Metal-Free Reduction of Nitrobenzene to Aniline in Subcritical Water

Article abstract of DOI:10.1021/acs.joc.8b00406

An environmentally friendly approach for the reduction of nitrobenzene to aniline promoted by carbonaceous bio-based materials was successfully achieved under subcritical water conditions. The proposed methodology features a metal-free process, no-hydroge

Full text of DOI:10.1021/acs.joc.8b00406

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Article
Metal-Free Reduction of Nitrobenzene to Aniline in Subcritical Water
Sarra Tadrent, Denis Luart, Olivier Bals, Anissa Khelfa, Rafael Luque, and Christophe Len
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00406 • Publication Date (Web): 11 Jun 2018
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Metal-Free Reduction of Nitrobenzene to Aniline in Subcritical Water
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Sarra Tadrent,† Denis Luart,‡ Olivier Bals,† Anissa Khelfa,‡ Rafael Luque,§,¥ and Christophe
9
⊥
Len,*,†,
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† Sorbonne Universités, Université de Technologie de Compiègne, Centre de Recherches de
Royallieu, CS 60319, F-60203 Compiègne cedex, France.
‡
Ecole Supérieure de Chimie Organique et Minérale, 1 allée du Réseau Jean-Marie
Buckmaster, F-60200 Compiègne, France.
§ Departamento de Quimica Organica, Universidad de Cordoba, Campus de Rabanales, Ed.
Marie Curie (C3), Ctra Nnal IV-A, Km 396, E-14014 Cordoba, Spain.
¥
Peoples Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Str.,
Moscow, 117198, Russia
⊥ PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris,
11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France. Fax: +33 (0)344 971 591;
Tel: +33 (0)638 500 976; E-mail: christophe.len@chimie-paristech.fr
KOH
H2O
KHCO3
H2O
H2O
KOH
H2O
H2O
KHCO3
H2O
KOH
KHCO3
NORIT GAC 12-40
H2 H2 H2
O
O
NH2
N
NORIT GAC 12-40
ABSTRACT:
An environmentally friendly approach for the reduction of nitrobenzene to aniline
promoted by carbonaceous bio-based materials was successfully achieved under subcritical
water conditions. The proposed methodology features a metal-free process, no-hydrogen input
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as reductor, the use of commercial bio-based carbon materials having low cost and
availability and water as green solvent under subcritical conditions. Using optimized
conditions, reduction of nitrobenzene in the presence of commercial NORIT GAC 12-40 or
DACARB PC1000 was accomplished at 310 °C for 6 h and quantitatively furnished the target
aniline. Treatment of NORIT GAC 12-40 with KOH allowed to decrease charcoal loading
(6 g vs 40 g) and increase aniline yields (80% vs 66%).
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KEYWORDS: metal-free, reduction, green chemistry, subcritical water, carbonaceous
materials
INTRODUCTION
Aniline derivatives represent an important class of nitrogen heterocyclic compounds
extensively employed in the chemical industry as dyes, antioxidants, pharmaceuticals and
agricultural chemicals.1 Aniline is used for the production of rigid polyurethane (PU) foams
via methylene diisocyanate (MDI) formation. Aniline is also employed as building block for
the synthesis of a number of molecules of interest present in rubber products, consumer
goods, agriculture, transportation, adhesives/sealants, textile, packaging, manufacturing,
coatings, photography, electronics, pulp and care, and pharmaceuticals.2
Aromatic amines are generally produced from their corresponding nitroarenes by catalytic
hydrogenation using molecular hydrogen3 or reducing agents such as hydrazine hydrate,4
10
silanes,5 sodium hydrosulphite,6 formates,7 decaborane,8 glucose9 and NaBH4 as hydrogen
sources. It is interesting to note that hydrogen can also be generated from water by laser
irradiation starting from carbon powder.11 Although this process has not been used for
chemical organic reactions, hydrogen production from carbonaceous materials and water is
very interesting for different reasons. Carbon and water are among most abundant materials
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on earth and their direct use as efficient and low cost reagents is an attractive topic and meets
the requirements of green and sustainable chemistry. Next to catalytic hydrogenations,
catalytic transfer hydrogenation (CTH) is also used in presence of alcohols, hydrocarbons,
hydrazines, organic acids and their salts in protocols generally emplying metals.12
In parallel with academic and industrial applications, organic chemists have a growing
interest for green chemistry and try to contribute partially or totally to the development of
alternative technologies including catalysis and metal-free conditions in safer solvents. In this
regard, simple, inexpensive and facile scale-up production of aromatic amines from
nitroarenes using D-glucose as hydrogen donor under catalyst-free aqueous conditions was
previously reported.9 In order to provide a more general protocol for a more sustainable
synthesis of anilines, herein we disclose a novel reduction of nitrobenzene into aniline using
metal-free conditions without added hydrogen in the presence of carbonaceous materials
under sub-critical water.
