Facile preparation of benzylic iodides under solvent-free conditions using microwave irradiation

Article abstract of DOI:10.1081/SCC-120037924

Benzylic alcohols are rapidly converted to the corresponding benzylic iodides using combination of p-toluenesulfonic acid (PTSA) and potassium iodide under solvent-free microwave irradiation conditions.

Full text of DOI:10.1081/SCC-120037924

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Facile Preparation of Benzylic Iodides Under
Solvent‐Free Conditions Using Microwave Irradiation
a
a
a
Jong Chan Lee , Jin Young Park & Eun Sang Yoo
a
Department of Chemistry, Chung‐Ang University, Seoul, 156‐756, South Korea
Published online: 20 Aug 2006.
To cite this article: Jong Chan Lee , Jin Young Park & Eun Sang Yoo (2004): Facile Preparation of Benzylic Iodides Under
Solvent‐Free Conditions Using Microwave Irradiation, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:11, 2095-2099
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w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 11, pp. 2095–2099, 2004
Facile Preparation of Benzylic Iodides
Under Solvent-Free Conditions Using
Microwave Irradiation
*
Jong Chan Lee, Jin Young Park, and Eun Sang Yoo
Department of Chemistry, Chung-Ang University, Seoul, South Korea
ABSTRACT
Benzylic alcohols are rapidly converted to the corresponding benzylic
iodides using combination of p-toluenesulfonic acid (PTSA) and potass-
ium iodide under solvent-free microwave irradiation conditions.
Key Words: Benzylic alcohols; Iodides; Microwave; p-Toluenesulfonic
acid.
INTRODUCTION
Benzylic iodides have recently attracted increasing attention as versatile
intermediate in organic synthesis.
[1,2]
Conversion of benzylic alcohols into
*
Correspondence: Jong Chan Lee, Department of Chemistry, Chung-Ang University,
Seoul 156-756, South Korea; Fax: þ82-2-825-4736; E-mail: jclee@cau.ac.kr.
2
095
DOI: 10.1081/SCC-120037924
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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2
096
Lee, Park, and Yoo
benzylic iodides can be achieved using a number of reagent systems which
[4]
[3]
include methanesulfonic acid/NaI, KI/boron trifluoride diethyl etherate,
[5]
and cerium(III) chloride/NaI. However, these methods usually suffered
from one or more drawbacks such as use of excess organic solvents, employ-
ment of toxic reagents, or long reaction times.
In continuation of our investigations on microwave promoted reactions
under solvent-free conditions, we now report a facile and efficient method
for synthesis of various benzylic iodides utilizing the reaction of benzylic
alcohols with potassium iodide in the presence of p-toluenesulfonic acid
(
PTSA) under microwave irradiation (Sch. 1). Treatment of benzylic alcohols
with KI (2.0 equiv.) and PTSA (1.5 equiv.) under microwave irradiation
readily provided benzylic iodides in high yields for 80 sec.
A variety of benzylic alcohols were converted into the corresponding
benzylic iodides as presented in Table 1. It is noteworthy to mention that
this method is generally applicable to the iodination of secondary and ter-
tiary benzylic alcohols (entries 5, 9, and 10) as well as primary benzylic
alcohols, which feature is hardly expected from the already existing
methods. The reactions are presumably occurred by initial PTSA induced
protonation of hydroxyl oxygen of benzylic alcohols followed by nucleo-
philic substitution by iodide ion. The analogous mechanism has been
suggested in the reaction of benzhydrol with carboxylic acids in the
[
6]
presence of PTSA.
In summary, we have developed a facile and rapid protocol for the
conversion of benzylic alcohols into benzylic iodides using solvent-free
microwave irradiation conditions. We believe this novel method can be served
as a useful alternative to the existing methods.
EXPERIMENTAL
All reactions were performed in a commercial domestic microwave
1
oven (Samsung RE-21C). H NMR spectra were obtained on Varian
Gemini 2000—a 300 MHz spectrometer. Mass spectra were recorded with a
Micromass Autospec system.
Scheme 1.

