A simple and efficient approach for highly selective preparation of nitrocyclohexane from cyclohexane with tert-butyl nitrite catalyzed by N-hydroxyphthalimide

Article abstract of DOI:10.1007/s11164-015-2144-9

A simple and effective approach for highly selective preparation of nitrocyclohexane from cyclohexane using tert-butyl nitrite as a nitrating agent under atmospheric pressure has been successfully developed in this work. The results indicate that the N-hydroxyphthalimide catalyst gave the best results with 27.3 % of cyclohexane conversion and 88.0 % of selectivity to nitrocyclohexane under optimal reaction conditions. The present reaction provides a novel strategy for the synthesis of nitroalkanes from the nitration of low-carbon alkanes because of the mild reaction condition, simple experimental procedure and high selectivity towards the desired product. This method may be very significant to establish such a synthesis method for aliphatic nitro-compounds from the low-carbon alkanes in organic fields.

Full text of DOI:10.1007/s11164-015-2144-9

Res Chem Intermed
DOI 10.1007/s11164-015-2144-9
A simple and efficient approach for highly selective
preparation of nitrocyclohexane from cyclohexane
with tert-butyl nitrite catalyzed by
N-hydroxyphthalimide
Shuilin Liu1 Kuiyi You1,2 Jian Jian1
•
•
•
Qing Luo1 Pingle Liu1,2 Qiuhong Ai1,2
He’an Luo1,2
•
•
•
Received: 9 April 2015 / Accepted: 18 June 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A simple and effective approach for highly selective preparation of
nitrocyclohexane from cyclohexane using tert-butyl nitrite as a nitrating agent under
atmospheric pressure has been successfully developed in this work. The results
indicate that the N-hydroxyphthalimide catalyst gave the best results with 27.3 % of
cyclohexane conversion and 88.0 % of selectivity to nitrocyclohexane under opti-
mal reaction conditions. The present reaction provides a novel strategy for the
synthesis of nitroalkanes from the nitration of low-carbon alkanes because of the
mild reaction condition, simple experimental procedure and high selectivity towards
the desired product. This method may be very significant to establish such a syn-
thesis method for aliphatic nitro-compounds from the low-carbon alkanes in organic
fields.
Keywords Cyclohexane Á Nitrocyclohexane Á Tert-butyl nitrite Á NHPI Á Nitration
Introduction
The nitration of alkanes to nitroalkanes is an important process since nitroalkanes
are not only chemical commodities but also very important intermediates for
synthesis of a variety of chemicals such as pharmaceuticals and agrochemicals [1].
&
&
1
Kuiyi You
youkuiyi@126.com
He’an Luo
heanluo@126.com
School of Chemical Engineering, Xiangtan University, Xiangtan 411105,
People’s Republic of China
2
National and Local United Engineering Research Center for Chemical Process Simulation and
Intensification, Xiangtan University, Xiangtan 411105, People’s Republic of China
123

