Poly(4-vinylpyridinium bromochromate): An efficient reagent for bromination of aromatic compounds

Article abstract of DOI:10.1007/s00706-012-0779-4

A simple and efficient method for the bromination of various aromatic compounds by using poly(4-vinylpyridinium bromochromate) is reported. This method has several advantages such as good selectivity between ortho and para positions of aromatic compounds, simple workup, short reaction times, and high yields of the products.

Full text of DOI:10.1007/s00706-012-0779-4

Monatsh Chem (2013) 144:179–181
DOI 10.1007/s00706-012-0779-4
ORIGINAL PAPER
Poly(4-vinylpyridinium bromochromate): an efficient reagent
for bromination of aromatic compounds
Jalal Albadi
Masoumeh Abedini
•
Hassan Tajik
•
Mosadegh Keshavarz
•
Received: 3 August 2011 / Accepted: 24 April 2012 / Published online: 24 May 2012
Ó Springer-Verlag 2012
Abstract A simple and efficient method for the bromin-
ation of various aromatic compounds by using poly(4-
vinylpyridinium bromochromate) is reported. This method
has several advantages such as good selectivity between
ortho and para positions of aromatic compounds, simple
workup, short reaction times, and high yields of the
products.
bromination of different organic compounds have been
reported, the main disadvantage of these is the relative
difficulty in the preparation of the reagents and in the
workup of the reaction mixture. Moreover in the case of
active aromatic compounds such as anilines and phenols,
elemental bromination usually results in a complex mixture
of mono-, di-, tri-, and even tetrabrominated products. It is
especially difficult to perform selective monobromination
of highly activated aromatic compounds, such as aniline
and phenol derivatives. Polymer-bound brominating agents
were one of the earliest examples of polymeric reagents
which alleviate these difficulties. Therefore, it is not sur-
prising that several polymer-bound halogenating reagents
have been established in the 20 years since the early days
of functionalized polymers [14]. In most cases cross-linked
polystyrene, cross-linked PVPy, or cross-linked copoly-
mers of styrene and 4-vinylpyridine have been used as
polymeric supports for halogenating reagents. Some of the
reagents like poly(vinylpyridinium hydrobromide perbro-
mide) [15] and poly(vinylpyridinium bromine) [16] are
reported as polymeric brominating reagents.
Keywords Poly(4-vinylpyridinium bromochromate) Á
Bromination Á Aromatic compounds
Introduction
Bromination of organic compounds is a crucial step in the
preparation of various synthetic intermediates. Bromoare-
nes have been used widely in industrially important
products and biologically active substrates as antitumor,
antifungal, antibacterial, and antiviral compounds [1, 2].
Various methods have been used for the bromination
of aromatic compounds, e.g., KBr-benzyltriphenylphos-
phonium peroxymonosulfate [3], peroxodisulfate [4], NBS
[
5], NBS/[Bmim]Br [6], NBS/NH OAc [7], NBS/hv [8],
4
isoquinolinium bromochromate (IQBC) [9], pyridinium
bromochromate [10], Br /SO Cl [11], pyridinium hydro-
Results and discussion
2
2
2
bromide perbromide [12], and benzyltriethylammonium
polybromide [13]. Although many useful procedures for
Herein we report a simple, efficient, and selective method
for the bromination of aromatic compounds by using
poly(4-vinylpyridinium bromochromate) (P VPyBC) as the
4
source of bromine in acetonitrile as the solvent. The results
are given in Table 1 (Scheme 1).
J. Albadi (&) Á M. Keshavarz
Department of Chemistry, College of Science,
Khatam Al-Anbia, University of Technology, Behbahan, Iran
e-mail: J.albadi@iaug.ac.ir
All the reactions were performed at room temperature
for the appropriate times. A wide range of aromatic
compounds were successfully reacted to afford the
desired monobrominated products in excellent yields with
complete regioselectivity. Among the various substrates
H. Tajik Á M. Abedini
Department of Chemistry, College of Science,
University of Guilan, Rasht, Iran
123

1
80
J. Albadi et al.
Table 1 Bromination of aromatic compounds by P VPyBC
4
Table 1 continued
a
a
Entry Substrate
Product
Time/ Yield/ M.p./°C
Entry Substrate
Product
Time/ Yield/ M.p./°C
b
b
min
%
min
%
1
25
85
Liq
Liq
13
10
85
71–73
2
3
60
8
82
88
1
1
4
5
70
32
79
84
107–109
91–93
Liq
4
5
6
18
35
70
85
85
82
68–70
Liq
1
1
6
7
80
85
82
111–113
97–98
120
Liq
1
1
2
8
9
0
25
7
86
88
90
48–50
102–104
Liq
7
8
15
10
88
88
61–62
59–60
5
9
12
17
82
90
34–36
Liq
a
Products were characterized by comparison of their physical and
spectral data with authentic samples [17–22]
1
0
b
Isolated yields
R
R
1
1
1
2
8
89
88
55–57
64–65
P4PVyBC
3
CH CN , r.t.
18
Br
R = OCH , OH, CH , Cl, Br, NO , NH , N(CH )
3 2
3
3
2
2
Scheme 1
1
23

P4VPy-BC: efficient reagent for bromination
181
studied, compounds containing electron-donating substitu-
ents were most reactive and converted to the corresponding
monobrominated products in shorter reaction times. How-
ever, the rate of the reaction was slower when the ring
contained an electron-withdrawing group (Table 1, entries
contents were cooled to 0 °C and then 10.0 g poly(4-
vinylpyridine) was added over 15–20 min to give a brown
solid. The solid was separated and dried at 50 °C for 24 h
to give poly(4-vinylpyridinium bromochromate).
1
4–15). Chemoselective conversion of the aromatic com-
General procedure
pounds to their para-substituted products was achieved in
excellent yields. When the para position was blocked,
monobrominated products were obtained over longer
reaction times (Table 1, entries 2, 6, 12, 14). Anisole gave
the para isomer as the major product in short reaction time
A mixture of aromatic compound (1 mmol) and 0.2 g
3
P VPyBC in 3 cm acetonitrile was stirred at room tem-
4
perature for the appropriate time according to Table 1.
After completion of the reaction (monitored by TLC), the
reaction mixture was filtered. Evaporation of the solvent
followed by recrystallization of the crude product or
column chromatography on silica gel gave the corre-
sponding brominated compounds in good to excellent
yields (Table 1).
(
Table 1, entry 1). However, 4-methylanisole was bromi-
nated after 1 h to afford 2-bromo-4-methylanisole (Table 1,
entry 2). Also, it was observed that para orientation in the
product is more favorable than ortho orientation from the
fact that 2-methylanisole was more readily brominated than
4
-methylanisole (Table 1, entries 2, 4). Phenol, o-cresol,
Acknowledgments We are thankful to the Islamic Azad University,
Gachsaran branch, for the partial support of this work.
o-nitrophenol, and o-cholorophenol were converted to the
para-brominated products with respect to the hydroxyl
groups in good yields (Table 1, entries 7, 9, 15, 18). The
substrate was brominated ortho to the phenolic OH only
when the para position was occupied (entry 10). Similar
results were observed for aniline derivatives (Table 1,
entries 11, 12, 13).
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In conclusion, P VPyBC as a polymeric reagent is
4
efficiently able to perform the chemoselective bromination
of aromatic compounds under room temperature condi-
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2
Preparation of poly(4-vinylpyridinium bromochromate)
3
A solution of 10 g chromium trioxide (0.1 mol) in 20 cm
3
water was cooled to 0 °C. To this solution, 17 cm 47 %
HBr (0.1 mol) was added slowly with constant stirring. The
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123