Metal-free chemoselective reduction of nitroaromatics to anilines via hydrogen transfer strategy

Article abstract of DOI:10.1007/s11696-018-0634-0

A novel protocol for chemoselective reduction of aromatic nitro compounds to aromatic amines has been established. The metal-free reduction goes through a hydrogen transfer process. Various easily reducible functional groups can be well tolerated under the optimized reaction conditions.

Full text of DOI:10.1007/s11696-018-0634-0

Chemical Papers
https://doi.org/10.1007/s11696-018-0634-0
ORIGINAL PAPER
Metal‑free chemoselective reduction of nitroaromatics to anilines
via hydrogen transfer strategy
Qi Shuai1,2 · Jun Li1 · Feng Zhao3 · Weike Su1,2 · Guojun Deng3
Received: 14 June 2018 / Accepted: 2 November 2018
© Institute of Chemistry, Slovak Academy of Sciences 2018
Abstract
A novel protocol for chemoselective reduction of aromatic nitro compounds to aromatic amines has been established. The
metal-free reduction goes through a hydrogen transfer process. Various easily reducible functional groups can be well toler-
ated under the optimized reaction conditions.
Keywords Metal-free · Chemoselective reduction · Nitrobenzene · Elemental sulfur
Introduction
and Hilmersson 2007) in combination with large excess of
various proton sources, and thus generate huge amounts of
wastes. Nowadays, transition-metal catalyzed hydrogenation
of aromatic nitro compounds to aromatic amines has been
considered as a potential alternative and signifcant pro-
gress has been made (Nishimura 2001; Orlandi et al. 2018;
Jagadeesh et al. 2013; Wang et al. 2010; Corma et al. 2008).
Generally, to achieve high chemoselectivity for the forma-
tion of amines, delicately supported nanoscale noble metal,
such as Pd (Shi et al. 2017; Li et al. 2011; Wu et al. 2009),
Pt (Takasaki et al. 2008; Pandarus et al. 2011; Motoyama
et al. 2009), Rh (Nakamula et al. 2011), and Au (Yamane
et al. 2009; Wang et al. 2014; Chen et al. 2006; Corma and
Serna 2006), was required as catalyst for the hydrogenation
process, making it unsuitable for production on industrial
scale. In addition, when hydrogen is utilized as the reduc-
ing agent, elevated temperature and pressure are normally
required, resulting in demanding requirements for devices
and may leading to potential safety risk. Besides, in the
presence of transition-metal catalyst, other reducing agents,
such as boranes (Bae et al. 2000), silanes/siloxanes (Rahaim
and Maleczka 2005, 2006; Pehlivan et al. 2010; Junge
et al. 2010; Brinkman et al. 1996; Noronha et al. 2009),
and sodium borohydride (Pogorelic et al. 2007; Mazaheri
and Kalbasi 2015; Chinnappan and Kim 2013), have also
been successfully explored for the selective reduction of
nitroaromatics with a satisfactory functional group toler-
ance. However, expensiveness of these reducing agents and
large quantity required makes these methods less attractive
for industrial applications.
Diverse functionalized aromatic amines are vital frameworks
for the construction of pharmaceuticals, agrochemicals, pol-
ymers, dyes, and a variety of other industrially important
fne chemicals (Patai 1996; Lawrence 2004; Ricci 2008).
In general, selective reduction of nitroarenes to aromatic
amines has served as one of the most constantly used meth-
ods in both industry and laboratory (Kabalka and Varma
1991; Ullmann 2012; Blaser et al. 2001; Nishimura 2001;
Arnold et al. 2008; Nugent 2010). Conventionally employed
methods require the use of stoichiometric amounts of iron
(Chandrappa et al. 2010; Desai et al. 2001; Gamble et al.
2007) or other metals (Kelly and Lipshutz 2014; Khan et al.
2003; Mahdavi and Tamami 2005; Basu et al. 2000; Ankner
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-018-0634-0) contains
supplementary material, which is available to authorized users.