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RESULTS AND DISCUSSION
The commercial charcoals NORIT GAC 12-40, DACARB PC1000 and UNTRETED 4-8
MESH were characterized using scanning electron microscopy (SEM), energy dispersive X-
ray diffraction (EDX), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption
measurements. The morphology of NORIT GAC 12-40 and DACARB PC1000 was
determined by SEM and no significant difference could be observed between these materials
(Fig S1). On the other hand, UNTREATED 4-8 MESH exhibited a different morphology
(more organized) with a honeycomb-like structure (Fig S1). The surface elemental
composition of the materials was confirmed by EDX spectra (Fig S3) and XPS analysis
(Table S1 and Fig S5-S12). NORIT GAC 12-40 and DACARB PC1000 possess carbon and
oxygen as well as aluminum and potassium, respectively. UNTREATED 4-8 MESH has
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almost exclusively carbon. BET analysis showed that NORIT GAC 12-40 and DACARB
PC1000 have a total surface area and pore volume over 900 m2 g-1 and 0.5 cm3 g-1, whereas a
negligible one (30 m2 g-1 and 0.01 cm3 g-1) was measured for UNTREATED 4-8 MESH
(Table S2). The content of surface oxygen functional groups was determined by the Boehm
method. The three carbonaceous materials have got mainly basic functional groups (Table 4).
Initital catalytic studies were performed for nitrobenzene conversion (10 mmol) using NORIT
GAC 12-40 (6 g) in water at 300 °C under 90 bar as model reaction. At this temperature
(higher than 100°C and lower than 374°C) and pressure (higher than 0.1 Mpa and lower than
22.1 mPa), the reduction of the nitroarene takes place in subcritical water conditions. This
state of water has particular physicochemical properties with (i) a density equivalent to that of
the liquid; (ii) a low viscosity approaching that of the gas; (iii) a diffusion coefficient at least
ten times higher as compared to the liquid; (iv) a very important transfer coefficient and (v) a
low dielectric constant which is close to that of organic solvents. The altered physical
properties of subcritical water result in different solvent behavior. Under preliminary
investigated conditions, aniline was obtained in 62% after 6 hours (Figure 1). Nitrobenzene
loadings varying from 5 to 25 mmol were then investigated to find that nitrobenzene
concentration can significantly influence aniline yields, with optimum results observed using
10 mmol starting material.
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0
Aniline yield (%)
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Nitrobenzene conversion
(%)
5
7.5
10
15
25
a
Figure 1. Effect of nitrobenzene loading on reduction of nitrobenzene to aniline. Reaction
conditions: nitrobenzene (5 mmol – 25 mmol), NORIT GAC 12-40 (6 g), water (55 mL),
300 °C, 90 bar, 6 h.
With the aim of determining the most favorable reaction temperature, variations from
275 °C to 320 °C for 6 h were investigated under batch conditions (Figure 2). Lower reaction
temperatures (275 °C) seemed to be insufficient for the conversion of nitrobenzene to aniline
after 6 hours. An increase in reaction temperature (310 ºC) benefits aniline production, with
yields reaching a maximum value of 65% at complete nitrobenzene conversion. However,
aniline yields remarkably decreased to 53% when the reaction temperature increased to
320 °C, probably related to product degradation.
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Aniline yield (%)
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Nitrobenzene conversion
(%)
Reaction temperature °C
275
300
310
320
Figure 2. Effect of temperature on reduction of nitrobenzene to aniline. aReaction conditions:
nitrobenzene (10 mmol), NORIT GAC 12-40 (6 g), water (55 mL), 6 h.
Kinetics studies of the reaction were aimed to optimize reaction times for the reduction of
nitrobenzene in presence of NORIT GAC 12-40 (310 °C, 6 h, Figure 3). Aniline yields
increased with reaction time and reached complete conversion and maximum aniline yield
(66%). It is interesting to note that aniline yields severely decreased to 46% when the reaction
time was prolonged to 7 hours. This may be due to ongoing side-reactions such as various
decomposition pathways.
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Aniline yield (%)
Reaction
time (h)
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Figure 3. Effect of reaction time on reduction of nitrobenzene to aniline. aReaction
conditions: nitrobenzene (10 mmol), NORIT GAC 12-40 (6 g), water (55 mL), 310 °C, 90
bar, 6 h.
