Regioselective oxyiodination of aromatic compounds using potassium iodide and oxone

Article abstract of DOI:10.1081/SCC-120006002

A highly efficient, simple, mild and regioselective method for oxyiodination of aromatic compounds is reported. The electrophilic substitution of iodine generated in situ from KI as an iodine source and oxone as an oxidant for the first time.

Full text of DOI:10.1081/SCC-120006002

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REGIOSELECTIVE OXYIODINATION OF AROMATIC
COMPOUNDS USING POTASSIUM IODIDE AND OXONE®*
N. Narender a , P. Srinivasu a , S. J. Kulkarni b & K. V. Raghavan a
a Catalysis Group, Indian Institute of Chemical Technology, Hyderabad, 500007, India
b Catalysis Group, Indian Institute of Chemical Technology, Hyderabad, 500007, India
Published online: 16 Aug 2006.
To cite this article: N. Narender , P. Srinivasu , S. J. Kulkarni & K. V. Raghavan (2002) REGIOSELECTIVE OXYIODINATION OF
AROMATIC COMPOUNDS USING POTASSIUM IODIDE AND OXONE®*, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 32:15, 2319-2324, DOI: 10.1081/SCC-120006002
To link to this article: http://dx.doi.org/10.1081/SCC-120006002
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SYNTHETIC COMMUNICATIONS
Vol. 32, No. 15, pp. 2319–2324, 2002
REGIOSELECTIVE OXYIODINATION OF
AROMATIC COMPOUNDS USING
POTASSIUM IODIDE AND OXONEÕ
*
N. Narender, P. Srinivasu, S. J. Kulkarni,y
and K. V. Raghavan
Catalysis Group, Indian Institute of Chemical
Technology, Hyderabad-500007, India
ABSTRACT
A highly efficient, simple, mild and regioselective method for
oxyiodination of aromatic compounds is reported. The
electrophilic substitution of iodine generated in situ from
KI as an iodine source and oxoneÕ as an oxidant for the
first time.
Aryl iodides have widely been successfully used as synthetic intermedi-
ates in the formation of new carbon–carbon bonds via replacement of their
iodine atoms with electrophiles.[1] For more than a century, e.g., in the
synthesis of Fanta[2] and Heck,[3] more extensive progress has retarded
due to the lack of simple and reliable methods of their preparation.[4]
However, synthetic methods leading to aromatic iodides[5] by direct iodina-
tion of aromatic compounds are relatively limited compared with those of
*IICT Communication No. 4786
yCorresponding author. Fax: 0091-40-7173387/7173757; E-mail: sjkulkarni@iict.ap.
nic.in
2319
DOI: 10.1081/SCC-120006002
Copyright & 2002 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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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.

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OXYIODINATION OF AROMATICS
2321
Scheme 1.
The best results were obtained by using methanol as a solvent compared to
others.
We surveyed the iodination with various oxidants such as oxoneÕ,
tert-butylhydroperoxide, hydrogen peroxide and molecular O2. However,
oxoneÕ is far superior to the other oxidants. The role of oxoneÕ was
confirmed by conducting a blank experiment where the formation of iodo
compounds was not observed.
ArH þ KI þ 2KHSO5 ꢀ KHSO4 ꢀ K2SO4
ÀÀ! ArI þ KOH þ K2S2O8 ꢀ KHSO4 ꢀ K2SO4 þ H2O
2KHSO5 ꢀ KHSO4 ꢀ K2SO4 þ KI
ð1Þ
ÀÀ! KOH þ HOI þ K2S2O8 ꢀ KHSO4 ꢀ K2SO4
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ꢀ
ꢀ
2HOOSO3K ÀÀ! 2HO þ 2 OSO3K
ꢀ
KI þ 2HO þ 2 OSO3K ÀÀ! KOH þ HOI þ K2S2O8
ArH þ HOI À! ArI þ H2O
A typical oxyiodination of an aromatic compounds in the presence
of oxoneÕ proceeds according to the stoichiometry of Eq. (1). It is believed
that the iodination proceeds via the formation of hypoiodous acid.
The hypoiodous acid has higher instability due to pronounced ionic
nature and thus more reactivity towards the aromatic nucleus. The absence
of iodination of the ring methyl group (Table 1, Entries 11, 12 and 13) is
indicative of the electrophilic mechanism of the reaction rather than a
radical pathway.
OxoneÕ, in direct comparison, has a higher onset of decomposition
than hydrogen peroxide and liberates less energy. This reaction is performed
at lower temperature, which provides a larger margin of safety. Additionally
oxoneÕ is a solid, allowing for the addition of precisely weighed amounts of
reagent to be used in the reaction.
In conclusion, we have developed a novel system using oxoneÕ as an
interesting alternative to hydrogen peroxide in the oxidative iodination of