* Weike Su
pharmlab@zjut.edu.cn
* Guojun Deng
gjdeng@xtu.edu.cn
1
Collaborative Innovation Center of Yangtze River Delta
Region Green Pharmaceuticals, Zhejiang University
of Technology, Hangzhou 310014, China
2
College of Pharmaceutical Sciences, Zhejiang University
of Technology, Hangzhou 310014, China
3
Key Laboratory of Environmentally Friendly Chemistry
and Application of Ministry of Education, College
of Chemistry, Xiangtan University, Xiangtan 411105, China
Vol.:(0123456789)
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Chemical Papers
Table 1 Optimization
of
condition
Recently, the development of catalytic transfer hydro-
genation (Watson and Williams 2010; Nixon et al. 2009;
Guillena et al. 2010) has further extended the regents for
chemoselective reduction of nitroarenes to hydrazine
(Kumbha et al. 1998; Kumarraja and Pitchumani 2004;
Jagadeesh et al. 2011; Shi et al. 2006; Cantillo et al. 2012,
2013; Rai et al. 2014; Kim et al. 2011; Vass et al. 2001;
Sharma et al. 2010, 2011), formic acid/formate (Wienhoe-
fer et al. 2011; Sorribes et al. 2012; Jagadeesh et al. 2015;
Kunf et al. 2017), ammonium salts (Saha and Ranu 2008;
Berthold et al. 2002), ammonia borane (Zhou et al. 2017),
alcohol (Kim et al. 2012; Gawande et al. 2013), and even
CO/H2O system (He et al. 2009). Especially, our group and
others have reported various protocols for the synthesis of
N-substituted amines from nitroarenes (Liu et al. 2011; Feng
et al. 2010; Tang et al. 2011; Cui et al. 2011) and alcohols or
cyclohexanones (Xie et al. 2012).
A
Entry
[S] source
Base
Solvent
Yield (%)a
1b
2
3
S
S
S
K2CO3
K2CO3
Na2CO3
KHCO3
K3PO4
KF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
NMP
DMSO
CH3CN
Dioxane
Toluene
PhCI
70
71
65
60
61
21
32
47
68
58
55
16
13
0
4
5
S
S
6
7
S
S
KOH
8
9
S
S
CH3ONa
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
10
11
12
13
14
15
16
17
18c
19d
S
S
S
S
S
S
In general, all the above-mentioned metal-catalyzed
reduction of nitroarenes via hydrogen transfer strategy still
sufers from the metal contamination and large stoichiomet-
ric excess of reducing agents. In continuation of our interest
in developing efcient methods for the reduction of aromatic
nitro compounds via hydrogen transfer strategy, we herein
demonstrated a novel metal-free reduction of nitroarenes
(Yang et al. 2014; Li and Xu 2009; SuwiBski and Wag-
ner 1996; Sharma et al. 2014; Gallagher et al. 2012) using
elemental sulfur or sodium sulfde as the reducing reagent
under relatively mild conditions, which is potentially attrac-
tive due to the avoidance of both metal and hydrogen gas.
Previously, Niknam et al. reported selective reduction of
nitroaromatics using sulfur with alumina supported NaOH
(Niknam et al. 2003). An improved version (McLaughlin
and Barnes 2006) was presented by McLaughlin and Barnes,
which used NaHCO3 as base and achieved reduction at ele-
vated temperature. However, serious dehalogenation was
observed with some halo-substituted substrates. In terms of
using Na2S as reducing agent for nitro group (Leleu et al.
2004), Brase et al. (Zimmermann et al. 2007) developed
a single-electron transfer catalyzed-selective reduction
of nitroarenes with the addition of 10 equiv of Na2S and
K2CO3. Obviously, it is still quite desirable to develop new
methods for efcient chemoselective reduction of nitroaro-
matics with good tolerance of functional groups under facile
conditions.
0
7
68
69
92
Na2S·9H20
P2S5
S
DMF
DMF
DMF
DMF
S
Conditions: nitrobenzene (0.2 mmol), [S] source (0.6 mmol), base
(0.3 mmol), solvent (0.8 mL), H2O (0.1 mL), 110 °C, 20 h under air
unless otherwise noted
aGC yield
b10 mol% Cu(OAc)2 was used
c10 mol% TBAB was used
d150 °C
cosolvent was stirred at 110 °C for 20 h. To our delight, the
desired product was obtained in 70% yield (entry 1).
