Pronounced catalytic effect of micellar solution of sodium dodecyl sulfate (SDS) for regioselective iodination of aromatic compounds with a sodium iodide/cerium(IV) trihydroxide hydroperoxide system

Article abstract of DOI:10.1002/adsc.200505222

Micellar solutions of sodium dodecyl sulfate (SDS) catalyze the regioselective iodination of a wide range of aromatic compounds with sodium iodide in the presence of the easily prepared, water-resistant and recyclable cerium(IV) trihydroxide hydroperoxide, Ce(OH)₃O₂H, at room temperature. By this protocol, structurally diverse aromatic compounds including benzene and naphthalene were iodinated in good to excellent yields.

Full text of DOI:10.1002/adsc.200505222

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DOI: 10.1002/adsc.200505222
Pronounced Catalytic Effect of Micellar Solution of Sodium
Dodecyl Sulfate (SDS)for Regioselective Iodination of Aromatic
Compounds with a Sodium Iodide/Cerium(IV)Trihydroxide
Hydroperoxide System
Habib Firouzabadi,* Nasser Iranpoor,* Atefeh Garzan
Department of Chemistry, College of Sciences, Shiraz University, Shiraz, 71454, Iran
Fax: (þ98)-711-228-0926, e-mail: firouzabadi@chem.susc.ac.ir; iranpoor@chem.susc.ac.ir
Received: March 3, 2005; Accepted: September 5, 2005
Abstract: Micellar solutions of sodium dodecyl sul-
fate (SDS) catalyze the regioselective iodination of
a wide range of aromatic compounds with sodium io-
dide in the presence of the easily prepared, water-re-
sistant and recyclable cerium(IV) trihydroxide hy-
droperoxide, Ce(OH)3O2H, at room temperature.
By this protocol, structurally diverse aromatic com-
pounds including benzene and naphthalene were io-
dinated in good to excellent yields.
and has been investigated in detail for different reac-
tions in aqueous solutions.[6,7] However, micellar-aided
organic reactions are still at their preliminary stages. Re-
cently, we have reported the successful ring-opening of
epoxides with various types of nucleophiles[8] and Mi-
chael addition of amines and thiols to a,b-unsaturated
ketones in micellar solutions of sodium dodecyl sulfate
(SDS).[9]
Iodoarenes as valuable and versatile synthetic inter-
mediates have found wide applications in medicine
and biochemistry.[10,11] Due to the weaker electrophilic
nature of iodine than bromine and chlorine, and also
for otherreasons, the use of molecular iodine for the syn-
thesis of this important class of compound is not exten-
sively applied.[11–13] Except for Pb(OAc)4/HOAc,[14] the
other reported procedures such as vanadium salts/
CF3SO3H,[15] KMnO4/H2SO4,[16] HIO4/H2SO4.[17,18] in-
Keywords: aromatic compounds; cerium(IV) trihydr-
oxide hydroperoxide; iodination; sodium dodecyl
sulfate; sodium iodide
Regarding environmental problems and pollution, clean clude highly powerful oxidizing agents which are used
organic reaction processes which do not use harmful or- in strongly corrosive acidic media. Some other reported
ganic solvents are encouraged and are in great demand methods suffer from using not easily available com-
today.[1] Water as a cheap and relatively green solvent pounds and others use highly corrosive, toxic or expen-
could be considered as an alternative reaction media sive reagents. Examples are: I2/HgX2,[12a] I2/Ag2SO4,[19]
,
for organic processes.[2,3] However, water with its physi- NaI/CF3SO3H.[12b] Other milder procedures used for
cal and chemical properties imposes selectivity and re- the direct iodination of aromatic compounds are
activity in reactions conducted in this media which can- NaOCl/NaI,[20] Fe(NO3)3 ·1.5 N2O4/charcoal.[21]
not be observed in organic solvents.[4] However, the heat
We now introduce a system composed of cerium(IV)
capacity of water is not favourable and isolation and dry- trihydroxide hydroperoxide [Ce(OH)3O2H][22] and so-
ing of the product sometimes encounter serious prob- dium iodide as a cheap, easily prepared, stable, regener-
lems especially, for large-scale operations. Moreover, able system for the direct iodination of aromatic com-
organic solvents are still used in most organic reactions pounds in micellar aqueous media. Aqueous solutions
for the reasons given below; first of all, most organic sub- of sodium dodecyl sulfate (SDS) at its critical micellar
strates are not soluble in water, therefore, it cannot play concentration (CMC) catalyze the direct regioselective
the role of reaction medium. Second, many reactive sub- iodination of structurally diverse aromatic compounds
strates, catalysts, reagents and products of the reactions including benzene and naphthalene at room tempera-
are not stable in water and are decomposed or deactivat- ture (Scheme 1).
ed in aqueous media. One way to surmount the solubil-
In order to optimize the reaction conditions we chose
ity problem is the use of surface-active compounds anisole (1 mmol) as an activated aromatic compound
which are able to form micelles or vesicular structures which was reacted with Ce(OH)3O2H (1 mmol) and