The nature of the solvent and the concentration of the reagents have a remarkable influence
in reaction yields especially near the critical point. At 310 °C, the volume of water has also a
great influence on aniline yields. For volumes over 65 mL, the extremely high generated
pressure (> 200 bar) prevented the reaction to progress. On the other hand, aniline yields did
not exceed 53% with volumes under 30 mL, for which 55 mL water was selected as
compromise for subsequent reactions. In this process, hydrogen is generated via consumption
of carbonaceous bio-based materials and water (Scheme 1). Therefore, an increase in the
volume of water generates more H2 and thus facilitates the reduction of nitrobenzene to
aniline. In order to substitute water, several protonated solvents (water, methanol, ethanol,
propan-1-ol, butan-1-ol and propan-2-ol) were also tested (Figure 4). In function of the
properties of the alcohols, the temperature and generated pressure were modified to be under
subcritical temperature and pressure conditions (Table 1). All experiments resulted in an
aniline yields < 25% excepted for butan-1-ol (Figure 4, d), which gave aniline in 57% yield
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(at 91% conversion). However, this result is inferior to that obtained with water under
otherwise identical reaction conditions, supporting the use of subcritical water as green
solvent for the rest of the optimization experiments.
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a: methanol
b: ethanol
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80
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40
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0
a
c
a
b
d
e
c: propan-1-ol
d: butan-1-ol
e: propan-2-ol
Aniline yield (%)
Nitrobenzene conversion
(%)
Temperature °C
200 220 240 250 220 240 240 240 265 240
Figure 4. Effect of the nature of the solvent and temperature on reduction of nitrobenzene to
a
aniline. Reaction conditions: nitrobenzene (10 mmol), NORIT GAC 12-40 (6 g), protonated
solvent (55 mL), 200-265 °C, 60-80 bar, 6 h.
Table 1. Critical temperature and pressure of the tested protonated solvents
critical temperature critical pressure
(°C)
239
(bar)
80
methanol
ethanol
240
61
propan-1-ol
butan-1-ol
propan-2-ol
263.6
289.8
235
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With our first optimized reaction conditions in hand, a range of carbonaceous materials
such as activated charcoals and graphites were subsequently screened (Figure 5). Among
them, NORIT GAC 12-40, NORIT SA2, NORIT A supra, DACARB PC 1000 and
OXBOW 1 furnished aniline in yields >60% and therefore were further utilized for
optimization purposes. As expected, graphite provided a low aniline yield (36 %), probably
due to the absence of surface functionalities (it is interesting to note that untreated carbon
gave aniline in 27% yield). Therefore, this carbonaceous material has been chosen as a point
of comparison in order to understand structure-activity relationships.
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Aniline yield (%)
30
20
10
0
A B C D E F G H I J K L M N S T U V W X
Figure 5. Effect of the nature of the carbonaceous materials on reduction of nitrobenzene to
aniline. aReaction conditions: nitrobenzene (10 mmol), carbonaceous material (6 g), water (55
mL), 310 °C, 90 bar, 6 h. NORIT GAC 12-40 (A), MONARCH 1300 (B), ELFTEX 125 (C),
GRAPHITE (D), BPL4X10 (E), NC35 1.25-1.35 (F), AC 40 (G), NORIT CN1 (H), NORIT
SA2 (I), NORIT A SUPRA (J), UNTREATED (K), NORIT TPK 1-3 (L), DARCA 12.20
(M), DACARB PC1000 (N), DACARB PBC1 (S), DACARB PBB (T), OXBOW 1 (U),
OXBOW 2 (V), DACARB PCC1200 (W), DACARB PM300 (X).
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Among selected carbonaceous materials (NORIT GAC 12-40, NORIT SA2, NORIT A
supra, DACARB PC 1000 and OXBOW 1), the loading influence was subsequently studied
(Figure 6). A pseudo-linear increase in aniline yields could be observed at increased carbon
loadings. Gratifyingly, aniline was selectively produced in quantitative yields using
DACARB PC 1000 (16 g), for which this carbonaceous material was employed in subsequent
reactions.
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N
T
I
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A
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Aniline yield (%)
mass of
charchoal (g)
3
6 12 20 30 40 6 12 14 15 16 20 20 20 12 15
a
Figure 6. Effect of the charcoal loading on reduction of nitrobenzene to aniline. Reaction
conditions: nitrobenzene (10 mmol), carbonaceous material (3 - 40 g), water (55 mL), 310 °C,
90 bar, 6 h. NORIT GAC 12-40 (A), NORIT SA2 (I), NORIT A SUPRA (J), DACARB
PC1000 (N), OXBOW 1 (U).
Using DACARB PC1000 (20 g), kinetic time-dependent studies from 2h to 9h at 310 °C
were then conducted (Table 2). As expected, aniline yields were found to increase with
reaction time, reaching quantitative yields (>99%) after 6 h reaction. Aniline yields severely
decreased to 80% at longer reaction times (7-9 h). This phenomenon is likely to be related to
the presence of side reactions (e.g. chemical decomposition) at prolonged reaction times.
