Efficient reductions of various nitroarenes with scrap automobile catalyst and NaBH4

Article abstract of DOI:10.1016/j.catcom.2015.04.008

The effect of scrap automobile catalyst (SAC), a waste material, was investigated as a catalyst for the reduction of nitroarenes to the corresponding amines with sodium borohydride in aqueous ethanol at 5-25 °C. Along with the observed high conversions, the SAC and NaBH₄ combination also exhibits a selectively catalyzed reduction in compounds containing other reducible functionalities, such as CN, Br, Cl and I. Recycling automobile wastes into a catalyst for organic reactions will offer both environmental protection and economic advantages. As a result, an effective, easy to use, low-priced and reliable method has been developed.

Full text of DOI:10.1016/j.catcom.2015.04.008

Catalysis Communications 67 (2015) 64–67
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Efficient reductions of various nitroarenes with scrap automobile catalyst
and NaBH4
Hayriye Genc
Sakarya University, Faculty of Arts and Sciences, Esentepe Campus, 54187 Serdivan, Sakarya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The effect of scrap automobile catalyst (SAC), a waste material, was investigated as a catalyst for the reduction of
Received 15 February 2015
Received in revised form 30 March 2015
Accepted 2 April 2015
nitroarenes to the corresponding amines with sodium borohydride in aqueous ethanol at 5–25 °C. Along with the
observed high conversions, the SAC and NaBH combination also exhibits a selectively catalyzed reduction in
4
compounds containing other reducible functionalities, such as \CN, \Br, \Cl and \I. Recycling automobile
wastes into a catalyst for organic reactions will offer both environmental protection and economic advantages.
As a result, an effective, easy to use, low-priced and reliable method has been developed.
Available online 7 April 2015
Keywords:
Reduction
©
2015 Elsevier B.V. All rights reserved.
Scrap automobile catalyst
Catalytic convertors
Aromatic amine
Nitro group
Sodium borohydride
1
. Introduction
harmful compounds [10]. Platinum group metals (PGMs) constitute the
main component of catalytic convertors, being mainly platinum, palla-
dium and sometimes rhodium located on the inert aluminum support
[11]. The total PGM amount changes in between 0.5–2 g/kg [12]. The
recycling of PGMs is vital in terms of the ability to reuse the valuable
metals in its content, protect the environment by decreasing waste,
management of natural resources and decrease both electricity con-
sumption and contaminating emissions [13]. Thus, many methods
have been developed enabling the recycling of PGMs from catalytic con-
vertor [14–16]. In our study, waste catalytic convertors have been dem-
onstrated to be useable in the place of Pd/C as a catalyst [17,18].
The role of catalytic activity of SAC in reducing various nitroarenes to
Aromatic amines are vital initial and intermediate products in chem-
ical production of various industry branches such as dye, pigment, agro-
chemical, polymer and pharmacology [1]. Moreover, they may easily be
replaced by some other groups, such as H, F, Cl, Br, I, OH, or diazonium
groups. The most practical method for substituted aniline synthesis is
nitration of simple aromatic compounds, followed by reduction of the
nitro group to the relevant amine. The classical approach to catalytic hy-
drogenation requires tough conditions for reduction [2,3]. NaBH4, which
has been used for more than 100 years and is among the leading reduc-
tants due to its moderate conditions, is insufficient for reducing the
nitro groups by itself [4–6]. However, the researchers had succeeded
4
the corresponding aromatic amines by NaBH has been demonstrated
4
to reduce the nitro groups by using the combinations of NaBH with
(Scheme 1).
transition metals [7]. Pursuing these aims, many catalysts have been de-
veloped since the 1960s which operate quickly and at high efficiency
under moderate conditions and are considered practical in reducing
the nitro compounds [8]. But the referred methods suffer disadvantages
such as high catalytic loading, inability to re-use the catalyst and high
costs. Today, catalysts comprised of nano-particles co-operating with
NaBH are under development [9]. Researchers are attempting to over-
4
come the aforementioned problems and develop environmentally
friendly alternatives.
2. Experimental
2.1. Purification of catalyst
The used automobile catalytic convertor (SAC) was procured from
TEKNOTROM AŞ. It was first rinsed with acetone and hot water several
times. To ensure removal of hydrocarbon wastes, it was kept for 1 h in
an oven in 400 °C, then was grinded in agate mortar and sieved (diam-
eter b100 lm). Then the chemical composition of SAC was determined
with an X-ray fluorescence spectrometer (WD-XRF) S8 Tiger, Bruker
using a semi-quantitative method (QUANT-EXPRES/Bruker). During
analysis of XRF, it was decided to include various metal and oxides as
well as 0.115 wt.% Pd and 0.491 wt.% Pt (Table 1).
For the past 30 years, automobile manufacturers have used catalytic
convertors to convert unburned hydrocarbons (HC), carbon monoxides
(
CO) and nitrogen oxides (NOx) in internal combustion engines to less
E-mail address: hayriyegenc@sakarya.edu.tr.
http://dx.doi.org/10.1016/j.catcom.2015.04.008
566-7367/© 2015 Elsevier B.V. All rights reserved.
1