in aqueous reaction media.[5] The use of micellar and NaI (1 mmol) in dry CH3CN (4 mL) at room tempera-
vesicle-forming surfactants as catalysts is widespread ture for 24 h. Work-up of the reaction mixture resulted
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benzene is not an easy task and, in most of the methods,
it proceeded under harsh conditions with low yields.[23]
In this report, benzene was iodinated with NaI/
Ce(OH)3O2H system at room temperature in 80% yield
after 3 h in SDS micellar media (Table 1, entry 7). Using
this micellar effect, chloro- and bromobenzenes can be
also easily iodinated at room temperature in good yields
(Table 1, entries 9 and 10). We have also observed the
formation of the ortho isomer of the iodinated com-
pounds in 2–8% in the reaction mixture.
Scheme 1.
The regeneration of Ce(OH)3O2H is of practical and
in 4-iodoanisole in only 10% yield. Other solvents such economical importance. The regeneration can be easily
as CH2Cl2 and CHCl3 were also tested but were com- achieved by the filtration of the pale yellow solid residue
plete failures. Then we decided to run the reaction in wa- of the cerium species from the reaction mixture. This
ter. The results show that 4-iodoanisole was produced in residue upon washing with H2O2 (35%) produces the or-
5% yield after 24 h. We have also studied a similar reac- ange-red powder of Ce(OH)3O2H immediately in al-
tion in a mixture of CH3CN and water (1/1 by volume). most quantitative yield. This regenerated reagent is as
After 24 h, 4-iodoanisole was detected (GC) in only reactive as the freshly prepared one.
20% yield.
In conclusion, in this study, we have reported the re-
Next, we performed the iodination of anisole gioselective iodination of benzene, naphthalene and
(1 mmol) with NaI (1 mmol) and Ce(OH)3O2H some other aromatic compounds catalyzed by SDS sol-
(1 mmol) in 4 mL SDS micellar solution at its CMC ution at its CMC using the NaI/Ce(OH)3O2H system at
(8.1Â10À3 M) at room temperature. This reaction pro- room temperature. The protocol could be considered as
ceeded well and produced 4-iodoanisole in 97% yield af- a relatively eco-friendly procedure which proceeded
ter 1.5 h with high regioselectivity (Table 1, entry 1). We purely in water.
believe that this rate enhancement is due to the strong
catalytic activity of the vesicle of the droplets of micellar
SDS. The pronounced effect of micellar SDS solution in
the reaction could be explained as follows: molecules of
Ce(OH)3O2H, sodium iodide and the aromatic com-
pound are accumulated inside the vesicle of the droplets
of micellar SDS in which the distance between the react-
ing species could decrease drastically which facilitates
the progress of the reaction and rate enhancement is ob-
Experimental Section
Typical Procedure for Iodination of Anisole with NaI
To a mixture of anisole (1 mmol, 0.108 g) and NaI (1 mmol,
0.150 g) in 4 mL SDS micellar solution at its CMC (8.1Â
10À3 M), cerium(IV) trihydroxide hydroperoxide (1 mmol,
served. The similar hydrophobic nature of the aryl io- 0.224 g) was added at room temperature. After 1.5 h, the reac-
tion mixture was treated with Na2S2O4 solution (10%, 10 mL)
and extracted with diethyl ether (2Â10 mL). This extract
was dried over anhydrous sodium sulfate. After filtration and
evaporation of the solvent, the crude product was obtained.
Further purification was performed using chromatography
over a short column of silica gel which, after evaporation of
the solvent, afforded the desired pure p-iodoanisole; yield:
dide product with the hydrophobic core of the micellar
droplet could be considered as another factor for the
rate enhancement of the reaction. These explanations
are schematically presented in Figure 1.
We therefore applied similar reaction conditions to
benzene, naphthalene and other benzenes substituted
with electron-releasing and electron-withdrawing
groups (Table 1). The strong feature of this procedure
is the preparation of the iodobenzene in good yield.
1
0.227 g (97%). H NMR (250 MHz, CDCl3): d¼3.80 (s, 3H,
OCH3), 6.94 (d, J¼8.5 Hz, 2H, Ar), 7.28 (d, J¼8.5 Hz, 2H,
Ar); 13C NMR (63 MHz, CDCl3): d¼55.2, 87.2, 113.9, 138.2,
The synthesis of iodobenzene by direct iodination of 160.7.
Figure 1.
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Adv. Synth. Catal. 2005, 347, 1925 – 1928

Regioselective Iodination of Aromatic Compounds
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Table 1. Iodination of aromatic compounds with NaI and
Ce(OH)3O2H in SDS micellar solution at its critical micellar
concentration (CMC) at room temperature.
Acknowledgements
We are thankful to Iran Chapter of TWAS based at ISMO and
ShirazUniversity Research Council and the Grant No. 503614
from the Ministry of Science, Research and Technology of
Iran for the support of this work.
Entry Substrate
Product
Time [h] Yield [%][a]
1
1.5
1.5
2
97
96
87
93
95
94
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Adv. Synth. Catal. 2005, 347, 1925 – 1928