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Interestingly, the optimized reaction time (6 h) was found to be identical for both NORIT
GAC 12-40 and DACARB PC 1000.
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Table 2. Effect of reaction at 310 °C time with DACARB PC1000 a
entry
time (h)
yield (%)
conversion (%)
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2
4
6
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9
91
95
100
100
100
100
100
100
100
81
80
80
aReaction conditions: nitrobenzene (10 mmol), DACARB PC1000 (20
g), water (55 mL), 310 °C, 90 bar.
Variation of nitrobenzene and carbonaceous material loadings using NORIT GAC 12-40
and DACARB PC1000 separately pointed to two optimized processes: nitrobenzene (15
mmol) and NORIT GAC 12-40 (40 g) as method A (Table 3, entry 3) and nitrobenzene (10
mmol) and DACARB PC1000 (20 g) as method B (Table 3, entry 5). For the same
conversion and aniline yield, method A allows a higher volumetric productivity while method
B uses less carbonaceous material.
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Table 3. Effect of substrate loading with various amounts of activated carbon a
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5
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8
Entry
nitrobenzene
charcoal
charcoal
yield
(%)
62
conversion
(%)
(mmol)
10
(g)
6
9
1
2
3
4
5
6
A
A
A
A
N
N
100
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10
40
40
40
20
20
91
100
15
99
100
20
61
100
10
100
76
100
20
100
aReaction conditions: nitrobenzene (10 - 20 mmol), carbonaceous material A or N (6 - 40 g),
water (55 mL), 310 °C, 90 bar.
Recycling performance is a significant index to evaluate the performance of our selected
carbonaceous material which is mainly a carbon source for the formation of hydrogen. In our
case, five cycles of experiments were studied under optimized conditions to estimate the
properties of recovered material (Figure 7). As expected, after each cycle yield decreases due
to the consumption of the surface and the efficiency reached a level of 63% of the initial value
after four cycles. The characterization of the carbonaceous materials was conducted using the
same methods employed for the materials before reaction (Fig S2, S4, S13-S15 and Tables
S3, S4). The main differences between before and after reaction are the morphology of
carbonaceous materials and the total surface area and pore volume. The surface of NORIT
GAC 12-40 is damaged probably by temperature and the total surface area and pore volume
of DACARB PC1000 and NORIT GAC 12-40 are reduced after reaction. Another difference
is the absence of potassium on the surface for DACARB PC1000 and the decrease of
aluminium and carbon on the surface of NORIT GAC 12-40.
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Aniline yeild (%)
Number of
cycles
1
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5
a
Figure 7. Reusability of DACARB PC1000. Reaction conditions: nitrobenzene (10 mmol),
DACARB PC1000 (20 g), water (55 mL), 310 °C, 90 bar, 6 h.
The acid-base properties of the two selected carbonaceous materials: NORIT GAC 12-40
and DACARB PC1000 were subsequently evaluated and compared to those of UNTREATED
4-8 MESH (Table 4). Both activated carbons NORIT GAC 12-40 and DACARB PC 1000
exhibited basic surfaces of pH ranging from 9.2 to 10.1. These values are related to the
content of basic functional groups on the surface of the carbonaceous materials which varies
from 3.2 to 3.5 mmol g-1. In contrast with NORIT GAC 12-40, DACARB PC1000 also have
small amounts of acidic groups which did not seem to have any influence of the pH. Both
charcoals NORIT GAC 12-40 and DACARB PC1000 showed a good activity for the
reduction of nitrobenzene and these results might be explained by a combination of large
surface areas, mesoporous volumes and the basic properties.
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Table 4. Acid-base properties of the activated carbons obtained
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entry
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acidic groups basic groups total content of
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The addition of a base (KOH) and an acid (H3PO4) was subsequently attempted in the
optimized systems (NORIT GAC 12-40) and conditions to rule out the potential involvement
on basic/acid sites in promoting the reaction under subcritical water conditions (Figure 8). As
expected no conversion of nitrobenzene was observed in the presence of H3PO4. However,
aniline yield increases proportionally with the amount of KOH added until an optimum of
80% for 0.5 g KOH, clearly indicating the involvement of basicity in promoting aniline
production from nitrobenzene. Additionally, the reduction of nitrobenzene was less efficient
when the ratio KOH - NORIT GAC 12-40 was higher than 1:6 (wt/wt). This result pointed out
that a mixture of KOH and NORIT GAC 12-40 allowed a yield increase from 66% to 80%.
