Mononitration of phenol derivatives by guanidinium nitrate and silica sulfuric acid under mild conditions

Article abstract of DOI:10.1016/j.cclet.2011.07.012

A mixture of guanidinium nitrate and silica sulfuric acid acts as mild and heterogeneous media for the efficient mono nitration of phenolic compounds in dichloromethane at room temperature.

Full text of DOI:10.1016/j.cclet.2011.07.012

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1431–1434
www.elsevier.com/locate/cclet
Mononitration of phenol derivatives by guanidinium nitrate
and silica sulfuric acid under mild conditions
*
Arash Ghorbani-Choghamarani , Hamid Goudarziafshar,
Mohsen Nikoorazm, Zahra Naseri
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
Received 9 May 2011
Available online 13 October 2011
Abstract
A mixture of guanidinium nitrate and silica sulfuric acid acts as mild and heterogeneous media for the efficient mono nitration of
phenolic compounds in dichloromethane at room temperature.
# 2011 Arash Ghorbani-Choghamarani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Nitration; Phenol; Heterogeneous; Guanidinium nitrate; Silica sulfuric acid
The replacement of current chemical processing techniques with more environmentally benign alternatives is an
increasingly attractive subject [1]. Electrophilic aromatic substitution reactions are of considerable importance in the
production of fine chemicals [2]. Nitration of organic substrates is a widely studied reaction of great industrial
significance as many nitro-compounds are extensively utilized and act as intermediates for the manufacture of plastics,
dyes, perfumes, drugs andpharmaceuticals[3]. Nitrophenols arevery important organic intermediates andhence it is still
interesting to develop regiospecific pollution-free nitrating procedures for phenolic compounds under mild conditions
[4]. Traditionally, procedures for the nitration of phenolic compounds have applied a mixture containing concentrated
nitric acid and sulfuric acid, which have a lot of disadvantageous including harsh conditions, low selectivity and
difficultiesinhandling. Variousnitratingreagentsorreagentsystemsforthenitrationofphenolshavebeenemergedinthe
last decade such as WO3–HNO3 [2], Zeolite H–Y-supported copper(II) nitrate [5], TiO2–[Ti4H11(PO4)9]ÁnH2O/HNO3
[6], ([bmim][HSO4])–NaNO3 [7], Yb–Mo–HKSF–HNO3 [8], TBAB/HNO3 [9], M(NO+)nÁxH2O/PTSA [10],
Mg(HSO4)2 or NaHSO4/NaNO3 [11], Bi(NO3)3Á5H2O [12], nitric acid/zinc chloride [13] and Bi(NO3)3Á5H2O/
HNO3 [14]; but many of these methods suffer from some drawbacks, including low selectivity, tedious work-up, toxicity,
un-degradable reagents and catalyst and long reaction times. Therefore, we decided to overcome mentioned limitations
by introducing of an environmentally friendly procedure for the preparation of nitrophenols.
In continuation of our studies on the designing of new systems for the organic functional group transformations
[15–27] we became interested to design a metal-free, green and heterogeneous media for the production of mono
nitrated phenol derivatives. Recently we have introduced a catalytic method for the selective oxidation of sulfides into
* Corresponding author.
E-mail addresses: arashghch58@yahoo.com, a.ghorbani@mail.ilam.ac.ir (A. Ghorbani-Choghamarani).
1001-8417/$ – see front matter # 2011 Arash Ghorbani-Choghamarani. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.07.012

1432
A. Ghorbani-Choghamarani et al. / Chinese Chemical Letters 22 (2011) 1431–1434
NH2+
O
S
H2N
NH2
NO3-
S
R1
R2
R1
R2
SiO2-OSO3H
NH4Br (Cat.)
CH2Cl2, rt
R1 and R2= Alkyl or Aryl
Scheme 1.
NH +
2
OH
OH
H N
NH
2
2
NO -
3
NO
2
Silica sulfuric acid
Wet SiO ,CH Cl , rt
2
2
2
X
X
Scheme 2.
sulfoxides using guanidinium nitrate, silica sulfuric acid and catalytic amounts of ammonium bromide (Scheme 1)
[19]. Therefore we decided to apply similar system for the nitration of substituted phenols.
A mixture of guanidinium nitrate, as non-metallic and green nitrate salt, and silica sulfuric acid might generate
+
nitronium ion (NO2 ), which is usable for the nitration of activated aromatic compounds. Consequently a wide variety
of phenolic compounds were subjected for the nitration reaction using guanidinium nitrate I and silica sulfuric acid II
in the presence of wet SiO2 (50%, w/w) in dichloromethane (Scheme 2 and Table 1).
Table 1
Nitration of substituted phenols to their corresponding substituted o-nitrophenols using guanidinium nitrate I, silica sulfuric acid II and wet SiO2
(50%, w/w) in dichloromethane at room temperature.
Entry
1
Substrate
Product
Reagent/substrate (mmol)a
Time (min)
360
Yieldsb (%)
m.p. (8C)
I
II
OH
OH
2
0.25
35
43–44
NO2
OH
OH
2
3
1.75
0.25
0.25
180
420
56
70
81–84
71–73
NO
2
Cl
Cl
OH
OH
2
NO2
F
F
OH
OH
4
2
0.25
120
37
78–80
NO2
OMe
OMe