Later, it was found out that, without the addition of
cupric acetate, the transformation still went smoothly, and
similar result was achieved (entry 2). However, the base
potassium carbonate was essential for this reaction. Fur-
ther screening of other bases did not give better results
(entries 3–8). And then, the solvent efect on this reac-
tion was examined. Employing DMA as reaction media
got a similar result (entry 9). A slightly negative efect
was observed when the reaction was carried out in NMP
or DMSO (entries 10–11). Further investigation revealed
that solvent with high polarity was critical for this reduc-
tion and no product was detected when low-polar solvent
was used (entries 12–15). Other sulfur sources as reduc-
ing agent have also been tested. The use of sodium sulfde
nonahydrate resulted a much lower yield (entry 16). How-
ever, good yield was achieved when phosphorus penta-
sulfde was employed (entry 17). Addition of phase-trans-
fer catalyst tetrabutylammonium bromide to the mixture
did not improve the yield (entry 18). Finally, a satisfying
Results and discussion
Our studies were focused on the direct reduction of nitroben-
zene using elemental sulfur or other sulfur source as reduc-
ing agent (Table 1). Initially, in the presence of a catalytic
amount of cupric acetate, a mixture of nitrobenzene, sul-
fur powder and potassium carbonate in water/DMF (1/8)
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Chemical Papers
Table 2 Optimization of condition using Na2S (method B)
Table 3 Scope of nitroaromatics
Entry
Acid
Solvent
Yield (%)b
1
2
3
4
DMF
DMF
DMF
DMF
DMF
DMF
10
93
91
85
88
93
AcOH
PivOH
PhCOOH
p-TsOH
AcOH
5
6b
Conditions: nitrobenzene (0.2 mmol), Na2S·9H2O (0.6 mmol), acid
(0.6 mmol), DMF (0.8 mL), 150 °C, 20 h under air unless otherwise
noted
aGC yield
bAt room temperature
result was achieved when the reaction was conducted at
elevated temperature (150 °C) (entry 19).
In view of sodium sulfde nonahydrate’s potential dual
role of sulfur source and base, we then further tried to opti-
mize the reaction conditions (Table 2). Unexpectedly, the
yield was not increased when the reaction was performed at
150 °C (entry 1). However, the transformation was signif-
cantly improved with the addition of organic acid. And then,
a variety of acids were investigated, and acetic acid turned
out to be the best one (entries 2–5). To our surprise, the
reduction of nitrobenzene in the presence of sodium sulfde
nonahydrate and acid could proceed efciently even at room
temperature (entry 6). With the optimized conditions set up,
various aromatic nitro compounds were examined to dem-
onstrate the wide applicability of the transfer hydrogenation
process and the results are summarized in Tables 3 and 4.
In general, for the same substrate, the isolated yields of
product were similar under condition A and condition B. As
shown in Table 3, a variety of alkyl substituted nitroarenes
were reduced efficiently, providing the corresponding
anilines (2b–2h) in high yields. Substrates bearing other
electron-donating groups, such as methoxy, amino, also
displayed good reactivities under the optimized conditions
(2h–2i). Notably, halogenated nitroarenes were selectively
reduced to amines (2k–2m) in good yields, leaving the
halogen moieties untouched. The product 3-(trifuorome-
thyl) aniline (2n), which is widely used for the synthesis
of drugs, such as trifupromazine, fumethiazide and fume-
tramide, was produced successfully. Interestingly, for dini-
troarenes, only one nitro group was selectively reduced (2o).
Sterically hindered nitro group of 1-nitronaphthalene was
also efectively reduced (2p). Other nitro heterocycles also
proved to be good substrates for this transformation and the
corresponding amino-substituted heterocycles, which are
key skeletons in pharmaceuticals and agrochemicals, were
acquired in good yields (2q–2r).
a
Condition A: Nitroarenes (0.2 mmol), [S] (0.6 mmol), K2CO3
(0.3 mmol), DMF (0.8 mL), H2O (0.1 mL), 150 °C, 20 h. Condi-
tion B: Nitroarenes (0.2 mmol), Na2S·9H2O (0.6 mmol), AcOH
(0.6 mmol), DMF (0.8 mL), rt, 20 h. Isolated yields
From a synthetic point of view, it is worth noting that selec-
tive reduction of nitro group of substrates functionalized with
other sensitive moieties is more challenging. Fortunately, the
reducible functional groups like nitrile, ketone, ester and even
oxime were well tolerated under the reaction conditions and
the corresponding aniline derivatives were achieved (Table 4,
3a–3k). Moreover, the yields and selectivities were inde-
pendent of the positions where the functional groups were
anchored. To further extend the practical application of this
method, reduction of 8-nitroquinoline in gram-scale was tested
and the product 8-aminoquinoline was still obtained with good
yield (Scheme 1), which is remarkable for both scalability and
environmental compatibility of the transition-metal-free condi-
tions. Furthermore, this reduction could be carried out using
water as the reaction media at room temperature and only a
slightly decreased yield was observed (Scheme 2).
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Chemical Papers
Table 4 Scope of nitroaromatics bearing other reducible groups
Scheme 3 Control experiments
of aromatic nitro compounds was proposed by Haber (1898).
Generally, two diferent reaction pathways are proposed. In
the direct pathway, the nitro group was reduced to the nitroso
group, which was then transformed into the corresponding
hydroxylamine (Blaser 2006). Subsequently, the aniline
product was formed by the reduction of hydroxylamine.
