Oxidative halogenation of aromatic compounds with metal halides and sodium bismuthate

Article abstract of DOI:10.1002/hlca.200390007

A new mild and efficient method for aromatic halogenation with a wide variety of halides in the presence of sodium bismuthate NaBO₃ in AcOH is reported. Metal halides of groups Ia, IIa, IIIa, IVa, Va, and the first row of transition elements are suitable for this method.

Full text of DOI:10.1002/hlca.200390007

1
64
Helvetica Chimica Acta ± Vol. 86 (2003)
Oxidative Halogenation of Aromatic Compounds with Metal Halides and
Sodium Bismuthate
by Hussni A. Muathen
Department of Chemistry , Umm Al Qura University, P.O. Box 7283, Makkah, Saudi Arabia
(e-mail: h_muathen@hotmail.com)
A new mild and efficient method for aromatic halogenation with a wide variety of halides in the presence of
sodium bismuthate NaBO in AcOH is reported. Metal halides of groups Ia, IIa, IIIa, IVa, Va, and the first row
3
of transition elements are suitable for this method.
There has been a growing interest in the last few years in metal halides as
alternatives to molecular halogens in halogenations of aromatic compounds [1][2].
Halides of transition metals of groups I, IV, and V have received particular attention
[
3± 6]. Generation of halogens from these metal halides requires very drastic
conditions [7][8]. Other methods involve oxidation of certain halides with hardly
available and expensive oxidizing agents such as peroxyacetic acid [9], lead
tetraacetate [10], and nitrogen dioxide [11].
Bismuthate ion is a strong oxidizing agent, but little attention has been paid to its
potential in organic synthesis [12]. It has long been known that the ion oxidizes halides
to the corresponding halogen in aqueous HClO [13][14]. No studies have been carried
4
out regarding the exploitation of the reagent in the halogenation of organic compounds
with metal halides.
À
V
III
2
X ‡ Bi ! X ‡ Bi (X ˆ Cl,Br)
(1)
2
We hereby wish to report a new method for aromatic chlorination and bromination
with various halides in the presence of NaBiO3.
Results and Discussion. ± Appropriate amounts of the aromatic substrate and the
halide were allowed to react with NaBiO in AcOH at room temperature. The reaction
3
was monitored with a moist starch-iodide paper held over the reaction vessel. The blue
color indicated the presence of free halogen in the reaction mixture.
All metal halides of groups Ia, IIa, IIIa, IVa, Va, and the first row of transition
metals react with NaBiO in AcOH and produce the corresponding halogen. The
3
reactivity of NaBiO with halides varies from metal to metal. We found that the rate of
3
halogen production increases as we go from the top of the group to the bottom. The
reactivity is also affected by the amount of H O present in the halide crystals.
2
Anhydrous forms are more reactive than their hydrated forms.
Naphthalene was chosen for a comparative study of aromatic chlorination and
bromination with various metal chlorides and bromides. The results are summarized in
Tables 1 and 2.

