Supported tetramethylamonium nitrate/silicasulfuric acid as a useful reagent for nitration aromatic compounds under solvent-free conditions

Article abstract of DOI:10.1080/00397910500184685

A variety of aromatic compounds are nitrated to the parent nitro aromatic compounds under solvent-free conditions using supported tetramethylammonium nitrate/silicasulfuric acid as a useful reagent. This methodology is useful for nitration of activated and deactivated aromatic rings. Copyright Taylor & Francis, Inc.

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Supported
Tetramethylamonium Nitrate/
Silicasulfuric Acid as a Useful
Reagent for Nitration Aromatic
Compounds Under Solvent‐Free
Conditions
a b
a
Abdol R. Hajipour
, Amin Zarei , Leila Khazdooz
a
b
&
A. E. Ruoho
a
Pharmaceutical Research Laboratory , College
of Chemistry, Isfahan University of Technology ,
Isfahan, Iran
b
Department of Pharmacology , University of
Wisconsin Medical School , Madison, Wisconsin, USA
Published online: 18 Aug 2006.
To cite this article: Abdol R. Hajipour , Amin Zarei , Leila Khazdooz & A. E. Ruoho
(2005) Supported Tetramethylamonium Nitrate/Silicasulfuric Acid as a Useful
Reagent for Nitration Aromatic Compounds Under Solvent‐Free Conditions, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:17, 2237-2241
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Synthetic Communications , 35: 2237–2241, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500184685
Supported Tetramethylamonium Nitrate/
Silicasulfuric Acid as a Useful Reagent
for Nitration Aromatic Compounds
Under Solvent-Free Conditions
Abdol R. Hajipour
Pharmaceutical Research Laboratory, College of Chemistry,
Isfahan University of Technology, Isfahan, Iran and Department of
Pharmacology, University of Wisconsin Medical School, Madison,
Wisconsin, USA
Amin Zarei and Leila Khazdooz
Pharmaceutical Research Laboratory, College of Chemistry,
Isfahan University of Technology, Isfahan, Iran
A. E. Ruoho
Department of Pharmacology, University of Wisconsin Medical School,
Madison, Wisconsin, USA
Abstract: A variety of aromatic compounds are nitrated to the parent nitro aromatic
compounds under solvent-free conditions using supported tetramethylammonium
nitrate/silicasulfuric acid as a useful reagent. This methodology is useful for
nitration of activated and deactivated aromatic rings.
Keywords: Nitration, silicasulfuric acid, solvent-free
Received in the U.K. November 3, 2004
Address correspondence to Abdol R. Hajipour, Pharmaceutical Research Labora-
tory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran.
E-mail: haji@cc.iut.ac.ir
2
237

2
238
INTRODUCTION
Conventional methods for the nitration of aromatic rings utilize a mixture of
A. R. Hajipour et al.
[1]
nitric and sulphuric acids or nitronium tetrafluroborate. In the case of
[1]
borane/nitronium salt, HF and BF are liberated. We have been engaged in
3
[2]
the synthesis of azido aromatic compounds as photoaffinity ligands. The
nitro compounds required for the synthesis of these derivatives were prepared
[3]
by the conventional nitric sulfuric acid or nitronium tetraborate methods.
[4–6]
Reaction under solvent-free conditions have recently attracted attention.
The advantage of these methods over the conventional classical method is
that they show cleaner reactions, decreased reaction time, and easier workup.
RESULTS AND DISCUSSION
In continuation of our ongoing program to develop environmentally benign
[
7]
methods under solvent-free conditions,
we report here a convenient
method for nitration of aromatic compounds with supported tetramethyl-
ammonium nitrate/silicasulfuric acid under solvent-free conditions.
Supported nitration reagent (tetramethylammonium nitrate/silicasulfuric
[8]
acid) is prepared by grinding 2.4 mmol (0.66 g) of silicasulfuric acid with
.2 mmol of tetramethylammonium nitrate (0.16 g) in a mortar with a pestle
1
to produce a homogenous mixture. The process in its entirely involves
grinding a mixture of 1 molar ratio of aromatic compounds, and 1.2 molar
ratio of nitration reagent in a mortar. The resulting mixture was left at room
temperature for the time specified in Table 1. This reaction proceeds rapidly
and purification of product is straightforward (Scheme 1).
Aromatic compounds with oxidizable functional groups such as thio-
phenol, benzaldehyde, and anthracene are converted to diphenyldisulfide,
benzoic acid, and anthraquinone respectively. The site of the electophilc
attack by this reagent was found to be identical to the conventional
[
1–3]
methods (Table 1).
To evaluate the efficiency of this reaction under solvent-free conditions in
comparison with the reaction in solution, several experiments were performed.
We performed the reaction of naphthalene in several solvents, such as aceto-
nitrile, diethylether and dichloromethane. We determined that dichloro-
methane is the best solvent for this reaction. When naphthalene was treated
with 1.2 molar ratio of this reagent, only 80% of naphthalene was converted
to 1-nitro naphthalene after 5 h of stirring at room temperature. In acetonitrile
only 55% of naphthalene was converted to 1-nitro naphthalene after 5 h and in
diethyl ether the yield of the product was obtained trace.
In summary, we report here a novel method for nitration of aromatic
compounds under solvent-free conditions. This procedure is an efficient,
mild, and green method for nitration of activated and deactivated aromatic

