Ap p lica tion of F u n ction a l Ion ic Liqu id s
P ossessin g Tw o Ad ja cen t Acid Sites for
Aceta liza tion of Ald eh yd es
Dongmei Li,†,‡ Feng Shi, J iajian Peng, Shu Guo, and
†
†
†
Youquan Deng*,†
F IGURE 1. Acetalization reactions with acid functional ionic
liquid as catalyst.
Centre for Green Chemistry and Catalysis, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China, and State Key Laboratory of
Applied Organic Chemistry, Lanzhou 730000, China
4
in a mutually cis position, and all these studies offered
us the possibility of designing suitable catalysts for this
reaction.
On the other hand, because of the great potential of
room temperature ionic liquids as environmentally be-
nign media for catalytic processes, much attention has
Received J une 19, 2003
5
Abstr a ct: Several acid functional ionic liquids, in which
cations possess two adjacent acid sites, were synthesized and
used for the acetalization of aldehydes with good catalytic
performance under mild reaction conditions.
currently been focused on the organic reactions catalyzed
with or in ionic liquids, and many organic reactions,
especially in the reactions promoted with acid-base
catalysts, were performed in ionic liquids with high
6
performances. At the same time, the acidic ionic liquid
The acetalization reaction is a process that is widely
used in organic synthesis to protect the carbonyl group
of aldehydes and ketones. Afterward, acetals became
3
used in previous literature was usually based on AlCl ,
which was not stable, and the reusability was also
1
7
difficult. Recently, the syntheses of “task-specific” ionic
important reactants for synthesis of enantiomerically
pure compounds which were widely used as steroids,
pharmaceuticals, and fragrances. Previously, the cata-
liquids with special functions according to the require-
ment of a specific reaction have become an attractive
field.8 Herein, according to the requirement of the
catalysts for the acetalization reactions as mentioned
above, a series of acid functional ionic liquids with two
adjacent acid sites, i.e., the acid group introduced and
the N in the imidazolium, were synthesized and used
for the acetalization reactions with good results (Figure
1).
2
lysts used in the acetalization reactions were generally
proton acids, Lewis acids, and a number of transitional
3
metal complexes including Rh, Pd, and Pt. Although
+
good results were obtained, the separation of the products
from the catalyst system after the reaction was still
difficult to overcome and the noble metal catalysts used
4
were quite expensive and usually unstable. Therefore,
Our new approach reported here involves the use of
to design and synthesize a catalytic system that may be
stable, easily separable, and reusable has long been
pursued. Furthermore, the basic requirements for achiev-
ing high catalytic activity, as it was reported in previous
literature, were the presence of sufficient acidity and the
existence of two adjacent acid sites to have the reactants
room temperature ionic liquids based on -CO
and -SO H, Figure 2. All chemical reagents were puri-
fied by distillation before use. The ionic liquids [AcMIm]-
Cl, [AcBIm]Cl, [AcOIm]Cl, [(CH SO HMIm]CF SO
[(CH SO HMIm]TSO, and MIm(CH SO were synthe-
2
H, -SOCl,
3
2
)
4
3
3
3
,
2
)
4
3
2
)
4
3
sized according to the procedures reported in previous
literature.8
b,e,f
*
To whom correspondence should be addressed. Fax: +86-931-
8
277088.
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†
Chinese Academy of Sciences.
State Key Laboratory of Applied Organic Chemistry.
‡
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0.1021/jo034859l CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/21/2004
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J . Org. Chem. 2004, 69, 3582-3585