Acid-catalyzed regioselective nitration of o-xylene to 4-nitro-o-xylene with nitrogen dioxide: Br?nsted acid versus lewis acid

Article abstract of DOI:10.1080/00397911.2013.873468

Nitration of o-xylene with nitrogen dioxide imparts remarkable selectivity to 4-nitro-o-xylene. The addition of Br?nsted acids and Lewis acids can effectively improve the selectivity for 4-nitro-o-xylene and/or yield, and the Lewis acids present a better influence on the reactions than Br?nsted acids do. A 71% yield of mononitro-o-xylene with high selectivity for 4-nitro-o-xylene (ratio 4-/3- / 3.91) has been achieved by the assistance of bismuth trichloride under solvent-free conditions. Copyright

Full text of DOI:10.1080/00397911.2013.873468

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Acid-Catalyzed Regioselective Nitration
of o-Xylene to 4-Nitro-o-xylene with
Nitrogen Dioxide: Brønsted Acid Versus
Lewis Acid
Bo Tang a , Songbo Wei a & Xinhua Peng a
a School of Chemical Engineering, Nanjing University of Science and
Technology , Nanjing , China
Accepted author version posted online: 04 Apr 2014.Published
online: 09 Jun 2014.
To cite this article: Bo Tang , Songbo Wei & Xinhua Peng (2014) Acid-Catalyzed Regioselective
Nitration of o-Xylene to 4-Nitro-o-xylene with Nitrogen Dioxide: Brønsted Acid Versus Lewis Acid,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 44:14, 2057-2065, DOI: 10.1080/00397911.2013.873468
To link to this article: http://dx.doi.org/10.1080/00397911.2013.873468
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Synthetic Communications1, 44: 2057–2065, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.873468
ACID-CATALYZED REGIOSELECTIVE NITRATION OF
O-XYLENE TO 4-NITRO-O-XYLENE WITH NITROGEN
DIOXIDE: BRØNSTED ACID VERSUS LEWIS ACID
Bo Tang, Songbo Wei, and Xinhua Peng
School of Chemical Engineering, Nanjing University of Science and
Technology, Nanjing, China
GRAPHICAL ABSTRACT
Abstract Nitration of o-xylene with nitrogen dioxide imparts remarkable selectivity to
4-nitro-o-xylene. The addition of Brønsted acids and Lewis acids can effectively improve
the selectivity for 4-nitro-o-xylene and/or yield, and the Lewis acids present a better influ-
ence on the reactions than Brønsted acids do. A 71% yield of mononitro-o-xylene with high
selectivity for 4-nitro-o-xylene (ratio 4-/3- ¼ 3.91) has been achieved by the assistance of
bismuth trichloride under solvent-free conditions.
Keywords Acid catalysis; nitration; nitrogen dioxide; 4-nitro-o-xylene; regioselective
INTRODUCTION
It is well known that 1,2-disubstituted benzenes often pose even more complicated
problems in regioselective nitrations than monosubstituted benzenes do.[1] As in the
mononitration of o-xylene, resulting from the interaction of ortho-para directing effects
of the two adjacent methyl groups, the nitro group could be introduced into any one of
the four nonsubstituted positions on the aromatic ring. Consequently, an equal amount
of 4-nitro-o-xylene and 3-nitro-o-xylene should be formed theoretically during the
mononitration of o-xylene, which makes it extremely difficult to realize regioselective
nitration of o-xylene to the commercially more desirable 4-nitro-o-xylene isomer. When
o-xylene was nitrated by the classic methodology based on nitric acid–sulfuric acid,[2,1c]
a
Received September 14, 2013.
Address correspondence to Xinhua Peng, School of Chemical Engineering, Nanjing University of
Science and Technology, Nanjing 210094, China. E-mail: xhpeng@mail.njust.edu.cn
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/lsyc.
2057

