Regioselective mononitration of biphenyl by use of stoichiometric quantities of nitrogen dioxide and molecular oxygen over rare earth cationexchanged β-Zeolite catalysts

Article abstract of DOI:10.1007/s11164-015-1954-0

In the presence of molecular oxygen and zeolite La-b with Si/ Al₂ = 260, regioselective mononitration of biphenyl with stoichiometric quantities of liquid nitrogen dioxide occurs at 20 °C to yield mononitrobiphenyl, as the main product, in yields up to 82.7 %. The 2-nitrobiphenyl:4-nitrobiphenyl isomer ratio is 0.34. The process is eco-friendly and inexpensive, and the zeolite is easily regenerated by simple work-up to give results similar to those obtained with the fresh catalyst.

Full text of DOI:10.1007/s11164-015-1954-0

Res Chem Intermed
DOI 10.1007/s11164-015-1954-0
Regioselective mononitration of biphenyl by use
of stoichiometric quantities of nitrogen dioxide
and molecular oxygen over rare earth cation-
exchanged b-zeolite catalysts
•
Yan Fang Tai Xiong Zi Dong Hao Shu Xu
•
•
•
Chun Jie Shi Xin Hua Peng
Received: 9 October 2014 / Accepted: 5 February 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract In the presence of molecular oxygen and zeolite La-b with Si/
Al2 = 260, regioselective mononitration of biphenyl with stoichiometric quantities
of liquid nitrogen dioxide occurs at 20 °C to yield mononitrobiphenyl, as the main
product, in yields up to 82.7 %. The 2-nitrobiphenyl:4-nitrobiphenyl isomer ratio is
0.34. The process is eco-friendly and inexpensive, and the zeolite is easily regen-
erated by simple work-up to give results similar to those obtained with the fresh
catalyst.
Keywords Biphenyl Á Nitrogen dioxide Á Mononitration Á Rare earth cations Á
b-Zeolite Á Regioselectivity
Introduction
Nitration of aromatics is an extremely important organic reaction for production of
important organic intermediates for synthesis of many useful materials, for example
dyes, pharmaceuticals, and plastics [1, 2]. Unfortunately, nitration has many
disadvantages, including substantial amounts of acid waste, low selectivity, over-
nitration, and expense. Major efforts have therefore been made to develop novel
catalyst systems that facilitate environmentally friendly and clean nitration of
aromatics [3, 4].
Y. F. Tai Á X. Z. Dong Á H. S. Xu Á X. H. Peng (&)
School of Chemical Engineering, Hefei University of Technology,
Hefei 230009, People’s Republic of China
e-mail: orgpeng@gmail.com
Y. F. Tai Á C. J. Shi
School of Applied Chemistry and Environmental Engineering, Bengbu College,
Bengbu 233000, People’s Republic of China
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Y. F. Tai et al.
Previous attempts to nitrate biphenyl derivatives by use of nitric acid with sulfuric
acid or acetic anhydride as nitrating agent gave a mixture of 4-nitrobiphenyl and
2-nitrobiphenyl with the ortho/para ratio ranging from 0.7 to 2.74 [5, 6]. With regard
to its hydrogen atoms, the phenyl in biphenyl is a p-donor substituent which stabilizes
the arenium ion intermediate and also stabilizes the transition state and lowers the
activation energy for electrophilic aromatic nitration; it thus acts as an ortho/para
directing group [7] and no 3-nitrobiphenyl has been detected. Except for the low yield
of 4-nitrobiphenyl, generation of dilute acid waste is costly and causes environmental
problems. Recently, many novel methods for nitration of biphenyl have been reported.
Yuan et al. [8] performed nitration of biphenyl and other aromatic compounds with
65 % nitric acid at reflux temperature over MCM-41-supported metal bis[(per-
fluoroalkyl)sulfonyl]imides, with 98.8 % yield of the mononitration product and a
2-nitrobiphenyl:4-nitrobiphenyl isomer ratio of 0.52. Conversation of only 89 % with
an ortho/para ratio of 0.61 was obtained over lanthanide triflate catalysts [9]. A yield
of nitrobiphenyl of only 52 % and an ortho/para ratio of 0.53 was achieved by use of
liquid Ag0.51 K0.42Na0.07 NO3 [10]. Yields of 4-nitrobiphenyl of 70 and 43 % were
achieved by use of nitric acid over H-b and H3PO4/TiO2-ZrO2, respectively [11, 12].
