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2320
NARENDER ET AL.
preparing aromatic chlorides and bromides because of the low electrophilic-
ity of iodine.
Although halogenation of aromatic compounds with halogens is well
known reaction, bromination and chlorination easily proceed with or some-
times without Lewis acid catalysts, but iodination usually more difficult to
take place. Except for active substrates, oxidizing reagents such as nitric
acid, iodic acid, sulfurtrioxide, sulfuric acid and hydrogen peroxide must
normally used in order to generate a better electrophile[6] by oxidation of
molecular iodine. It was also reported that the aromatic iodination with
molecular iodine was catalyzed by stoichiometric amounts of metal halides,
such as AlCl3–CuCl2,[7] or SbCl5,[8] and a direct iodination was carried out
by using NH4l catalytic amounts of NOBF4 in CF3COOH/CH2Cl2 or
CF3COOH/CH3COOH with molecular oxygen.[9] These procedures suffer
some deficiencies. The most serious of these are substrate limitations due to
reaction conditions and the loss of iodine from the reaction as hydrogen
iodide or metallic iodide.
We have designed a novel system to generate electrophilic iodine
in situ from easily available KI as an iodine source, commercially available
oxoneÕ as an oxidant for the oxyiodination as a possible alternative to
solve the disadvantages described in the earlier methods. In this commu-
nication we report a new method for the para selective oxyiodination of
aromatic compounds using oxoneÕ as an oxidant, and KI as an iodine
source.
Potassium peroxymonosulfate is an inexpensive and readily accessible
oxidizing agent. It is commonly used as OxoneÕ (2KHSO5ꢀKHSO4ꢀK2SO4)
and is a versatile oxidant for the transformation of a wide range of func-
tional groups.[10]
A number of different aromatic compounds were subjected to the
iodination reaction to test the generality of this method and the results
are presented in Table 1. These reactions proceeded efficiently under mild
conditions in methanol with high yields and regioselectivity with KI and
oxoneÕ. As Table 1 shows that the reaction gives high yields and para-
selectivity for a range of substituted benzenes of high activity. The results
in Table 1 indicate that activated aromatic compounds are more selective for
nuclear iodination. Introduction of an electron-withdrawing group on the
aromatic ring substantially decreases the rate of ring iodination (Table 1,
Entries 2 and 4) while on electron donating group increases it. 2-methoxy
naphthalene gives 1-iodo-2-methoxy naphthalene (Scheme 1). When the less
reactive aromatics such as nitro benzene, benzoic acid failed to undergo
iodination under the same reaction conditions.
A wide range of solvents has been used in these reactions including
carbon tetrachloride, hexane, dichloromethane, methanol and acetonitrile.