Helvetica Chimica Acta ± Vol. 86 (2003)
165
Table 1. Chlorination of Napthalene with Metal Halides and NaBiO
3
Naphthalene [mmol]
MCl
m
(mmol)
NaBiO
3
[mmol]
Time [h]
1-Chloronaphthalene
Yield [%]
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
NaCl (10)
KCl (10)
RbCl (10)
CsCl (10)
5
5
5
5
5
5
5
5
5
368
1
1
1
2
1
1
1
0.5
0.5
1
376
0.5
378
2
0.5
0.5
2
82
85
87
74
85
83
86
88
84
80
MgCl
CaCl
SrCl
BaCl
AlCl
GaCl
InCl
2
(5)
(5)
(5)
(5)
(5)
2
2
3
3
3
(5)
(5)
5
5
2
SnCl
SnCl
PbCl
SbCl
SbCl
2
4
(5)
(5)
(5)
(5)
(5)
(5)
(5)
10
5
10
10
5
5
5
10
5
5
88
2
3
75
87
85
72
82
85
83
78
84
87
86
5
TiCl
4
CrCl
3
MnCl
FeCl
CoCl
NiCl
Cu Cl
2
(5)
(5)
(5)
(5)
(5)
2
1
1
2
1
1
0.5
3
2
2
5
10
5
2
2
CuCl
ZnCl
2
2
(5)
(5)
5
The general stoichiometric equation representing various metal halides, MXm,
in their reactions with bismuthate V ion to give the corresponding halogens is as
follows:
ꢀ2
nꢁ
ꢀ
ꢁ
2n
3
‡
m‡
‡ n Na‡
MX ‡ n NaBiO ‡ 6n AcOH ! n X ‡‡ n Bi
‡
M
m
3
2
m
m
À
À
‡
6n AcO ‡ (m À 2) X ‡ 3n H O
(3
)
2
It was found that metals with two valence states, like copper and tin, require 2 equiv. of
NaBiO , one for the conversion of the metal to the higher-valence state, and the other
3
for the generation of the halogen (Eqn. 4). It is also noted that reactions involving
metals of low-valence state require longer reaction times.
2‡
3‡
‡
À
Cu Cl ‡2 NaBiO ‡12 AcOH ! Cl ‡2 Cu ‡2 Bi ‡2 Na ‡12 AcO ‡6 H O (4)
2
2
3
2
2

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66
Helvetica Chimica Acta ± Vol. 86 (2003)
Table 2. Bromination of Napthalene with Metal Halides and NaBiO
3
Naphthalene [mmol]
MCl
m
(mmol)
NaBiO
3
[mmol]
Time [h]
1-Bromonaphthalene
Yield [%]
5
5
5
5
5
5
5
5
5
5
5
5
5
5
NaBr (10)
KBr (10)
5
5
5
5
5
24
12
12
12
6
60
70
73
71
86
83
81
78
76
CaBr
BaBr
2
(5)
(5)
(5)
(5)
(10)
(5)
2
AlBr
SnBr
SnBr
SbBr
3
4
5
4
2
2
3
10
10
10
5
5
10
5
12
12
377
12
8
MnBr
FeBr
CoBr
Cu Br
2
(5)
(5)
3
2
(5)
(5)
(5)
(5)
73
75
72
74
2
2
CuBr
ZnBr
2
6
6
2
5
4‡
5‡
3‡
4‡
2‡
The influence of the Lewis acid character of Sn , Sb , Al , Ti , and Zn halides is
apparent from the data of Tables 1 and 2. The high reaction rates involving these
halides are expected, since they exhibit strong to moderate activity as Friedel-Crafts
catalysts [15]. These halides may have a dual function when used in excess. The primary
function is to produce halogen and the other is to act as a Lewis acid to activate the
produced halogen.
d‡
MX2
dÀ
MX2
NaBiO À! X À! X ÀX Á Á Á M X
ꢀ5†
3
2
2
The metal halides, which possess Lewis acid characteristics, vary in their levels of
activity as Friedel-Crafts catalysts. The reactivity follows the order AlBr > AlCl >
3
3
FeCl > SbCl > BF > SnCl > ZnCl [16].
3
5
3
4
2
Zinc halides ZnCl and ZnBr , although the least reactive, are very cheap, easy to
2
2
handle, easy to dry, and well-soluble in acetic acid. In addition to their Lewis acid
properties, they are capable of trapping the resulting hydrogen halide, which usually
reduces the halogenation rate (Eqns. 5 and 6) [17].
ArH ‡ X ! ArX ‡ HX
(6)
(7)
2
HX ‡ ZnX ! HZnX
2
3
Owing to these findings, we decided to investigate the impact of a large excess of zinc
halide in the halogenation of some aromatic compounds in comparison with reactions
involving 1 equiv. of the same halide. The results are summarized in Tables 3 and 4.
The results from Tables 3 and 4 indicate that the excess of zinc halides enhanced the
reactivity of halogens towards aromatic halogenation. The reaction with alkylbenzenes

