One-step C=N, C=O bonds cleavage and C=O, C=N bonds formation over supported ionic liquid in water

Article abstract of DOI:10.1016/j.tetlet.2004.07.006

At ambient reaction temperature, the silica gel confined ionic liquid catalysts were perfectly combined with water as an effective catalytic system for simultaneous C=N and C=O bonds transformation with a TONs exceeding 300 mol mol^-1.

Full text of DOI:10.1016/j.tetlet.2004.07.006

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 6791–6794
One-step C@N, C@O bonds cleavage and C@O, C@N
bonds formation over supported ionic liquid in waterq
Dongmei Li, Feng Shi and Youquan Deng*
Centre for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China
Received 29 May 2004; revised 30 June 2004; accepted 5 July 2004
Abstract—At ambient reaction temperature, the silica gel confined ionic liquid catalysts were perfectly combined with water as an
effective catalytic system for simultaneous C@N and C@O bonds transformation with a TONs exceeding 300molmolÀ1
Ó 2004 Elsevier Ltd. All rights reserved.
.
Recently, interest has been growing in studying organic
reactions in water due to its natural abundance, the
inherent advantages as well as the increasing environ-
mental consciousness of the chemical community, which
led to the search for more efficient and environmentally
friendly methods for chemical synthesis.1 Many reac-
tions traditionally carried out in organic solvents, espe-
cially in which old bonds cleavage or new bonds
formation occurred, can be carried out in water now
with additional interesting features,2 while the need of
water-soluble catalysts usually inhibited its extensive
application. At the same time, on the basis of the highly
charged nature, ionic liquids, which combine good and
tunable solubility properties with the absence of measur-
able vapor pressure and excellent thermal and chemical
stabilities, have attracted significant attentions in recent
years3 and were widely recognized and accepted. Its fea-
sibility for replacing volatile organic solvents and toxic
catalysts in alkylation,4 polymerization,5 hydrogena-
tion,6 carbonylation,7 etherization,8 Heck reactions,9
carbon dioxide activation10 and Beckmann rearrange-
ment,11 etc., was successfully conducted. Unfortunately,
large amounts of organic solvents were usually used
both in the separation of product from the ionic liquid
and in the washing of the ionic liquid catalyst system
for reuse, which caused unamiable chemical processes.
Therefore, to develop a new process using supported
ionic liquid catalyst12 and water solvent together should
be highly desired because the application of organic sol-
vents can be avoided and the separation of ionic liquid
catalysts from the product can also be simplified.
Herein, we report a novel reaction, oxime transforma-
tion, in which the silica gel supported ionic liquid cata-
lysts and water media together were used. In this
process, remarkable features different from those deoxi-
mation13 (only one C@N bond cleavage) or oximation14
(only one C@N bond formation) reactions reported pre-
viously are that the C@N, C@O bonds (two chemical
bonds) cleavage and new C@O, C@N bonds (two chem-
ical bonds) formation occurred simultaneously (Fig. 1).
The same amounts of new ketone and oxime could be
obtained as the amounts of oxime and ketone con-
sumed, for example, the hydroxylamine from the oxime
was transferred into the given ketone stoichiometrically
with the formation of a new ketone.
The reaction between cyclohexanone oxime and acetone
was firstly conducted to investigate the possibility of
C@N and C@O bonds transformation using ionic liquid
catalysts, for example, DMImBF4, in water. Only 22.5%
of conversion was achieved when bulk ionic liquid
DMImBF4 was used as catalyst directly and similar
results were obtained if pure silica gel was used together
OH
OH
water
O
N
O
N
+
Keywords: Ionic liquid; Water; Supported.
q This work was financially supported by National Natural Science
Foundation of China (No. 20233040 and No. 20225309).
+
ionic liquid/
silica gel
R1
R2
R3
R4
R3
R4
R1
R2
*
Figure 1. C@N and C@O bonds transformation over ionic liquid/silica
gel in water.
Corresponding author. Tel./fax: +86-931-4968116; e-mail: ydeng@
ns.lzb.ac.cn
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.07.006