Another indirect pathway frstly involved the condensation
between nitrosoarene and hydroxylamine, afording azoxy
compound. And then, the azoxy group was reduced sequen-
tially to primary amine via the azo and hydrazo interdedi-
ates. To elucidate which pathway, the reaction may undergo,
we conducted several control experiments under condition
B (Scheme 3). Firstly, when the reduction of nitrobenzene
was carried out under condition B, none of any proposed
intermediates was detected by GC–MS in 5 min (eq 1).
Secondly, reduction of nitrosobenzene was performed and
almost quantities of aniline was obtained (eq 2). Thirdly,
when azobenzene was used as substrate, only<1% of reduc-
tion product aniline was determined by GC–MS (eq 3).
Based on the results discussed above, we proposed that the
reduction of nitroarenes in both of our systems would pref-
erentially take place through the direct pathway, which was
illustrated in Scheme 4. It is believed that both of the two
reduction systems would generate hydrosulphide ions (HS−)
as active reducing agent for the reduction of nitro group to
nitroso group (Niknam et al. 2003; McLaughlin and Barnes
2006; Maity et al. 2006). The resulting HSO− would serve
as both reducing agent for nitro and nitroso group which is
transformed into hydroxylamine (Yadav et al. 2003; Mondal
et al. 2016). Finally, further reduction of hydroxylamine by
HSO2− afords aniline product.
Condition A: Nitroarenes (0.2 mmol), [S] (0.6 mmol), K2CO3
(0.3 mmol), DMF (0.8 mL), H2O (0.1 mL), 150 °C, 20 h. Condi-
tion B: Nitroarenes (0.2 mmol), Na2S·9H2O (0.6 mmol), AcOH
(0.6 mmol), DMF (0.8 mL), rt, 20 h. Isolated yield
aGC yield
Scheme 1 Gram-scale reduction of 8-nitroquinoline
In summary, we have developed two green and sustain-
able methods which enabled the highly efcient reduction
of various functionalized aromatic nitro compounds to cor-
responding arylamines in both good yield and selectivity. A
series of reducible groups can also be tolerated under our
protocols. This mild and transition-metal-free condition can
be potentially applied to the industrial production of aro-
matic amines.
Scheme 2 Reduction of nitrobenzene in water
Conclusions
So far, the commonly accepted mechanism for the reduction
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Chemical Papers
0.6 mmol), acetic acid (36 mg, 0.6 mmol), nitrobenzene
(24.6 mg, 0.2 mmol), DMF (0.8 mL). The reaction vessel
was closed under air and the resulting solution was stirred
at room temperature for 20 h. Then the reaction mixture was
fltered through a pad of silica gel and washed with 5 mL
ethyl acetate for three times. The fltrate was removed under
vacuum and the residue was purifed by fash column chro-
matography (silica gel, petroleum ether/ethyl acetate=4:1)
to give the desired product.
Aniline (2a)
1H NMR (400 MHz, CDCl3) δ 7.16 (t, J=7.6 Hz, 2H), 6.76
(t, J=7.2 Hz, 1H), 6.70 (d, J=7.6 Hz, 2H), 3.64 (s, 2H); 13
C
NMR (100 MHz, CDCl3) δ 146.4, 129.3, 118.5, 115.1; MS
(EI) m/z (%) 93 (100), 78, 73, 66, 52.
Scheme 4 Proposed mechanism
o‑Toluidine (2b)
The reaction was conducted with 2-nitrotoluene (27.2 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=4:1) to give the desired product.
Experimental
Chemicals
All experiments were carried out under an atmosphere of air.
Flash column chromatography was performed over silica gel
1H NMR (400 MHz, CDCl3) δ 7.05–7.01 (m, 2H),
6.72–6.65 (m, 2H), 3.57 (s, 2H), 2.16 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 144.5, 130.4, 126.9, 122.2, 118.6,
114.9, 17.2; MS (EI) m/z (%) 106 (100), 89, 77, 63, 52.
1
48–75 μm. H NMR and 13C NMR spectra were recorded
on Bruker-AV (400 and 100 MHz, respectively) instrument
internally referenced to SiMe4 or chloroform signals. MS
analyses were performed on an Agilent 5975 GC–MS instru-
ment (EI). High-resolution mass spectra were recorded at
Institute of Chemistry, Chinese Academy of Sciences. The
structures of known compounds were further corroborated
by comparing their NMR data and MS data with those of
literature. All reagents were used as received from com-
mercial sources without further purifcation. Sulfur powder
employed in the experiments was 99.99% purity.
m‑Toluidine (2c)
The reaction was conducted with 3-nitrotoluene (27.2 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.03 (t, J=7.6 Hz, 1H),
6.57 (d, J=7.2 Hz, 1H), 6.58–6.48 (m, 2H), 3.56 (s, 2H),
2.26 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 146.3, 139.0,
129.1, 119.4, 115.9, 112.2, 21.3; MS (EI) m/z (%) 106 (100),
89, 77, 63, 52.
