Acid-catalysed selective monoiodination of electron-rich arenes by alkali metal iodides

Article abstract of DOI:10.1081/SCC-200026240

The reaction of electron-rich arenes with alkali metal iodides such as sodium and potassium iodides in the presence of cone. H₂SO ₄ gives p-iodoarenes in high yields.

Full text of DOI:10.1081/SCC-200026240

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Acid‐Catalysed Selective
Monoiodination of
Electron‐Rich Arenes by Alkali
Metal Iodides
a
b
M. A. Pasha & Yi Yi Myint
a
Department of Chemistry, Central College
Campus , Bangalore University , Bangalore, 560
0
01, India
b
Department of Chemistry , Yadanabon
University , Myanmar
Published online: 10 Jan 2011.
To cite this article: M. A. Pasha & Yi Yi Myint (2004) Acid‐Catalysed Selective
Monoiodination of Electron‐Rich Arenes by Alkali Metal Iodides, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 34:15, 2829-2833, DOI: 10.1081/SCC-200026240
To link to this article: http://dx.doi.org/10.1081/SCC-200026240
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SYNTHETIC COMMUNICATIONS
Vol. 34, No. 15, pp. 2829–2833, 2004
Acid-Catalysed Selective Monoiodination of
Electron-Rich Arenes by Alkali Metal Iodides
1,* 2
M. A. Pasha and Yi Yi Myint
1
Department of Chemistry, Central College Campus, Bangalore
University, Bangalore, India
2
Department of Chemistry, Yadanabon University, Myanmar
ABSTRACT
The reaction of electron-rich arenes with alkali metal iodides such as
2 4
sodium and potassium iodides in the presence of conc. H SO gives
p-iodoarenes in high yields.
Key Words: Iodination; Arenes; Sodium iodide; Potassium iodide;
Conc. H SO .
2
4
INTRODUCTION
Iodination of organic compounds and the chemistry of organic iodides are
[1]
of interest as major chemical fields. Their industrial application is wide.
*
Correspondence: M. A. Pasha, Department of Chemistry, Central College Campus,
Bangalore University, Bangalore 560 001, India; E-mail: m_af_pasha@yahoo.co.in.
2
829
DOI: 10.1081/SCC-200026240
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

2
830
Pasha and Myint
Iodination is one of the classical reactions of aromatic compounds and has
been thoroughly investigated for both its theoretical and synthetic value.
The iodination reactions of aromatic structures have generated a wealth of
physico-organic data that define the structure–reactivity relationships and
[2]
the steric and electronic factors that control this system. Aromatic iodo com-
pounds are useful for the preparation of organometallic reagents and some are
potential intermediates for the synthesis of pharmaceutical and bioactive
materials. They are also useful in metal catalysed coupling reactions which
[3]
are widely applied in the preparation of complex molecules.
Since the iodine molecule is the least reactive among the halogens toward an
electrophilic substitution process, most of the synthetic effort has been placed in
[4]
converting molecular iodine into a more active species. Aromatic compounds
iodinated can be generally by iodine only in the presence of a Lewis acid, a
[5]
hydrogen iodide trap, or most commonly in the presence of an oxidizing agent.
The reagents reported for iodination of aromatic compounds include use
[
6]
[7]
[8]
[9]
of N-iodosuccinimide (NIS), I /Ag SO , I /Cr O , I /Pb(OAc) ,
2
[11]
2
4
2
2
3
2
2
[10]
I /TlOAc,
2
I /KI/Hg(OAc) ,
2
NaI/chloramine-T in methanol,
NaOCl/NaI in aqueous alcohol
[14]
2
[12]
[13]
medium,
and KI/HIO in H SO .
4 2 4
Most of these reagents are complex, costly or involve toxic heavy metal cat-
alysts with potential environmental problems due to the generation of hazar-
dous waste. In this paper, we wish to report an efficient, new environmentally
benign procedure for aromatic iodination.
Owing to the various synthetic utilities of aromatic halo compounds, an
attempt has been made in our laboratory to synthesize p-haloarenes from tetra-
[15]
alkylammonium halides in the presence of conc. H SO in high yields.
To
2
4
extend this reaction, we believe that alkali metal iodides can serve as iodinating
agents. We carried out the reaction of aromatic hydrocarbons with alkali metal
iodides such as sodium and potassium iodides in the presence of conc. H SO
2
4
and it was found that, iodination of arenes is possible with alkali metal iodides
Sch. 1).
The reaction of chlorobenzene and alkali metal iodides (NaI or KI) was
(
carried out at different reaction temperatures (258C, 408C, 608C, 808C,
Scheme 1.