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Facile Preparation of Benzylic Iodides
2097
Table 1. Conversion of benzylic alcohols to benzylic iodides.
Substrate Product
a
Entry
Yield (%)
1
92
93
93
85
90
82
2
3
4
5
6
7
71
83
8
9
82
74
1
0
a
Isolated yield.
General Procedure
A mixture of benzylic alcohol (1.0 mmol), PTSA (0.285 g, 1.5 mmol), and
potassium iodide (0.332 g, 2.0 mmol) was placed in a 50 mL of glass tube. The
reaction mixture was inserted in an alumina bath inside a domestic microwave
oven and irradiated (850 W) four times for a period of 20 sec with 10 sec
intervals. On completion of the reaction, the product was extracted with
dichloromethane and washed with water. The organic layer was separated
and dried over MgSO . After evaporation of solvent, the product was purified
4
by flash column chromatography on silica gel using dichloromethane as eluent
to give pure benzylic iodide.
[
7]
1
Benzyl iodide (1a). M.p.: 23–248C (lit. 238C). H NMR (CDCl ) d:
3
þ
4
.42 (s, 2H), 7.24–7.35 (m, 5H); MS m/z: 218 (M ).

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098
Lee, Park, and Yoo
[8]
1
p-Chlorobenzyl iodide (2a). M.p.: 61–628C (lit. 62–638C). H NMR
þ
(
CDCl ) d: 4.40 (s, 2H), 7.22–7.32 (m, 4H); MS m/z: 252 (M ).
3
[9]
p-Methoxybenzyl iodide (3a). M.p.: 31–328C (lit. 32.5–32.88C).
H NMR (CDCl ) d: 3.73 (s, 3H), 4.42 (s, 2H), 6.76–7.28 (m, 4H); MS
þ
1
3
m/z: 248 (M ).
[7]
p-Nitrobenzyl iodide (4a). M.p.: 125–1268C (lit.
125–1278C).
H NMR (CDCl ) d: 4.48 (s, 2H), 7.51–8.17 (m, 4H); MS m/z: 263 (M ).
1
þ
3
[
10]
1
-(1-Iodoethyl)benzene (5a). B.p.: 1218C/5 Torr (lit.
70–808C/
Torr). H NMR (CDCl ) d: 2.19 (d, 3H), 5.38 (q, 1H), 7.21–7.44 (m, 5H);
I
2
MS m/z: 232 (M ).
3
þ
[8]
1
o-Nitrobenzyl iodide (6a). M.p.: 74–758C (lit. 73–758C). H NMR
þ
11]
(
CDCl ) d: 4.78 (s, 2H), 7.44–8.04 (m, 4H); MS m/z: 263 (M ).
3
[
3
,5-Dinitrobenzyl iodide (7a). M.p.: 90–928C (lit.
92–938C).
1
H NMR (CDCl ) d: 4.57 (s, 2H), 8.55 (s, 2H), 8.93 (s, 1H); MS m/z:
þ
3
3
08 (M ).
0
[12]
1
a,a -Diiodo-m-xylene (8a). M.p.: 105–1068C (lit.
1068C). H NMR
þ
(
CDCl ) d: 4.39 (s, 4H), 7.20–7.37 (m, 4H); MS m/z: 358 (M ).
3
[7]
1
Diphenyliodomethane (9a). M.p.: 70–718C (lit. 728C). H NMR
þ
(
CDCl ) d: 5.53 (s, 1H), 7.09–7.27 (m, 10H); MS m/z: 294 (M ).
3
[
13]
Triphenylmethyl iodide (10a). M.p.: 132–1338C (lit.
132–1338C).
1
þ
H NMR (CDCl ) d: 7.22–7.32 (m, 15H); MS m/z: 370 (M ).
3
ACKNOWLEDGMENT
This work was supported by the research grant of Chung-Ang University.
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1
Received in Poland December 12, 2003

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