Zeolite-assisted regioselective mononitration of naphthalene with nitrogen dioxide/molecular oxygen

Article abstract of DOI:10.1007/s11164-012-0827-z

The nitration process using nitrogen dioxide and oxygen instead of the classical nitric acid-sulfuric acid system appears to be attractive and promising in the selective preparation of nitro compounds. The ratio of 1-nitronaphthalene isomer to 2-nitronaphthalene can reach 11 in a moderate yield of 60 % when the reaction is carried out in acetonitrile with 5.0 mmol naphthalene, 10 mmol nitrogen dioxide, and 0.13 g HZSM-5 under molecular oxygen atmosphere at -15 C. The isomeric distribution of the product nitro-naphthalene was found to be superior to traditional methods. The zeolite could be easily regenerated and recycled and reused by simple work-up to give results similar to those obtained with the fresh catalyst.

Full text of DOI:10.1007/s11164-012-0827-z

Res Chem Intermed
DOI 10.1007/s11164-012-0827-z
Zeolite-assisted regioselective mononitration
of naphthalene with nitrogen dioxide/molecular oxygen
Chunjie Shi
Xiongzi Dong
•
Xinhua Peng
•
•
Yanfang Tai
•
Haocai Wang
Received: 29 May 2012 / Accepted: 20 September 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract The nitration process using nitrogen dioxide and oxygen instead of the
classical nitric acid–sulfuric acid system appears to be attractive and promising in
the selective preparation of nitro compounds. The ratio of 1-nitronaphthalene iso-
mer to 2-nitronaphthalene can reach 11 in a moderate yield of 60 % when the
reaction is carried out in acetonitrile with 5.0 mmol naphthalene, 10 mmol nitrogen
dioxide, and 0.13 g HZSM-5 under molecular oxygen atmosphere at -15 °C. The
isomeric distribution of the product nitro-naphthalene was found to be superior to
traditional methods. The zeolite could be easily regenerated and recycled and reused
by simple work-up to give results similar to those obtained with the fresh catalyst.
Keywords Naphthalene Á 1-Nitronaphthalene Á Nitration Á Nitrogen dioxide Á
Zeolite
Introduction
Nitration of aromatics is an important organic reaction in the preparation of
intermediates of many compounds including pharmaceuticals, dyestuffs, explosives,
pesticides, and so on [1–4]. However, the preparation of nitro compounds in
industry still employs classical processes involving large quantities of nitric and
sulfuric acid, which have many disadvantages [5–7], such as poor selectivity, over-
nitration, oxidized byproducts, and waste acids. Therefore, it is urgent to develop an
environmentally economic method for the preparation of nitro compounds.
In recent years, various clean nitration approaches have been explored which
employ nitrogen oxides as nitrating agents, such as nitrogen dioxide [8, 9], dinitrogen
tetroxide [10], dinitrogen pentoxide [11], etc., in the presence of some solid catalysts
C. Shi Á X. Peng (&) Á Y. Tai Á X. Dong Á H. Wang
School of Chemical Engineering, Hefei University of Technology, Hefei 230009, People’s Republic
of China
e-mail: orgpeng@gmail.com
123

