Convenient and efficient method for the iodination of benzylic and aliphatic alcohols by using Al(HSO4)3/KI in nonaqueous solution

Article abstract of DOI:10.1080/00397910500330577

A simple and efficient method for the iodination of benzylic and aliphatic alcohols by using Al(HSO₄)₃/KI in n-hexane as solvent is reported. Mild reaction conditions and good to excellent yields of the products are the noteworthy advantages of the method. Copyright Taylor & Francis LLC.

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Convenient and Efficient Method for the
Iodination of Benzylic and Aliphatic Alcohols
by Using Al(HSO ) /KI in Nonaqueous Solution
4
3
a
a
b
a
Hassan Tajik , Farhad Shirini , Mohammad Ali Zolfigol & Faeze Samimi
a
Department of Chemistry, Guilan University, Rasht, Guilan, Iran
b
Department of Chemistry, Bu Ali Sina University, Hamadan, Iran
Published online: 21 Aug 2006.
To cite this article: Hassan Tajik , Farhad Shirini , Mohammad Ali Zolfigol & Faeze Samimi (2006) Convenient
and Efficient Method for the Iodination of Benzylic and Aliphatic Alcohols by Using Al(HSO ) /KI in
4
3
Nonaqueous Solution, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 36:1, 91-95, DOI: 10.1080/00397910500330577
To link to this article: http://dx.doi.org/10.1080/00397910500330577
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Synthetic Communications , 36: 91–95, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500330577
Convenient and Efficient Method for the
Iodination of Benzylic and Aliphatic
Alcohols by Using Al(HSO ) /KI in
4
3
Nonaqueous Solution
Hassan Tajik and Farhad Shirini
Department of Chemistry, Guilan University, Guilan, Iran
Mohammad Ali Zolfigol
Department of Chemistry, Bu Ali Sina University, Hamadan, Iran
Faeze Samimi
Department of Chemistry, Guilan University, Guilan, Iran
Abstract: A simple and efficient method for the iodination of benzylic and aliphatic
4 3
alcohols by using Al(HSO ) /KI in n-hexane as solvent is reported. Mild reaction
conditions and good to excellent yields of the products are the noteworthy advantages
of the method.
Keywords: Al(HSO ) , benzylic alcohols, benzylic iodides, iodination
4
3
Alkyl and aryl iodides are frequently used in organic chemistry for coupling
reactions and organometallic synthesis. They can also be employed as inter-
mediates in substitution and elimination reactions. Therefore, various
[1–4]
methods have been reported for the synthesis of these compounds, and
benzylic and aliphatic iodides can be obtained from the corresponding
Received in the UK April 28, 2005
Address correspondence to Hassan Tajik, Department of Chemistry, Guilan
University, Rasht, 41335-1914, Iran. E-mail: tajik@guilan.ac.ir and hasan_tajik@
yahoo.com
91

9
2
H. Tajik et al.
a
Table 1. Iodination of some benzylic and aliphatic alcohols with Al(HSO
b
in n-hexane
4
)
3
/KI
Time
(h)
Yield
c
(%)
Entry
1
Substrate
Product(s)
0.5
90
95
2
3
0.5
0.5
95
90
4
5
2.0
3.0
92
6
7
2.0
0.5
85
96
8
9
1.0
93
0.5
1.0
0.5
93
87
85
1
1
0
1
(
continued)

Iodination of Alcohols
93
Table 1. Continued
Time
(h)
Yield
c
(%)
Entry
Substrate
Product(s)
1
2
3
1.0
0.5
80
90
1
a
b
Molar ratio of substrate/Al(HSO
All of the reactions were performed at room temperature, except for the entries 4, 5,
4 3
) /KI, 1 : 1 : 1.2.
6
, and 10, which were performed under reflux conditions.
c
Isolated yield.
[
5]
.
alcohols by using a variety of systems such as ClSiMe /NaI, BF3 Et O/
3
2
[6]
[7]
[8]
[9]
.
BF Et O/KI,
.
CeCl3 7H O/NaI,
NaI,
(CH ) SiI,
Amberlist 15/NaI,
3
10]
2
2
[
[11]
and P I .
2 4
3
3
Despite the variety of methods, some of them suffer from drawbacks such
as contamination with side products, toxicity or low stability of the reagents,
long reaction times, harsh reaction conditions, and low yields. To overcome
some of the problems, new methods have been introduced in which low
toxicity, greater stability of the reagents, mild reaction conditions, higher
[12,13]
selectivity, and yields have been the focus of attention.
We report herein a mild and efficient method for the iodination of
benzylic and aliphatic alcohols by using potassium iodide as the iodine
[
14,15]
source and aluminium hydrogen sulfate
as solvent. The results are given in Table 1 (Scheme 1).
as the Lewis acid in n-hexane
We first examined the reactions at room temperature and, when
necessary, heated the mixture to reflux for the appropriate time. As shown
in Table 1, this system is suitable for benzylic iodination of benzylic
alcohols (Table 1, entries 1–9), and benzylic alcohols with electron-
donating or electron-withdrawing groups on the rings were iodinated success-
fully. However, the rate of reaction was slower when the ring contains an
electron-withdrawing group (Table 1, entries 4–8). The method can also be
Scheme 1.

9
4
H. Tajik et al.
employed for the conversion of aliphatic alcohols to the corresponding iodides
in good yields (Table 1, entries 10–12). 1-Adamantanol, a tertiary alcohol,
was converted to its iodide in good yield (Table 1, entry 13). The easy
procedure, simple workup, short reaction times, and excellent to good
yields of the products will make this method a useful addition to the
available methodologies.
EXPERIMENTAL
All of the products were characterized by comparison of their physical and
spectral data with those of the known samples or analyzing using GC or
mass spectrometry. All chemicals were purchased from the Merck or Fluka
Chemical Company. Aluminium hydrogen sulfate was prepared according
[14,15]
to the previously reported method.
Iodination of Alcohols with KI and Al(HSO ) in n-Hexane;
4
3
General Procedure
Al(HSO ) (1 mmol) was added to a mixture of alcohol (1 mmol) and KI
4
3
(1.2 mmol) in n-hexane (5 mL), and the resulting mixture was stirred at
room temperature for 0.5–1.0 h or refluxed for 1–3 h. The progress of
reaction was monitored by TLC (eluent: n-hexane/CCl , 1 : 2) or GC. After
4
completion of the reaction, the mixture was filtered, and the filtrate was
separated and diluted with n-hexane (5.0 mL). The resulting solution was
transferred to a separatory funnel and washed with aqueous solution of
Na S O (0.1 M, 10 mL) and then H O (10 mL). The organic layer was
2
2
3
2
separated and dried over anhydrous Na SO . Evaporation of the solvent
2
4
under reduced pressure gave the pure product. If necessary, the product was
purified by column chromatography (eluent: n-hexane/CCl , 1 : 2).
4
ACKNOWLEDGMENT
We are thankful to the Guilan University Research Council for the partial
support of this work.
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