Regioselective iodination of aromatic compounds with potassium iodide in the presence of benzyltriphenylphosphonium perchlorate

Article abstract of DOI:10.1016/j.cclet.2011.12.010

A simple and efficient method for the selective iodination of various aromatic compounds by using potassium iodide in the presence of benzyltriphenylphosphonium perchlorate, is reported. This method provides several advantages such as good selectivity between ortho and para positions of aromatic compounds and high yields of the products.

Full text of DOI:10.1016/j.cclet.2011.12.010

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 261–264
www.elsevier.com/locate/cclet
Regioselective iodination of aromatic compounds with potassium
iodide in the presence of benzyltriphenylphosphonium perchlorate
b
a
Jalal Albadi a, , Masoumeh Abedini , Nasir Iravani
*
a Young Research Club, Gachsaran branch, Islamic Azad University, Gachsaran, Iran
b Department of Chemistry, College of Science, University of Guilan, Rasht, Iran
Received 24 August 2011
Available online 24 January 2012
Abstract
A simple and efficient method for the selective iodination of various aromatic compounds by using potassium iodide in the
presence of benzyltriphenylphosphonium perchlorate, is reported. This method provides several advantages such as good selectivity
between ortho and para positions of aromatic compounds and high yields of the products.
# 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Benzyl triphenylphosphonium perchlorate; Iodination; Aromatic compound; Potassium iodide
Aryl iodides are important intermediates for the synthesis of various pharmaceutical and bioactive compounds.
They can be used in Heck reactions as well as Still and Negishi cross couplings reactions and have found applications
in numerous medicinally and industrially valuable product [1,2]. Due to the low reactivity of iodine, direct iodination
of aromatic compounds is difficult and requires the presence of an activating agent such as oxidizing reagents to
produce a strongly electrophilic I+ species. In addition, direct iodination by iodine, generates hydrogen iodide, which
is corrosive, toxic and pollutes the environment. Various methods have been used for the iodination of aromatic
compounds which of them CAN/I2 [3], 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate/I2 [4], HIO3/I2 [5],
N-iodosaccharin [6], NH4I/H2O2 [7], I2/O2/H5PV2Mo10O40 [8], NaI/cerium(IV) trihydroxide/SDS [9], ICl/In(OTf)3
[10], NaClO2/NaI/HCl [11], and KI/tert-butyl hydroperoxide [12], pyridinium iodochloride (PyICl) [13], potassium
ferrate supported on montmorillonite [14], PVP-H2O2/KI or I2 [15]. However, in spite of their potential utility, the
practical application of most of these reagents suffers from disadvantages such as harsh reaction conditions, low
regioselectivity, the use of expensive or less easily available reagents, long reaction times, low yields and tedious
work-up. Therefore, due to importance of aryliodides, introduction of new methods for the preparation of these
compounds in terms of increase of the selectivity and also the yields of the para-products, potential simplicity, and
short reaction times, is still in demand.
1. Experimental
General: All products are known and therefore, their physical data are not reported. Products were identified by
comparison of their spectral and physical data with those of the known samples. Chemicals were purchased from
* Corresponding author.
E-mail address: J.albadi@iaug.ac.ir (J. Albadi).
1001-8417/$ – see front matter # 2011 Jalal Albadi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.12.010