C. Shi et al.
and supports [12–15]. A significant improvement of the isomer product ratios in the
zeolite-assisted double Kyodai-nitration of toluene and chlorobenzene has been
observed [16]. Especially, zeolite was a very attractive catalyst to make positive
contributions to the positional selectivity in the novel nitration process. In this paper,
we report the catalytic performance of zeolite for the mononitration of naphthalene
with nitrogen dioxide as a nitration agent. Furthermore, the nitrogen dioxide/
molecular oxygen system is a promising nitration process, while nitrogen dioxide and
dioxygen are very cheap and easy for clean manufacture in industry.
Experimental
Regents and apparatus
1
H NMR spectra were determined in CDCl on a Bruker 400 MHz spectrometer.
3
TLC was performed with silica gel GF254 percolated on class plates, and spots were
visualized with UV. HPLC (Shimadzu LC-10Avp Plus) was utilized to determine
product isomer compositions. IR measurements were made on a Hitachi IR meter
2
60-10 for KBr pellets and only characteristic peaks were recorded. Melting points
were determined on a WRS-2 apparatus and uncorrected. Zeolites were purchased
from New Materials Research Center of Tianjin in China. All other chemicals were
analytical grade without any further purification.
General procedure
Typical experimental procedure for zeolite cation-exchange
The standard procedure for cation-exchange involved stirring a supplied commer-
cial zeolite (5.0 g) in a refluxing aqueous solution of the corresponding metal
-
chloride (0.2 mol L , 100 mL) for 24 h. The solid was filtrated, washed with
1
deionized water until halide-free, and dried at 110 °C for 3 h, then calcined in air at
5
50 °C for 6 h.
Nitrate progress with nitrogen dioxide/molecular oxygen
Quantitative naphthalene, nitrogen dioxide, zeolite, and acetonitrile were placed in a
flask. Oxygen was passed into the system to replace air, and a balloon filled with
oxygen was connected. The mixture was stirred at a certain temperature and
progress of the reaction was monitored by TLC. When the reaction was complete,
excess nitrogen dioxide was removed by blowing air into the solution, and collected
in a cold trap for reuse. The zeolite was removed by filtration and the filter liquor
was washed with water, a 5 % aqueous solution of sodium bicarbonate followed by
water. The organic phase thus separated was dried with anhydrous sodium sulfate,
and concentrated under reduced pressure to give a yellow solid residue. The product
was analyzed by HPLC. The yellow solid with further purification was analyzed by
1
H NMR. The used zeolite was recovered by washing and calcination.
1
23

Zeolite-assisted regioselective mononitration of naphthalene
1
1
-Nitronaphthalene H NMR (400 MHz, CDCl ): d = 8.56 (d, 1H), 8.23 (d, 1H),
3
8
1
.12 (d, 1H), 7.96 (d, 1H), 7.72 (t, 1H), 7.62 (t, 1H), 7.54 (t, 1H); IR (KBr): 1,600,
-
1
,569, 1,519, 1,339, 1,261, 872, 804, 789, 764 cm
1
.
2
.06–7.86 (m, 3H), 7.74–7.55 (m, 2H); IR (KBr): 1,630, 1,604, 1,531, 1,502, 1,442,
-Nitronaphthalene H NMR (400 MHz, CDCl ): d = 8.75 (s, 1H), 8.23 (d, 1H),
3
8
1
-
1
,347, 1,081, 800, 769 cm
.
Results and discussion
-Nitronaphthalene 2 is an important fine chemical with a constantly increasing
1
world market owing to its usefulness as synthetic intermediates. The traditional
method, using nitric acid and nitro-sulfuric acids, gave a mixture of 1-nitronaph-
thalene 2 and 2-nitronaphthalene 3 in the isomer ratio of around 4.3 and 5.0,
respectively (entries 1 and 2 in Table 1). However, when substrate naphthalene 1
was subjected to the combined action of nitrogen dioxide and molecular oxygen, the
formation of 2 was highly favored up to a ratio of 7.0–9.0 in 2–3 (entries 3–8 in
Table 1), and an increase of the amount of nitrogen dioxide lowered the 2:3
mononitro isomer ratio. Moreover, a principal formation of dinitronaphthalenes of
Table 1 Nitration of naphthalene with nitrogen dioxide/molecular oxygen
NO2
NO2
nitration
+
1
2
3
a
b
Yield (%)
c
Isomer proportion (%)
Entry
Nitrating agent
Reaction condition
2:3 ratio
2
3
d
3
1
2
3
4
5
6
7
8
a
HNO
CH
CH
CH
CH
CH
CH
CH
CH
2
2
3
3
3
3
3
3
Cl
2
2
, reflux
76
93
72
87
71
73
82
70
81
82
89
88
84
90
89
85
19
18
11
12
16
10
11
15
4.3
5.0
8.3
7.0
7.3
9.1
8.4
8.1
e
4
HNO
3
–H
2
SO
Cl
, 0 °C
NO
NO
NO
NO
NO
NO
2
2
2
2
2
2
–O
–O
–O
–O
–O
–O
2
2
2
2
2
2
(1:2)
(1:4)
(1:6)
(1:2)
(1:4)
(1:6)
CN, reflux
CN, reflux
CN, reflux
CN, 5 °C
CN, 5 °C
CN, 5 °C
The ratio data in parentheses equal a molar amount in nitrogen dioxide to naphthalene. The reaction
was carried out in acetonitrile (5.0 mL). The mixture was stirred at a certain temperature and the progress
of the reaction was monitored by TLC
b
Combined yield of 2 and 3 based on consumed 1
c
Proportion of products was determined by HPLC with nitrobenzene as internal standard
d
The reaction was carried out in dichloromethane (5.0 mL) using 1 (5.0 mmol), 95 % nitric acid
10 mmol)
(
e
The reaction was conducted in dichloromethane (5.0 mL) using 1 (5.0 mmol), 95 % nitric acid
10 mmol) and 98 % sulfuric acid (10 mmol)
(
123

