Efficient and regioselective bromination of aromatic compounds with ethylenebis(N-methylimidazolium) ditribromide (EBMIDTB)

Article abstract of DOI:10.1080/00397910903019975

A regioselective and highly efficient method for bromination of phenol and aniline derivatives using ethylenebis(N-methylimidazolium) ditribromide (EBMIDTB) as an efficient reagent in dichloromethane at ambient temperature is reported. The reagent can be recovered and reused several times.

Full text of DOI:10.1080/00397910903019975

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Efficient and Regioselective Bromination
of Aromatic Compounds with
Ethylenebis(N-methylimidazolium)
Ditribromide (EBMIDTB)
a
a
Rahman Hosseinzadeh , Mahmood Tajbakhsh , Maryam
b
a
Mohadjerani & Zahra Lasemi
a
Department of Organic Chemistry , Faculty of Chemistry,
Mazandaran University , Babolsar, Iran
b
Department of Biology , Faculty of Science, Mazandaran
University , Babolsar, Iran
Published online: 22 Feb 2010.
To cite this article: Rahman Hosseinzadeh , Mahmood Tajbakhsh , Maryam Mohadjerani &
Zahra Lasemi (2010) Efficient and Regioselective Bromination of Aromatic Compounds with
Ethylenebis(N-methylimidazolium) Ditribromide (EBMIDTB), Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 40:6, 868-876, DOI:
10.1080/00397910903019975
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1
Synthetic Communications , 40: 868–876, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903019975
EFFICIENT AND REGIOSELECTIVE BROMINATION OF
AROMATIC COMPOUNDS WITH ETHYLENEBIS(N-
METHYLIMIDAZOLIUM) DITRIBROMIDE (EBMIDTB)
1
Rahman Hosseinzadeh, Mahmood Tajbakhsh,
1
2
Maryam Mohadjerani, and Zahra Lasemi
1
1
Department of Organic Chemistry, Faculty of Chemistry, Mazandaran
University, Babolsar, Iran
2
Department of Biology, Faculty of Science, Mazandaran University,
Babolsar, Iran
A regioselective and highly efficient method for bromination of phenol and aniline derivatives
using ethylenebis(N-methylimidazolium) ditribromide (EBMIDTB) as an efficient reagent
in dichloromethane at ambient temperature is reported. The reagent can be recovered and
reused several times.
Keywords: Anilines; bromination; ethylenebis(N-methylimidazolium) ditribromide; phenols
INTRODUCTION
Brominated aromatic compounds have gained increasing attention as versatile
intermediates for the synthesis of biologically active compounds such as potent
[
1]
antitumor, antibacterial, antifungal, antiviral, and antioxidizing agents. These
halides also undergo carbon–carbon bond formation via cross-coupling reactions
[
2]
[3]
[4]
[5]
such as Stille, Suzuki, Heck, and Sonogashira or carbon–heteroatom bond
[
6]
formation via aromatic functionalization protocols.
Conventional bromination methods typically use elemental bromine, generat-
[
7]
ing toxic and corrosive hydrogen bromide and leading to environmental pollution.
The reagents reported for this transformation include Br –Lewis acids,
[
8]
2
[10]
[
N-bromosuccinimide (NBS)–H SO –CF CO H, NBS–NaOH,
9]
[11]
NBS–SiO ,
2
2
[13]
4
3
2
[
12]
[14]
Br –Al O ,
2
NBS–Amberlyst,
NBS–H-form zeolite-5 (HZSM-5),
[16]
NBS–sulfonic-acid-functionalized silica,
tert-
NBS=
2
3
[15]
BuOOH– or H O –HBr,
2
2
[
17]
[18]
[19]
BF –H O,
3
NBS–NH OAc,
4
NBS–tetraethyl ammonium bromide (TEAB),
2
[20]
[21]
NBS–Pd(OAc) , NBS-para-toluene sulfonic acid (PTSA), hexamethylenetetra-
2
[
mine–Br2, Br =SO Cl =zeolite, tribromoisocyanuric acid, bromodichloroiso-
22]
[23]
[24]
2
2
2
[25]
[26]
[27]
[28]
cyanuric acid,
However, some of these methods are associated with drawbacks such as the use of
NH VO –H O –HBr,
NaBr-PhI(OAc)2
and CuBr2.
4
3
2
2
Received March 17, 2009.
Address correspondence to Rahman Hosseinzadeh, Department of Organic Chemistry, Faculty of
Chemistry, Mazandaran University, Babolsar, Iran. E-mail: r.hosseinzadeh@umz.ac.ir
8
68