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D. Li et al. / Tetrahedron Letters 45 (2004) 6791–6794
Table 1. Results of C@N and C@O bonds transformation between cyclohexanone oxime and acetone over ionic liquid/silica gel in water
Entry
Ionic liquida
Con (%)b
Sel. (%)c
TONd
1
DMImBF4
22.5
93.8
93.1
92.8
94.0
92.1
ꢀ2
>99
>99
>99
>99
>99
>99
>99
>99
12
240
170
140
150
200
1.2
2
DMImPF6/silica gel
EMImPF6/silica gel
BPyBF4/silica gel
BMImBF4/silica gel
DMImBF4/silica gel
DMImBF4/silica gel
DMImBF4 + silica gel
3
4
5
6
7e
8f
22
12
a CMIm = 1-cetyl-3-methyl imdazolium; DMIm = 1-decyl-3-methyl imidazolium; BMIm = 1-butyl-3-methyl imidazolium; EMIm = 1-ethyl-3-methyl
imidazolium; BPy = N-butyl pyridinium.
b Conversions of cyclohexanone oxime.
c Selectivities to acetone oxime.
d TON = mole of oxime converted per mole of ionic liquid.
e Without addition of water as solvent.
f The silica gel was synthesized through same procedure as other catalysts without addition of ionic liquid.
with the ionic liquid DMImBF4 (Table 1, entry 1). The
catalytic activities of other ionic liquids such as
In order to investigate the universality of the catalyst,
DMImBF4 /silica gel was further used in C@N and
C@O bonds transformation reactions between several
other oximes and acetone. As it was shown in Table 2,
longer reaction time was needed to get good results
when using aromatic oximes, for example, p-methoxyl
benzaldoxime and p-nitro benzaldoxime, as reactants,
which conversions and selectivities were all nearly
100% (entries 1–2). At the same time, poor result was
obtained when using acetophenone oxime as reactant.
The conversion was only 31.0% after reacted for 96h
(entry 3), which may be attributed to the steric hin-
drance of acetophenone oxime. The results of C@N
and C@O bonds transformation reactions between ali-
phatic oximes and acetone were not so good as that
using aromatic oximes as reactants and the conversions
were only 74.8% and 92.1% when using acetaldehyde
oxime and butanone oxime, respectively (entries 4–5).
BMImBF4,
CMImBF4,
BMImPF6, DMImPF6,
CMImPF6, etc. were also investigated in this reaction,
and 10–30% of conversion and >99% of selectivity were
also achieved. In order to further improve the conver-
sion of the reaction, a series of silica gel confined ionic
liquid catalysts were synthesized and used in this reac-
tion, and >90% of conversions and nearly 100% selectiv-
ities were obtained (entries 2–6). The application of
water as solvent was also a key factor for the high cata-
lytic efficiency because the reaction could not proceed
effectively without addition of water (entry 7). It is
worthwhile to note that the TONs of the silica gel con-
fined ionic liquid catalysts were 10–20 times higher than
that using bulk ionic liquids as catalysts (entry 8). These
results suggested that some synergism occurred between
the silica gel and ionic liquids after confinement.
Table 2. Results of C@N and C@O bonds transformation between different kinds of oximes and acetone over catalyst DMImBF4/silica gel in watera
Entry
Oxime
Product
t (h)
Con. (%)
Sel. (%)
TON
OH
H
O
O
N
1
96
>99
>99
160
MeO
H
H
MeO
O2N
OH
H
N
2
3
96
96
>99
31.0
>99
>99
150
60
O2N
OH
O
N
OH
O
N
4
5
96
24
74.8
92.1
>99
>99
310
310
H
H
N
OH
O
a Same reaction condition as in Table 1 was used.