Helvetica Chimica Acta ± Vol. 86 (2003)
167
2 3
Table 3. Chloronation of Aromatic Compounds with ZnCl and NaBiO
Substrate
Benzene
Products
Molar ratio
Subst./ZnCl
Time [h]
Yield [%]
2
/NaBiO
3
Chlorobenzene
1 : 1 : 1
12
5
54
68
1
: 10 : 1
Toluene
o-/p-Chlorotoluene 2 : 31 : 1 : 1
6
73
m-Xylene
4-Chloro-1,3-dimethylbenzene
1 : 1 : 1
: 10 : 1
1 : 1 : 1
: 10 : 1
1 : 1 : 1
: 10 : 1
1 : 1 : 1
: 10 : 1
1 : 1 : 1
1 : 1 : 1
1 : 1 : 1
1 : 1 : 1
4
2
1
76
82
81
90
74
86
84
86
76
90
72
86
86
78
76
1
Mesitylene
Durene
2-Chloromesitylene
3-Chlorodurene
1
0.25
0.5
0.25
0.5
0.25
0.5
0.25
0.5
0.5
0.25
1
1
Anisole
o-/p-Chloroanisole 1 : 4
1
Phenol
Acetanilide
Aniline
2,4,6-Trichlorophenol
o-/p-Chloroacetanilide 3: 7
2,4,6-Trichloroaniline
1-Chloronaphthalene
Naphthalene
1
: 10 : 1
Anthracene
Phenanthrene
9,10-Dichloroanthracene
9-Chlorophenanthrene
1 : 10 : 1
1 : 1 : 1
0.5
Table 4. Bromination of Aromatic Compounds with ZnBr
2
and NaBiO
3
Substrate
Products
Molar ratio
Subst./ZnBr
Time [h]
Yield [%]
2
/NaBiO
3
Benzene
Toluene
m-Xylene
Mesitylene
Durene
Bromobenzene
1 : 1 : 1
24
12
10
6
6
382
2
0.5
2
0.5
2
0.5
1
0.5
0.5
6
20
38
74
80
73
1
: 10 : 1
o-/p-Bromotoluene 3: 7
4-Bromo-1,3-dimethylbenzene
2-Bromomesitylene
3-Bromodurene
1 : 1 : 1
1
: 10 : 1
1 : 1 : 1
1
: 10 : 1
1 : 1 : 1
: 10 : 1
1 : 1 : 1
: 10 : 1
1 : 1 : 1
: 10 : 1
81
90
75
82
78
86
73
85
70
74
88
1
1
Anisole
o-/p-Bromoanisole 1 : 9
1
Phenol
Acetanilide
Aniline
2,4,6-Bromophenol
1 : 1 : 1
1 : 1 : 1
1 : 1 : 1
1 : 1 : 1
o-/p-Bromoacetanilide 1 : 4
2,4,6-Tribromoaniline
1-Bromonaphthalene
Naphthalene
1
: 10 : 1
1.5
352
2
Anthracene
Phenanthrene
9,10-Dibromoanthracene
9-Bromophenanthrene
1 : 1 : 1
1 : 1 : 1
70
76
1
: 10 : 1
1
gave only nuclear-halogenated compounds, and no side-chain attack was observed.
Furthermore, the reactivity of alkylbenzenes towards ZnCl and NaBiO increased with
2
3
increasing number of alkyl groups.

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Helvetica Chimica Acta ± Vol. 86 (2003)
To avoid side oxidation of reactive substrates like phenols and aniline by
bismuthate ion, the halide is first allowed to react with NaBiO for 15 min, then the
3
aromatic substrate is added. Monohalogenation of phenols and anilines could not be
achieved owing to their high reactivity compared with other aromatic compounds.
Experimental. ± General Procedure for Halogenation with Metal Halides and NaBiO
.5 mmol) was added in one portion to a stirred mixture of the aromatic substrate (5 mmol) and zinc halide
50 mmol) in glacial AcOH (50 ml). The mixture was stirred vigorously for the specified time and then diluted
with CH Cl (50 ml). The resulting solid was filtered off, and the filtrate was washed successively with H O and
aq. NaHCO
3 3
. NaBiO (1.55 g,
5
(
2
2
2
3
, and dried (Na
2
SO
4
). Evaporation in vacuo afforded the required halo compound.
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[
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[
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Received July 20, 2002