2058
B. TANG, S. WEI, AND X. PENG
mixture of 4-nitro-o-xylene (39–42%) and 3-nitro-o-xylene (58–61%) were obtained with
relatively poor selectivity for 4-nitro-o-xylene. Moreover, the mixed acid nitration can-
not avoid the production of large amounts of waste acid and water.
Various of alkyl nitrates[3] assisted by acid catalysts have also been used to
nitrate o-xylene with a isomer distribution of ratio 4-=3- (4-nitro-o-xylene=3-nitro-
o-xylene) ¼ 0.67–1.27, but the selectivity for 4-nitro-o-xylene is still not satisfactory.
o-Xylene has also been nitrated by nitroxyl salts[4] with even worse selectivity (ratio
4-=3- ¼ 0.25–0.61). Zolfigol has developed two novel nitration systems of nitrate salts
[5]
(NaNO3=silica sulfuric acid–SiO2 and [Msim]NO3[6]) that selectively nitrate
o-xylene to 4-nitro-o-xylene with good yields of 85% and 89%, respectively. Unfortu-
nately very large quantities of the silica sulfuric acid–SiO2 were required and the
preparation of [Msim]NO3 needs highly corrosive chlorosulfonic acid and nitric acid
(100%). Researchers have also focused on nitration of o-xylene with different con-
centrations of nitric acid (30–100%) in the presence of numerous solid acid catalysts
(zeollite H-b,[7] zeollite-b,[8] UDCaT-8,[9] MoO3=TiO2=SiO2,[10] MoO3=TiO2=
ZrO2,[11] Al(H2PO4)3,[12] Zn2þ or Fe3þ modified montmorillonite,[13] and TiO2-
[Ti4H11(PO4)9] ꢀ 4H2O[14]), which still have more or less the same problems:
requirement of high temperature, poor conversion of o-xylene, complicated
preparative process of catalyst, and=or relatively low ratio of 4-=3-.
In recent years, nitrogen dioxide treated as a nonacidic nitration agent for the
preparative aromatic nitration has received a great deal of attention,[15] generally
accompanied by superior regioselectivity relative to traditional nitration methods.
An extremely high selectivity for 4-nitro-o-xylene (ratio 4-=3- ¼ 8.09) has been
obtained by irradiating the dichloromethane solution of o-xylene and nitrogen diox-
ide with kexc > 415 nm at ꢁ78 ꢂC; however, the conversion of o-xylene is pitifully low
(2%) even after 6 h.[16] Nitration of o-xylene with NO2=O2 system in the presence of
mercury(II) acetate and acetic acid can also give a relatively high selectivity for
4-nitro-o-xylene (ratio 4-=3- ¼ 4.56).[17] The replacement of molecular oxygen with
air reduced the ratio 4-=3- sharply to 3.17, indicating that in pursuit of greater
selectivity for 4-nitro-o-xylene molecular oxygen is indispensable and brings
inconvenience in the experimental operation. Apart from this, the extremely toxic
mercury(II) acetate and acetic acid as solvent are environmentally unfriendly. There-
fore, in an attempt to develop a method that would realize highly regioselective
nitration of o-xylene to 4-nitro-o-xylene, the nitrogen dioxide was considered to be
a preferable nitration agent. In addition, to avoid the mentioned drawbacks as much
as possible, the exploration of effective, inexpensive, and low-toxicity catalysts is a
major task. Eventually, the reactions of o-xylene and nitrogen dioxide in the absence
and presence of Brønsted acids and Lewis acids were investigated. We now describe
the entire results of nitration of o-xylene with nitrogen dioxide.
RESULTS AND DISCUSSION
To discover the intrinsic performance of nitration of o-xylene with nitrogen
dioxide and the influence of circumstantial factors such as reagent=substrate ratio
and temperature on the reactions, comparative experiments was initially carried
out in the absence of Brønsted acids and Lewis acids compared with Scheme 1.
The results are shown in Table 1.