D. Li et al. / Tetrahedron Letters 45 (2004) 6791–6794
6793
Table 3. Results of C@N and C@O bonds transformation between different ketones (aldehydes) and acetone oxime over catalyst DMImBF4/silica
gel in watera
Entry
Ketone (aldehyde)
Oxime
t (h)
Con. (%)
95.1
Sel. (%)
>99
TON
320
OH
H
O
N
1
10
H
OH
O
N
2
18
94.6
>99
320
OH
O
N
3
4
6
95.2
16.0
>99
>99
320
50
OH
O
N
48
OH
H
O
N
5
3
93.6
>99
320
H
a Same reaction condition as in Table 1 was used.
In summary, a novel reaction for stoichiometrical trans-
formation of C@N and C@O bonds was effectively
developed over silica gel confined ionic liquid catalysts
O
OH
R1
R2
H2O
N
R1
Ionic liquid
/silica gel
OH
R2
using water as solvent with
.
a TONs exceeded
The supported ionic liquids were
OH
R4
H2N
H2O
N
300molmolÀ1
O
perfectly combined with water, which simplified the sep-
aration of ionic liquid catalysts from the products and
completely avoided the using of organic solvents.
R3
Ionic liquid
/silica gel
R3
R4
Figure 2. A possible procedure for C@N and C@O bond
transformation.
Ionic liquid/silica gel catalysts were synthesized as follow-
ing procedure: Ten millilitre of tetraethyl silicate
(TEOS), 1mL of ionic liquid and 7mL of ethanol were
added into a 100mL of conical flask, respectively. After
the formation of clean and homogeneous liquid mixture,
5mL of hydrochloric acid (5M) was added and the mix-
ture became coagulated gradually. After aged at 60°C
for 12h, the resulted solid mixture was dried in vacuum
for 3h with ca. 1–5mmHg vacuum at 150°C and 4–5g
solid catalyst samples were obtained, the contents of
ionic liquids in silica gel were 20–25wt%.
A series of oximes and acetone could also be obtained
efficiently through this method if using the correspond-
ing ketones and acetone oxime as reactants. The conver-
sion of acetone oxime was about 94–95% and
selectivities of acetone and corresponding oximes, for
example, benzaldoxime, butanone oxime and cyclohexa-
none oxime, were all >99% except that using acetophe-
none as reactant (Table 3, entries 1–4). An unexpected
result was obtained when using acetaldehyde as reac-
tant, which conversion reached to 93.6% if reacted for
3h (entry 5) while the conversion of acetaldehyde oxime
was only 74.8% between the C@N and C@O bonds
transformation of acetaldehyde oxime and acetone
under same reaction conditions.
Reaction conditions: Oxime (0.2g), catalyst (0.01g), ke-
tone or aldehyde (2mL) and water (6mL) were respec-
tively, added into a 25mL round bottom and stirred at
room temperature (ca. 20°C) for 2–96h. Qualitative
analyses were conducted with a HP 6890/5793 GC–
MS. Quantitative analyses were conducted with a HP
1790 GC. The results were given by the chemstation.
In consideration of all the results discussed above, it
could be conjectured that there was an equilibrium point
between the added and newly formed oximes and
ketones. A possible procedure for this process was given
in Figure 2. The deoximation of oximes in the presence
of water should be the first step, then the hydroxylamine
simultaneously reacted with the ketone/aldehyde pre-
sented, which behaves as hydroxylamine acceptors,
and the reaction stopped at the equilibrium point.
References and notes
1. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and
Practice; Oxford University Press, 1998.
2. (a) Li, C.-J. Chem. Rev. 1993, 93, 2023; (b) Wei, C.; Li,
C.-J. J. Am. Chem. Soc. 2003, 125, 9534.

6794
D. Li et al. / Tetrahedron Letters 45 (2004) 6791–6794
9. Deshmukh, R. R.; Rajagopal, R.; Srinivasan, K. V. Chem.
3. (a) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem.
Rev. 2002, 102, 3667; (b) Welton, T. Chem. Rev. 1999, 99,
2071.
4. Song, C. E.; Shim, W. H.; Roh, E. J.; Choi, J. H. Chem.
Commun. 2000, 1695.
5. Zhang, H.; Hong, K.; Jablonsky, M.; Mays, J. W. Chem.
Commun. 2003, 1356.
6. Boxwell, C. J.; Dyson, P. J.; Ellis, D. J.; Welton, T. J. Am.
Chem. Soc. 2002, 124, 9334.
Commun. 2001, 1544.
10. Shi, F.; Deng, Y.; SiMa, T.; Peng, J.; Gu, Y.; Qiao, B.
Angew. Chem., Int. Ed. 2003, 42, 3257.
11. Peng, J.; Deng, Y. Tetrahedron Lett. 2001, 42, 403.
12. (a) Mehnert, C. P.; Cook, R. A.; Dispenziere, N. C.;
Afeworki, M. J. Am. Chem. Soc. 2002, 124, 12932; (b)
Valkenberg, M. H.; deCastro, C.; Ho¨lderich, W. F. Green
Chem. 2002, 88.
`
7. Calo, V.; Giannoccaro, P.; Nacci, A.; Monopoli, A. J.
13. Bandgar, B. P.; Kunde, L. B.; Thote, J. L. Synth.
Commun. 1997, 27, 1149.
14. Abdulkarim, H. A. M.; Gopalpur, N. Tetrahedron Lett.
2003, 44, 2753.
Organomet. Chem. 2002, 645, 152.
8. Shi, F.; Xiong, H.; Gu, Y.; Guo, S.; Deng, Y. Chem.
Commun. 2003, 1054.