Direct, easy, and scalable preparation of (diacetoxyiodo)arenes from arenes using potassium peroxodisulfate as the oxidant

Article abstract of DOI:10.1016/j.tetlet.2006.09.009

The reaction of arenes with potassium peroxodisulfate, elemental iodine, and acetic acid in the presence of concd sulfuric acid, efficiently generates the corresponding (diacetoxyiodo)arenes in good yields, providing an easy, safe, and effective method for preparing (diacetoxyiodo)arenes from arenes and iodine.

Full text of DOI:10.1016/j.tetlet.2006.09.009

Tetrahedron Letters 47 (2006) 7889–7891
Direct, easy, and scalable preparation of (diacetoxyiodo)arenes
from arenes using potassium peroxodisulfate as the oxidant
Md. Delwar Hossain and Tsugio Kitamura*
Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University,
Honjo-machi, Saga 840-8502, Japan
Received 26 July 2006; revised 25 August 2006; accepted 4 September 2006
Available online 25 September 2006
Abstract—The reaction of arenes with potassium peroxodisulfate, elemental iodine, and acetic acid in the presence of concd sulfuric
acid, efficiently generates the corresponding (diacetoxyiodo)arenes in good yields, providing an easy, safe, and effective method for
preparing (diacetoxyiodo)arenes from arenes and iodine.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Over the past decade, the use of hypervalent iodine
reagents has gained importance as mild oxidants and
as a safe alternative to heavy-metal reagents for
performing
a variety of organic transformations.
(Diacetoxyiodo)arenes, [ArI(OAc)2], and the parent
compound, (diacetoxyiodo)benzene [PhI(OAc)2], have
been known for a long time.1–5 Particularly the parent
(diacetoxyiodo)benzene is a crystalline compound and
is fairly stable in air, which can be stored for long
periods in the dark. It is a potent, often chemoselective
oxidant, and is widely used in modern organic synthesis.
(Diacetoxyiodo)benzene is also used for the facile
synthesis of, for example, iodosylbenzene, [bis(trifluoro-
acetoxy)iodo]benzene, [hydroxyl(tosyloxy)iodo]benzene
(Koser’s salt, selective oxidants), and aromatic iodonium
salts (arylating reagents).2–6 Several methods are avail-
able for the preparation of (diacetoxyiodo)benzene.
Historically, the first member, (diacetoxyiodo)benzene
was synthesized by Willgerodt in 1892, by dissolving
iodosylbenzene in hot acetic acid.7 The representative
methods, as shown in Scheme 1, involve the reaction
of iodosylbenzene with acetic acid,7 the direct oxidation
of iodobenzene in acetic acid,3–5,8–12 and the reaction of
(dichloroiodo)benzene with metal acetates or acetic
acid.13,14 In most of the above methods, iodobenzene
is used as a starting material to prepare (diacetoxy-
Scheme 1.
iodo)benzene. Iodobenzene is readily available but
expensive.
The most ideal procedure for (diacetoxyiodo)benzene
should involve a straightforward synthesis from benzene
and iodine. This procedure gives a direct and efficient
method that does not contain the step via iodobenzene
synthesis. However, to the best of our knowledge, there
are no methods for preparing (diacetoxyiodo)benzene
directly from benzene and iodine. Very recently, Shreeve
and co-workers reported a direct synthesis of (diacet-
oxyiodo)arenes mediated by Selectflour.15 In the Select-
fluor-mediated method, electron-rich di- and tri-
substituted benzenes were used as starting materials to
obtain the corresponding ArI(OAc)2 in good yields.
However, it seems that this method cannot be applied
for benzene, mono-substituted benzenes, and electron-
deficient arenes, judging from the Selectfluor-mediated
iodination of arenes.16 During the course of our system-
atic studies on effective and easy preparations of
ArI(OAc)2, we have already devised two methods for
their synthesis from iodoarenes.17 Herein, we wish to
Keywords: (Diacetoxyiodo)arenes; Arenes; Elemental iodine; Potas-
sium peroxodisulfate; Hypervalent iodine; Oxidation.
*
Corresponding author. Tel./fax: +81 952 28 8550; e-mail: kitamura@
cc.saga-u.ac.jp
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.09.009