General procedure: aniline
Condition A: An oven-dried pressure tube (10 mL) was
charged with sulfur powder (19.2 mg, 0.6 mmol), potas-
sium carbonate (44.4 mg, 0.6 mmol), nitrobenzene (24.6 mg,
0.2 mmol), H2O (0.1 mL), DMF (0.8 mL). The reaction
vessel was closed under air and the resulting solution was
stirred at 150 °C for 20 h. After cooling to room tempera-
ture, the reaction mixture was fltered through a pad of silica
gel and washed with 10 mL ethyl acetate for three times. The
fltrate was removed under vacuum and the residue was puri-
fed by fash column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
p‑Toluidine (2d)
The reaction was conducted with 4-nitrotoluene (27.2 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 6.96 (d, J=7.6 Hz, 2H),
6.60 (d, J=7.6 Hz, 2H), 3.47 (s, 2H), 2.23 (s, 3H); 13C NMR
Condition B: An oven-dried pressure tube (10 mL)
was charged with sodium sulfde nonahydrate (144 mg,
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Chemical Papers
(100 MHz, CDCl3) δ 143.8, 129.7, 127.7, 115.2, 20.3; MS
p‑Anisidine (2i)
(EI) m/z (%) 106 (100), 89, 77, 63, 52.
The reaction was conducted with 4-nitroanisole (30.6 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=4:1) to give the desired product.
4‑Isopropylaniline (2e)
The reaction was conducted with 4-nitrocumene (33.4 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 6.75 (d, J=8.8 Hz, 2H),
6.65 (d, J=8.8 Hz, 2H), 3.75 (s, 3H), 3.20 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 152.7, 139.8, 116.3, 114.7, 55.6; MS
(EI) m/z (%) 123, 108 (100), 80, 65, 53.
1H NMR (400 MHz, CDCl3) δ 7.02 (d, J=8.0 Hz, 2H),
6.63 (d, J=8.0 Hz, 2H), 3.27 (s, 2H), 2.84 – 2.75 (m, 1H),
1.20 (d, J = 6.8 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ
144.1, 139.2, 127.1, 115.2, 33.2, 24.2; MS (EI) m/z (%) 135,
120 (100), 91, 77, 65.
p‑Phenylenediamine (2j)
The reaction was conducted with 4-nitroaniline (27.6 mg,
0.2 mmol) under the standard conditions A or B. The fltrate
was removed under vacuum and the residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=1:1) to give the desired product.
4‑tert‑Butylaniline (2f)
The reaction was conducted with 4-nitro-tert-butylbenzene
(35.8 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.18 (d, J=8.0 Hz, 2H),
6.64 (d, J=8.0 Hz, 2H), 3.41 (s, 2H), 1.27 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 143.8, 141.4, 126.0, 114.9, 33.9, 31.5;
MS (EI) m/z (%) 149, 134 (100), 120, 106, 94.
1H NMR (400 MHz, CDCl3) δ 6.57 (s, 4H), 3.32 (s, 4H);
13C NMR (100 MHz, CDCl3) δ 138.6, 117.7; MS (EI) m/z
(%) 108 (100), 91, 80, 65, 53.
3‑Chloroaniline (2 k)
The reaction was conducted with 1-chloro-3-nitrobenzene
(31.5 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.05 (t, J=8.0 Hz, 1H),
6.71 (d, J=7.6 Hz, 1H), 6.66 (s, 1H), 6.53 (d, J=8.0 Hz,
1H), 3.69 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 147.7,
134.8, 130.3, 118.4, 114.9, 113.2; MS (EI) m/z (%) 127
(100), 100, 92, 65, 52.
2,4‑Dimethyl aniline (2g)
The reaction was conducted with 2,4-dimethylnitrobenzene
(30.2 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 6.87–6.83 (m, 2H), 6.58
(d, J=8.0 Hz, 1H), 3.42 (s, 2H), 2.22 (s, 3H), 2.14 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 142.0, 131.1, 127.8,127.3,
122 4, 115.1, 20.3, 17.1; MS (EI) m/z (%) 121 (100), 106,
91, 77, 65.