Interestingly, the use of a KOH and NORIT GAC 12-40 mixture (2:12, wt/wt) and (3:18,
wt/wt) gave aniline in 89% and 92%, respectively at quantitative conversion, keeping a 1:6
ratio charcoal-base using just larger quantities for the reaction. These results showed clearly
that for a mixture of designed carbonaceous material such as KOH and NORIT GAC 12-40 in
a ratio 1:6 (wt/wt), the higher the charcoal and KOH loads, the higher the aniline yield.
Different bases including NaOH, K2CO3, NH4OH were tested with the optimized conditions
but the best result was obtained with KOH. The influence of KOH could be explained by the
thermodynamic limitation of the production of hydrogen from water and CO known as Water-
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Gas Shift Reaction (WGSR) (Scheme 1). In our process, carbonaceous materials and water
generated hydrogen and CO (in the first step), then CO2 and more hydrogen in a second
reaction. The last step never proceeds toward completion therefore hydrogen concentration
does not exceed a certain limit. On the other hand, KOH reacted with CO2 to generate KHCO3
and shifted the equilibrium towards completion with maximised hydrogen production. In
subcritical water (310 °C and 90 bar), the reduction of nitrobenzene into aniline proceeds
using metal-free conditions via conventional mechanism after formation of nitrosobenzene,
phenylhydroxylamine and aniline, successively.
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Aniline yield (%)
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a
Figure 8. Effect of KOH and H3PO4 on reduction of nitrobenzene to aniline. Reaction
conditions: nitrobenzene (10 mmol), NORIT GAC 12-40 (6 g), KOH (0.02 – 4 g) or H3PO4
(0.5-1 g), water (55 mL), 310 °C, 90 bar, 6 h.
With our optimized reaction conditions in hand, a range of nitroarene derivatives having
different electronic and steric demands was evaluated. Conversions are quantitative (> 99%)
but only traces of pure aniline could be observed regardless of the ring substituents (F, I, Cl,
COOH, NHCOCH3, CHO, COOCH3) and their position (ortho, meta and para). No other
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product was detected due to efficient degradation (mineralization). The reported successful
process is exclusive for nitrobenzene.
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Scheme 1. Plausible mechanism on the reduction of nitrobenzene to aniline via hydrogen
production from water and carbonaceous materials.
CONCLUSIONS
A simple, green protocol has been optimized for the reduction of nitrobenzene to aniline
under subcritical water conditions. The proposed methodology features a metal-free process
without added hydrogen in presence of commercial basic carbonaceous materials. Two high
yielding conditions could be obtained affording the target aniline in quantitative yields: the
first one in presence of NORIT GAC 12-40 having a better volumetric productivity as
compared to a second one in presence of DACARB PC1000. A basic treatment of NORIT
GAC 12-40 with KOH allowed a reduction in the amount of carbonaceous material (6 g vs 40
g) as well as a slight increase aniline yields (80% vs 66%). The scope of the proposed
environmentally friendly reduction of nitrobenzene will be subsequently translated to
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different nitroarene derivatives in batch reactors as well as in continuous flow, to be reported
in due course.
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EXPERIMENTAL SECTION
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Materials. Substrates and solvents were purchased from Acros
(Nitrobenzene ≥ 99%, aniline 99%, xylan from p-Xylene ≥ 90%,
methanol, ethanol, propan-1-ol, acetone, butan-1-ol, and propan-
2-ol). All materials were used without further purification. The
water used in all experiments had a Millipore Milli-Q grade.
Charcoals were purchased from Acros (NORIT GAC 12-40, NORIT SA2, NORIT
A SUPRA, NORIT CN1), DACARB (DACARB PC1000, DACARB PBC1), Carbot
(MONARCH 1300, ELFTEX125), Chemviro BPL4X10, CECA (NC35 1.25-3.15, AC40
3mm), Sigma-Aldrich (UNTRETED 4-8 MESH, DARCO 12.20, NORIT TPK 1-3).
Materials characterization. Elemental analysis was performed using a model kratos Axis
Ultra DLD.
SEM (Scanning Electron Microscopy)-EDX (Energy Dispersive X-ray Diffraction)
analysis of charcoal was performed on a Quanta FEG 250 (FEI) equipped with a
microanalysis detector for EDX (Brucker). SEM micrographs acquired in secondary electron
mode were obtained at low vacuum, 15 kV of accelerating voltage with a 10 mm working
distance. EDX spectra were collected at 30° angle, 15 kV accelerating voltage and 10 mm
working distance.