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Md. D. Hossain, T. Kitamura / Tetrahedron Letters 47 (2006) 7889–7891
report a direct, easy method for the preparation
of (diacetoxyiodo)benzene from benzene. Also we
describe the application to toluene and less reactive
halobenzenes.
of (diacetoxyiodo)benzene. The reaction of 10- or 50-
fold scale to that in entry 2 did not lead to the decrease
in the yield (entries 3 and 4). Toluene also gave 4-
(diacetoxyiodo)toluene in good yield. Interestingly, are-
nes bearing weakly deactivated groups such as chloro,
bromo, and fluoro groups gave (diacetoxyiodo)arenes
in good yields. In order to broaden the scope of this
reaction, we conducted the oxidation of xylene, mesityl-
ene, and tert-butylbenzene. Actually these substrates
underwent the oxidation reaction. However, we found
that these reactions resulted in the formation of iodosyl-
benzene derivatives, respectively. Therefore, it is consid-
ered that relatively electron-rich property of these
compounds causes hydrolysis of (diacetoxyiodo)arenes
during the reaction or the workup procedure. This
method was not applicable for arenes with strong elec-
tron-donating groups. For example, naphthalene and
anisoles were quickly oxidized in the reaction mixtures,
but the reaction resulted in the decomposition and the
formation of tarry products. This method was also unaf-
fected for arenes with strong electron-withdrawing
groups such as trifluoromethyl and nitro groups due to
their decreased reactivity.
In our laboratory, we found a direct and efficient
method for preparing ArI(OAc)2 in good yield from
the corresponding arenes with iodine in AcOH, using
commercial potassium peroxodisulfate, K2S2O8, as the
oxidant.18 The results are given in Table 1. Addition
of concd H2SO4 is essential to generate (diacetoxy-
iodo)arenes. Trifluoromethanesulfonic acid was also
effective but H2SO4 was convenient for handling and
workup. K2S2O8 is used as a strong oxidizing agent in
many applications. It has the particular advantages of
being almost non-hygroscopic, a particularly good
storage stability, and is easy and safe to handle. The
oxidation of arenes to (diacetoxyiodo)arenes can be
easily scaled up, given the advantages of K2S2O8 out-
lined above, together with the complete absence of
effluent or byproduct problems. The essence of our
novel method is described in Scheme 2.
The oxidative reactions shown in Scheme 2 were carried
out at 40 ꢁC, in a mixture of AcOH, C2H4Cl2, iodine,
and concd H2SO4. The presence of K2S2O8 (in stoichio-
metric quantities) in the reaction mixture was indis-
pensable because without its addition the oxidation
reactions did not proceed. When K2S2O8 was replaced
for sodium peroxodisulfate, Na2S2O8, the final yields
of ArI(OAc)2 were lowered by ca. 20–25%. Attempt to
use NaBO3 for this preparation was unsuccessful. De-
crease in the amount of AcOH did not affect the yield
Mechanistically, there are two possible routes for gener-
ating (diacetoxyiodo)arenes, as shown in Scheme 3:
Route A: iodination of arenes, followed by diacetoxyl-
ation leading to (diacetoxyiodo)arenes;
Route B: generation of triacetoxyiodine(III), followed
by electrophilic aromatic substitution to give
(diacetoxyiodo)arenes.
The latter route may be suitable because I(OAc)3 is a
reactive electrophile and reacts with aromatics. Accord-
ing to Shreeve’s result,15 I(OAc)3 is only effective for tri-
substituted electron-rich aromatics such as mesitylene
and 1-tert-butyl-3,5-dimethylbenzene. In our case,
however, our method is effective for benzene and
electron-deficient, less reactive halobenzenes. Therefore,
a plausible route is the former one.
Table 1. Direct synthesis of (diacetoxyiodo)arenes from arenesa
Entry Arene
Time (h) Product
Yield (%)
1
Benzene
20
24
28
30
12
PhI(OAc)2
PhI(OAc)2
PhI(OAc)2
PhI(OAc)2
4-MeC6H4I(OAc)2 70
4-ClC6H4I(OAc)2 71
4-BrC6H4I(OAc)2 70
4-FC6H4I(OAc)2 69
73
70
66
64
2b
3c
4d
5
Benzene
Benzene
Benzene
Toluene
Chlorobenzene 20
Bromobenzene 20
Fluorobenzene 20
6
7
8
In order to detect the intermediate iodoarene in route A,
we examined the reaction with a less amount of K2S2O8.
When benzene was reacted with iodine in the presence of
2 equiv of K2S2O8 under the same conditions, iodobenz-
ene was formed in 66% yield, together with 21% yield
a The reaction of an arene (1.18 mmol) was carried out in AcOH
(5 mL), I2 (0.5 mmol), C2H4Cl2 (2 mL), and H2SO4 (4 mmol) in the
presence of K2S2O8 (5 mmol) at 40 ꢁC.
b Benzene (1.18 mmol), AcOH (2 mL), I2 (0.5 mmol), C2H4Cl2 (2 mL),
H2SO4 (4 mmol), and K2S2O8 (5 mmol).
c Benzene (11.8 mmol), AcOH (20 mL), I2 (5 mmol), C2H4Cl2 (20 mL),
H2SO4 (40 mmol), and K2S2O8 (50 mmol).
d Benzene (59.0 mmol), AcOH (100 mL), I2 (25 mmol), C2H4Cl2
(100 mL), H2SO4 (200 mmol), and K2S2O8 (250 mmol).
Scheme 2.
Scheme 3.

Md. D. Hossain, T. Kitamura / Tetrahedron Letters 47 (2006) 7889–7891
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18. General procedure (Table 1, Scheme 2): A solution of an
appropriate arene (1.18 mmol) in a mixture of AcOH
(5 mL), C2H4Cl2 (2 mL), concd H2SO4 (4 mmol), and I2
(0.5 mmol) was heated with stirring to 40 ꢁC for 15 min.
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synthesis was conducted for (diacetoxyiodo)benzene in a
similar manner. A solution of benzene (4.62 g, 59 mmol) in
a mixture of AcOH (100 mL), C2H4Cl2 (100 mL), concd
H2SO4 (200 mmol), and I2 (6.34 g, 25 mmol) was heated
with stirring to 40 ꢁC. Next, K2S2O8 (250 mmol) was
added portionwise over 20 min and the stirring was
continued for 30 h. Workup of the reaction mixture gave
the purified product (10.79 g, 64%).
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