3‑Bromoaniline (2l)
The reaction was conducted with 1-bromo-3-nitrobenzene
(40.4 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 6.99 (t, J=8.0 Hz, 1H),
6.86 (d, J=8.0 Hz, 1H), 6.83 (s, 1H), 6.58 (d, J=7.8 Hz,
1H), 3.66 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 147.8,
130.6, 123.1, 121.4, 117.9, 113.6; MS (EI) m/z (%) 171
(100), 143, 117, 92, 65.
2,4,6‑Trimethylaniline (2 h)
The reaction was conducted with 2,4,6-trimethylnitroben-
zene (33.4 mg, 0.2 mmol) under the standard conditions A
or B. The fltrate was removed under vacuum and the residue
was purifed by column chromatography (silica gel, petro-
leum ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 6.76 (s, 2H), 3.43 (s, 2H),
2.20 (s, 3H), 2.15 (s, 6H); 13C NMR (100 MHz, CDCl3) δ
140.1, 128.8, 127.1, 121.8, 20.3, 17.4; MS (EI) m/z (%) 135,
120 (100), 91, 77, 65.
3‑Iodoaniline (2 m)
The reaction was conducted with 1-iodo-3-nitrobenzene
(49.8 mg, 0.2 mmol) under the standard conditions A or B.
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Chemical Papers
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.08–7.05 (m, 2H), 6.85
(t, J = 8.0 Hz, 1H), 6.62 (d, J = 8.0 Hz, 1H), 3.64 (s, 2H);
13C NMR (100 MHz, CDCl3) δ 147.7, 130.7, 127.5, 123.8,
114.3, 94.9; MS (EI) m/z (%) 219 (100), 127, 110, 92, 65.
6‑Aminobenzothiazole (2q)
The reaction was conducted with 6-nitrobenzothiazole
(36.0 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the residue
was purifed by column chromatography (silica gel, petro-
leum ether/ethyl acetate = 4:1) to give the desired prod-
1
uct. H NMR (400 MHz, CDCl3) δ 8.70 (s, 1H), 7.89 (d,
J = 8.8 Hz, 1H), 7.17 (d, J= 2.0 Hz, 1H), 6.87 (dd, J= 8.8,
2.0 Hz, 1H), 3.85 (s, 2H); 13C NMR (100 MHz, CDCl3) δ
149.7, 148.1, 146.7, 144.8, 135.4, 123.9, 115.8, 105.6; MS
(EI) m/z (%) 150 (100), 123, 118, 106, 96.
3‑Aminobenzotrifuoride (2n)
The reaction was conducted with 3-nitrobenzotrifuoride
(38.2 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.24–7.22 (m, 1H), 6.99
(d, J=7.6 Hz, 1H), 6.89 (s, 1H), 6.82 (d, J=8.0 Hz, 1H),
3.81 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 146.7, 131.5
(q, J = 32.0 Hz), 129.7, 124.2 (q, J= 271.0 Hz), 117.9 (d,
J=1.0 Hz), 114.9 (q, J=4.0 Hz), 111.3 (q, J=4.0 Hz); MS
(EI) m/z (%) 161 (100), 142, 120, 114, 65.
8‑Aminoquinoline (2r)
The reaction was conducted with 8-nitroquinoline
(34.8 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the residue
was purifed by column chromatography (silica gel, petro-
leum ether/ethyl acetate = 2:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 8.76 (d, J = 2.8 Hz,
1H), 8.07 (d, J = 8.0 Hz, 1H), 7.39–7.32 (m, 2H), 7.16 (d,
J = 8.0 Hz, 1H), 6.94 (d, J = 7.2 Hz, 1H), 4.98 (s, 2H); 13
C
4‑Nitroaniline (2o)
NMR (100 MHz, CDCl3) δ 147.4, 143.9, 138.4, 136.0,
128.8, 127.3, 121.3, 116.0, 110.0; MS (EI) m/z (%) 144
(100), 117, 89, 72, 63.
The reaction was conducted with 1,4-dinitrobenzene
(33.6 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 8.08 (d, J=8.8 Hz, 2H),
6.63 (d, J=8.8 Hz, 2H), 4.38 (s, 2H); 13C NMR (100 MHz,
CD3COCD3) δ 156.1, 138.3, 127.1, 113.7; MS (EI) m/z (%)
138 (100), 108, 92, 80, 65.
Anthranilonitrile (3a)
The reaction was conducted with 2-nitrobenzonitrile
(29.6 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the residue
was purifed by column chromatography (silica gel, petro-
leum ether/ethyl acetate = 1:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.39 (d, J = 7.6 Hz, 1H),
7.35–7.31 (m, 1H), 6.76–6.72 (m, 2H), 4.40 (s, 2H); 13C
NMR (100 MHz, CDCl3) δ 149.5, 133.9, 117.9, 117.6,
115.1, 95.9; MS (EI) m/z (%) 118 (100), 91, 75, 65, 52.