Surface area and pore size of samples were measured using Micromeritics Surface
Analyzer ASAP 2010 surface area analyzer by nitrogen adsorption-desorption method. The
samples were degassed at 350 °C for 6 h before adsorption isotherm were generated by N2 at -
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196 °C. The surface area (SBET) was calculated with the BET equation, the total pore volume
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(VT) was obtained from the adsorption isotherm at P/P0 =0.95 %. the micropore area (Smic
)
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and volume (Vmic) were obtained using the t-plot method. The average pore size (r) was
estimated by the following equation:
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r= 4 VT/ SBET
XPS measurements were performed in an ultrahigh vacuum (UHV) multipurpose surface
analysis system (SpecsTM model, Germany) operating at pressures of <10−10 mbar using a
conventional X-ray source (XR-50, Specs, Mg K, 1253.6 eV) in a “stop-and-go” mode to
reduce potential damage due to sample irradiation. The survey and detailed Fe and Cu high-
resolution spectra (pass energy 25 and 10 eV, step size 1 and 0.1 eV, respectively) were
recorded at room temperature with a Phoibos 150-MCD energy analyzer. Powdered samples
were deposited on a sample holder using double-sided adhesive tape and subsequently
evacuated under vacuum (<10−6 Torr) overnight. Eventually, the sample holder containing
the degassed sample was transferred to the analysis chamber for XPS studies. Survey spectra
were first recorded, after which detailed element XPS (typically C, O, and S) were recorded.
Data were processed using the program Casa XPS.
General procedure for the synthesis of aniline in subcritical water. In a typical
experiment, a batch reactor (100 mL) charged with water (55 mL), nitrobenzene (1.23 g, 10
mmol), charcoal (6 - 40 g). Autoclave was sealed, placed in the heating collar and heated to
the desired temperature for the desired time. Temperature in the autoclave was measured by
probe. At the end of the reaction, autoclave was cooled down to 40°C. The aqueous phase was
diluted with ethyl acetate (100 mL) under magnetic stirring (500 rpm). The organic phase was
filtered prior to analysis through a syringe filter (PTFE, 0.45 µm, VWR). All experiments
were repeated at least three times, and the deviation was lower than 5%.
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Regeneration of DACARB PC1000. After completion of the reaction DACARB
PC1000 was separated from the products by filtration and immersed in absolute methanol for
90 minutes. The carbonaceous material was then dried at 110 °C for 12 hours. Then the
activated charcoal was used again, and the cycle was repeated five times and the yield
calculated each time.
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Product analysis. Each sample of the reaction mixture was analyzed separately by means
of a GC with a FID detector. The mobile phase was N2. The column oven was set at 40 °C.
Nitrobenzene conversion (X) (eq 1) and aniline yield (Yi) (eq 2) were calculated using
standard equations.
(
)
(
)
(ꢀꢁꢂꢃꢂꢄꢅ ꢁꢂꢃꢆꢇꢈꢉꢁꢊꢉꢁꢉ ꢄꢋꢇꢌꢁꢃ ꢋꢇꢅ ꢍꢎꢂꢁꢄꢅ ꢄꢁꢂꢅꢂꢁꢉ ꢄꢋꢇꢌꢁꢃ ꢋꢇꢅ )
푋 =
푥 100
(1)
(2)
ꢀꢁꢂꢃꢂꢄꢅ ꢁꢂꢃꢆꢇꢈꢉꢁꢊꢉꢁꢉ ꢄꢋꢇꢌꢁꢃ (ꢋꢇꢅ)
ꢎꢂꢁꢄꢅ ꢄꢁꢂꢅꢂꢁꢉ ꢄꢋꢇꢌꢁꢃ (ꢋꢇꢅ)
푥 100
푌푖 =
ꢀꢁꢂꢃꢂꢄꢅ ꢁꢂꢃꢆꢇꢈꢉꢁꢊꢉꢁꢉ ꢄꢋꢇꢌꢁꢃ (ꢋꢇꢅ)
ASSOCIATED CONTENT
Supported Information
Morphology and surface properties of carbonaceous material NORIT GAC 12-40, DACARB
PC 1000, UNTREATED, SEM; elemental composition of carbonaceous material NORIT
GAC 12-40, DACARB PC 1000, UNTREATED, EDX; determination of material surface
atoms and elemental analysis, XPS; surface area and pore size of charcoal, nitrogen
adsorption-desorption method. The experimental conditions to evaluate the surface oxygen
atom and surface pH of charcoal are provide.
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AUTHOR INFORMATION CONTENT
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Corresponding Author
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*E-mail: christophe.len@chimieparistech.psl.eu
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The publication has been prepared with support from RUDN University Program 5-100.
REFERENCES
1
(a) Downing, R. S.; Kunkeler, P. J.; van Bekkum, H. Catalytic Syntheses of Aromatic
Amines. Catal. Today 1997, 37, 121-136. (b) Ono, N. The Nitro Group in Organic
Synthesis, Wiley-VCH, New York, 2001. (c) Wang, L.; Li, P.; Wu, Z.; Yan, J.; Wang,
M.; Ding, Y. Reduction of Nitroarenes to Aromatic Amines with Nanosized Activated
Metallic Iron Powder in Water. Synthesis 2003, 13, 2001-2004.