The yield of the para isomer can improved to[70 % by use of bismuth subnitrate–
thionyl chloride or silica–sulfuric acid [13, 14].
To improve the atom economy of nitration, nitrogen dioxide has been used as
nitrating agent to nitrify benzene, toluene, and halobenzenes, and good conversion,
yield, and selectivity were achieved [15–17]. Our group has also nitrified toluene
and halobenzenes with nitrogen dioxide and oxygen over a series of zeolites and
obtained a good selectivity [18]. However, high pressure and excess nitrogen
dioxide were used in the nitration. In pursuit of our attempts to achieve nitration of
biphenyl by use of nitric acid over ZSM-5-zeolite and b-zeolite catalysts [19, 20],
we have investigated the selectivity and yield of mononitration of biphenyl with
stoichiometric quantities of nitrogen dioxide over rare earth cation-exchanged b-
zeolite with Si/Al2 = 260 at ambient temperature and pressure.
Materials and methods
Materials
Zeolites were purchased from the New Materials Research Center of Tianjin in China.
All other chemicals were analytical grade and used without any further purification.
Characterization of catalysts
SEM
Scanning electron micrographs of zeolites were acquired with an Hitachi SU8020
microscope. The dried samples were mounted on specimen studs and sputter coated
with a thin film of gold to prevent charging. The gold-coated surface was then
scanned at different magnifications.
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Nitrogen dioxide/molecular oxygen over rare earth cations
TGA–DTA
Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were
performed with a Netzsch STA 449F3 thermogravimetric analyzer, in static air,
from 25 to 600 °C at a heating rate of 5 ° min-1
.
XRD
XRD data for the catalysts were collected by use of a Philips PW 1729 power
˚
diffractometer (Cu Ka,k = 1.54 A) in the scanning range between 5 and 60° (2h)
and using a step size of 0.02°.
FT-IR
FT-IR transmittance spectra were acquired with an Hitachi IR meter 260-10
spectrophotometer at ambient temperature in the range 400–4000 cm-1, as KBr
pellets.
Nitrogen adsorption
Textural properties (BET surface areas, pore volumes) were determined by nitrogen
adsorption with a Micromeritics Tristar II 3020 surface area and pore size analyzer.
Before the adsorption measurements at 77 K, the powdered zeolites (0.1 g) were
evacuated at 150 °C for 12 h.
1H NMR
1H NMR spectra were acquired with a Bruker 400 MHz spectrometer; CDCl3 was
used as solvent.
General procedure
Typical experimental procedure for zeolite rare earth cation-exchange
The standard procedure for rare earth cation-exchange involved stirring commercial
zeolite (2.00 g) in an aqueous solution of the corresponding metal nitrate (0.1 mol/
L, 50 mL) at reflux for 24 h. The solid was filtered, washed with deionized water
until removal of nitrate anions was complete, dried at 110 °C for 6 h, and then
calcined in air at 550 °C for 6 h.
Nitration with nitrogen dioxide and molecular oxygen
The materials were synthesized under an oxygen atmosphere, by use of a vacuum
line. In a typical run, 4 mmol biphenyl (0.61 g) and freshly activated zeolite (0.3 g;
zeolites were calcined at 550 °C for 2 h in air before use) were placed in a 100-mL
three necked flask with 5 mL acetic anhydride, and a balloon filled with oxygen was
123

Y. F. Tai et al.
connected to the reactor. The reaction was conducted, with stirring, at 20 °C.
Samples of the mixture were withdrawn at regular intervals and analyzed by gas
chromatography (GC; GC-2041C, Wondacap-1 df = 1.5 lm 0.53 mm
I.D. 9 30 m). On completion of the reaction, excess nitrogen dioxide was removed
by blowing air into the solution, and collected in a cold trap for reuse. The mixture
was filtered through a sintered glass funnel, the filtrate was diluted with water, and
the organic phase was extracted with dichloromethane. The concentrated mixture
was separated by column chromatography, and the nitro isomer distribution and
yield were determined from GC peak areas, by use of the internal standard
technique. Nitrobiphenyl products were identified by comparison of their analytical
data with those of authentic samples.
Catalyst regeneration
The used zeolite was recovered from the reaction mixture by filtration and washed
with dichloromethane. The catalyst was dried at 110 °C for 4 h in an oven, ground
into powder, then calcined at 550 °C for 6 h.