Table 1. Nitration of aromatic compounds 2 with reagent 1 to nitroarens 3 under solvent-free conditions at room temperature
c
Yield (%)
a,b
a,b
[1–3,9]
Entry
ArH (2)
ArNO (3) (o : m : p ratio)
2
Time (min)
M
(8C) (lit)
1
2
3
4
5
6
7
8
9
Benzene
Toluene
Nitrobenzene
1
1
90
92
92
85
90
60
92
90
97
95
51
72
86
80
95
82
Oil
49–51 (54.5)
Oil
Nitrotoluene (15 : 0 : 85)
2,5-Dimethyl-1-nitrobenzene
Nitromesitylene
1,4-Dimethylbenzene
Mesitylene
Naphthalene
1
2
41–43 (44)
57–59 (61.5)
90 (89.5)
1-Nitronaphthalene
1,3-Dinitrobenzene
2
Nitrobenzene
10
2
Bromobenzene
Chlorobenzene
Benzyl bromide
Benzyl chloride
Biphenyl
Bromo-nitrobenzene (5 : 0 : 95)
Chloro-nitrobenzene (20 : 0 : 80)
4-Nitrobenzyl bromide
4-Nitrobenzyl chloride
4-Nitrobiphenyl
122–125 (127)
79–81 (83)
2
2
99–101 (98–100)
70–72 (71)
1
1
1
1
1
1
1
0
1
2
3
4
5
6
2
10
10
3
113–115 (114)
137–140 (139–142)
146–147 (—)
283–285 (286)
59–61 (58–60)
121–123 (122)
Benzoic acid
3-Nitobenzoic acid
2,6-Dimethylepyridine N-oxide
Anthracene
Thiophenol
1-Nitro 2,6-dimethylepyridine N-oxide
Anthraquinone
Diphenyldisulfide
3
1
Benzaldehyde
Benzoic acid
5
a
b
c
Confirmed by comparison with authentic samples (IR, TLC, and NMR).
Molar ratio of 1 : 2 (1 : 1).
Yield of isolated pure product after purification.

2240
A. R. Hajipour et al.
Scheme 1.
compounds to the corresponding nitro aromatic compounds under solvent-free
conditions.
EXPERIMENTAL
All of the yields refer to isolated products after purification. All of the products
1
were characterized by comparison of their spectral (IR, H NMR, and TLC)
[
1–3,9]
and physical data (melting) with those of authentic samples.
1
All
H NMR spectra were recorded at 300 MHz in CDCl relative to TMS as an
3
internal standard. All of the reactions were carried out in the absence of
solvent at room temperature under a hood with strong ventilation.
Preparation of Silicasulfuric Acid
A 500-mL suction was equipped with a constant-pressure dropping funnel
containing chlorosulfonic acid (46.6 g, 0.4 mol) and gas inlet tube for conduct-
ing HCl gas over an adsorbing solution (i.e., water) and charged 60.0 g of
silica gel. Chlorosulfonic acid was added dropwise over a period of 40 min
at rt. The HCl gas evolved from the reaction vessel immediately after the
addition was completed and the mixture was shaken for 30 min at room
[8]
temperature. A white solid (silicasulfuric acid; 92.0 g) was obtained.
Typical Experimental Procedure: Nitration of Naphthalene
with Tetramethylammonium Nitrate Silicasulfuric Acid
The reagent (tetramethylammonium nitrate/silicasulfuric acid) was prepared
by mixing silica sulfuric acid (2.4 mmol, 0.66 g) with tetramethylammonium
nitrate (1.2 mmol, 0.16 g) using a pestle and mortar for 5 s. Then, naphtha-
lene (1 mmol, 0.13 g) was added and ground with a pestle in a mortar for
2
min. The progress of the reaction was followed by TLC or GC. Then,
diethylether (2 Â 10 mL) was added to the reaction mixture. After
vigorous stirring it was filtered through a sintered glass funnel and the
solvent was evaporated under vacuum. The crude product was purified by
column chromatography on silica gel using a mixture of cyclohexane and

Tetramethylamonium Nitrate/Silicasulfuric Acid
2241
ethyl acetate as eluent (80 : 20) to give 1-nitro naphthalene in 90% yield
0.155 g, mp: 57–59).
(
ACKNOWLEDGMENTS
We gratefully acknowledge the funding support received for this project from
the Isfahan University of Technology (IUT), IR Iran (A. R. H.), and Grant GM
3
3138 (A. E. R.) from the National Institutes of Health, USA. Further financial
support from Center of Excellency in Chemistry Research (IUT) is gratefully
acknowledged.
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