2
(a) Wang, J.; Yuan, Z.; Nie, R.; Hou, Z.; Zheng, X. Hydrogenation of Nitrobenzene to
Aniline over Silica Gel Supported Nickel Catalysts. Ind. Eng. Chem. Res. 2010, 49,
4664-4669. (b) Corma, A.; Concepción, P.; Serna, P. A Different Pathway for the
Reduction of Aromatic Nitro Compounds on Gold Catalysts. Angew. Chem. Int. Ed.
2007, 46, 7266-7269. (c) Travis, S.; Rappoport, Z. (Ed.), The Chemistry of Anilines,
John Wiley & Sons, Ltd., Chichester, UK, 2007.
3
(a) Lara, P.; Philippot, K. The Hydrogenation of Nitroarenes Mediated by Platinium
Nanoparticles : an Overview. Catal. Sci. Technol. 2014, 4, 2445-2465. (b) Kasparian, A.
J.; Savarin, C.; Allgeier, A. M.; Walker, S. D. Selective Catalytic Hydrogenation of
ACS Paragon Plus Environment

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The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Nitro Groups in the Presence of Activated Heteroaryl Halides. J. Org. Chem. 2011, 76,
9841-9844. (c) Corma, A.; Gonzalez-Arellano, C.; Iglesias, M.; Sanchez, F. Gold
Complexes as Catalysts : Chemoselective Hydrogenation on Nitroarenes. Appl. Catal.
A: Gen. 2009, 356, 99-102. (d) Wu, H.; Zhuo, L.; He, Q.; Liao, X.; Shi, B.
Heterogeneous Hydrogenation of Nitrobenzenes over Recyclable Pd(0) Nanoparticle
Catalysts Stabilized by Polyphenol-Grafted Collagen Fibers. Appl. Catal. A: Gen. 2009,
366, 44-56. (e) Corma, A.; Serna, P.; Concepción, P.; Calvino, J. J. Transforming
Nonselective into Chemoselective Metal Catalysts for the Hydrogenation of Substituted
Nitroaromatics. J. Am. Chem. Soc. 2008, 130, 8748-8753. (f) Corma, A.; Serna, P.
Chemoselective Hydrogenation of Nitro Compounds with Supported Gold Catalysts.
Science 2006, 313, 332-334. (g) Chen, Y.; Wang, C.; Liu, H.; Qiu, J.; Bao, X. Ag/SiO2:
A Novel Catalyst with High Activity and Selectivity for Hydrogenation of
Chloronitrobenzenes. Chem. Commun. 2005, 5298-5300. (h) Tafesh, A.M.; Weiguny, J.
A Review of the Selective Catalytic Reduction of Aromatic Nitro Compounds into
Aromatic Amines, Isocyanates, Carbamates, and Ureas using CO. Chem. Rev. 1996, 96,
2035-2052. (i) Meng, X.; Cheng, H.; Akiyama, Y.; Hao, Y.; Qiao, W.; Yu, Y.; Zhao, F.;
Fujita, S.I.; Arai, M. Selective Hydrogenation of Nitrobenzene to Aniline in dense
Phase Carbon Dioxide over Ni/-Al2O3: Significance of Molecular Interactions. J.
Catal. 2009, 264, 1-10.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
(a) Sharma, U.; Kumar, P.; Kumar, N.; Kumar, V.; Singh, B. Highly Chemo- and
Regioselective Reduction of Aromatic Nitro Compoundss Catalyzed by Recyclable
Copper(II) as well as Cobalt(II) Phthalocyanines. Adv. Synth. Catal. 2010, 354, 1834-
1840. (b) Sharma, U.; Verma, P. K.; Kumar, N.; Kumar, V.; Bala, M.; Singh, N.
Phosphane-Free Green Protocol for Selective Nitro Reduction with an Iron-Based
Catalyst. Chem.–Eur. J. 2011, 17, 5903-5907. (c) Sharma, U.; Kumar, N, Verma, P. K.;
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1
2
3
4
5
6
7
8
Kumar, V.; Singh, B. Zinc Phthalocyanine with PEG-400 as a Recyclable Catalytic
System for Selective Reduction of Aromatic Nitro Compounds. Green Chem. 2012, 14,
2289-2293.
9
5
(a) Junge, K.; Wendt, B.; Shaikh, N.; Beller, M. Iron-Catalyzed Selective Reduction of
Nitroarenes to Anilines using Organosilanes. Chem. Commun. 2010, 46, 1769-1771. (b)
Rahaim, R. J.; Maleczka, R. E. Pd-Catalyzed Silicon Hydride Reductions of Aromatic
and Aliphatic Nitro Groups. Org. Lett. 2005, 7, 5087-5090.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6
7
Redemann, C. T.; Redemann, C. E. 5-Amino-2,3-Dihydro-1,4-Phthalazinedione. Org.