BROMINATION OF AROMATIC COMPOUNDS
869
Scheme 1. R ¼ OH, NH ; R ¼ electeron releasing and withdrawing groups.
2
nonselective hazardous mineral acids and metal halides, which can lead to separation
difficulties and toxic and corrosive wastes, use of expensive heavy transition metals,
and formation of polysubstituted and other side products. The replacement of such
reagents with nontoxic and more selective compounds is very desirable and
represents an important goal in the context of clean synthesis.
Because of their ease of handling and ability to maintain the desired stoichi-
ometry, solid organic ammonium tribromides such as pyridiniumhydrobromide
[
29]
[30,31]
perbromide (PyHBr3),
phenyltrimethylammonium tribromide (PTATB),
tetramethylammonium tribromide (TMATB),
32]
[
cetyltrimethylammonium
[34]
tetrabutyl ammonium tribromide (TBATB),
[33]
tribromide (CetTMATB),
,2-dipyridiniumditribromide-ethane, and
[
are finding increasing applications as alternative substitutes for toxic
[35]
[36]
1
alkylpyridinium tribromide,
37]
[
Bmim]Br3
and hazardous molecular bromine in various organic reactions in recent years. Some
tribromide reagents have also been successfully used for efficient and more ecologi-
[
38]
cally acceptable solvent-free brominations of activated aromatic compounds.
In the present work, we report efficient and regioselective bromination of
aromatic compounds with ethylenebis(N-methylimidazolium) ditribromide
(EBMIDTB) (Scheme 1).
RESULTS AND DISCUSSION
EBMIDIB is easily and cheaply prepared from N-methylimidazole, 1,2-
We prepared EBMIDTB and used it for bromin-
[39]
dibromoethane, and bromine.
ation of aromatic compounds.
Initially, phenol was chosen as a model substrate to find optimal conditions.
When phenol was treated with 0.5 mmol of EBMIDTB at room temperature in
dichloromethane (DCM) after 30 min, p-bromophenol was formed in 95% yield.
This reaction was carried out in different protic and aprotic solvents, and the best
yield of p-bromophenol was achieved in CH Cl .
2
2
As indicated in Table 1, phenol, methyl-substituted phenols, and b-naphtol
were smoothly reacted with EBMIDTB at room temperature and gave correspond-
ing regioselective p-brominated product in excellent yield after 30 min (Table 1,
entries 1–8). We have analyzed the products by gas chromatography (GC) and did
not find any polybrominated isomers. However, when electron-withdrawing substi-
tuted phenols were applied in this reaction, only moderate yield of the corresponding
monobrominated isomer was obtained (Table 1, entries 9–11).
EBMIDTB was also used to brominate aniline derivatives at ambient tem-
perature. Various activated and deactivated anilines were brominated upon simple
mixing with reagent in DCM (Table 2). The reaction with aniline itself (Table 2,

870
R. HOSSEINZADEH ET AL.
Table 1. Bromination of phenol derivatives using EBMIDTB
a
b
ꢀ
Mp ( C)
[Ref.]
Entry
1
Substrate
Product
Time (min)
Yield (%)
[
40a]
40a]
30
97
64–66
62–64
[
2
3
4
5
30
30
30
30
80
90
97
90
[
[
[
40a]
40a]
40b]
61–63
55–57
82–84
[40a]
85–87
6
7
30
90
[40a]
76–79
30
30
90
95
[40a]
83–85
8
9
[
[
40a]
40a]
240
270
270
60
82
64
47–50
1
1
0
1
34–36
[40a]
113–116
a
1
All of the products were identified by comparing melting point and H NMR with those of authentic
samples reported in the literature.
b
Yields refer to isolated products.

BROMINATION OF AROMATIC COMPOUNDS
871
Table 2. Bromination of aniline derivatives using EBMIDTB
a
b
ꢀ
Mp ( C)
[Ref.]
Entry
1
Substrate
Product
Time (min)
Yield (%)
[
40a]
40a]
30
75
61–63
77–79
[
2
3
4
5
30
30
30
30
75
71
75
80
[
[
40a]
40a]
27–29
59–61
[40c]
Liquid
[40a]
54–56
6
7
30
30
80
80
[40a]
31–33
[
40a]
40a]
40d]
8
9
60
60
75
86
95
50
78–80
[
64–66
[
1
1
1
0
1
2
270
270
20
89–92
[40a]
102–104
c
60
40e]
73–75
c
57
40a]
100–102
13
25
(
Continued )