A. Ghorbani-Choghamarani et al. / Chinese Chemical Letters 22 (2011) 1431–1434
1433
Table 1 (Continued )
Entry
Substrate
Product
Reagent/substrate (mmol)a
Time (min)
300
Yieldsb (%)
m.p. (8C)
I
II
OH
OH
5
1.5
0.187
58
83–84
NO2
Br
Br
OH
OH
6
2
0.25
50
69
Oil
NO2
OPh
OH
OPh
OH
7
8
2
2
0.25
0.25
100
71
67
Oil
NO
3
2
CH CH
2
CH CH
2
3
OH
OH
60
30–32
NO2
CH
OH
3
CH3
OH
9
2.5
0.25
0.25
0.25
25
25
15
54
61
67
68–69
NO
2
Ph
Ph
OH
OH
10
11
2
Oil
NO
2
C(CH
OH
)
3 3
C(CH3
)
3
OH
2
Oil
NO2
CH(CH
)
3 2
CH(CH3
)
2
OH
OH
12
2
2
0.25
0.25
330
360
84
74
89–90
NO2
Me
Me
OH
OH
13
122–127
Cl
NO
2
Cl
Cl
Cl
a
Wet SiO2:substrate = 0.2 g:1 mmol.
b
Yields after purification by column chromatography.

1434
A. Ghorbani-Choghamarani et al. / Chinese Chemical Letters 22 (2011) 1431–1434
All reactions were heterogeneously performed via mixing of one of the substituted phenols with guanidinium
nitrate, silica sulfuric acid and wet SiO2 in dichloromethane and stirring the resulting mixture at room temperature for
specific times. Pure product could be obtained easily by flash column chromatography.
In the described system, wet SiO2 provide a wet surface for the combination of nitrate salt and acid, which generate
+
in situ nitronium ion (NO2 ).
In summary we have delineated an environmentally friendly and heterogeneous procedure for the preparation of
substituted phenols. Furthermore, this method exhibits substrate versatility, mild reaction conditions, non-metallic
conditions and easy and clean work-up of products.
1. Experimental
Chemicals were purchased on Fluka, Merck and Aldrich chemical companies. The nitration products were
characterized by comparison of their spectral (IR, 1H NMR, and 13C NMR) and physical data with authentic samples.
1.1. Mononitration of 2,4-dichlorophenol by guanidinium nitrate and silica sulfuric acid
A15-mLround-bottomflaskwaschargedwith2,4-dichlorophenol(0.163 g, 1 mmol), silicasulfuricacid(0.25 g), wet
SiO2 (50%, w/w, 0.2 g), guanidinium nitrate (0.244 g, 2 mmol) and dichloromethane (5 mL). Resulting mixture was
stirred at room temperature for 6 h (the progress of the reaction was monitored by TLC). After reaction completion,
reaction mixture was passed on short column chromatography (column packed by silica gel) using CH2Cl2 as eluent.
Eventually, CH2Cl2 was removed by simple distillation and pure 2,4-dichloro-6-nitrophenol obtained in 74% yield
(0.154 g) as crystalline pale yellow solid; mp 122–127 8C; 1H NMR (400 MHz, CDCl3): d 10.93 (s, 1H), 8.07–8.08 (d,
1H, J = 2.4 Hz), 7.71–7.72 (d, 1H, J = 2.4 Hz); 13C NMR (100 MHz, CDCl3): d 150.3, 137.3, 134.2, 125.8, 124.7, 123.1.
Acknowledgment
This work was supported by the research affairs of Ilam University, Ilam, Iran.
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