Catalytic hydrogenation and reduction of 4-(2,2,2-trifluoroethoxy)nitrobenzene

Article abstract of DOI:10.14233/ajchem.2014.16601

4-(2,2,2-Trifluoroethoxy)nitrobenzene was used as raw material to create a reaction for 1 h at 70°C by using ethanol and palladium carbon as solvent and catalyst, respectively, to obtain the desired product 4-(2,2,2-trifluoroethoxy)aniline with 97% yield and 99.9% purity. NMR, IR, MS, GC and other analysis and detection methods were used to conduct qualitative and quantitative analyses of the desired product. This paper discussed the process conditions of hydrogenation and reduction reaction and mainly investigated the impact of dosage and recycling of catalyst.

Full text of DOI:10.14233/ajchem.2014.16601

Asian Journal of Chemistry; Vol. 26, No. 21 (2014), 7289-7291
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16601
Catalytic Hydrogenation and Reduction of 4-(2,2,2-Trifluoroethoxy)nitrobenzene
1,*
2
1
HAIYING CHEN , MING LU and JIALIN SHEN
1Nanjing Institute of Geology and Mineral Resources, Nanjing, Jiangshu, P.R. China
2School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu, P.R. China
*Corresponding author: E-mail: chy198181@163.com
Received: 29 October 2013;
Accepted: 10 December 2013;
Published online: 30 September 2014;
AJC-16121
4-(2,2,2-Trifluoroethoxy)nitrobenzene was used as raw material to create a reaction for 1 h at 70 °C by using ethanol and palladium
carbon as solvent and catalyst, respectively, to obtain the desired product 4-(2,2,2-trifluoroethoxy)aniline with 97 % yield and 99.9 %
purity. NMR, IR, MS, GC and other analysis and detection methods were used to conduct qualitative and quantitative analyses of the
desired product. This paper discussed the process conditions of hydrogenation and reduction reaction and mainly investigated the impact
of dosage and recycling of catalyst.
Keywords: 4-(2,2,2-Trifluoroethoxy)aniline, Palladium carbon, Catalytic hydrogenation, Recycling of catalyst.
INTRODUCTION
EXPERIMENTAL
As an important intermediate, trifluoroethoxy aniline is
extensively applied in the field of medicine; it is also used in
pesticides and dyestuff, among other applications. Combined
1,3-diamino-4-(2,2,2-trifluoroethoxy)benzene and salt is used
as hair dye-because of its advantages, such as better chroma-
ticity, rapid dyeing and nontoxicity1.
Nitro reduction is currently used in different industrial
applications, such as reduction of metals in acid, neutral and
alkaline systems; reduction of reductive compound; electro-
chemical reduction and catalytic hydrogenation reduction2.
However, the first three methods cause environmental pollution
and are inefficient and complicated. Catalytic hydrogenation
reduction is characterized by a clean process, mild reaction
conditions, convenient post-treatment and high yield. Catalytic
hydrogenation is used in both laboratory research and industrial
production. Given the advantages of this process, the present
experiment adopted catalytic hydrogenation. The specific
synthetic route is as Fig. 1.
The following equipment were used in this experiment:
Yansco micro melting point apparatus (uncalibrated thermo-
meter); BrukerAvance DPX 300 MHz nuclear magnetic reso-
nance spectrometer; TSQ Quantum Ultra Am high-resolution
mass spectrometer from Finnigan Corporation; and Nexus 870
FTIR infrared spectrometer from US Nicolet Corporation. 4-
Chloronitrobenzene and sodium hydride are chemically pure
reagents; ethanol, acetic ether and petroleum ether are analytic
reagents; and trifluoroethanol, palladium carbon and hydrogen
are industrial products.
Synthesis of 4-(2,2,2-trifluoroethoxy)nitrobenzene:
First, 2.4 g (0.1 mol) of sodium hydride and 120 mL of N,N-
dimethyl formamide were added into a dried four-neck 250 mL
flask. Then, 10 g (0.1 mol) trifluoroethanol was dropped slowly
into the flask under the protection of nitrogen ice. The mixture
was stirred for about 0.5 h and clear and transparent liquid
was obtained. Afterward, 7.88 g (0.05 mol) 4-chloronitro-
benzene was added and the temperature was slowly increased
to 100 °C to generate a reaction for 3 h. After 2/3 of the solvent
was removed through decompression, the mixture was natu-
rally cooled to room temperature. Diluted hydrochloric acid
was used to adjust the pH to a slightly acidic value. The mixture
was then stored at room temperature.Yellow crystals gradually
appeared overnight. Solids were extracted and filtered. After
recrystallization with ethanol (95 %), white solids were obtained,
with a yield of 98 %, m.p. 69 to 71 °C (value from the literature3:
75.5 to 76.5 °C); MS m/z (%), 220.9 (M+,100), 191.0, 156.0.
Cl
OCH2CF3
OCH2CF3
CF3CH2ONa
H2
Pd/C
NO2
NO2
NH2
Fig. 1. Synthetic route of 1,3-diamino-4-(2,2,2-trifluoroethoxy)benzene