S. Liu et al.
The nitro group on alkanes can be easily replaced selectively with maintenance of
other functional groups and reduced to afford various nitrogen-containing
compounds [2]. For instance, nitrocyclohexane can be partly hydrogenated into
cyclohexanone oxime, a raw material of e-caprolactam, which in turn leads to
nylon-6 [3]. Also, it can be completely hydrogenated into cyclohexylamine that is
mainly used for fuel, pigments and pharmaceuticals or is further oxidized into
cyclohexanone oxime.
Compared with nitration of aromatic hydrocarbons, the selective nitration of
aliphatic hydrocarbons and cycloalkanes are very difficult because of their
exceedingly low reactivity [4]. Traditionally, there are the following two synthetic
routes for nitrocyclohexane. Firstly, the nitration of benzene by nitric acid can be
used for production of nitrobenzene [5, 6], which is hydrogenated to nitrocyclo-
hexane. Secondly, benzene can be completely hydrogenated to cyclohexane, which
can be converted into nitrocyclohexane by nitric acid or nitrogen dioxide [7, 8] (as
shown in Scheme 1). However, these methods suffer a series of disadvantages, such
as generation of large numbers of waste acids, low selectivity towards the desired
product and consumption of a large quantity of Lewis acid as activators [9].
Meanwhile, those acids are environmentally unfriendly and costly to treat.
Therefore, the development of highly selective preparation of nitrocyclohexane
from cyclohexane has been desired for a long time in the chemical industry.
Currently, the nitrations of cyclohexane to nitrocyclohexane by nitrogen dioxide
or nitric acid as a nitrating reagent are performed at fairly high temperatures
(250–400 °C), and they proceed by free radical chain reactions involving C–H bond
homolysis or cleavage of the C–C skeleton [10, 11]. Therefore, it is very difficult to
obtain high selectivity of nitrocyclohexane. Ishii et al. [12, 13] developed a novel
catalytic method for the nitration of aliphatic hydrocarbons and low-carbon
cycloalkanes with nitric acid or nitrogen dioxide using N-hydroxyphthalimide
(NHPI) as a key catalyst under mild conditions. Yamaguchi et al. [14] also reported
a catalytic method for the nitration of various alkanes with nitric acid using
[VO(H2O)5]H[PMo12O40] as a key catalyst in acetic acid. However, the control of
selectivity to nitroalkanes is still difficult issues. Ishii et al. also put forward
synthesis of nitrosocycloalkanes or cycloalkanone oximes from cyclohexanes and
tert-butyl nitrite (TBN) by using NHPI as key catalyst in the presence of acetic acid
under argon [15–17].
OH
N
H
NO2
O
N
H2
H2
NO2
H2
O
H2
NH2
NO2/catalyst
Scheme 1 The routes for the manufacture of nitrocyclohexane
123

A simple and efficient approach for highly selective…
NHPI is a cheap, nontoxic catalyst easily prepared by the reaction of phthalic
anhydride and hydroxylamine [18]. The use of NHPI in free radical reactions is
suitable not only for classical oxidations but also for some important synthetic
transformations such as carbon–carbon and carbon–nitrogen bond formation
reactions [19]. Phthalimido-N-oxyl radical (PINO, derived from NHPI) serves as
a carbon-radical-producing catalyst and can abstract hydrogen atoms from the C–H
bonds in saturated hydrocarbons, forming the corresponding alkyl radicals under
relatively mild conditions [20].
Herein, we report a simple and effective approach for highly selective preparation
of nitrocyclohexane from cyclohexane by using commercially available TBN as a safe
and effective nitrating agent with the help of NHPI in this work, as is shown in
Scheme 2. Compared with the existing nitration methods, the most promising feature
of the approach are more environmentally friendly because of TBN instead of nitric
acid or nitrogen dioxide as a nitrating agent. Generally, several alkyl nitrites are
industrially produced from the corresponding alcohols and gaseous NO under O2
atmosphere [21, 22]. The TBN was found to be converted into tert-butyl alcohol and
gaseous NO. And it could be prepared in good to excellent yield by treating tert-butyl
alcohol with nitrous acid or other nitrosating agents. This method may be very
significant to establish such a synthesis method for aliphatic nitro-compounds from
the low-carbon alkanes in organic fields.
Experimental
Reagents and instrument
Cyclohexane (AR) was purchased from Shanghai Chemical Co., Ltd., China. Tert-
butyl nitrite (AR) (TBN) was purchased from Shanghai Adamas Reagent Co., China.
The other reagents were purchased from Aladdin Industrial Corporation. Except where
specified, all chemicals were of analytical grade and used as received. Gas
chromatography (GC) was performed on a Shimadzu GC-2010 plus equipped with a
DB-5 (30 m 9 0.25 mm 9 0.25 lm) column for quantitative analysis by using
chlorobenzene as internal standard. Gas chromatography–mass spectrometry (GC–MS)
was run on a Shimadzu GCMS-QP2010 PLUS for qualitative analysis of products.
Typical experimental procedure
The nitration reaction of cyclohexane with TBN was carried out in liquid-phase at a
certain set temperature in a 100 ml round-bottomed flask reactor equipped with a
OH
O
ONO2
NO2
TBN, air
Catalyst
+
+
+
Scheme 2 The novel preparation route of nitrocyclohexane from the nitration of cyclohexane with TBN
123