REGIOSELECTIVE NITRATION OF O-XYLENE
2059
Scheme 1. Acid-catalyzed nitration of o-xylene with nitrogen dioxide.
As can be seen from Table 1, nitrogen dioxide exhibited a remarkable
selectivity for 4-nitro-o-xylene with a 4-=3- ratio readily greater than 2 in the
nitration of o-xylene, and the circumstantial factors had a significant effect on the
reactions. Both conversion and 4-=3- ratio increased with the ratio of nitrogen
dioxide to o-xylene. However, when a large excess of nitrogen dioxide was used,
there appears to be a decreased yield of both 4-nitro-o-xylene and 3-nitro-o-xylene
despite the increased conversion (compare entries 4 and 5 in Table 1). This is presum-
ably because the side reactions leading to the production of other nonring aromatic
nitration substances (aldehydes, phenols, alcohols, nitric acid esters, alkyl nitro com-
pounds)[18,15c] become more pronounced. Therefore, there is a balance that should be
struck between the selectivity for 4-nitro-o-xylene and the yield to determine the
appropriate amount of nitrogen dioxide used.
It was of interest to know the effects of various reaction temperatures on the
reactions. Lowering the reaction temperature significantly retards the rate of
reaction, and the conversion of o-xylene was diminished to only 53.3% even over
a 24-h period (entry 7 in Table 1). Also, surprisingly at lower temperature the ratio
of 4-=3- did not appear to be increased but reduced (compare entries 4 and 7 in
Table 1), suggesting that there is no major advantages to be gained from carrying
out the reactions at low temperature. Elevating the reaction temperature to 50 ꢂC
gave a slightly greater conversion but with a dramatic decrease of the ratio
4-=3- to 2.25 (compare entries 4 and 6 in Table 1).
Table 1. Nitration of o-xylene with NO2 under several conditionsa
Product yield (%)c
Temperature
(ꢂC)
NO2=o-xylene
molar ratio
Conversionb
(%)
Entry
3-
4-
4-=3-
1
rt
rt
rt
rt
rt
50
0
1
2
3
4
5
4
4
63.2
71.1
76.3
80.3
85.4
86.6
53.3
2.9
5.8
6.2
17.0
21.0
26.3
22.3
23.5
12.3
2.11
2.94
3.16
3.19
3.48
2.25
2.51
2
3
6.6
8.2
4
5
6.4
6
7d
10.5
4.9
aAll reactions were carried out with 5.0 mmol of o-xylene for 12 h, unless otherwise noted.
bBased on o-xylene and determined by calibrated quantitative GC analysis using an internal standard.
cAbsolute yield (internal standard) based on o-xylene.
dReaction time 24 h.

2060
B. TANG, S. WEI, AND X. PENG
Therefore, it is clear from the results in Table 1 that it is preferable to nitrate
o-xylene with nitrogen dioxide of 3–4 equivalent amounts at room temperature in
view of regioselecive nitration of o-xylene to 4-nitro-o-xylene with good selectivity
and yield.
On the basis of the optimum conditions mentioned previously, a range of
different Brønsted acids was primarily tested for efficacy at catalyzing the reaction
according to Scheme 1. The representative results are recorded in Table 2. The
results given in Table 2 show that adding Brønsted acids to the reaction mixture
generally causes the decrease of the 4-=3- ratio in different degrees except for trifluor-
oacetic acid (entries 1–5 in Table 2). Therefore, prior to other Brønsted acids trifluor-
oacetic acid was selected for further investigation to improve the conversion and
yield. However, only a little benefit was obtained by varying the amount of
trifluoroacetic acid and nitrogen dioxide, and more often with a slight decrease of
4-=3- ratio (entries 5–8 in Table 2). Even though a greater selectivity (ratio
4-=3- ¼ 3.51) has been received when less trifluoroacetic acid was added (entry 6 in
Table 2), the conversion and yield declined to the lowest amounts. It suggests that
trifluoroacetic acid can offer a relatively good selectivity for 4-nitro-o-xylene but
has limited improvement in the conversion and yield. In contrast, sulfuric acid exhib-
ited a distinguishing effect. Even though a small amount of sulfuric acid was added,
the ratio of 4-=3- decreased remarkably. With the increase of the added amount of
sulfuric acid, the ratio of 4-=3- fell more significantly than with trifluoroacetic acid.
Fortunately, sulfuric acid at least can provide good conversion and yield. The
addition of equivalent sulfuric acid (relative to o-xylene) readily ensures the complete
consumption of o-xylene with ca. 80% yield of mononitro-o-xylene (entry 12 in
Table 2). Therefore, sulfuric acid allowed a rapid reaction with good yield of mono-
nitro-o-xylene accompanied by the cost of remarkably dropped selectivity for
4-nitro-o-xylene. From a mechanistic perspective, the distinctive manifestation
Table 2. Nitration of o-xylene with NO2 in the presence of Brønsted acidsa
Product yield (%)
NO2=o-xylene
molar ratio
Conversion
(%)
Entry
Additives (mol%)b
—
3-
4-
4-=3-
1
2
4
4
4
4
4
4
4
3
4
4
3
2
80.3
71.4
96.2
88.7
81.7
79.8
84.3
83.9
87.6
99.7
99.8
100.0
8.2
5.8
26.3
15.6
26.9
34.6
34.7
32.6
33.8
34.7
30.0
51.2
50.2
48.6
3.19
2.70
2.69
2.68
3.43
3.51
2.86
2.78
3.00
1.95
1.80
1.51
TsOH
CH3SO3H
H2SO4
50
3
50
50
10.0
12.9
10.1
9.3
4
5
CF3COOH
CF3COOH
CF3COOH
CF3COOH
H2SO4
50
10
6
7
100
100
10
11.8
12.4
10.0
26.2
27.9
32.2
8
9
10
11
12
H2SO4
H2SO4
H2SO4
100
100
100
aAll reactions were carried out with 5.0 mmol of o-xylene at room temperature for 12 h, unless otherwise
noted. The definitions of conversion and product yield are consistent with Table 1.
bRelative to o-xylene.