H. Genc / Catalysis Communications 67 (2015) 64–67
65
Table 2
Reduction of nitrobenzene under different reaction conditions.
Nitrobenzene
mmol)
EtOH/H
(ml)
2
O
NaBH
(mmol)
4
Timea
SAC
(mg)
Converted
%
(
4
Scheme 1. Reduction reaction of nitroarenes with SAC and NaBH .
1
1
1
1
1
1
1
1
1
1
1
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
10/20
10/20
10/20
10/20
10/20
10/20
10/10
10/10
10/10
10/10
10/10
2.0
2.0
3.0
3.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
2 h
6 h
2 h
6 h
2 h
4 h
4 h
4 h
4 h
4 h
16 h
300
300
300
300
300
300
300
100
300
400
–
10
10
35
40
2
.2. General procedure for the reduction of nitro compounds, catalyzed
50
by SAC
N99
N99
55
75
N99
–
4
SAC (300 mg) and NaBH (4.0 mmol) were added to a solution of
nitroarenes (1.0 mmol) in EtOH/water (1/1) (20 ml). The reaction
mixture was stirred for 4 h at the temperature indicated in Table 3. At
the end of the reaction, the catalyst was removed by filtering and the fil-
trate was extracted with 3 × 70 ml EtOAc. The combined organic layers
a
The reaction time was determined by TLC analysis.
4
were dried over MgSO and concentrated in a vacuum.
Experiments were performed at different temperatures, ranging
2
.3. Reuse of catalyst
After the reactions, the SAC was simply filtered off and washed with
from ice bath to reflux temperature. At this phase, it was observed
that nitroarenes bearing a hydroxyl or an amine group formed
more byproducts at temperatures above 40 °C. Thus, it was per-
formed at 5 °C to avoid this byproduct formation. As a fairly high
conversion rate was enabled at different temperatures in the reduc-
tion of other compounds, experiments were carried out at room
temperature (Table 3). Reduction did not occur without SAC over a
two day period, indicating that a catalyst including transition metals
must be present for reduction with NaBH4.
ethanol, water and acetone and then dried in air for using another re-
duction. The catalyst was able to be reused more than five times without
a decrease in catalytic activity (Table 4).
3
. Result and discussion
This experimental study revealed that the optimum reaction condi-
tions for reduction of 1 mmol nitroarene were 300 mg SAC, 4 mmol
To optimize the reaction conditions, the reduction of nitrobenzene
was based on a model reaction. Various reaction conditions, including
NaBH in an EtOH/water ratio 1:1 or 1:2 for a period of 4 h.
4
catalyst and SAC concentrations, rate of EtOH/H
ture and reaction time were examined.
The effect of catalyst loading on reaction time and yield was exam-
ined. 300 mg SAC was sufficient for 1 mmol nitroarene reduction and
conversion time did not shorten when increased to 400 mg. Variable
2
O mixture, tempera-
As shown in Table 3, optimized conditions were examined with
other nitroarenes in order to make comparisons and determine the
applicability of this method. Isolated yields were found to vary be-
tween 82 and 97%. The highest yields of 97% were obtained from re-
ductions of 2-chloro-6-nitropyridine and 2-nitrofluorene (entry 17
and 20), while a relatively low yield was obtained from reduction
of 1-iodo-3-nitrobenzene (entry 12). Nitroarenes with an electron-
withdrawing group were reduced in higher yields than for those
containing an electron-donating group. Additionally, the presence
of a group such as hydroxyl or amine caused a lower yield by slightly
dissolution of nitroarenes in water through extraction. Although the
best results were generally obtained in 5 °C, as some nitroarenes did
not dissolve in EtOH/water mix, their reductions were carried out in
equivalents of NaBH
duction. The best results were obtained by 4 mmol NaBH
mined that extending the time in which less NaBH was used did not
4
were examined against 1 mmol nitrobenzene re-
4
. It was deter-
4
contribute to the percentage rate of conversion. The mixed EtOH/
water solvent was tested at ratios of 1:1 and 1:2; however, reduction
yield apparently remained independent of the solvent ratio (Table 2).
2
0 and 25 °C (entry 17, 18, 19 and 20). However, very high yields
Table 1
XRF analysis of SAC.
(91–97%) were also obtained in these cases.
a
Element
Al
Content (wt.%)
4
. Conclusion
2
O
3
39.840
22.100
4.640
3.891
3.800
3.339
3.230
1.140
1.030
1.000
0.609
0.491
0.437
0.318
0.306
0.255
0.220
0.210
0.115
0.110
SiO
CeO
ZrO
SO
Fe
MgO
2
2
SAC, including valuable metals, was evaluated in this study. The cat-
2
alytic activity of SAC was investigated for the reduction of nitroarenes to
aromatic amines with NaBH . The catalyst is reusable and the method is
3
4
2
O
3
selective for reduction of nitro groups in the presence of \CN, \Br, \Cl,
\I like groups. Considering the annual SAC waste rate, their recovery
without any additional chemical processes is important in terms of
both economic efficiency and environmental protection. Consequently,
this method has been demonstrated to be an effective, easy to use, low-
priced and secure method which may be used in the high-efficiency re-
duction of nitroarenes.
2 5
P O
CaO
TiO
BaO
Pt
2
La
Cr
2
O
O
3
3
2
2
K O
PbO
SrO
Acknowledgments
Na
Pd
Cl
2
O
The author thanks TEKNOTROM AŞ., Sakarya for supplying spent
automotive catalyst materials and Senol Ozturk (Gizem Frit Sakarya)
for XRF analysis.
a
It was determined using a semi-quantitative method
QUANT-EXPRES/Bruker).
(

