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J. Iran. Chem. Soc., Vol. 7, No. 1, March 2010, pp. 114-118
JOUIRrNaAnLiaOnF THE
Chemical Society
A Rapid and Convenient Method for the Synthesis of Aldoximes under Microwave
Irradiation Using in situ Generated Ionic Liquids
a
b
A.R. Hajipoura, b, , F. Rafiee and A.E. Ruoho
*
aPharmaceutical Research Laboratory, College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran
bDepartment of Pharmacology, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI, USA
53706-1532
(Received 25 October 2008, Accepted 30 January 2009)
We have developed a chemoselective, simple and efficient method for the preparation of aldoximes using microwave
irradiation in the presence of tribenzylamine or 1,4-diazabicyclo[2.2.2]octane or 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane
bromide as bases and useful precursors for in situ generation of ionic liquids.
Keywords: Oxime, Hydroxylamine hydrochloride, Ionic liquid, Microwave irradiation
INTRODUCTION
simplified purification [9].
In recent years, ionic liquids have attracted intensive
interestfor their being a possible replacement of traditional
solvents for organic reactions, particularly in the area of green
chemistry, due to their advantageous properties, including
negligible vapor pressure and high thermal and chemical
stability. They have also been referred to as ‘designer
solvents’ as their physical and chemical properties could be
adjusted by a careful choice of cation and anion [10].
Microwave-assisted organic transformation coupled with
ILs has attracted attention because of enhanced reaction rates,
easier workup, and straightforward purification. The dipole
characteristics of IL translate into rapid excitation by
microwaves and consequently faster reactions [11].
In the past decade, there has been a great interest for
development of new ionic liquids (ILs) [12]. Recently
quaternary ammonium salts as ionic liquids were synthesized
in good to excellent yields [13]. The dabco-based IL has
shown wide electrochemical application as a highly stable
electrolyte for lithium ion rechargeable batteries, fuel cells,
capacitors, solar cells, actuators, and so on [14].
Oximes are highly crystalline materials and oximation is
very efficient method for characterization and purification of
carbonyl compounds. These compounds not only represent a
useful series of derivatives of carbonyl compounds but also
may be used as intermediates for the preparation of amides by
the Beckmann rearrangement [1], nitrones [2], hydroximinoyl
chlorides, nitrile oxide [3] and chiral ꢀ-sulfinyl oximes [4].
The usual method for preparation of oximes [5,6] involves
treatment of carbonyl compounds with hydroxylamine
hydrochlorides in a basic aqueous medium with adjusted pH.
Application of microwave heating technique has been
currently under intensive investigation [7] and has been
recently reviewed [8]. The advantages of using microwave
irradiation are: (a) decrease in the reaction time and (b) cleaner
reaction with straightforward work-up. The coupling of
microwave irradiation with ionic liquids enhance reaction
rates due to the ionic character of ionic liquids which make
them microwave active solvents with easier work-up and
*Corresponding author. E-mail: haji@cc.iut.ac.ir
In continuation of our effort to develop new methods in