A mild and simple iodination of phenols with trichloroisocyanuric acid/I2/wet SiO2 system

Article abstract of DOI:10.1590/S0103-50532010000100002

Molecular iodine in the presence of trichloroisocyanuric acid and wet sio₂ has been utilized efficiently for iodination of phenols under mild reaction conditions.

Full text of DOI:10.1590/S0103-50532010000100002

J. Braz. Chem. Soc., Vol. 21, No. 1, 3-6, 2010.
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A Mild and Simple Iodination of Phenols
with Trichloroisocyanuric Acid/ I2 /Wet SiO2 System
Batool Akhlaghinia*,a,b and Marzieh Rahmanib
aDepartment of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
bSchool of Chemistry, Damghan University of Basic Sciences, Damghan, Iran
Iodo molecular na presença de ácido tricloroisocianúrico e solução aquosa de SiO2 foi utilizado
com eficiência na iodinação de fenóis em condições reacionais brandas.
Molecular iodine in the presence of trichloroisocyanuric acid and wet SiO2 has been utilized
efficiently for iodination of phenols under mild reaction conditions.
Keywords: iodination, trichloroisocyanuric acid, phenols, wet SiO2
Introduction
On the other hand, there is intense current research and
general interest in heterogeneous systems because of the
perceived opportunities such systems present for basic
research and because of the unquestioned importance they
haveinindustryandindevelopmenttechnologies.17Recently,
Zolfigol and co-workers18,19 reported the mononitration
and dinitration of phenols by using trichloroisocyanuric
acid/NaNO2/wet SiO2. Trichloroisocyanuric acid,20,21 which
used primarily as a disinfectant has found little application
in organic chemistry so far.22,23 Therefore, in continuation
of our study 24 we were interested in using this reagent
for the iodination of aromatic compounds when used in
conjunction with I2 and wet SiO2 in CH2Cl2.
Aromatic iodo compounds are important intermediates
for the synthesis of various pharmaceutical and bioactive
compounds.1,2 They are also useful in metal-catalyzed
cross coupling reactions, such as Heck, Stille and
Negishi reactions which are utilized in C–C and C–N
bond formation.3,4 However, direct iodination of aromatic
compounds is difficult due to the low electrophilicity
of molecular iodine compared to that of molecular
chlorine and bromine. Generally, arenes are iodinated
by iodine in the presence of a Lewis acid or an oxidizing
agent. Direct iodination methods have been reported
using various iodonium donating systems, such as NIS–
CF3SO3H,5 iodine–Ag2SO4,6 iodine–HgO,7 NIS,8 iodine–
tetrabutylammonium peroxydisulfate,9 n-BuLi–CF3CH2I,10
ICl,11 and triiodoisocyanuric acid.12-14 However, most of
these methods require toxic and costly reagents, high
temperatures and long reaction times. Thus it is desirable to
apply a simple, inexpensive and non-toxic reagent system
for iodination of aromatic compounds.
Our goal, in undertaking this line of work, was to
overcome the limitations and drawbacks of the reported
methods which mentioned above and moreover to develop
a high-yielding one-pot synthesis of iodo arenes using a
novel combination of reagents.
In addition, any reduction in the amount of liquid acids
needed and/or any simplification in handling procedures
would be highly convenient in terms of risk reduction,
economic advantage and environment protection.15,16
Results and Discussion
We wish to report a simple method for the effective
mono iodination of phenols by using trichloroisocyanuric
acid as a cheap commercially available reagent, iodine and
wet SiO2 under mild and heterogeneous conditions.
Initially, the test reaction was carried out on 4-hydroxy
benzaldehyde with trichloroisocyanuric acid/ I2/ wet SiO2
in CH2Cl2. 4-Hydroxy-3-iodo-benzaldehyde was obtained
immediately in 98% yield.
Different substituted phenols were also subjected
to iodination in the presence of trichloroisocyanuric
acid, I2, and wet SiO2 (50% m/m) in dichloromethane
(Scheme 1).
The iodo phenols were obtained immediately under
mild and completely heterogeneous conditions at room
temperature with 100% conversion (substrate consumption)
which determined by GC (Table 1).
*e-mail: akhlaghinia@ferdowsi.um.ac.ir, b_akhlaghinia@dubs.ac.ir

