Convenient and efficient method for the iodination of aromatic amines by pyridinium iodochloride

Article abstract of DOI:10.1080/00397910801989659

A simple and efficient method for the iodination of aromatic amines using pyridinium iodochloride (PyICl) in methanol as solvent is reported. Mild reaction conditions, short reaction time, and good to excellent yields of the product are the noteworthy advantages of the method. Pyridinium iodochloride is an efficient solid iodinating reagent and can be handled safely. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910801989659

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Convenient and Efficient Method for the
Iodination of Aromatic Amines by Pyridinium
Iodochloride
Sandeep V. Khansole a , Subhash B. Junne a , Mudassar A. Sayyed a &
Yeshwant B. Vibhute a
a P. G. Department of Chemistry, Yeshwant Mahavidyalaya, Nanded, India
Published online: 09 May 2008.
To cite this article: Sandeep V. Khansole , Subhash B. Junne , Mudassar A. Sayyed & Yeshwant B. Vibhute
(2008): Convenient and Efficient Method for the Iodination of Aromatic Amines by Pyridinium Iodochloride,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
38:11, 1792-1798
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Synthetic Communicationsw, 38: 1792–1798, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910801989659
Convenient and Efficient Method for the
Iodination of Aromatic Amines by
Pyridinium Iodochloride
Sandeep V. Khansole, Subhash B. Junne, Mudassar A.
Sayyed, and Yeshwant B. Vibhute
P. G. Department of Chemistry, Yeshwant Mahavidyalaya, Nanded, India
Abstract: A simple and efficient method for the iodination of aromatic amines using
pyridinium iodochloride (PyICl) in methanol as solvent is reported. Mild reaction con-
ditions, short reaction time, and good to excellent yields of the product are the note-
worthy advantages of the method. Pyridinium iodochloride is an efficient solid
iodinating reagent and can be handled safely.
INTRODUCTION
Aromatic iodides have long been used in organic synthesis as versatile
intermediates that can be transformed to variety of functional groups.[1]
They can be easily functionalized through metal-catalyzed cross-coupling
reactions[2] in the synthesis of many interesting natural products[3] and
also bioactive material.[4] Iodoaromatic compounds are used in medicine
as drug or diagnostic aids, contractors,[5] and radioactively labelled
markers.[6] They also have importance in medicinal and pharmaceutical
research.[7]
In recent years, direct iodination methods have been intensively developed
using iodinium donating systems, such as iodine nitrogen dioxide,[8] iodine-
F-TEDA-[1-chloromethyl-4-fluoro-1, 4-diazoniabicyclo [2,2,2] octane-bis-
(tetrafluoroborate)][9] bis-N-iodosuccinimide,[10] iodine-di-iodine pentaoxide,[11]
mercury(II)-oxide-iodine,[12] iodine monochloride,[13] bis(pyridine)iodonium(I)
Received in India November 23, 2007
Address correspondence to Yeshwant B. Vibhute, P. G. Department of Chemistry,
Yeshwant Mahavidyalaya, Nanded, 431 602, India. E-mail: drybv@rediffmail.com
1792

Iodination of Aromatic Amines
1793
tetrafluorobrate CF3SO3H,[14] NIS-CF3SO3H,[15] iodine silver sulfate,[16] iodine-
mercury salts,[17] NaOCl-NaI,[18] iodine/Na2S2O8,[19] and iodine-(NH4)2S2O8-
CuCl2-Ag2SO4.[20]
Recently, in our previous communication, iodination of aromatic
compounds has been done by iodine and iodine acid as iodinating
agents.[21,22] We report here iodination of several aromatic amines using pyr-
idiuium iodochioride as iodinating agent.
The advantages of this method are easy preparation of reagent, no need of
catalyst, mild conditions, simple operation, and short reaction time with
excellent yield of product. Because the reagent is solid, it can be easily
weighted, has no hazardous effect, and is ecofriendly.
To illustrate the advantage of the proposed reagent, we chose several
reactive aromatic amines (Scheme 1). These reactions were carried out by
heating amines with pyridinium iodichloride on a water bath for 1 h using
methanol as solvent. A variety of reactive aromatic amines were investigated
for a reaction with PyICl (Table 1). The product was obtained in a regioselec-
tive manner, with iodination occurring at the electron-rich ortho or para
positions. When the ortho position was blocked with substituent, only iodina-
tion took place at the para position.
EXPERIMENTAL
General Procedures
Melting points were determined in an open capillary tube and are uncor-
rected. IR spectra were recorded in KBr on a Perkin-Elmer spectrometer.
1H NMR spectra were recorded on a Gemini 300-MHz instrument in
CDCl3 as solvent and TMS as an internal standard. Elemental analysis
was carried out on a Carlo Erba 1108 analyzer. All the products were ident-
ified by comparison of their spectral and physical data with those of the
known sample. The purity of products was checked by thin-layer chromato-
graphy (TLC) on silica-gel on silica gel polygram SIL UV 254 plates. All
amines and other chemicals were purchased from Merck Chemical
Company.
Scheme 1.