Results and discussion
Current trends in the preparation of nitro compounds emphasize minimizing
byproduct formation and improved regiocontrol of the desired product by use of
catalysts. Combined use of nitrogen oxides and molecular oxygen seems more
attractive and promising than use of conventional mixtures of acids. Moreover,
regioselective nitration to give the desired product with smaller amounts of nitrogen
dioxide, to achieve atom economy, has been achieved by use of a variety of zeolite
catalysts [21, 22]. Rare earth elements are important in modification of some of
these catalysts, for example faujasites, to increase their stability and activity in the
cracking reaction [23]. Biphenyl, 1, is usually commercially nitrated to give a
mixture of 2-nitrobiphenyl, 2a, 4-nitrobiphenyl, 2b, and dinitrobiphenyl, 3
(Scheme 1). The traditional process using mixed acids led to mixtures with isomer
ratios of approximately 0.7–1.39 (entry 2 in Table 1). The traditional process using
nitric acid and acetic anhydride gave mixtures with isomer ratios of approximately
O2N
+
NO2
NO2 / O2
Nitration
2a ortho
2b para
O2N
O2N
1
+O2N
+
O2N
NO2
NO2
3c
3b
3a
Scheme 1 Preparation of nitrobiphenyl
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Nitrogen dioxide/molecular oxygen over rare earth cations
Table 1 Regioselectivity in the preparation of mononitrobiphenyl using nitrogen dioxide and molecular
oxygen over a variety of zeolite catalystsa
Entry Nitrating agent Catalystb Conversionc (%) Yield of 2c (%) 2a:2bd
Yield of 3 (%)c
1e
2e
3
HNO3
–
–
–
1.96–2.74
0.7–1.39
1.88
–
HNO3
H2SO4
–
–
–
–
NO2
31.7
57.8
75.8
91.2
89.2
91.6
95.2
90.6
94.5
89.8
93.2
21.4
50.4
70.8
81.5
82.9
82.6
86.7
81.5
83.6
87.5
76.6
Trace
Trace
1.2
6.7
2.1
5.8
3.7
5.3
7.4
0.8
11.8
4
NO2–O2
NO2
–
1.80
5
H-b
H-b
Sm-b
Nv-b
La-b
Pr-b
Ce-b
Gd-b
Y-b
0.40
6
NO2–O2
NO2–O2
NO2–O2
NO2–O2
NO2–O2
NO2–O2
NO2–O2
NO2–O2
0.40
7
0.39
8
0.45
9
0.39
10
11
12
13
a
0.39
0.42
0.41
0.46
All reactions were performed in acetic anhydride (5.0 mL) using substrate 1 (4.0 mmol), NO2 0.13 mL
(4.0 mmol), catalyst (0.3 g, 50 wt% based on biphenyl) at room temperature for 12 h under an oxygen
atmosphere
b
Zeolites were calcined at 550 °C for 2 h in air before use
The combined yield of 2a and 2b on the basis of the amount of 1 consumed
c
d
The ratio of the products was determined by GC with 4-nitrotoluene as internal standard
e
Refs. [5, 6]
1.96–2.74 (entry 1 in Table 2). However, we found that formation of 2b was highly
favored when the substrate was subjected to the combined action of nitrogen dioxide
and molecular oxygen in the presence of b-zeolites, with substantially different
2-nitrobiphenyl:4-nitrobiphenyl isomer ratios. Some typical results are shown in
Table 1.
A variety of rare earth cation-exchanged b-zeolites were screened for nitration of
biphenyl a stoichiometric quantity of nitrogen dioxide. 4-Nitro selectivity was
higher for b-zeolite (entries 5–13 in Table 1) than for mineral acids (entries 1–2 in
Table 1). Regioselectivity for the 4-nitro isomer was high, and the 2-nitro/4-nitro
isomer ratio was 0.38–0.46 (entries 5–13 in Table 1). Among all the rare earth
cation-exchanged zeolites, La-b was resulted in maximum conversion, 95.2 %, and
an isomer ratio of 0.39. The different yields and isomer ratios obtained by use of
different rare earth elements indicate that the rare earth elements are involved in the
reaction. SEM images revealed morphological variation of the cation-exchanged
samples (Fig. 1), which may be one of the factors responsible for catalytic activity.
La-b has a higher Brønsted acidity than the other rare earth cation-exchanged b-
zeolites [24], suggesting a direct correlation between biphenyl conversion and
Brønsted acidity.
The presence of oxygen substantially promoted conversion of biphenyl,
suggesting oxygen is involved in the reaction; regioselectivity was no different
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Y. F. Tai et al.