REGIOSELECTIVE NITRATION OF O-XYLENE
2061
between trifluoroacetic acid and sulfuric acid is probably because the different
interaction of Brønsted acids and nitrogen dioxide, which may result in the gener-
ation of different reactive intermediates (e.g., NOþ, NO2þ, etc.) derived from the ionic
dissociation of dinitrogen tetroxide. Induced by trifluoroacetic acid, nitrosonium
(NOþ) is preferable to form and the more para-selective nitrosation would princi-
pally take place rather than nitration,[19] which is why the ratio of 4-=3- can still
maintain a relatively high magnitude with the addition of trifluoroacetic acid to
the mixture of o-xylene and nitrogen dioxide. With respect to sulfuric acid, nitronium
(NOþ2 ) is favored to be produced,[20] and therefore the conventional nitration with
the characteristics of fast reaction rate and poor selectivity would occupy a dominant
part, especially with the increase of the quantity of added sulfuric acid. This is con-
sistent with the results given by sulfuric acid. The remaining p-toluene sulfonic acid
and methanesulfonic acid gave a poor conversion of o-xylene and=or a poor yield of
nitration product in addition to worse selectivity for 4-nitro-o-xylene, otherwise
having no particular advantages for the selective nitration of o-xylene to 4-nitro-o-
xylene. Therefore, it was not considered worthwhile to conduct a detailed study of
two of them.
In an attempt to seek an even more effective catalyst, several Lewis acids were
investigated for this purpose (Scheme 1). Table 3 records the results of reactions in
the presence of Lewis acids. It is especially noteworthy that the addition of nitrogen
dioxide to the mixture of o-xylene and Lewis acids assigned to aluminum trichloride
or antimony trichloride instantly causes a lump of sticky solid, unable to be stirred.
In the case of the two mentioned Lewis acids, dichloromethane has to be added
beforehand as solvent (entries 2 and 3 in Table 3). Unexpectedly, both of them led
to a sharp decrease of ratio 4-=3- and had no obviously beneficial effect on the
conversion and yield (compare entries 1–4 in Table 3), suggesting that it was not
considered worthwhile to conduct a detailed study of aluminum trichloride or
antimony trichloride. Because the reactions involving bismuth trichloride and ferric
trichloride were capable of being carried out under solvent-free conditions, it is
Table 3. Nitration of o-xylene with NO2 in the presence of Lewis acidsa
Products yield (%)
NO2=o-xylene
molar ratio
Time
(h)
Conversion
(%)
Entry
Additives (mol%)b
—
3-
4-
4-=3-
1
4
4
4
4
4
4
4
3
3
12
12
12
12
12
12
24
24
24
80.3
76.4
63.8
78.1
83.3
81.3
92.6
95.2
100.0
8.2
12.0
9.7
26.3
24.5
25.5
34.0
38.6
35.61
43.1
51.3
56.8
3.19
2.04
2.64
3.58
3.73
3.40
3.75
3.81
3.91
2c
3c
4c
5
AlCl3
SbCl3
BiCl3
BiCl3
FeCl3
BiCl3
BiCl3
BiCl3
25
25
25
25
25
25
25
50
9.5
10.4
10.5
11.5
13.5
14.5
6
7
8
9
aAll reactions were carried out with 5.0 mmol of o-xylene at room temperature, unless otherwise noted.
The definitions of conversion and product yield is consistent with Table 1.
bRelative to o-xylene.
cDichloromethane (3 mL) was added as solvent.