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J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
Fluka, Merck, and Aldrich Chemical Companies. Benzyl triphenylphosphonium perchlorate, was prepared according
to the previously reported same method [18].
General procedure for iodination of aromatic compounds: A mixture of aromatic compound (1 mmol), benzyl
triphenylphosphonium perchlorate, (1 mmol) and potassium iodide (1 mmol) in acetonitrile (3 mL), was heated under
reflux conditions. After completion of the reaction (monitored by TLC), the reaction mixture was filtered and poured
into an aqueous sodium thiosulfate solution (1 mol/L) and extracted with dichloromethane (3ꢀ 5 mL). The organic
layer is dried over anhydrous calcium chloride. Evaporation of the solvent followed by recrystallization or column
chromatography on silica gel gave the corresponding iodinated compounds in high yields (Table 1).
Table 1
Iodination of aromatic compounds with KI in the presence of BTPPPC.
Entry
Substrate
Product
Time(h)
1
Yield (%)a
OCH
1
I
OCH
OCH
86
3
3
H C
3
H C
3
OCH
2
3
2
80
88
3
3
I
I
OCH
3
OCH
0.5
3
H CO
3
H CO
3
OCH
I
OCH
3
3
4
5
1
87
85
CH
CH
3
OCH
I
Cl
I
OCH
3
1.2
3
Cl
Cl
OCH
Cl
OCH
3
6
2
83
3
I
OH
OH
7
8
0.5
88
89
I
OH
OH
0.45
H C
H C
3
3
OH
I
OH
9
0.5
1
85
90
CH
CH
3
3
I
10
Cl
OH
Cl
OH
CH3
CH
3

J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
263
Table 1 (Continued )
Entry
Substrate
Product
Time(h)
3
Yield (%)a
H COC
3
OH
H COC
3
OH
11
12
13
14
75
77
80
78
I
I
OH
OH
3
NO
NO
2
2
O N
2
OH
O N
2
OH
4.5
I
I
O N
OH
6
2
O N
2
OH
NO
2
NO
2
15
16
OH
I
OH
1.2
0.3
87
90
Cl
Cl
OH
I
OH
HO
HO
17
18
19
0.5
2
85
86
72
N(CH3
)
2
I
N(CH3)2
I
CH3
CH3
5
COOH
COOH
I
a
Isolated yields.
2. Results and discussion
In continuation of our research on the halogenations of aromatic compounds [16], we herein, report the highly
efficient and selective iodination of aromatic compounds employing potassium iodide as the source of iodine and
benzyltriphenylphosphonium perchlorate (BTPPPC), as the oxidant in acetonitrile as solvent (Scheme 1).
At first, for the optimization of the reaction conditions, the iodination of anisole, using potassium iodide and
BTPPPC in various solvents was examined. The best result was achieved by caring out the reaction of anisole,
potassium iodide and BTPPPC (with 1:1:1 mol ratio) in acetonitrile under reflux conditions (Table 1, entry 1). Awide
range of aromatic compounds, were successfully reacted to afford the desired iodinated products. Results show that

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J. Albadi et al. / Chinese Chemical Letters 23 (2012) 261–264
R
R
KI/BTPPPC
CH3CN, reflux
I
Scheme 1.
compounds containing electron donating were found to be most reactive and converted to the corresponding mono-
iodinated products in shorter reaction times (Table 1, entries 1,3,7,17). However, the rate of reaction was slower when
the ring contains an electron-withdrawing groups (Table 1, entries 12,14,15). It has been observed that chemoselective
conversion of aromatic compounds to their para substituted products was achieved in excellent yield. When the para-
position was blocked, monoiodinated products were obtained over longer reaction times (Table 1, entry 2,6,11,13,14).
Anisole gave mainly the para isomer as the major product in short reaction time (Table 1 entries 1). However 4-methyl
anisole was iodinated after 2 h to afford 2-iodo-4-methylanisol (Table 1, entry 2). Phenol, ortho-cholorophenol, ortho-
cresol and ortho-nitrophenol were quantitatively converted to the para iodinated products with respect to the hydroxyl
groups in good yields (Table 1, entries 7,9,12,15). Plausible mechanism of the reaction is shown in Eq. (1), based on
the literature [17], our observations and obtained results.
1: ArH þ KI þ PhCH2PPh3ClO4 ! ArI þ KOH þ PhCH2PPh3ClO3
or
(1)
2: KI þ pHCH2PPh3ClO4 ! KOI þ PhCH2PPH3ClO3
KOI þ ArH ! ArI þ KOH
In conclusion, we have described an efficient method for the iodination of aromatic compounds using KI and
BTPPPC, under reflux conditions. Simple work-up, good chemoselectivity, high yields of the products and short
reaction time will make this procedure a useful addition to the available methods.
Acknowledgment
We are thankful to the Gachsaran branch, Islamic Azad University, for the partial support of this work.
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