Synth. 1955, 3, 69.
(a) Imai, H.; Nishiguchi, T.; Fukuzumi, K. Homogeneous Catalytic Reduction of
Aromatic Nitro-Compounds by Hydrogen Transfer. Chem. Lett. 1976, 655-656. (b)
Berthold, H.; Schotten, T.; Honig, H. Transfer Hydrogenation in Ionic Liquids under
Microwave Irradiation. Synthesis 2002, 1607-1610. (c) Gowda, S.; Abiraj, K.; Gowda,
D. C. Reductive Cleavage of Azo Compounds Catalyzed by Commercial Zinc Dust
using Ammonium Formate or Formic Acid. Tetrahedron Lett. 2002, 43, 1329-1331. (d)
Abiraj, K.; Srinivasa G. R.; Gowda, D. C. Palladium-Catalyzed Simple and Efficient
Hydrogenative Cleavage of Azo Compounds using Recyclable Polymer-Supported
Formate. Can. J. Chem. 2005, 83, 517-520.
8
(a) Bae, J. W.; Cho, Y. J.; Lee, S.H.; Yoon, C.O.M.; Yoon, C. M. A One-Pot Synthesis
of N-Alkylaminobenzenes from Nitroaromatics: Reduction Followed by Reductive
Amination using B10H14. Chem. Commun. 2000, 1857-1858. (b) Bae, J. W.; Cho, Y. J.;
Lee, S. H.; Yoon, C. M. Chemoselective Reduction of Nitroaromatics to Anilines using
Decaborane in Methanol. Tetrahedron Lett. 2000, 41, 175-177.
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The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Kumar, M.; Sharma, U.; Sharma, S.; Kumar, V.; Singh, B.; Kumar, N. Catalyst-Free
Water Mediated Reduction of Nitroarenes using Glucose as a Hydrogen Source. RSC
Adv. 2013, 3, 4894-4898.
9
10 Menuel, S.; Léger, B.; Addad, A.; Monflier, E.; Hapiot, F. Cyclodextrins as effective
Additives in AuNP-Catalyzed Reduction of Nitrobenzene Derivatives in a Ball-Mill.
Green Chem. 2016, 18, 5500-5509.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
11 Akimoto, I.; Maeda, K.; Ozaki, N. Hydrogen Generation by Laser Irradiation of Carbon
Powder in Water. J. Phys. Chem. C 2013, 117, 18281-18285.
12 (a) Takasaki, M.; Motoyama, Y.; Higashi, K.; Yoon, S.-H.; Mochida, I.; Nagashima, H.
Chemoselective Hydrogenation of Nitroarenes with Carbon Nanofiber-Supported
Platinum and Palladium Nanoparticles. Org. Lett. 2008, 10, 1601-1604. (b) Mohapatra,
S. K.; Sonavane, S. U.; Jayaram, R. V.; Selvam, P. Heterogeneous Catalytic Transfer
Hydrogenationof Aromatic Nitro and Carbonyl Compounds over Cobalt(II) Substituted
Hexagonal Mesoporous Aluminophosphate Molecular Sieves. Tetrahedron Lett. 2002,
43, 8527-8529. (c) Jagadeesh, R. V.; Wienhöfer, G.; Westerhaus, F. A.; Surkus, A.E.;
Pohl, M. M.; Junge, H.; Junge, K.; Beller, M. Efficient and Highly Selective Iron-
Catalyzed Reduction of Nitroarenes. Chem. Commun. 2011, 47, 10972-10974. (d) Saha,
A.; Ranu, B. C. Highly Chemoselective Reduction of Aromatic Nitro Compounds by
Copper Nanoparticles/Ammonium Formate. J. Org. Chem. 2008, 73, 6867-6870. (e)
Nomura, K. Efficient Selective Reduction of Aromatic Nitro Compounds by Ruthenium
Catalysis under COH2O Conditions. J. Mol. Catal. A 1995, 95, 203-210. (f) He, L.;
Wang, L.-C.; Sun, H.; Ni, J.; Cao, Y.; He, H. Y.; Fan, K. N. Efficient and Selective
Room-Temperature Gold-Catalyzed Reduction of Nitro Compounds with CO and H2O
as the Hydrogen Source. Angew. Chem. Int. Ed. 2009, 48, 9538-9541. (g) Niquirilo, R.
V.; Teixeira-Neto, E.; Buzzo, G. S.; Suffredini, H. B. Formic Acid Oxidation at Pd, Pt
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4
5
6
Areas. Int. J. Electrochem. Sci. 2010, 5, 344-354.
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