2062
B. TANG, S. WEI, AND X. PENG
necessary to ascertain the effect of added dichloromethane. Therefore, the control
experiments in the presence and absence of dichloromethane (entries 4 and 5 in
Table 3) were carried out in which bismuth trichloride was chosen as a representative
Lewis acid, under otherwise identical conditions. It is apparent that at least in terms
of bismuth trichloride the existence of solvent is really disadvantageous to the reac-
tions in all aspects, presumably because the dilution of reaction mixture with dichlor-
omethane is not beneficial to the selectivity for 4-nitro-o-xylene and conversion of o-
xylene.[21] Accordingly, to obtain better results from the reactions involving bismuth
trichloride and ferric trichloride, optimization procedures were uniformly performed
under solvent-free conditions. It appears that the former presented a little more ben-
eficial effect on the reactions than the latter did (compare entries 5 and 6 in Table 3).
Consequently, bismuth trichloride was ultimately selected for further investigation,
uniformly under solvent-free conditions. In consideration of the incomplete trans-
formation of o-xylene, initially the reaction time was prolonged. As expected, the
conversion of o-xylene increased successfully but just to a certain level (entry 7 in
Table 3). Thus it was next of interest to vary the amount of bismuth trichloride
and nitrogen dioxide. Fortunately, o-xylene was eventually consumed completely
(entry 9 in Table 3). The greater selectivity for 4-nitro-o-xylene (ratio 4-=3- ¼ 3.91)
and a good yield of mononitro-o-xylene (71%) were particularly striking.
Explanation of the excellent effect obtained by the addition of Lewis acids,
especially bismuth trichloride (BiCl3), should show a deep level of mechanistic
insight. The proposed reaction pathway of nitration of o-xylene with nitrogen diox-
ide in the absence and presence of Lewis acid is shown in Scheme 2.[16] In the absence
of Lewis acid, the ionic disproportionation of dinitrogen tetroxide induced by the
reactive aromatic donor o-xylene results in the formation of electron donor–acceptor
(EDA) complexes ([ArH, NOþ]NO3ꢁ), followed by charge-transfer (CT) to produce
radical pair ([ArH.þ, NO]NOꢁ3 ) and homolytic coupling of generated cation radical
(ArH.þ) and NO2 to r-complexes, which ultimately collapse into nitration products
by deprotonation. Therefore the existence of added Lewis acid would stabilize the
EDA complexes via coordination to the anionic nitrate moiety, providing additional
driving force to shift the disproportionation equilibrium to the right, and simul-
taneously the nucleophilic attack of nitrate anion (NOꢁ3 ) to cation radical (ArH.þ)
is greatly suppressed. The generation of aromatic nitration products would be
eventually promoted by adding Lewis acids. The extraordinarily good selectivity
for 4-nitro-o-xylene exhibited in the case of bismuth trichloride is possibly due to
a larger atomic radius of bismuth ions.
In summary, the addition of Brønsted acids and Lewis acids can effectively
improve the selectivity and=or yield in the regioselective nitration of o-xylene to
4-nitro-o-xylene with nitrogen dioxide. The latter exhibits a superior effect on the
Scheme 2. Proposed reaction pathway of nitration of o-xylene with nitrogen dioxide.