Table 2 Effect of nitrogen dioxide-to-biphenyl molar ratios in the preparation of nitrobiphenyla
Temp. (°C)
Nitrating agentb
Conversionc
Yield of 2c (%)
2a:2bd
Yield of 3c (%)
20
20
20
20
20
a
NO2–O2 (0.5:1)
NO2–O2 (1.0:1)
NO2–O2 (1.5:1)
NO2–O2 (2.0:1)
NO2–O2 (2.5:1)
48.8
94.2
82.6
77.9
77.4
50.6
86.7
80.8
75.0
74.0
0.37
0.39
0.40
0.40
0.43
Trace
3.7
4.3
3.3
3.3
All reactions were performed in acetic anhydride (5.0 mL) using substrate 1 (4.0 mmol) and H-b
(0.3 g, 50 wt% based on biphenyl) for 12 h under an oxygen atmosphere. b-Zeolite was calcined at
550 °C for 2 h in air before use
b
The data in parentheses are the molar ratios of nitrogen dioxide to biphenyl
c
Combined yield of 2a and 2b on the basis of the amount of 1 consumed
d
The ratio of the products was determined by GC with 4-nitrotoluene as internal standard
Fig. 1 SEM images of rare earth cation-exchanged b-zeolites: a H-b, b Ce-b, c Y-b, d La-b
from that obtained by use of mineral acids, however (entry 4 in Table 1). The
acidity of the zeolite will be reduced by water released during the nitration reaction.
It is necessary to scavenge the water from the reaction zone to facilitate regeneration
of active acid sites on the catalyst [21]. The acetic anhydride present reacts with the
water molecules giving acetic acid, thereby maintaining the acidity of the zeolite.
Acetic anhydride can also react with the nitric acid produced to form acetyl nitrate,
123

Nitrogen dioxide/molecular oxygen over rare earth cations
+ 4 NO2 + O2
+ HNO3 + H2O
NO2
3
3
+
HNO3
H2O
Ac2O
Ac2O
AcONO2
2AcOH
+
AcOH
+
+ AcONO2
+
AcOH
NO2
+ 4 NO2+ O2 + 2Ac2O
4
4
+
4AcOH
NO2
Scheme 2 A possible reaction pathway for the biphenyl nitration with NO2/O2 in the acetic anhydride
which is a stronger nitrating agent than nitrogen dioxide. Thus, this reaction may be
related to the following reaction sequences (Scheme 2) [11, 15–17].
Zeolites contain three-dimensional channels and large pores for shape selectivity
in the nitration of biphenyl. Because the diameter of 2-nitrobiphenyl is larger than
that of 4-nitrobiphenyl, its movement is more restricted than that of 4-nitrobiphenyl
in b-zeolites.
In the hope of improving reactivity further, the amounts of nitrogen dioxide and
biphenyl were varied; representative results are summarized in Table 2. Increasing
the amount of nitrogen dioxide did not improve selectivity and yield. The
gasification of high concentrations of nitrogen dioxide could expel oxygen
molecular above surface of liquid nitrogen dioxide dramatically.
To optimize the reaction temperature for maximum mononitration yield and
selectivity, samples were analyzed at different temperatures ranging from 0 to 40 °C
(Table 3). At 30 and 40 °C a low yield of mononitrobiphenyl and higher selectivity for
4-nitrobiphenyl were observed. The results showed that the selectivity for the 4-nitro
isomer increased with increasing temperature. Higher temperatures were not preferable,
because of fasterdiffusionof nitrogendioxide, and raising thetemperature to30 °C, which
is well above the boiling point of nitrogen dioxide, could expel oxygen molecular above
surface of liquid nitrogen dioxide and dramatically reduce the concentration of liquid
nitrogen dioxide. If the temperature was too low, however, a decrease of mononitration
yield was observed. This could be ascribed to low reaction rate. Hence, the optimum
temperature was approximately 20 °C, close to the boiling point of nitrogen dioxide.
The effect of the quantity of b-Zeolite catalyst on selectivity was also
investigated (Table 3). Increasing the amount of the catalyst improved regioselec-
tivity for 4-nitrobiphenyl and the yield of the isomers. This could be because of the
three-dimensional interconnecting channel system, and the increase in the number
of accessible pores of the catalyst. However, use of a large amount of catalyst could
cause absorption of substrate and products, resulting in a slight decrease in the yield
of mononitration. DTA–TGA analysis was performed on recovered La-b-zeolite
(Fig. 2). Weigh loss was observed when La-b-zeolite was heated from 95 and
280 °C in the atmosphere. This weight loss is attributed to removal of water and
biphenyl present in the cavities of catalyst and which could not be removed by
washing with solvent (Table 4; Fig. 3).