Monoiodination of Electron-Rich Arenes
2831
1
008C, and 1208C) in the presence of conc. H SO . The reaction goes to
2
4
completion within 1.5 hr at 608C and p-chloroiodobenzene can be obtained
in high yields.
To generalise the iodination reaction of arenes, different substituted
aromatic hydrocarbons were chosen and the reaction was carried out under
similar reaction conditions (Table 1). From the table it is clear that, except
anisole, other arenes give iodination successfully in high yields.
Hot sulphuric acid is known to decompose sodium and potassium halides
[16]
with evolution of halogen molecule as shown below.
Iodine thus formed
reacts with arenes to give rise to iodoarenes as shown in Sch. 2.
In summary, a novel approach to iodination of arenes using alkali metal
iodides and conc. H SO has been described.
2
4
EXPERIMENTAL
Nicolet 400D FT-IR spectrophotometer was used for IR spectral analysis
and NMR spectra were recorded on a JEOL 90 FQ, Bruker AC 250 instrument.
Yields refer to the isolated yields of the products.
Table 1. Reaction of different substituted arenes with alkali metal iodides in the pre-
sence of conc. H
2
SO
4
at 608C.
Entry
Substrate
Metal halide
Product
Yield (%)
1
2
3
4
5
Chlorobenzene
Chlorobenzene
Toluene
NaI
KI
p-Chloroiodobenzene
p-Chloroiodobenzene
p-Iodotoluene
84
87
76
78
59
19
67
18
81
79
80
82
75
77
74
75
86
83
NaI
KI
Toluene
Anisole
p-Iodotoluene
NaI
i) p-Iodoanisole
ii) p-Iodophenol
i) p-Iodoanisole
ii) p-Iodophenol
p-Iodophenol
6
Anisole
KI
7
8
9
Phenol
Phenol
NaI
KI
p-Iodophenol
p-Iodoaniline
p-Iodoaniline
Aniline
Aniline
NaI
KI
1
1
1
1
1
1
1
0
1
2
3
4
5
6
o-Cresol
o-Cresol
Naphthalene
Naphthalene
2-Naphthol
2-Naphthol
NaI
KI
4-Iodo-2-methylphenol
4-Iodo-2-methylphenol
1-Iodonaphthalene
1-Iodonaphthalene
1-Iodo-2-naphthol
1-Iodo-2-naphthol
NaI
KI
NaI
KI

2
832
Pasha and Myint
Scheme 2.
Iodination of Arenes: General Procedure
Chlorobenzene (1.125 g, 10 mmol) and sodium iodide (3.0 g, 20 mmol)
were added to conc. H SO (1.96 g, 20 mmol) and then heated at 608C. The
reaction was monitored by TLC (light petroleum). After completion of the
2
4
reaction (1.5 hr), water (10 mL) was added and extracted with ether
(
3 Â 10 mL). The combined ethereal extract was washed with saturated
sodium bicarbonate solution, water, and dried over anhydrous sodium sul-
phate. Solvent was removed, the residue purified on silica gel using pentane
[17]
to give p-chloroiodobenzene (1.72 g, 90%), m.p. 548C (lit. m.p. 568C ).
ACKNOWLEDGMENTS
Yi Yi Myint thanks the Ministry of Education, Government of Myanmar,
the Bangalore University and Prof. S. Chandrasekaran of Indian Institute of
Science, Bangalore for providing NMR facilities and the Indian Council for
Cultural Relations for a fellowship and financial assistance.
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1
Received in India April 15, 2004