7290 Chen et al.
Asian J. Chem.
Synthesis of 4-(2,2,2-trifluoroethoxy)aniline: First, 11.05
Catalyst
g (0.05 mol) 4-(2,2,2-trifluoroethoxy)nitrobenzene, 150 m
ethanol and 0.3 g palladium carbon were added to a 500 mL
autoclave. Hydrogen was injected into the autoclave to increase
the pressure to 0.5 Mpa and then the reaction was generated
for 1 h at 75 °C. Once the pressure stopped falling, it was
maintained for 0.5 h.After the reaction, the mixture was filtered
and the filtered liquid was distilled to remove solvent ethanol.
Fractions with a temperature range of 140 to 158 °C were
collected to create recrystallized V(petroleum ether): V(ethyl
acetate) = 10:1. White flaky crystals were obtained with a yield
of 97 %, m.p. 66 °C to 68 °C. 1H NMR (CDCl3,δ): δ6.80-6.83
(d, 2H, Ar-H), 6.65-6.69 (d, 2H, Ar-H), 2.90 (s, 2H, -NH2),
4.29 (m, 2H, OCH2CF3); IR (KBr, νmax, cm-1): 3462(m),
1504(s), 1258(s), 1202(s), 753(s). MS m/z (%), 192.1(M),
163.0, 109.0, 107.9.
Effect of catalyst dosage on the reaction: One hundred
fifty milliliters of ethanol were added to 11.05 g (0.05 mol) 4-
(2,2,2-trifluoroethoxy)nitrobenzene. Palladium carbon with a
load of 5% was used as catalyst and H2 pressure was 0.5 Mpa.
The reaction was maintained at 70 °C until the pressure in the
autoclave increased. In this experiment, the amount of the
catalyst was changed to examine the effect of catalyst dosage
on the reaction. The results are shown as Table-2.
TABLE-2
IMPACT OF CATALYST DOSAGE ON THE REACTION
The amount of palladium carbon
1 % 3 % 4 % 5 %
(relative to mass ratio of raw materials)
Hydrogenation time/min
Yield (%)
120
60
50
40
97.1 97.5 98.1 97.6
The above table indicates that the reaction became faster
and hydrogenation time decreased with the increase of the
amount of palladium carbon. However, when the amount of
palladium carbon was increased to a certain degree, the yield
remained at a certain level.When the feeding amount of palladium
carbon was 5 %, the reaction speed was rapid and strongly
exothermic. Moreover, the yield increased. Therefore, a feeding
amount of 3 % is suitable.
Impact of catalyst recycling on the reaction: Catalyst
loss occurs during recycling, thereby affecting the reaction
speed. In this paper, catalyst recycling was analyzed and studied
and an experiment on the process was conducted. The reaction
conditions are discussed earlier and the amount of catalyst
was 3 % (Table-3).
RESULTS AND DISCUSSION
Process conditions of hydrogenation reduction
Selecting hydrogenation reduction solvent: 4-(2,2,2-
Trifluoroethoxy)nitrobenzene reduction is a heterogeneous
catalytic reaction in which the solvent has an important
function. Solvent polarity has different effects on the catalytic
hydrogenation rate and catalyst selection. These different
effects are mainly due to the fact that the solvent changes the
catalytic activity and the adsorption of unsaturated substrate,
which in turn changes hydrogen adsorption4,5.
Liquid phase catalytic hydrogenation uses inert solvents
that are stable to hydrogen, such as water, methanol, ethanol,
isopropyl alcohol, ethyl acetate and tetrahydrofuran. Table-1
shows the polarities and boiling points of these solvents.
Ethanol (b.p. 79 °C) (which is higher than the reaction
temperature) and proper polarity can better dissolve products.
Ethanol is miscible with water, which ensures that catalyst