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Y. F. Tai et al.
Table 3 Effect of temperature and amount of La-b-zeolite in the preparation of nitrobiphenyla
Temp. (°C)
Amount of La-b (g)
Yield of 2b (%)
2a:2bc
Yield
of 3b (%)
20
20
20
20
20
0
0.3
0.45
0.6
0.75
0.9
0.3
0.3
0.3
86.7
85.6
84.1
83.6
82.7
74.8
47.5
45.5
0.39
0.39
0.37
0.36
0.34
0.37
0.31
0.29
3.7
4.3
4.8
4.7
5.4
5.8
30
40
a
Trace
Trace
All reactions were performed in acetic anhydride (5.0 mL) using substrate 1 (4.0 mmol), biphenyl-to-
nitrogen dioxide ratio = 1:1, reaction time = 12 h, under an oxygen atmosphere
b
Combined yield of 2a and 2b on the basis of the amount of 1 consumed
c
The ratio of the products was determined by GC with 4-nitrotoluene as internal standard
Fig. 2 DTA–TGA pattern of recovered La-b
Table 4 Surface properties of La-b-zeolite
Catalyst
BET surface
area (m2 g-1
Pore volume
(cm3 g-1
)
Average pore
volume (nm)a
)
Fresh La-b
Used La-b
Regenerated La-b
a
345
252
341
0.265
0.211
0.262
3.07
3.36
3.07
Average pore diameter calculated by use of the relationship 4 9 pore volume/BET surface area
123

Nitrogen dioxide/molecular oxygen over rare earth cations
Fig. 3 XRD patterns of a fresh, b recovered, and c regenerated La-b
Fig. 4 FT-IR spectra of a fresh, b recovered, and c regenerated La-b
The nature of the species adsorbed on the catalyst sites was determined by FT-IR
spectroscopy of the used La-b catalyst after nitration in acetic anhydride solvent.
The IR bands (Fig. 4) at 1521 and 1347 cm-1 are ascribed to asymmetric and
symmetric vibrations, respectively, of the nitro product. The intense band at
123

Y. F. Tai et al.
Table 5 Efficiency of recycled La-b-zeolites in the preparation of nitrobiphenyla
Recycle number
Yield of 2b (%)
2a:2bc
Yield of 3b (%)
Fresh
86.7
85.2
85.5
85.4
0.39
0.39
0.39
0.40
3.6
5.2
4.2
4.2
1
2
3
a
Reaction conditions: biphenyl-to-acetic anhydride ratio = 0.6:5 (v/v), biphenyl-to-nitrogen dioxide
ratio = 1:4, La-b-zeolite 0.53 g (100 wt% based on biphenyl), reaction temperature = 35 °C, reaction
time = 12 h, under oxygen atmosphere
b
Combined yield of 2a and 2b on the basis of the amount of 1 consumed
c
The ratio of the products was determined by GC with 4-nitrotoluene as internal standard
1719 cm-1 reveals the presence of acetic acid formed during the reaction [25]. The
FT-IR spectrum obtained after activation at 550 °C for 6 h is similar to that of the
fresh catalyst, indicating successful regeneration of the catalyst (Fig. 4).
For reuse, b-zeolite was easily recovered from the reaction mixture by simple
filtration. To study the re-usability of the catalyst, the reaction was performed with
reused and thermally regenerated La-b-zeolite. Even after use of the b-zeolite four
times, only slight changes in selectivity and yield were observed, with little loss of
the original activity (Table 5). The XRD spectrum of fresh and regenerated catalyst
contained two typical peaks located at 2h 22.5 and 7.4, indicative of the similar
structure of the b-zeolite. A substantial decrease of the intensity of the characteristic
peak at 2h = 7.8 was recovered after regeneration (Fig. 3). SEM and FT-IR
afforded similar results. Thus, the surface properties of used La-b-zeolite were also
recovered after regeneration (Table 4).
Conclusion
In conclusion, 4-nitrobiphenyl was prepared highly selectively in good yield from
stoichiometric quantities of nitrogen dioxide and molecular oxygen in the presence
of H-b and rare-earth exchanged b-zeolite. Furthermore, the reaction is environ-
mentally friendly because of atom economy and easy work up of b-zeolite.
Moreover, this process has potential for clean and highly selective preparation of
nitroaromatic compounds.
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