Selective para-iodination of methoxyarenes, phenols, and anilines with iodine in the presence of poly (4-vinylpyridine)-supported peroxodisulfate

Article abstract of DOI:10.1081/SCC-200031032

A mild and efficient method for the direct iodination of methoxyarenes, phenols, and anilines using iodine and poly (4-vinylpyridine)-supported peroxodisulfate in acetonitrile solution, is presented. Selective para-substitution and also, the rather general applicability of this system is the advantage of the method.

Full text of DOI:10.1081/SCC-200031032

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Selective Para‐Iodination of
Methoxyarenes, Phenols,
and Anilines with Iodine
in the Presence of Poly
(4‐Vinylpyridine)‐Supported
Peroxodisulfate
a
b
Hassan Tajik , Iraj Mohammadpoor‐Baltork
&
a
Hassan Rafiee Rasht‐Abadi
a
Department of Chemistry , Guilan University ,
Rasht, 41335‐1914, Iran
b
Department of Chemistry , Isfahan University ,
Isfahan, Iran
Published online: 10 Jan 2011.
To cite this article: Hassan Tajik , Iraj Mohammadpoor‐Baltork & Hassan Rafiee
Rasht‐Abadi (2004) Selective Para‐Iodination of Methoxyarenes, Phenols,
and Anilines with Iodine in the Presence of Poly (4‐Vinylpyridine)‐Supported
Peroxodisulfate, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:19, 3579-3585, DOI: 10.1081/
SCC-200031032
To link to this article: http://dx.doi.org/10.1081/SCC-200031032
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SYNTHETIC COMMUNICATIONS
Vol. 34, No. 19, pp. 3579–3585, 2004
Selective Para-Iodination of Methoxyarenes,
Phenols, and Anilines with Iodine in the
Presence of Poly (4-Vinylpyridine)-
Supported Peroxodisulfate
1
,
2
*
Hassan Tajik, Iraj Mohammadpoor-Baltork,
and Hassan Rafiee Rasht-Abadi
1
1
Department of Chemistry, Guilan University, Rasht, Iran
Department of Chemistry, Isfahan University, Isfahan, Iran
2
ABSTRACT
A mild and efficient method for the direct iodination of methoxyarenes,
phenols, and anilines using iodine and poly (4-vinylpyridine)-supported
peroxodisulfate in acetonitrile solution, is presented. Selective para-sub-
stitution and also, the rather general applicability of this system is the
advantage of the method.
Key Words: Iodination; Anilines; Phenols; Methoxyarenes; Poly
(
4-vinylpyridine)-supported peroxodisulfate.
*
Correspondence: Hassan Tajik, Department of Chemistry, Guilan University, Rasht
1335-1914, Iran; E-mail: tajik@guilan.ac.ir or hasan_tajik@yahoo.com.
4
3
579
DOI: 10.1081/SCC-200031032
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3
580
Tajik, Mohammadpoor-Baltork, and Rasht-Abadi
Selective iodination of aromatic compounds is an important reaction in
organic synthesis. In most of the methods some reagents like Lewis acids or
an oxidizing agent may be needed to activate the iodine for introducing into
[1–6]
the ring.
The wide range of methods reported so far revealed the lack
of an efficient and general enough procedure, but the reaction by iodine or
iodide in the presence of oxidants or Lewis acids is common and revealed
[
7–10]
some efficiency and selectivity.
n-butyltriphenylphosphonium peroxodisulfate as oxidizing agent with
We have recently reported the use of
[11]
molecular iodine in acetonitrile for iodination of aromatic compounds.
In
the course of our study on the nuclear iodination of aromatic compounds,
we have used poly (4-vinylpyridine)-supported peroxodisulfate and iodine
in acetonitrile under reflux conditions to iodinate some activated aromatic
compounds (Table 1). This system can be used successfully in order to
obtain the corresponding iodinated products (Sch. 1).
As shown in Table 1, aromatic ethers can be quantitatively and selectively
iodinated by this method in para position (Table 1, Entries 1–7). 1,2,3-
Trimethoxy benzene (Entry 5) was quantitatively monoiodinated by this
method, which was not reported in the previous work. Aromatic amines
(
Entries 8–10) were also successfully converted to the corresponding
p-substituted products. It is important to note that these compounds are
oxidized with a butyltriphenylphosphonium peroxodisulfate/iodine system
as reported previously by us. Phenols were converted to the corresponding
iodophenols selectively in para position (Table 1, Entries 11,12), which
were not achievable in our previous method. 2-Naphthol, however, was con-
verted to 1-iodo-2-naphthol (Entry 13). In some cases where the para position
is blocked, no reaction was observed even after a long reaction time (Table 1,
entry 14), and this is one of the advantages of this method over other methods
[
12–14]
reported in the literature.
In all of the cases, parallel reactions were performed to check the oxi-
dation products and no oxidation product was observed for all of the substrates
given in Table 1.
It is noteworthy that poly (4-vinylpyridine)-supported peroxodisulfate is
a mild oxidizing agent compared to unsupported peroxodisufate ion. It is also
a cheaper oxidizing agent and can be prepared easier compared with the other
oxidizing agent used in our previous work or other comparable reagents
reported in the literature. Furthermore, using polymer-supported oxidant pro-
vides the possibility of running the reaction to completion in the presence of
more than one equivalent ratio of the reagent to the substrate without serious
changes in the reaction products. In addition, in contrast to the other methods,
which mostly performed in aqueous solutions, these reactions were performed
in nonaqueous media and in the presence of polymer-supported oxidizing
agent in which the workup of the reaction mixture is easier. Most of the

