An efficient deprotection of oximes to carbonyls catalyzed by silica sulfuric acid in water under ultrasound irradiation

Article abstract of DOI:10.1016/j.ultsonch.2009.06.016

Deprotection of oximes to the corresponding carbonyl compounds in silica sulfuric acid/surfactant/paraformaldehyde system can be carried out in excellent yields at 50 °C in water under ultrasound irradiation.

Full text of DOI:10.1016/j.ultsonch.2009.06.016

Ultrasonics Sonochemistry 17 (2010) 14–16
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Short Communication
An efficient deprotection of oximes to carbonyls catalyzed by silica sulfuric acid
in water under ultrasound irradiation
*
Ji-Tai Li , Xian-Tao Meng, Bo Bai, Ming-Xuan Sun
College of Chemistry and Environmental Science, Hebei University, Key Laboratory of Analytical Science and Technology of Hebei Province, Baoding 071002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 May 2009
Received in revised form 25 June 2009
Accepted 29 June 2009
Deprotection of oximes to the corresponding carbonyl compounds in silica sulfuric acid/surfactant/para-
formaldehyde system can be carried out in excellent yields at 50 °C in water under ultrasound irradiation.
Ó 2009 Elsevier B.V. All rights reserved.
Available online 2 July 2009
Keywords:
Deoximation
Oxime
Paraformaldehyde
Silica sulfuric acid
Ultrasound irradiation
1. Introduction
Water offers many practical and economic advantages as a reac-
tion solvent including low cost, safe handling, and environmental
Recovery of ketone and aldehyde from oximes is an important
reaction because oxime serves as an efficient protective group for
carbonyls, which are extensively used for the purification of car-
bonyl compounds [1]. Since many valuable reactions have been
developed to prepare oximes from non-carbonyl compounds [2],
the regeneration of carbonyl compounds from oximes represents
a potential route for synthesis of ketones and aldehydes. Various
methods have been developed for the cleavage of oximes, such
as acid-catalyzed hydrolysis [3], oxidative deoximation [4], reduc-
tive deoximation [5] and deoximation of exchange of oximes with
other carbonyl compounds [6]. However, some of these methods
have suffered from different drawbacks such as requirements for
refluxing temperature, tedious work-up, drastic conditions, long
reaction times, undesired chemical yields and use of toxic reagent.
Silica sulfuric acid is an excellent candidate for sulfuric acid or
chlorosulfonic acid replacement in organic reactions without any
limitation such as destruction of acid sensitive functional groups,
use of rather toxic solvents and expensive reagents or solvents
[7]. Because of its advantages such as stable, reusable, cheap and
facile, silica sulfuric acid has been used as catalyst in some organic
reactions [8].
compatibility. In recent years, organic reactions conducted in aque-
ous media have received much attention from chemists [9] be-
cause of concerns about the environment [10]. Also, most organic
reactants including catalysts are insoluble in water, and the surfac-
tants, due to their hydrophobic and hydrophilic nature, form mi-
celles of the reactants and promote the reaction to occur in
water [11]. On the other hand, a large number of organic reactions
can be carried out in higher yield, shorter reaction time and milder
conditions under ultrasonic irradiation than at classical conditions
[12]. Recently, our laboratory reported the synthesis of oximes and
methylene dioximes under ultrasound irradiation [13]. Here, we
wish to report an efficient and simple procedure for deoximation
to the corresponding carbonyl compounds by silica sulfuric acid/
sodium dodecylsulfonate (SDS)/paraformaldehyde in water under
ultrasound irradiation (Scheme 1).
2. Method
2.1. Materials and measurements
The starting materials, oximes were prepared according to the
method reported in literatures [13a,13b,14]. Silica sulfuric acid
was obtained according to the method reported in literature [15].
Sonication was performed in Shanghai Branson-BUG25–06 ultra-
sonic cleaner with a frequency of 25 kHz. The reaction flasks were
immersed in every place of the cleaner in such way that the surface
* Corresponding author. Address: College of Chemistry and Environmental
Science, Hebei University, Wusi East Road No.180, Baoding 071002, PR China.
Fax: +86 312 5079628.
E-mail addresses: lijitai@hbu.cn, lijitai@mail.hbu.edu.cn (J.-T. Li).
1350-4177/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.06.016