REGIOSELECTIVE NITRATION OF O-XYLENE
2063
reactions. Among the entire range of acid catalysts, bismuth trichloride presents an
outstanding degree of selectivity for 4-nitro-o-xylene (ratio 4-=3- ¼ 3.91) with the
added practical advantages of capably avoiding the need for solvent. The
combination of bismuth trichloride with nitrogen dioxide provides a synthetically
useful method for the selective synthesis of 4-nitro-o-xylene from o-xylene.
EXPERIMENTAL
All reagents and solvents used were obtained from commercial sources without
any purification unless otherwise noted. Nitrogen dioxide (from Nanjing Shangyuan
Industrial Gas Factory, China) was released from compressed steel cylinder and then
passed through a preprepared cooling device equipped with condenser (cooling
liquid provided by cryostat), cooled to liquid nitrogen dioxide, and stored in the
refrigerator while further freezing to solid (stand-by service).
For the determination of the conversion of substrates and composition of the
products, gas chromatographic (GC) analysis was performed on an Agilent 6820 gas
chromatograph equipped with a flame ionization detector using a 30-m ꢃ 0.32-mm
capillary column (Agilent Technologies, SE-54). All products were known and
identified by direct comparison with the authentic samples. The products 3- and
1
4-nitro-o-xylenes were isolated by distillation and confirmed by H NMR, recorded
in CDCl3 on Bruker UX-300 spectrometers using tetramethylsilane (TMS) as an
internal reference. The characterized results are consistent with those reported by
Shi and Cui,[22] which confirms the formation of 3- and 4-nitro-o-xylenes.
3-Nitro-o-xylene
1H NMR (CDCl3, TMS, 300 MHz) d 2.40 (s, 6H, CH3), 7.20 (t, 1H, J ¼ 7.8 Hz,
Ar), 7.38 (d, 1H, J ¼ 7.3 Hz, Ar), 7.61 (d, J ¼ 8.0 Hz, 1H, Ar).
4-Nitro-o-xylene
1H NMR (CDCl3, TMS, 300 MHz) d 2.37 (s, 6H, CH3), 7.26 (d, 1H, J ¼ 8.0 Hz,
Ar), 7.95–8.0 (m, 2H, Ar).
General Procedure for the Nitration of o-Xylene with NO2
o-Xylene (0.53 g, 5.0 mmol) was added to a 50-mL single-necked flask. Next the
solid nitrogen dioxide stored in the refrigerator was warmed until the appearance of
a few drops of liquid, and liquid nitrogen dioxide (0.69 g, 15.0 mmol) was added rap-
idly. Simultaneously the flask was equipped with condenser (cooling liquid provided
by cryostat). The reaction mixture was then stirred at room temperature. After 12 h,
the reaction was quenched by the addition of aqueous sodium hydrogen carbonate
(5.00 g, 20%). After that m-nitro-toluene (internal standard) and dichloromethane
(5 mL) were added. The organic phase was separated, and the aqueous phase was
extracted twice with dichloromethane (2 ꢃ 5 mL). Combined organic layers were
washed with water, dried over anhydrous sodium sulfate, filtered off, and
evaporated. The samples finally were analyzed by GC.

2064
B. TANG, S. WEI, AND X. PENG
General Procedure for the Nitration of o-Xylene with NO2 in the
Presence of Brønsted Acids
o-Xylene (0.53 g, 5.0 mmol) and sulfuric acid (0.49 g, 4.9 mmol) were added to a
50-mL single-necked flask. Next liquid nitrogen dioxide (0.47 g, 10.2 mmol) was
rapidly added into the mixture of o-xylene and sulfuric acid. The reaction mixture
was then stirred at room temperature for 12 h. The workup was performed by the
procedure described previously. Under similar conditions, the nitration of o-xylene
in the presence of other Brønsted acids was also performed.
General Procedure for the Nitration of o-Xylene with NO2 in the
Presence of Lewis Acids
A solution of o-xylene (0.52 g, 4.9 mmol) in dichloromethane (3 mL) and anti-
mony trichloride (0.27 g, 1.2 mmol) was added to a 50-mL single-necked flask. Next
liquid nitrogen dioxide (0.92 g, 20.0 mmol) was rapidly added into the mixture of
o-xylene and antimony trichloride, The reaction mixture was then stirred at room
temperature. After 12 h, the reaction was quenched by the addition of aqueous
sodium hydrogen carbonate (5.00 g, 20%). A large amount of precipitate was pro-
duced, which was treated with suction to remove the solid. The solid was washed
three times with dichloromethane (3 ꢃ 2 mL). After that m-nitro-toluene (internal
standard) was added to the filtrate. The organic phase was separated and the aque-
ous phase was extracted twice again with dichloromethane (2 ꢃ 5 mL). The combined
organic layers were washed with water, dried over anhydrous sodium sulfate, filtered
off, and evaporated. The samples finally were analyzed by GC. Under similar
conditions, the nitration of o-xylene in the presence of other Lewis acids was also
performed.
Procedure for the Solvent-Free Nitration of o-Xylene with NO2 in the
Presence of BiCl3
o-Xylene (0.53 g, 5.0 mmol) and bismuth trichloride (0.76 g, 2.4 mmol) were
added to a 50-mL single-necked flask. Next liquid nitrogen dioxide (0.67 g,
14.5 mmol) was rapidly added into the mixture of o-xylene and bismuth trichloride.
The reaction mixture was then stirred at room temperature for 24 h. The workup was
performed by the procedure of Lewis acids described previously.
SUPPORTING INFORMATION
1H NMR spectrum and GC, as well as analysis parameters (conditions,
retention times), can be accessed on the publisher’s website.
REFERENCES
1. (a) Schofield, K. Aromatic Nitration; Cambridge University Press: Cambridge, 1980;
(b) Olah, G. A.; Malhotra, R.; Narang, S. C. Nitration: Methods and Mechanisms;

REGIOSELECTIVE NITRATION OF O-XYLENE
2065
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