S. Liu et al.
reflux condenser and a magnetic stirrer. The reactor was immersed in an oil bath. A
typical reaction procedure was as follows: 0.2 g catalyst and 20 mmol TBN were
added in a certain amount of cyclohexane. The obtained mixture was heated to the
reaction temperature and stirred for 24 h. After cooling to room temperature, the
catalyst was separated by filtration and the resulting mixture was analyzed by using
an Agilent 7890 gas chromatography with hydrogen flame ion detector (FID). The
quantitative analysis of products was calculated by internal standard methods. The
conversion of cyclohexane and selectivity of products were calculated using the
following formulas [Eqs. (1) and (2)]. All raw material and products were
established mass balances (including carbon mass balance and nitrogen mass
balance).
the amount ðmolÞ of cyclohexane converted
Conversion of cyclohexane ð%Þ ¼
the amount ðmolÞ of TBN
 100 %
ð1Þ
the amount ðmolÞ of product
Selectivity of product ð%Þ ¼
 100 %
ð2Þ
the amount ðmolÞ of cyclohexane converted
Results and discussion
Effects of various catalysts on nitration reaction of cyclohexane with TBN
Effects of various catalysts on the conversion of cyclohexane and selectivity of
products in the nitration reaction of cyclohexane were examined, and the results
were summarized in Table 1. In this catalytic system, the catalytic performances of
the present catalysts were different.
Table 1 Effects of various catalysts on nitration reaction of cyclohexane with TBN
Catalyst
Conversion (%)
Selectivity (%)
CH–ol
CH–one
CH–ONO2
CH–NO2
None
3.2
3.4
38.5
24.3
21.2
52.4
82.0
0.9
–
–
61.5
67.3
58.8
47.6
18.0
88.0
NiV2O6
VPO
–
8.3
20.0
–
4.6
–
SBA-15
HPW
3.8
–
4.4
–
–
NHPI
27.3
5.1
6.0
Reaction conditions: the molar ratio of cyclohexane to TBN is 4:1, the mass of cyclohexane is 6.72 g,
reaction time is 24 h, reaction temperature is 80 °C and the mass of catalyst is 0.2 g. CH–ol, CH–one,
CH–ONO2 and CH–NO2 stands for cyclohexanol, cyclohexanone, cyclohexyl nitrate and nitrocyclo-
hexane, respectively
123

