A new method for the mononitration of phenol derivatives by poly(4-vinylpyridinium nitrate) and silica sulfuric acid under mild conditions

Article abstract of DOI:10.1016/j.cclet.2012.01.032

This procedure works efficiently for high selective mono nitration of phenol and substituted phenol to corresponding nitro compounds in moderate to high yield using poly(4-vinylpyridinium nitrate) and silica sulfuric acid in dichloromethane at room temperature.

Full text of DOI:10.1016/j.cclet.2012.01.032

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Chinese Chemical Letters 23 (2012) 458–461
www.elsevier.com/locate/cclet
A new method for the mononitration of phenol derivatives
by poly(4-vinylpyridinium nitrate) and silica sulfuric acid
under mild conditions
Hamid Goudarziafshar
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
Abstract
Thisprocedureworksefficientlyforhighselectivemononitrationofphenolandsubstitutedphenoltocorrespondingnitrocompounds
in moderate to high yield using poly(4-vinylpyridinium nitrate) and silica sulfuric acid in dichloromethane at room temperature.
#
2012 Hamid Goudarziafshar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Poly(4-vinylpyridinium nitrate); Silica sulfuric acid; Phenol; Nitration
The nitration of aromatic compounds plays important roles in industrial process. Nitro aromatic compound so
produced act as a key substrate for synthesis of dyes, pharmaceuticals, perfumes, plastics and explosives [1–4]. The
classical nitration method usually requires the use of corrosive liquid phase nitric acid–sulfuric acid mixture, responsible
for the generation of large amounts of wastes, which are costly to treat. Moreover, the classical nitration process [4,5],
employing a nitrating mixture of nitric acid and sulfuric acid for the last 150 years has remained unchanged in the
commercial arena owing to uneconomical alternative options. By classical method with a mixture of nitric sulfuric acids,
predominantly ortho and para products close to the ratio of 1:2 are resulted [4,5]. In other hand, the nitration of phenolic
compounds with various nitrates such as AgNO [6], Bi(NO ) [7–9], Fe(NO ) Á9H O [10], Cu(NO ) [11], (Me N)NO
3
3 3
3 3
2
3 2
4
3
[
12], Mg(NO ) Á6H O [13], Ca(NO ) [14], NaNO [15–17], NaNO [18], (NH ) Ce(NO ) [19], ZrO(NO ) ÁxH O
3 3 3 3 2 4 3 2 2 4
3
2
2
3 2
2
3
4 2
3 6
3 2
2
[
20], VO(NO ) [21], Fe(NO ) Á1.5N O , Cu(NO ) ÁN O [22], guanidinium nitrate/silica sulfuric acid [23], have been
reported and gave satisfactory results but with some drawbacks. Regioselective nitration using solid acid catalysts [24–
0] is also used. Due to the attachment of the acid function to a solid surface, corrosion would be of less interest. Solid
3
acids play efficiently the role of sulfuric acid in the phenol nitration. Therefore, lots of efforts had been directed to seek
environmentally friendly and reusable alternatives in recent years using solid acids [31–38].
Inordertoovercomethelimitationsanddrawbacksoftheclassicmethodssuchasstronglyacidicmedia, tediouswork-
up [39,40], oxidation and poly nitration, and safety problems (storage, handling, using, and also presence of toxic
3
+
2+
2+
transition metal cations such as Cr , Hg , and Cu within molecular structure of the reagents) [41,42], and to develop a
high-yielding one-pot synthesis of nitro phenols a novel poly(4-vinylpyridinium nitrate) was introduced to be a mild and
highly efficient nitrating polymer for the selective nitration of substituted phenols in dichloromethane at room
temperature with moderate yields.
It is worthwhile considering an alternative highly selective nitration process using this reagent in the presence of
silica sulfuric acid, which is a mild and highly efficient nitrating system for the nitration of substituted phenols in
dichloromethane at room temperature (Scheme 1 and Table 1).
E-mail address: hamid_gafshar@yahoo.com.
1001-8417/$ – see front matter # 2012 Hamid Goudarziafshar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2012.01.032

H. Goudarziafshar / Chinese Chemical Letters 23 (2012) 458–461
459
H
C
H
C
2
OH
OH
N
H
NO2
NO3
n
SiO -OSO H
2
3
X
X
CH Cl , rt
2
2
Scheme 1.
Table 1
Nitration of substituted phenols using poly(4-vinylpyridinium nitrate) and silica sulfuric acid in dichloromethane at room temperature.
a
b
Entry
1
Substrate
Product
T (min)
Yield (%)
44
22 h
OH
OH
NO2
2
3
4
145
95
71
78
70
Cl
OH
Cl
OH
NO2
MeO
Br
OH
MeO
OH
NO2
OH
45
OH
OH
Br
NO2
OH
5
6
10
95
48
65
Ph
Ph
NO2
PhO
OH
PhO
OH
NO2
7
70
51
C2H5
OH
C2H5
OH
NO2
8
9
25
15
68
68
(
H C) C
OH
(H C) C
OH
3
3
3
3
NO2
NO2
(
H C) HC
OH
(H C) HC
OH
3
2
3
2

460
H. Goudarziafshar / Chinese Chemical Letters 23 (2012) 458–461
Table 1 (Continued )
b
Entry
Substrate
Product
T (min)
Yield (%)
49
10
OMe
OMe
OH
85
Me
OH
OH
Me
Me
NO2
11
25
82
53
80
90
Me
OH
NO2
1
1
1
2
3
4
45
MeO
OH
MeO
OH
NO2
140
OH
OH
NO2
Cl
Cl
200
Cl
OH
Cl
OH
NO2
a
Molar ratio of reagents: substrate/poly(4-vinylpyridinium nitrate)/silica sulfuric acid = 1 mmol/0.42 g/0.15 g.
Isolated yield.
b
In this work an efficient and heterogeneous procedure for the nitration of substituted phenols using poly(4-
vinylpyridinium nitrate) were carried out under mild and completely heterogeneous condition. Nitration reaction
performed easily by mixing a phenolic compound with nitrating polymer and silica sulfuric acid in dichloromethane.
When the reaction is completed, the resulting yellow to orange pasty mixture was purified using short column
chromatography. This method has the following advantages: (a) reactions were carried out under mild and
heterogeneous conditions; (b) nitrating polymer was mild, highly efficient and chemoselective mono nitrating reagent;
(
c) the procure was friendly environment; (d) the product work-up was easy and (e) the cost of reagents are low.
1
. Experimental
Chemicals were procured from Fluka, Merck and Aldrich chemical companies and used without further purification.
.1. Nitration of 2-tert-butyl-4-methylphenol using poly(4-vinylpyridinium nitrate) and silica sulfuric acid
To 0.164 g of 2-tert-butyl-4-methylphenol (1 mmol) dissolved in 5 mL CH Cl , 0.42 g poly(4-vinylpyridinium
1
2
2
nitrate) and 0.15 g silica sulfuric acid were added. The mixture was stirred for 25 min at room temperature. Reaction
proceeding was inspected by TLC on silica gel GF254 plates with n-hexane and acetone (8:2, v/v). After reaction

H. Goudarziafshar / Chinese Chemical Letters 23 (2012) 458–461
461
completion, crud product was passed through the short column chromatography (packed by silica gel) using CH Cl as
2
2
eluent. Solvent was removed by simple distillation and pure 2-tert-butyl-4-methyl-6-nitrophenol obtained in 82%
yield (0.170 g) as crystalline pale yellow solid; mp 86–88 8C.
Acknowledgment
This work was supported by the research affairs of Ilam University, Ilam, Iran
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