66
H. Genc / Catalysis Communications 67 (2015) 64–67
Table 3
Catalytic reduction of various nitroarenes using SAC.
a
Entry
1
Reactant
Product
Temperature (°C)
Converted
100
Yieldb (%)
95
Ref.c
[9a]
5
2
3
4
5
5
100
100
100
100
96
94
93
87
[9a]
[9a]
[9a]
[9a]
5
5
5
6
7
5
5
100
100
89
85
[9a]
[9a]
8
9
5
5
100
100
87
85
[9a]
[9a]
10
5
100
88
[9a]
1
1
1
2
5
5
100
100
84
82
[19]
[20]
1
1
1
3
4
5
5
5
5
100
100
100
86
96
92
[21]
[9a]
[22]

H. Genc / Catalysis Communications 67 (2015) 64–67
67
Table 3 (continued)
Entry Reactant
Product
Temperature (°C)
Converted
Yieldb (%)
Ref.c
16
5
100
93
[23]
1
7
8
20
20
100
100
97
91
[24]
[25]
1
1
2
9
0
25
25
100
100
94
97
[26]
[9a]
a
b
c
Reaction conditions: 1 mmol nitroarene, 300 mg SAC, 4 mmol NaBH
Isolated yield.
All products were characterized by 1H NMR and 13C NMR spectra and compared with authentic samples.
4 2
, and 20 ml EtOH/H O.
[
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(
Table 4
Reusing of SAC.
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2
3
4
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6
100
100
100
100
100
100
95
95
95
95
95
95
(
[
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Reaction conditions: 1 mmol nitrobenzene, 300 mg SAC, 4 mmol NaBH
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EtOH/H
2
O.
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