A simple and efficient approach for highly selective…
Nitrocyclohexane could be formed from cyclohexane with TBN in the absence of
any catalysts and the conversion of cyclohexane was only 3.2 %. When the
oxidation catalyst NiV2O6 and VPO were used, the conversion of cyclohexane and
selectivity to nitrocyclohexane is not significantly improved. When the solid acid
catalyst (phosphotungstic acid, HPW) is introduced to nitration reaction, the
selectivity to oxygenated product cyclohexanol was increased obviously, while the
selectivity to nitrocyclohexane was only 18.0 %. Among these catalysts, the NHPI
catalyst gave the best results. Under our conditions, 27.3 % of conversion with
88.0 % of the selectivity to nitrocyclohexane was obtained. This result showed that
free radical catalyst was very suitable for the nitration reaction.
Effects of reaction temperature on nitration reaction of cyclohexane
with TBN
Table 2 shows the effects of reaction temperature on the nitration reaction of
cyclohexane with TBN. It is clearly found that there is significant influence of
reaction temperature on the conversion and selectivity. The conversion of
cyclohexane increased rapidly from 9.6 to 27.8 % and the selectivity to nitrocy-
clohexane decreased gradually from 93.5 to 83.7 % when the reaction temperature
was elevated from 50 to 90 °C. Obviously, the selectivity of oxygenated product
cyclohexanol and cyclohexanone were found to increase with elevated tempera-
tures, while the selectivity of nitrocyclohexane showed the decline trend. This may
be due to the following reason. The nitration and oxidation reaction of cyclohexane
with TBN catalyzed by NHPI happened simultaneously and were competitive
reaction in this process. Maybe the reaction rate of oxidation reaction to form
cyclohexanol and cyclohexanone became faster when reaction temperature was
raised from 70 °C. While the reaction rate of the nitration reaction to form
nitrocyclohexane remains substantially unchanged. Thus, the selectivity of nitro-
cyclohexane was declined. Therefore, elevating temperature was not beneficial to
the selectivity of nitrocyclohexane. And a range of favorable reaction temperature
were about 70–80 °C from the points of the conversion of cyclohexane and
selectivity of nitrocyclohexane.
Table 2 Effects of reaction
temperature on nitration reaction
of cyclohexane
Reaction
temperature (°C)
Conversion Selectivity (%)
(%)
CH– CH–
ol
CH–
ONO2
CH–
NO2
one
50
60
70
80
90
9.6
16.8
27.2
27.3
27.8
0.5
0.7
0.8
0.9
1.9
1.4
1.6
2.7
5.1
6.6
4.7
6.5
8.4
6.0
7.8
93.5
91.2
88.1
88.0
83.7
Reaction conditions: the molar
ratio of cyclohexane to TBN is
4:1, the mass of cyclohexane is
6.72 g, reaction time is 24 h,
and the amount of NHPI catalyst
is 0.2 g
123

S. Liu et al.
Effects of molar ratio of cyclohexane to TBN on nitration reaction
Table 3 summarized the representative results of different molar ratio of
cyclohexane to TBN on nitration reaction. It can be seen that the conversion of
cyclohexane increases with raising the molar ratio. The selectivity of nitrocyclo-
hexane increases gradually from 81.3 to 88.0 % with the molar ratio from 0.5 to 4.
The selectivity to nitrocyclohexane shows the decline trend when the molar ratio of
cyclohexane to TBN is elevated to 8. These results show that the molar ratio is also
an important factor to affect the conversion and selectivity in the nitration reaction.
From the points of the conversion of cyclohexane and selectivity of nitrocyclohex-
ane, it is clearly found that the favorable molar ratio of cyclohexane to TBN is 4:1
under the reaction time of 24 h and the reaction temperature of 70 °C.
Effects of reaction time on nitration reaction of cyclohexane with TBN
Figure 1 shows the effects of different reaction time on nitration reaction of
cyclohexane with TBN at 70 °C. It can be seen that conversion of cyclohexane
gradually increases with prolonged reaction time, while the selectivity to
nitrocyclohexane is not changed obviously. These results show that the reaction
time mainly affects on the conversion of cyclohexane and the selectivity to
nitrocyclohexane almost remains unchanged. From the points of the conversion and
the selectivity, a suitable reaction time should not be beyond 24 h at 70 °C from
Fig. 1.
Effects of the amount of catalyst on nitration reaction of cyclohexane
with TBN
Table 4 shows the effects of the amount of catalyst on nitration reaction under the
reaction temperature of 70 °C and the reaction time of 24 h. It can be seen that the
conversion of cyclohexane seems to increase slowly with the elevated amount of
catalyst. The conversion of cyclohexane reached 27.3 % with 88.0 % of selectivity
Table 3 Effects of molar ratio of cyclohexane to TBN on nitration reaction
Molar ratio
Conversion (%)
Selectivity (%)
CH–ol
CH–one
CH–ONO2
CH–NO2
0.5:1
1:1
9.4
12.7
17.5
27.3
27.7
5.9
3.6
3.4
0.9
2.4
1.2
0.9
1.4
5.1
9.3
11.6
11.7
11.0
6.0
81.3
83.8
84.2
88.0
78.3
2:1
4:1
8:1
10.1
Reaction conditions: the mass of TBN is 2.06 g, reaction temperature is 70 °C, reaction time is 24 h, and
the mass of NHPI catalyst is 0.2 g
Molar ratio stands for the molar ratio of cyclohexane to TBN
123

