Efficient and direct iodination of alkyl benzenes using polymer/HIO4 and I2 under mild condition

Article abstract of DOI:10.4314/bcse.v28i2.15

An efficient and rapid method has been found for the iodination of aromatic compounds using iodine and polymer-supported periodic acid (PSPIA) as an oxidant under mild aprotic conditions. The reagent after the completion of the reaction was easily removed by filtration and was regenerated for further use. This method has some advantages such as: mild reaction conditions, straight forward procedure, inexpensive method, high yields and one-pot conversion.

Full text of DOI:10.4314/bcse.v28i2.15

Bull. Chem. Soc. Ethiop. 2014, 28(2), 305-308.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v28i2.15
ISSN 1011-3924
 2014 Chemical Society of Ethiopia
SHORT COMMUNICATION
EFFICIENT AND DIRECT IODINATION OF ALKYL BENZENES USING
POLYMER/HIO4 AND I2 UNDER MILD CONDITION
Sepideh Bahrami-Nasab, S. Mohamad Reza Nazifi and Ali Reza Pourali*
School of Chemistry, Damghan University, Damghan 36715/364, Iran
(Received September 7, 2013; revised December 27, 2013)
ABSTRACT. An efficient and rapid method has been found for the iodination of aromatic compounds using
iodine and polymer-supported periodic acid (PSPIA) as an oxidant under mild aprotic conditions. The reagent
after the completion of the reaction was easily removed by filtration and was regenerated for further use. This
method has some advantages such as: mild reaction conditions, straight forward procedure, inexpensive method,
high yields and one-pot conversion.
KEY WORDS: Iodine, Polymer-supported periodic acid, Oxidant, Iodination
INTRODUCTION
Iodobenzene derivatives are valuable compounds in organic synthesis, medicine, and
biochemistry [1]. Iodine is an elemental halogen that has less reactive than the other halides in
electrophilic substitution reactions, therefore iodination of arenes by use of iodine is hard [2]. In
many methods some reagents like Lewis acids or an oxidizing agent may be needed to activate
the iodine for introducing into the ring [3-6]. The wide range of methods reported until now
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 some efficiency and
selectivity [7-10].
To continuation our previous works on the preparation and application of polymer-
supported reagents in iodination reactions and organic synthesis [11-17] we report here a
practical and efficient aromatic iodination. A combination of iodine and polymer-supported
periodic acid has been found to be an excellent reagent for the efficient iodination of aromatic
compounds. These reactions are carried out at 40 oC using CH3CN as the solvent.
EXPERIMENTAL
Materials and instrumentation. Chemicals were obtained from Merck and Fluka chemical
companies. All compounds were known and identified by comparison of their physical and
spectroscopic data with those of authentic samples. Melting points were determined in open
capillary tubes with a Buchi 510 apparatus. Mass spectra were recorded on Micro Mass UKLTD
spectra. NMR spectra were recorded on a Bruker DPX 400 MHz instrument. Poly(1,4-
phenylene-2,5-pyridinedicarboxyamide) was prepared according to literature [15].
Typical procedure. To a solution of 1,2-dimethylbenzene (0.106 g, 1 mmol) in acetonitrile (10
mL), iodine (1 mmol. 0.126 g) and polymer-supported periodic acid (0.6 g, 1.05 mmol) were
o
added and the mixture was stirred for 1 hour at 40 C. The reaction progress was monitored by
thin layer chromatography (TLC) using a mixture of ethyl acetate and n-hexane (1: 9 v/v) as
__________
*Corresponding author. E-mail: S.universal@yahoo.com