1‑Aminonaphthalene (2p)
The reaction was conducted with 1-nitronaphthalene
(34.6 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=4:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.81 (t, J=8.4 Hz, 2H),
7.46–7.44 (m, 2H), 7.33–7.25 (m, 2H), 6.78 (d, J=6.8 Hz,
1H), 4.14 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 142.1,
134.4, 128.5, 126.3, 125.7, 124.7, 123.7, 120.8, 118.9,
109.6; MS (EI) m/z (%) 143 (100), 115, 89, 78, 63.
2‑Amino‑5‑methoxybenzonitrile (3b)
The reaction was conducted with 2-nitro-5-methoxybenzo-
nitrile (35.6 mg, 0.2 mmol) under the standard conditions
A or B. The fltrate was removed under vacuum and the
residue was purifed by column chromatography (silica
gel, petroleum ether/ethyl acetate=1:1) to give the desired
product.
1H NMR (400 MHz, CDCl3) δ 6.97 (dd, J=9.2, 2.8 Hz,
1H), 6.86 (d, J=2.8 Hz, 1H), 6.70 (d, J=9.2 Hz, 1H), 4.13
(s, 2H), 3.74 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 151.8,
1 3

Chemical Papers
144.2, 122.6, 117.4, 117.1, 115.0, 96.4, 55.9; MS (EI) m/z
146.7, 138.2, 129.5, 119.7, 118.9, 114.0, 26.7. MS (EI) m/z
(%) 148, 133 (100), 105, 78, 52.
(%) 135, 120 (100), 92, 65, 52.
3‑Aminobenzonitrile (3c)
4‑Aminoacetophenone (3 g)
The reaction was conducted with 3-nitrobenzonitrile
(29.6 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=1:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.24–7.20 (m, 1H), 7.02
(d, J = 7.2 Hz, 1H), 6.90–6.86 (m, 2H), 3.87 (s, 2H); 13C
NMR (100 MHz, CDCl3) δ 147.0, 130.0, 121.7, 119.2(4),
119.1(6), 117.3, 112.6; MS (EI) m/z (%) 118 (100), 91, 75,
64, 52.
The reaction was conducted with 4-nitroacetophenone
(33.0 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=3:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.81 (d, J=8.4 Hz, 2H),
6.65 (d, J=8.4 Hz, 2H), 4.12 (s, 2H), 2.50 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 196.3, 151.2, 130.8, 128.0, 113.7, 25.9;
MS (EI) m/z (%) 135, 120 (100), 92, 65, 52.
Methyl 4‑aminobenzoate (3 h)
4‑Aminobenzonitrile (3d)
The reaction was conducted with methyl 4-nitrobenzoate
(36.2 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the residue
was purifed by column chromatography (silica gel, petro-
leum ether/ethyl acetate=2:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.85 (d, J=8.4 Hz, 2H),
6.64 (d, J=8.4 Hz, 2H), 4.07 (s, 2H), 3.85 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 167.3, 151.0, 131.6, 119.6, 113.8, 51.7;
MS (EI) m/z (%) 151, 135, 120 (100), 92, 65.
The reaction was conducted with 4-nitrobenzonitrile (29.6
mg, 0.2 mmol) under the standard conditions A or B. The
fltrate was removed under vacuum and the residue was puri-
fed by column chromatography (silica gel, petroleum ether/
ethyl acetate=1:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.42 (d, J=8.4 Hz, 2H),
6.65 (d, J=8.4 Hz, 2H), 4.13 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ 150.4, 133.8, 120.0, 114.5; MS (EI) m/z (%) 118
(100), 102, 91, 75, 64, 52.
Benzocaine (3i)
2‑Aminoacetophenone (3e)
The reaction was conducted with ethyl 4-nitrobenzoate
(27.2 mg, 0.2 mmol) under the standard conditions A or B.
The fltrate was removed under vacuum and the residue was
purifed by column chromatography (silica gel, petroleum
ether/ethyl acetate=2:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.86 (d, J=8.4 Hz, 2H),
6.64 (d, J=8.4 Hz, 2H), 4.34–4.29 (m, 2H), 4.05 (s, 2H),
1.36 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ
166.7, 150.7, 131.5, 113.7, 60.3, 14.4; MS (EI) m/z (%) 165,
137, 120 (100), 92, 65.