C. Shi et al.
1
,5- and 1,8-dinitro isomers was produced. It was found that catalysts play
important roles in the improvement of the regioselectivity. Some typical results are
shown in Table 2.
Current trends in the nitration of aromatic compounds emphasize minimizing
byproduct formation and improving regioselective of the desired isomer product by
using a zeolite catalyst. Smith et al. [17] have reported that halobenzenes could be
nitrated with nitrogen dioxide and molecular oxygen in the presence of zeolite
HBEA catalyst to give products of nitration, in which the para-nitro isomer
predominated over the ortho-isomer, while Suzuki and co-workers [8] reported that
ZSM-5 appeared to have better catalytic selective characteristics. In the hope of
improving the selectivity of 1-nitronaphthalene in the NO –O –zeolite system,
2
2
hydrogen and its metal ion-exchanged BEA and ZSM-5 zeolites were employed.
Table 2 The effect of zeolite type on the nitration of naphthalene with nitrogen dioxide/molecular
oxygen
NO2
NO2
NO2
+
zeolite
1
2
3
a
b
Yield (%)
c
Isomer proportion (%)
Entry
Zeolite
Temp. (°C)
2:3 ratio
2
3
1
2
3
4
5
6
7
8
9
HBEA-25
HBEA-500
HBEA-25
HBEA-150
HBEA-280
HBEA-500
CdBEA-25
CuBEA-25
FeBEA-25
LaBEA-25
CoBEA-25
HZSM-5
5 °C
5 °C
74
73
58
72
67
64
56
77
77
80
68
70
52
54
58
74
83
85
84
85
85
86
86
86
85
84
84
91
90
90
90
90
17
15
16
15
15
14
14
14
15
16
16
4.9
5.7
6.1
5.7
5.7
6.1
6.1
6.1
5.7
6.1
6.1
10
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
5 °C
10
11
12
13
14
15
16
9.0
CoZSM-5
MgZSM-5
CuZSM-5
CdZSM-5
5 °C
5 °C
5 °C
5 °C
10
10
10
10
9.0
9.0
9.0
9.0
All reactions were carried out in acetonitrile (5.0 mL) using substrate 1 (0.64 g, 5.0 mmol), liquid NO
0.31 mL, 10 mmol) and catalyst (0.13 g). Oxygen was passed into the system to replace air, and a
2
(
balloon filled with oxygen was connected. Acetonitrile was dried over 0.4 nm molecular sieves
a
Zeolites were calcined at 550 °C for 2 h in air prior to use
A combined yield of 2 and 3 based on consumed 1 is given
b
c
Proportion of products was determined by HPLC with nitrobenzene as internal standard
1
23