4
A Mild and Simple Iodination of Phenols with Trichloroisocyanuric Acid/ I2 /Wet SiO2 System
J. Braz. Chem. Soc.
O
direct iodination methods have been recently developed
using “I+” donating systems. Most of these methods require
hazardous or toxic reagents or high reaction temperature for
long reaction time. The fresh finely powder obtained from
mixingdistilledwaterandSiO2 (50%m/m)inthepresenceof
trichloroisocyanuricacidasacommerciallyavailablereagent
(slightly soluble in CH2Cl2) smoothly produces HOCl28 as
a mild oxidizing agent and isocyanuric acid as a highly
polar compound which is completely insoluble in CH2Cl2
and was adsorbed by silica gel. Electrophilic iodine “I+” is
generated in situ by the reaction of HOCl with molecular
iodine. Wet SiO2 acts as a heterogeneous effective surface
area for iodeniumionwhich makingefficientlywork-upeasy
(Scheme2). However, highlyiodocompoundswereobtained
by simple filtration and subsequent evaporation of the
solvent.
Cl
Cl
N
N
/I2/wet SiO2
O
OH
OH
I
O
N
Cl
CH2Cl2 , room temperature
R
R
Scheme 1
As expected, all the substrates undergo iodination
reactions and delivered mono iodo product in good to
excellent yields.
By far iodination of activated aromatic compounds
was carried out by using molecular iodine or iodide ions
together with an oxidizing agent. Oxidizing reagents can
degrade sensitive groups present in the substrate. Other
Table 1. Iodination of different substituted phenols using trichloroisocyanuric acid/I2/ wet SiO2 in CH2Cl2 at room temperature
Entry
Substrate
Producta
Isolated Yield / %
Entry
Substrate
Producta
Isolated Yield / %
1
97
7
97
2
98
8
9
94
98
98
95
3
4
97
98
10
5
6
95
98
11
aThe product was identified by the comparison of its physical constants and IR and NMR spectral data with those of an authentic sample (4-fluoro-2-
iodophenol, mp120-123 oC, Lit.25 mp 123-124oC, 4-chloro-2-iodo phenol, mp75-77 oC, Lit.26 mp 78oC, 1-(4-hydroxy-3-iodophenyl) ethanone, mp 151-154 oC,
Lit.27 mp 153-155 oC, 4-hydroxy-3-iodo-benzoic acid, mp171-174 oC, Lit.26 mp 173.5-174.5 oC, 4-hydroxy-3-iodo-benzaldehyde, mp 111-114 oC, Lit.15
mp 113-115 oC, 4-hydroxy-3-iodobenzonitrile 1HNMR (CDCl3) d 7.96 (d,1H), 7.54 (dd, 1H), 7.04 (d, 1H), 5.92 (s, 1H), 2-iodo-4-methyl phenol,1HNMR
(CDCl3) d 2.24 (s, 3H), 5.20 (br s, 1H, exchanges with D2O), 6.86 (d, 1H), 7.02 (dd, 1H), 7.46 (d, 1H).

Vol. 21, No. 1, 2010
Akhlaghinia and Rahmani
5
O
N
O
Cl
Cl
O
N
N
HN
HN
SiO2
HOCl
Cl
O
O
NH
O
+ H2O
+
HOCl
2I+
I2
SiO2
Scheme 2
Conclusions
4-hydroxy-3-iodo-benzaldehyde in 98% yield. mp111-
114ºC, (Lit.15 mp 113-115 oC ).
Recently, iodination of benzene, naphthalene and other
aromatic compounds using molecular iodine in the presence
of trichloroisocyanuric acid and wet SiO2 system was
investigated by us.24 This motivated us to use this mixed
reagent in iodination of electron rich aromatic compounds.
In this research iodination of different para-substituted
phenols were studied. All iodo phenols were obtained
rapidly and very efficiently in high yield. In conclusion we
have provided a simple method for the direct, regioselective
iodination of phenols. Cheapness and availability of
reagents, easy and clean work-up and high yields make
this method attractive for organic chemists.
Acknowledgments
We gratefully acknowledge the partial support of this
study by Damghan University Research Council.
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A Mild and Simple Iodination of Phenols with Trichloroisocyanuric Acid/ I2 /Wet SiO2 System
J. Braz. Chem. Soc.
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Received: January 8, 2009
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Web Release Date: September 11, 2009