306
Sepideh Bahrami-Nasab et al.
solvent. After completion of the reaction, the mixture was cooled to room temperature and
filtered. The excess of iodine was removed from the filtrate by drop wise addition of sodium
bisulfite solution (1 M). The organic layers were separated, dried over magnesium sulfate,
filtered, and the solvent was removed by evaporation. The residue was purified by column
chromatography on silica gel using n-hexane and ethyl acetate. The related product was
obtained with 95% isolated yield, b.p.: 235 oC (lit. [18] b.p.: 234 oC).
4-Iodotoluene. 1H NMR (400 MHz, CDCl3) δ: 2.47 (s, 3H), 7.54 (dd, J = 7.6 Hz, 2H), 7.18 (dd,
J = 7.6 Hz); 13C NMR (400 MHz, CDCl3) δ: 21.3, 92.1, 134.6, 136.7,1 36.3 ppm; mass (m/z):
218 (M+), 127, 91 (100%), 65, 51.
1-Iodo-3,4-dimethylbenzene. 1H NMR (400 MHz, CDCl3) δ: 2.39 (s, 3H), 2.48 (s, 3H), 6.83 (d,
J = 7.2 Hz, 1H), 7.04 (dd, J = 7.2 Hz and 3.1 Hz, 1 H), 7.65 (d, J = 2.3 Hz, 1H) ppm; 13C NMR
(400 MHz, CDCl3) δ: 20.4, 21.5, 93.2, 132.3, 135.2, 136.1, 138.2, 139.8 ppm, mass (m/z): 232
(M+ 97%).
RESULTS AND DISCUSSION
It is noteworthy that polymer-supported periodic acid is a mild oxidizing reagent compared to
unsupported periodic acid ion. It is also a cheaper oxidizing reagent and can be prepared easier
comparable with the other oxidizing agent. Furthermore, using polymer-supported oxidant
provides the possibility of the 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. We first supported periodic acid on the poly(1,4-phenylene-2,5-pyridinedicarboxy-
amide) by stirring them in water at room temperature for 48 h. Then unsupported periodate was
removed by filtering and washing with H2O. Polymeric reagent was obtained and dried to afford
PSPIA (Figure 1) [15].
H
-
-
IO4
IO4
-
H
IO4
H
+
-
-
IO4
IO4
NH
H
H
CO
CONH
NH
-
-
IO4
IO4
n
-
-
H
IO4
IO4
H
P
H IO4
P
H
Figure 1. The structure of polymer-supported periodic acid.
I
P
I2
H IO4
/
CH3CN, 40 oC
X
X
X=alkyl
Figure 2. The direct iodination of alkylbenzenes.
By having weight of the polymeric reagent, we found that each gram of the reagent contains
1.75 mmol HIO4. Thus, we used 0.60 g of the polymeric reagent and iodine (1 mmol) for the
Bull. Chem. Soc. Ethiop. 2014, 28(2)

Short Communication
307
iodination of aromatic compound (1 mmol). We have studied direct iodination of arenes using
iodine and polymer-supported periodic acid under mild condition in CH3CN as an aprotic
solvent (Figure 2). A set of alkyl substituted benzenes were subjected to this iodination process
and monoiodination was achieved in each case with excellent yield of iodo product. The results
are summarized in Table 1.
Table 1. The iodination of alkylbenzenes with PSPIA/I2 in the presence of acetonitrile at 40 oC.
Mp/Bp(oC)
Yield a
(%)
Entry
1
Substrate
Product
Time (min)
90
Found.
Rep. [18]
32
33
Me
Me
I
80
Me
Me
235
234
2
60
95
Me
I
Me
Me
Me
111
110
3
4
75
60
85
95
Me
I
Me
I
114
112
Me
Me
Me
Me
Me
Me
29
30
Me
Me
I
5
60
85
Me
Me
112
112
Et
Et
I
6
7
90
75
90
83
256
258 [19]
tBu
tBu
I
Me
Me
286
-
8
9
90
85
80
I
I
Me
Me
281
-
120
a: The ratio of alkylbenzenes (mmol), acetonitrile (mL), PSPIA (g) and I2 (mmol) was 1:10:0.6:1.
The crude iodinated products that were obtained by this method were purified by column
chromatography over silica gel and authenticated by TLC. Finally the iodo products were
characterized by mass, 1H NMR and 13C NMR spectral studies.
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Sepideh Bahrami-Nasab et al.
CONCLUSION
In conclusion, this method is general, simple and efficient for iodination of alkylbenzenes. In
addition, simple workup, short reaction time and excellent yields are the other advantages of the
method, which makes it a useful addition to the available methodologies.
ACKNOWLEDGEMENT
We gratefully acknowledge the financial support from the Research Council of Damghan
University, Iran.
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