1794
S. V. Khansole et al.
Table 1. Physical and analytical data of iodoanilines
Sr. no.
1
Substrate
Product
Yield
75
Mp (8C) found (reported)
70 (70–73)[23]
2
3
90
85
40 (39–43)[24]
116 (115)[25]
4
83
122 (123)[26]
5
6
7
8
80
85
92
78
207 (208)[27]
95 (95–96)[23]
254 (259)[28]
77 (78)[29]
9
84
120
(continued)

Iodination of Aromatic Amines
1795
Table 1. Continued
Sr. no.
10
Substrate
Product
Yield
89
Mp (8C) found (reported)
58
11
12
13
76
77
81
120
255
80
Preparation of Pyridinium Iodochloride
To a solution of pyridine (7.9 g, 0.1 mol) in acetic acid, a solution of iodine
monochloride (16 g, 0.1 mol) in acetic acid was added slowly at 0 8C with con-
tinuous stirring. The pale yellow solid obtained was filtered, dried, and recrys-
tallised by ethyl alcohol. The purity of reagent was checked by thin-layer
chromatography (TLC).
General Procedure for Iodination of Aromatic Amines by
Pyridinium Iodochloride
Aromatic amine (1 mmol) and pyridinium iodochloride (1 mmol) were
dissolved in methanol (15 mL) and refluxed on a water bath for 1 h. The dark
yellow colors appeared in reaction mixture; the content was poured in ice-
cold water. The solid thus obtained was filtered and recrystallized from ethanol.
1
IR and H NMR Data of the Iodinated Products
2-Iodo, 5-nitroaniline: IR (cm21): 3355 (NH); 1611, 1550 (C55C). 1H NMR
(CDCl3) d: 4 (dd, 1H, 4 Ar-H), 7 (dd, 1H, 4 Ar-H). Anal. calcd. for

1796
S. V. Khansole et al.
C6H5IN2O2: C, 27.26; H, 1.89; I, 48.10; N, 5.33. Found: C, 27.20; H, 1.81; I,
48.23; N, 5.25.
1
2-Iodo, 5-chloroaniline: IR (cm21): 3311 (NH); 1604, 1518 (C55C). H
NMR (CDCl3) d: 4 (s, 2H, NH2), 7.4 (s, 1H, 2 Ar-H). Anal. calcd. for
C6H5IClN: C, 2845; H, 1.97; I, 50.19; N, 5.33. Found: C, 2834; H, 1.88; I,
50.30; N, 5.19.
2,5-Diodo, 4-methylaniline: IR (cm21): 3319 (NH), 1610, 1578 (C55C).
1H NMR (CDCl3) d: 2.2 (S, 3H, CH3), 4.25 (S, 2H, NH2), 7.5 (S, 2H, 2 and
6 Ar-H). Anal. calcd. for C7H7I2N: C, 23.39; H, 1.94; I, 70.75; N, 3.59.
Found: C, 23.49; H, 1.82; I, 70.67; N, 3.48.
4-Amino, 3-5-Diiodobenzoic acid: IR (cm21): 3345 (NH); 1609, 1546
1
(C55C). H NMR (CDCl3) d: 4.65 (S, 2H, NH), 7.85 (S, 2H, 3,5 Ar-H).
Anal. calcd. for C7H5I2NO2: C, 23.59; H, 1.28; I, 65.29; N, 3.59 Found: C,
23.47; H, 1.22; I, 65.34; N, 3.42.
2,5-Dichloro, 4-Iodoaniline: IR (cm21): 3355 (NH); 1611, 1550 (C55C).
1H NMR (CDCl3) d: 7.2 (dd, 1H, 4 Ar-H), 7 (dd, 1H, 4 Ar-H). Anal. Calcd.
for C6H4ICl2N: C, 25.01; H, 1.38; I, 44.09; N, 4.86. Found: C, 25.15; H,
1.43; I, 44.11; N, 4.73.
ACKNOWLEDGMENT
The authors are thankful to the principal Yeshwant Mahavidyalaya, Nanded,
for providing laboratory facilities. The authors are also thankful to the director
of Indian Institute of Chemical Technology (IICT), Hyderabad, for providing
spectra of synthesized compounds, and University Grants Commission (UGC)
Delhi, for providing a research grant.
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