poisoning can be avoided. Water generated from oxide reduc-
tion causes aggregation of metal particles, decreasing catalytic
activity. In addition, ethanol is nontoxic and easily recyclable.
Therefore, it was selected as the solvent.
Temperature for hydrogenation reduction: Hydroge-
nation is an exothermic reaction. An excessively high tempe-
rature will promote side reactions, which will affect product
conversion rate. Therefore, a lower temperature should be used
to ensure that the proper reaction can be obtained. The
hydrogenation temperature of the reaction in this experiment
is 70 °C.
Pressure for hydrogenation reduction: Increasing
pressure can accelerate reaction speed. However, excessive
pressure will cause an unusually severe reaction. Increased
heat will negatively affect the reaction equipment and impede
safe operation. Therefore, a lower temperature should be used
to ensure that the pressure is suitable for the reaction. The
recommended hydrogen pressure is 0.5 MPa.
TABLE-3
IMPACT OF PALLADIUM CARBON RECYCLING
ON THE REACTION
Catalyst recycling times
Yield (%)
1
97.0
2
93.9
3
91.7
4
84.9
5
82.5
The above results indicate that as catalyst recycling incre-
ased, hydrogenation speed decreased markedly. When catalyst
recycling occurred more than three times, the yield decreased
to 90 % and below. This decrease is due to various reasons.
First, catalyst loss occurred during the recycling process. Second,
foreign matters were adsorbed on the activated carbon carrier
during the reaction.As a result, the carrier was partially inacti-
vated. To ensure a stable reaction, a small amount of fresh
catalyst should be added when the catalyst has been used more
than three times.
Catalyst recycling: Recycling of precious metal catalysts,
particularly those in liquid phase hydrogenation, is a key issue
in precious metal catalysis. The recycling process for waste
palladium carbon involves the following steps: treatment of
activated carbon, burning of waste catalysts, dissolving of
palladium and preparation of new catalysts, among others6.
TABLE-1
POLARITIES AND BOILING POINTS OF SOLVENTS
Solvents
Polarities (25 °C)
Boiling points (°C)
Water
10.2
100
Methanol
6.6
Ethanol
4.3
79
Isopropyl alcohol
Ethyl acetate
Tetrahydrofuran
4.3
82
4.3
77
4.2
66
65

Vol. 26, No. 21 (2014)
Catalytic Hydrogenation and Reduction of 4-(2,2,2-Trifluoroethoxy)nitrobenzene 7291
The results verified that the palladium carbon catalysts obtained
by using the method presented in this paper are as efficient as
fresh catalysts.
catalyst has been used more than three times, a small amount of
fresh catalyst should be added. Palladium carbon catalysts
obtained through recycling are as efficient as fresh catalysts.
Conclusions
REFERENCES
• 4-(2,2,2-Trifluoroethoxy)nitrobenzene can be used as
raw material to obtain 4-(2,2,2-trifluoroethoxy)aniline through
palladium carbon catalytic hydrogenation with 97 % yield and
99.9 % purity.
• Catalytic hydrogenation reduction is conducted with the
use of ethanol as reactive solvent under a reactive temperature
of 70 °C and reactive pressure of 0.5 Mpa.
• In this experiment, the suitable amount of catalyst is
3 %. When the catalyst has been used more than three times,
the yield decrease to 90 % and below. Therefore, when the
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