Zeolite-assisted regioselective mononitration of naphthalene
Zeolite BEA was used as catalyst because preliminary screening suggested that it
was quite active. And ZSM-5, a medium-pore zeolite, was included for comparison.
2
?
Additionally, variation of the cation-exchanged zeolites was undertaken, with Co
,
,
2
Cd , Cu , Fe , and La being used in the case of zeolite BEA-25, and Mg
?
2?
3?
3?
2?
2
?
2?
2?
Co , Cd , and Cu in the case of zeolite ZSM-5. Thus, the effects of pore size,
channel structure, acidity, and cation size could be assessed. The results are shown
in Table 2.
With the Si/Al ratio increasing of HBEA, a high ratio of formation of
-nitronaphthalene was favored (entries 1–6 in Table 2). It may be due to the
1
dealuminiation modifying the distribution of the size and shape of pores in the
zeolites. However, with an increasing Si/Al ratio, the yield was lowered, probably
because of the lower density of the effective catalytic sites.
Several metal ion-exchanged BEA-25s were tested in an attempt to find an even
more selective catalyst. Among all the metal ion-exchanged zeolites, LaBEA-25
was observed to give a maximum yield of 80 % with 6.1 1-nitronaphthalene
selectivity (entry 10 in Table 2). It may be that rare earth cation-exchanged zeolite
would display both Lewis and Brunsted types of acidity due to a high charge
density which generated acidic hydroxyl groups inside the zeolite cavities.
Otherwise, HZSM-5 displayed better 1-nitronaphthalene selectivity than zeolite
BEA, while their difference was slight in total product yield (entry 12 in Table 2). It
may be that HZSM-5 zeolite is a strong acid catalyst. Interestingly, the nature of the
cation present appeared to have a negligible effect on the selectivity, the Co, Mg,
Cu, and Cd forms of the ZSM-5 zeolites giving the same results for each reaction.
The effect of temperature on the reaction was investigated and the results are
reported in Table 3. The results showed that the selectivity of 1-nitronaphthalene
decreased with increasing temperature. Lower temperatures were preferable since the
activation energy to generate 2-nitronaphthalene is higher than for 1-nitronaphthalene.
HZSM-5 was easily recovered to reuse from the reaction mixture by simple
filtration (Table 4). Even after three times usage there was only a slight observed
change in nitration selectivity and yield with little loss of original activity.
Table 3 Effect of reaction temperature in the nitration of naphthalene
a
Yield (%)
b
Isomer proportion (%)
Entry
Temp. (°C)
2:3 ratio
2
3
1
2
3
4
5
-15
5
60
54
49
78
61
92
91
89
87
84
8.0
9.0
11
10
25
45
65
11
13
16
8.5
6.5
5.3
All reactions were carried out in acetonitrile (5.0 mL) using substrate 1 (0.64 g, 5.0 mmol), NO
(0.31 mL, 10 mmol) and HZSM-5 (0.13 g). Acetonitrile was dried over 0.4 nm molecular sieves
2
a
A combined yield of 2 and 3 based on consumed 1 is given
b
Proportion of products was determined by HPLC with nitrobenzene as internal standard
123

C. Shi et al.
2:3 ratio
Table 4 Efficiency of recycled HZSM-5 in the nitration of naphthalene
a
Yield (%)
b
Isomer proportion (%)
Entry
2
3
Fresh
69
67
65
64
92
91
90
90
8.0
9.0
11
1
2
3
10
10
10
9.0
9.0
Besides the 0.4 g catalyst employed, other conditions were the same as those given in Table 2. Aceto-
nitrile was dried over 0.4 nm molecular sieves
a
A combined yield of 2 and 3 based on consumed 1 is given
b
Proportion of products was determined by HPLC with nitrobenzene as internal standard
Conclusion
Nitration of naphthalene in the presence of zeolites with a nitrogen dioxide/
molecular oxygen system can show higher 1-nitronaphthalene selectivity in
moderate yield. Furthermore, this system was atom economic to elemental reactions
for organic intermediates by means of clean, cheap and readily available molecular
oxygen. The solid catalysts can be recovered and reused with the avoidance of the
toxic waste generated by traditional mineral acid catalysts. Moreover, the present
reaction could provide a promising methodology for the clean synthesis of nitro
compounds.
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