The reaction was conducted with 2-nitroacetophenone
(33.0 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the resi-
due was determined by GC. The residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=10:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 7.71 (dd, J=8.3, 1.5 Hz,
1H), 7.31–7.21 (m, 1H), 6.70–6.60 (m, 2H), 2.57 (s, 3H).
13C NMR (100 MHz, CDCl3) δ 200.8, 150.3, 134.4, 132.1,
118.3, 117.2, 115.8, 27.9; MS (EI) m/z (%) 135, 120 (100),
92, 65, 52.
2‑Amino‑benzaldehyde‑(O‑methyl oxime) (3j)
3‑Aminoacetophenone (3f)
The reaction was conducted with 2-nitrobenzaldehyde-(O-
methyl oxime) (36.0 mg, 0.2 mmol) under the standard con-
ditions A or B. The fltrate was removed under vacuum and
the residue was purifed by column chromatography (silica
gel, petroleum ether/ethyl acetate=2:1) to give the desired
product.
The reaction was conducted with 3-nitroacetophenone
(33.0 mg, 0.2 mmol) under the standard conditions A or
B. The fltrate was removed under vacuum and the resi-
due was determined by GC. The residue was purifed by
column chromatography (silica gel, petroleum ether/ethyl
acetate=5:1) to give the desired product.
1H NMR (400 MHz, CDCl3) δ 8.17 (s, 1H), 7.15–7.08
(m, 2H), 6.71–6.68 (m, 2H), 5.43 (s, 2H), 3.96 (s, 3H); 13
C
1H NMR (400 MHz, CDCl3) δ 7.38–7.31 (m, 1H),
7.31–7.22 (m, 2H), 6.90 (ddd, J=7.9, 2.5, 1.0 Hz, 1H), 3.70
(s, 2H), 2.58 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 198.5,
NMR (100 MHz, CDCl3) δ 162.5, 152.0, 146.4, 132.2,
130.2, 116.7, 115.5, 114.3, 61.9; MS (EI) m/z (%) 150 (100),
119, 104, 92, 65.
1 3

Chemical Papers
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2‑Amino‑benzaldehyde‑(O‑benzyl oxime) (3 k)
The reaction was conducted with 2-nitrobenzaldehyde-(O-
benzyl oxime) (51.2 mg, 0.2 mmol) under the standard
conditions A or B. The fltrate was removed under vacuum
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1H NMR (400 MHz, CDCl3) δ 8.25 (s, 1H), 7.40–7.33
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2H), 5.18 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 152.4,
146.4, 137.5, 132.2, 130.2, 128.3, 128.2, 127.9, 76.2. MS
(EI) m/z (%) 226, 209, 118, 91 (100), 77; HRMS calcd.
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Procedure for gram‑scale reduction
of 8‑nitroquinoline (Condition B)
Chandrappa S, Vinaya K, Ramakrishnappa T, Rangappa KS (2010)
An efcient method for aryl nitro reduction and cleavage of azo
compounds using iron powder/calcium chloride. Synlett 20:3019–
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To a round bottom fask (500 mL) was added a solution of
8-nitroquinoline (1.74 g, 10 mmol) in DMF (100 mL), fol-
lowed by the addition of sodium sulfde nonahydrate (7.20 g,
30 mmol) in portions with stirring. And then, acetic acid
(18 mL, 30 mmol) was added to the mixture gradually. After
addition, the resulting mixture was stirred at room tempera-
ture until the starting material was consumed completely
(~ 20 h), which was tracked by TLC. After reaction, the
reaction mixture was concentrated under vacuum and the
residue was dissolved in ethyl acetate (150 mL), followed by
removal of undissolved stuf via simple fltration. The result-
ing solution was washed with water (3 times) and brine,
dried over Na2SO4, and concentrated under vacuum. The
resulting crude product was purifed by fash column chro-
matography (silica gel, petroleum ether/ethyl acetate=4:1)
to give the desired product.
Chen Y, Qiu J, Wang X, Xiu J (2006) Preparation and application
of highly dispersed gold nanoparticles supported on silica for
catalytic hydrogenation of aromatic nitro compounds. J Catal
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(bulk and nanofber composites) used as catalyst for reduction
of aromatic nitro compounds under mild conditions. RSC Adv
3:3399–3406. https://doi.org/10.1039/c2ra22639a
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Acknowledgements This work was supported by the National Natural
Science Foundation of China (21172185, 21372187, 21606202).
Desai DG, Swami SS, Dabhade SK, Ghagare MG (2001) FeS–NH
4Cl–
CH3OH–H2O: an efcient and inexpensive system for reduction
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