872
R. HOSSEINZADEH ET AL.
Table 2. Continued
a
b
ꢀ
[Ref.]
Entry
Substrate
Product
Time (min)
Yield (%)
Mp ( C)
c
55
40a]
167–170
14
25
a
1
All of the products were identified by comparing melting point and H NMR with those of authentic
samples reported in the literature.
b
Yields refer to isolated products.
c
1
.0 mmol of ditribromide were used.
entry 1) formed p-bromaniline as the main product (75%), along with 25% of
,4-dibromo isomer (Table 2, entry 1). N,N-Dimethyl or N,N-diethyl aniline reacted
2
with EBMIDTB to afford their p-bromo derivatives in good yields (Table 2, entries 6
and 7). Under reaction conditions, methyl and methoxy substituted anilines also
gave the monobrominated products in good yields (Table 2, entries 2–5). p-Chloro
aniline smoothly reacted with EBMIDTB, and a good yield of 2-bromo-4-chloroani-
line was formed (Table 2, entry 9). o-Bromo aniline under reaction conditions gave a
lesser yield of 2,4-dibromoaniline (Table 2, entry 8). p-Nitroaniline afforded only
5
0% of 2-bromo-4-nitroaniline in longer reaction time (Table 2, entry 11). o-Cyanoa-
niline required long reaction time but gave excellent yield of 4-bromo-2-cyanoaniline
Table 2, entry 10). In contrast to phenol derivatives, in the bromination of sub-
(
stituted anilines, a poor yield of the corresponding dibromo isomers (10–20%) was
formed. Having these data in hand, we have decided to apply this method for
heterocyclic compounds. N-Methyl imidazole and o- and p-amino pyridines were
reacted with EBMIDTB under reaction conditions, and in all cases only the
corresponding dibrominated products were obtained in moderate yield (Table 2,
entries 12–14).
An interesting feature of this method is that the reagent can be regenerated at
[
39]
the end of the reaction by extraction with water
without loosing its activity.
and can be used several times
In conclusion, we have developed an efficient and versatile method for the
monobromination of active aromatic compounds using ethylenebis(N-methylimida-
zolium) ditribromide. The method is highly regioselective, offering potential in
various synthetic applications. The mild reaction conditions, simple experimental
procedure, rapid conversion, good yields, and reusability of the reagent are notable
advantages of the method.
EXPERIMENTAL
General
Materials were purchased from Fluka and Merck companies. Products were
1
characterized by comparison of their spectroscopic data ( H NMR) and physical
properties with those of authentic samples.

BROMINATION OF AROMATIC COMPOUNDS
873
General Procedure for Bromination of Aromatic Compounds
In a 25-mL, round-bottomed flask, EBMIDTB (0.5 mmol, 0.336 g, but
.0 mmol for entries 12–14) was added to a solution of aromatic compound (1 mmol)
1
in DCM (10 mL). The reaction mixture was stirred at room temperature. After
disappearance of the starting material as monitored by GC, the reaction mixture
was transferred into a separatory funnel and washed with water (15 mL). The
organic layer was dried over anhydrous Na SO and filtered, and solvent was con-
2
4
centrated in a rotary evaporator. The crude product was purified by passing it over
a column of silica gel, using a mixture of hexane and ethyl acetate as the eluent (7:1).
1
All of the products were identified by comparing melting point and H NMR with
those of authentic samples reported in the literature.
Selected Data
1
-Bromo-2-methylphenol (Table 1, entry 2). H NMR (500 MHz, CDCl ):
4
3
d 2.26 (s, 3H), 5.19 (s, 1H), 6.70 (d, J ¼ 8.47 Hz, 1H), 7.20 (dd, J ¼ 8.47, 2.30 Hz, 1H),
7
.28 (d, J ¼ 2.30 Hz, 1H).
1
-Bromo-3-methylphenol (Table 1, entry 3). H NMR (500 MHz, CDCl ):
4
3
d 2.31 (s, 3H), 5.28 (br s, 1H), 6.54 (dd, J¼ 8.55, 2.81 Hz, 1H), 6.72 (d, J¼ 2.81 Hz, 1H),
7
.32 (d, J ¼ 8.55, 1H).
1
-Bromo-3-methylaniline (Table 2, entry 2). H NMR (500 MHz, CDCl ):
4
3
d 2.27 (s, 3H), 3.90 (br s, 2H), 6.72 (d, J¼ 8.14 Hz, 1H), 6.96 (dd, J ¼ 8.14, 1.30 Hz, 1H),
7
.28 (d, J ¼ 1.30 Hz, 1H).
1
-Bromo-4-methoxyaniline (Table 2, entry 5). H NMR (500 MHz,
2
CDCl ): d 3.72 (br s, 2H), 3.77 (s, 3H), 6.78 (m, 2H), 7.05 (t, J ¼ 1.43 Hz, 1H).
3
1
2
,4-Dibromoaniline (Table 2, entry 8). H NMR (500 MHz, CDCl ): d 3.70
3
(
br s, 2H), 6.63 (d, J ¼ 8.52 Hz, 1H), 7.18 (dd, J ¼ 8.52, 2.04 Hz, 1H), 7.52 (d,
J ¼ 2.04 Hz, 1H).
ACKNOWLEDGMENT
We are thankful to the Research Council of Mazandaran University for the
partial support of this work.
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