Photosynthesis of anilides from nitrobenzenes and anhydride in the presence of TiO2- P25 under
sunlight and blue LED irradiation.

Table 1. Photosynthesis of N-phenylacetamid from nitrobenzene and acetic anhydride in the presence of TiO2- P25
under sunlight and blue LED irradiation.
O
O
O
NO2
NHCMe
TiO2-P25
O
EtOH, Argon, light
Acetic
anhydride
(mmol)
Nitrobenzene
(mmol)
EtOH
(ml)
Conversion
(%)
Select
(%) a
Entry
TiO2 (g)
Light
Time (h)
1
2
0.02
0.05
0.022
0.052
0.01
0.03
4
1
2
100
100
100
100
10
3
0.1
0.12
0.05
20
4
100
100
4 b
5c
0.02
0.02
0.022
0.022
-
4
4
-
-
10
10
10
80
0.01
6 d
7
0.05
0
0.03
0.08
10
4
4
100
100
55
0.002
0.0025
30
100
LED
8
0.005
0.002
0.0055
0
0.1
4
4
48
30
35
18
70
LED
LED
9 d
0.08
100
a)
Reaction conditions room temperature (25-35 °C) and sunlight irradiation (intensity =90−100 × 103 lux).
Selectivity= cp/ (cr0-cr) 100%, cr0: the initial concentration of nitrobenzene; cr: the concentration of nitrobenzene
during the reaction; cp: the concentration of the product during the reaction. GC yield based on an internal-standard
method. (b) Aniline with acetic anhydride in the absence of TiO2. (c) Aniline with acetic anhydride in the presence of
TiO2. (d) Reduction of nitrobenzene to aniline in the absent the acetic anhydride.

Table 2. Photosynthesis of anilides from nitrobenzenes and anhydride in the presence of TiO2- P25 under
sunlight and blue LED irradiation.
Solar light b
LED c
Entry
Nitrocompound
Anhydride
Product
Yield
(%) a
Yield
(%) a
Time(h)
1
2
2
100
100
100
100
A
B
C
2.5
1.5
100
100
3
4
3
100
80
D
O
O2N
NHCPh
5
6
2
3
80
75
85
E
F
100
7
1
100
100
G
8
9
1
2.5
2
100
100
90
100
75
H
I
10
70
J
11
-
3.5
80
45
b
a GC yield, Reaction conditions: nitro compound (0.05 mmol), anhydride (0.052 mmol), TiO2 (0.03 g), EtOH
c
(10 ml) and irradiation with sunlight (10 am-2 pm, sunlight intensity between 90-10×103 Lux).
Reaction
conditions: nitro compound (2 × 10-3 mmol), anhydride (2.5 × 10-3 mmol), TiO2 (0.08 g), EtOH (4 ml) and
irradiation with four blue light LEDs (3 W electrical power, 80 Lumens) , 30 h.
16

Graphical Abstract

Highlights
 Anilide was synthesized from nitrobenzene under sunlight or blue LED irradiation.
 Photocatalyst TiO2 is able to promote two different transformations.
 The 2 in 1 reaction leads to enhancement of selectivity and yield of products.