Para-Iodination of Methoxyarenes, Phenols, and Anilines
3581
a
Table 1. Iodination of aromatic compounds with iodine and poly (4-vinylpyridine)-
supported peroxodisulfate in acetonitrile under reflux condition.
Percent Oxidant/
Time (h) conversion substrate
Entry
1
Substrate
Product(s)
8
7
100
100
2/1
2/1
2
3
b
c
6
5
72
2/1
4
5
100
2/1
7
100
2/1
1/1
6
7
5
2
100
100
1/1
1/1
8
9
0.3
3
100
100
c
2/1
(continued)

3
582
Tajik, Mohammadpoor-Baltork, and Rasht-Abadi
Table 1. Continued.
Percent Oxidant/
Time (h) conversion substrate
Entry
Substrate
Product(s)
1
0
1
0.4
2
100
66
2/1
2/1
b
1
1
2
1
2
100
2/1
1
3
4
100
–
2/1
1/1
1
No Reaction
10
a
Molar ratio of iodine/substrate 1 : 1.
Isolated yield.
Equiv. of iodine was added.
b
c
2
successful methods require hazardous or toxic reagents and need a long reac-
tion time. To the best of our knowledge there are no general, simple, and
reliable methods for the preparation of most iodoarens, especially a method
that reported such selectivity between the ortho and para positions of anilines,
[
15–19]
phenols, and methoxyarenes.
In conclusion, this method is general, simple, and efficient for iodination
of methoxyarenes, anilines, and phenols. In addition, simple workup and
excellent chemoselectivity and yields are the other advantages of the
method, which makes it a useful addition to the available methodologies.
Scheme 1.

Para-Iodination of Methoxyarenes, Phenols, and Anilines
EXPERIMENTAL
3583
All products were identified by comparison of their spectral and physical data
[20]
with those of the known samples. The purity of the products was checked by
thin-layer chromatography (TLC) on silica gel polygram SIL G UV 254 plates.
Potassium peroxodisulfate and also other chemicals were purchased from the
Merck chemical company. Poly (4-vinylpyridine), which was in the form of a
cross-linked polymer, was purchased from Fluka chemical company.
Preparation of Poly (4-Vinylpyridine)-Supported
Peroxodisulfate
To a solution of potassium peroxodisulfate (8.0 g) in distilled water
150 mL), 10 mL of concentrated hydrochloric acid was added. Poly (4-vinyl-
(
pyridine) (5 g) was added and the mixture was stirred for 2 h. The mixture was
filtered and the precipitate was washed with distilled water (4 ꢀ 20 mL). After
drying at 408C for 12 h, 8.6 g of the polymer-supported reagent was obtained.
0
.6 gram of the supported polymer was equal to 1.0 mmol peroxodisulfate.
Iodination of Aromatic Compounds with Iodine in the
Presence of Poly (4-Vinylpyridine)-Supported
Peroxodisulfate; General Procedure
To a solution of aromatic compound (1 mmol) in acetonitrile (5 mL),
iodine (1 mmol) and poly (4-vinylpyridine)-supported peroxodisulfate were
added and refluxed for 0.3–10 h. Progress of the reactions was monitored
by TLC (eluent: carbon tetrachloride/dimethyl ether, 4 : 2) or GC (capillary
column). The reaction mixture was cooled to room temperature and filtered.
The excess of iodine was removed from the filtrate by dropwise addition of
sodium bisulfite solution (1 M). Then dichloromethane (5 mL) was added
and the solution was transferred to a separatory funnel. The organic layer
was separated and dried over magnesium sulfate. Evaporation of the solvent
followed by column chromatography on silica gel gave the corresponding
compounds from good to excellent yields (Table 1).
ACKNOWLEDGMENT
We are thankful to the Guilan University Research Council for partial
support of this work.

3
584
Tajik, Mohammadpoor-Baltork, and Rasht-Abadi
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Received in Poland May 23, 2004