A simple and efficient approach for highly selective…
100
90
80
70
60
Conversion of cyclohexane
Selectivity to nitrocyclohexane
50
40
30
20
10
0
5
10
15
20
25
30
35
Reaction time(h)
Fig. 1 Effects of reaction time on nitration reaction. Reaction conditions: molar ratio of cyclohexane to
TBN is 4:1, the mass of cyclohexane is 6.72 g, reaction temperature is 70 °C, and the mass of NHPI
catalyst is 0.2 g
to nitrocyclohexane when reaction was added 0.2 g of NHPI. However, the
selectivity to nitrocyclohexane decreased obviously when the amount of catalyst
exceeded 0.4 g. This reason might be that the reaction rate of oxidation reaction to
form cyclohexanol and cyclohexanone became faster when the amount of catalyst
was relatively high under these reaction conditions. Therefore, the suitable amount
of catalyst adequately and efficiently catalyzed the nitration of cyclohexane with
TBN to nitrocyclohexane. From the points of the conversion and the selectivity, a
suitable amount of catalyst should be 0.2 g.
In summary, from the single factor experiment results, the optimal reaction
conditions were obtained that the reaction time was 24 h, reaction temperature was
70 °C, the amount of NHPI catalyst was 0.2 g, and the molar ratio of cyclohexane to
TBN was 4:1 in the nitration reaction.
Table 4 Effects of the amount of catalyst on nitration reaction of cyclohexane
Amount of catalyst (g)
Conversion (%)
Selectivity (%)
CH–ol
CH–one
CH–ONO2
CH–NO2
0.1
0.2
0.4
24.1
27.3
27.7
2.7
0.9
2.7
–
9.8
6.0
87.8
88.0
74.2
5.1
12.8
10.4
Reaction conditions: molar ratio of cyclohexane to TBN is 4:1, the mass of cyclohexane is 6.72 g,
reaction temperature is 70 °C, reaction time is 24 h, and catalyst is NHPI
123

S. Liu et al.
Effects of different environment on nitration reaction of cyclohexane
with TBN
Table 5 shows the effects of different environment on nitration reaction under the
reaction temperature of 70 °C and the reaction time of 24 h. It is clearly found that there
is significant influence of reaction environment on the conversion and selectivity. The
conversion of cyclohexane reached 27.3 % with 88.1 % of selectivity to nitrocyclo-
hexane when reaction was under air. Obviously, the conversion of cyclohexane could be
increased under oxygen atmosphere, however, the selectivity to nitrocyclohexane was
not ideal. This might be due to the following reason. The formed NO in the reaction was
very easily converted into NO2 under oxygen atmosphere. Owing to the higher
concentration of NO2 than under air, cyclohexane could react selectively with NO2 to
give oxygenated products in preference to nitrocyclohexane. Meanwhile, the formed
cyclohexanol could react with HNO3 to form cyclohexyl nitrate.
The nitration of linear alkane (n-hexane) and alkylbenzene (toluene)
with TBN
The results of the nitration of n-hexane and toluene with TBN by the present method
are shown in Table 6. Owing to the oxidizing ability of TBN, the nitration of
toluene with TBN led to oxygenated products benzaldehyde (58 %) and benzoic
acid (42 %). While n-hexane afforded a 11:51:38 regio-isomeric mixture of
nitrohexane, 2-nitrohexane, and 3-nitrohexane in 20.66 % conversion. These results
demonstrate the nitration of linear alkane and alkylbenzene with TBN are different
in nitration process.
Recyclability of the NHPI catalyst and purification of the target product
Stability and recyclability of catalyst is a key issue in catalysis reaction. After the
reaction, the NHPI could be easily separated from the reaction mixture by filtration.
The results indicated the recovered NHPI could be reused directly and the results
obtained in the optimal reaction conditions indicated that the selectivity to
nitrocyclohexane remained substantially unchanged and the conversion of cyclo-
hexane decreased slightly.
Since TBN generated only volatile residual products, such as tert butyl alcohol
and gaseous NO, almost pure nitrating product was easily obtained by simple
Table 5 Effects of different environment on nitration reaction of cyclohexane
Environment
Conversion (%)
Selectivity (%)
CH–ol
CH–one
CH–ONO2
CH–NO2
Air
27.3
0.9
2.3
5.1
6.0
88.0
Oxygen
47.21
16.7
44.95
36.05
Reaction conditions: molar ratio of cyclohexane to TBN is 4:1, the mass of cyclohexane is 6.72 g,
reaction temperature is 70 °C, reaction time is 24 h, and the mass of NHPI catalyst is 0.2 g
123

A simple and efficient approach for highly selective…
Table 6 NHPI-catalyzed nitration of different substrate with TBN under selected conditions
Substrate
Conversion (%)
20.66
Selectivity of product (%)
n-Hexane
Nitrohexane
11.0
2-Nitrohexane
3-Nitrohexane
38.0
51.0
Toluene
19.0
Benzaldehyde
58.0
Benzoic acid
42.0
Reaction conditions: the molar ratio of substrate to TBN is 4:1, the mass of TBN is 2.06 g, reaction
temperature is 70 °C, reaction time is 24 h, and the mass of NHPI catalyst is 0.2 g
distillation of the reaction mixtures. The reaction product was distilled by using a
rotary evaporator under the condition that vacuum degree was 0.09 Mpa and bath
temperature was raised from 40 to 80 °C. The mass fraction of nitrocyclohexane
could reach 95 % in the obtained sample by using a gas chromatography. This was a
meaningful superiority especially in the case of large scale reactions.
The possible reaction path of cyclohexane with TBN catalyzed by NHPI
On the basis of these results in this work, the possible formation pathway of
products in the catalytic nitration reaction of cyclohexane with TBN was proposed
in Scheme 3. Firstly, the nitration might be initiated by hydrogen-atom abstraction
from the hydroxyimide group of NHPI by TBN to generate a PINO radical. The
PINO radical readily abstracted a hydrogen atom from cyclohexane to form a
cyclohexyl radical, which undergoed nitration with NO2 to give a nitrocyclohexane.
TBN was decomposed to produce NO and tert-butyl alcohol via the O–N bond
cleavage under the action of NHPI. The formed NO was very easily converted into
NO2 under air. And cyclohexane also could react with NO2 to form a cyclohexyl
free radical and HNO2. The formed HNO2 could be converted into HNO3, H2O and
NO [23]. And the formed cyclohexyl free radical reacted with O2 to form
NO2
O
t-BuONO (TBN)
NO2
NOH
O
NO2
O
OH
O
O2
O
NO
O
t-BuOH
NO +
NO
HNO3
ONO2
O2
NO2
HNO2
Scheme 3 Possible reaction path of cyclohexane with TBN catalyzed by NHPI
123

S. Liu et al.
cyclohexanol, which was further oxidized to cyclohexanone. Meanwhile, the
formed cyclohexanol also reacted with HNO3 to form cyclohexyl nitrate.
Conclusions
In conclusion, a novel approach for highly selective preparation of nitrocyclohexane
from the nitration reaction of cyclohexane with TBN had been developed
successfully under atmospheric pressure in this work. The results indicated that
high selectivity (over 88 %) for nitrocyclohexane with 27.3 % of cyclohexane
conversion was obtained. And the possible reaction path had been proposed and
further studies for the optimization of the reaction conditions are now in progress.
Assuming that better catalysts can be developed, this method may be very
significant to establish such a synthesis method for aliphatic nitro-compounds from
the low-carbon alkanes in organic fields.
Acknowledgments The authors are grateful for the financial support for this work by the National
Natural Science Foundation of China (21276216), Specialized Research Fund for the Doctoral Program of
Higher Education (20124301130001), Project of Technological Innovation & Entrepreneurship Platform
for Hunan Youth (2014) and Major Science and Technology Projects of Hunan Province (2012FJ1001).
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