J.-T. Li et al. / Ultrasonics Sonochemistry 17 (2010) 14–16
15
O
NOH
R2
NOH
H
SiO2_OSO3H
(HCHO)n
+
+
R1
R2
R1
H
SDS , H2O, u.s.
1a-l
2a-l
Scheme 1. Deoximation of oximes with paraformaldehyde under ultrasound.
of reactants is slightly lower than water in the cleaner, and the
temperature of the water bath was controlled by the addition or
removal of circulated water.
in the water bath of the ultrasonic cleaner at 50 °C for the period
as indicated in Table. The progress of the reaction was monitored
by thin layer chromatography. After the completion of the reaction,
silica sulfuric acid was removed by filtration, and the filtrate was
extracted with 15 mL ethyl acetate for three times. The combined
organic layer was dried over anhydrous sodium sulfate and fil-
tered. Ethyl acetate was evaporated under reduced pressure to give
the crude product, which was separated by column chromatogra-
phy on silica (200–300 mesh), eluted with petroleum ether or
2.2. General procedure
To a solution of oxime (1, 1 mmol) in water (5 mL), 0.075 g sil-
ica sulfuric acid (0.25 mmol), 0.060 g paraformaldehyde (2 mmol)
and 0.015 g SDS (5 mol%) was added. The mixture was irradiated
Table 1
The effect of the reaction conditions on deoximation of acetophenone oxime in water under ultrasound irradiation*.
Entry
(HCHO)n (mmol)
Catalyst (mmol)
Temp. (°C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
2
2
2
2
2
2
2
1.5
2.5
0.5
0.5
0.5
0
0.1
0.2
0.25
0.25
0.25
30
40
50
50
50
50
50
50
50
3.5
2.5
1.5
4
4
2
1.5
2.1
1.5
85
96
94
0
78
91
93
93
94
*
Substrate: acetophenone oxime, 1 mmol; H2O, 5 mL; irradiation frequency, 25 kHz.
Table 2
Deoximation of oximes in silica sulfuric acid/surfactant/paraformaldehyde system in water at 50 °C under ultrasound irradiation.a
Entry
Substrate
Time (h)
1.5
Product
Isolated yield (%)
93, 95b
a
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
NOH
NOH
NOH
NOH
NOH
O
b
c
3
1
2
2
92
95
97
80
O
Cl
Cl
O
d
e
O
H3CO
O2N
H3CO
O2N
O
f
1f
1.5
2.5
2f
93
80
NOH
O
g
1g
2g
CHO
NOH
OCH3
OCH3
h
i
1h
1i
2
2
3
3
3
2h
2i
81, 80b
87
NOH
H3CO
Cl
CHO
CHO
CHO
CHO
CHO
H3CO
Cl
NOH
NOH
NOH
j
1j
2j
80
k
l
1k
1l
2k
2l
79, 75b
49
O2N
O2N
O2N
O2N
NOH
a
Substrate: oxime, 1 mmol; (HCHO)n, 2 mmol; SiO2–OSO3H, 0.25 mmol; SDS, 0.05 mmol; H2O, 5 mL.
Silica sulfuric acid was reused for the third time.
b

16
J.-T. Li et al. / Ultrasonics Sonochemistry 17 (2010) 14–16
the mixture of petroleum ether and ethyl acetate (10:1). All of the
products are known compounds and were identified by compari-
son of their physical properties (melt point and boil point) and Rf
values with standard sample.
in good yields (Table 2, 1b–1d, 92–97%), whereas ketoxime con-
taining electron-withdrawing group gave the ketone in 80% yield
(Table 2, 1e). In addition, the catalyst can be reused for the third
time without significant decrease in activity (Table 2, 2ab, 2hb
and 2kb). It is noted worthy that no Beckmann rearrangement
product was obtained in present procedure.
3. Results and discussion
The effect of the reaction conditions on deoximation of aceto-
phenone oxime (1a) with paraformaldehyde catalyzed by silica
sulfuric acid in the presence of SDS under ultrasound irradiation
is summarized in Table 1.
As shown in Table 1, the reaction time was shortened from 3.5
to 1.5 h by changing the reaction temperature from 30 to 50 °C. The
results showed that the reaction temperature had a significant ef-
fect, and all other reactions were carried out at 50 °C under ultra-
sound irradiation.
4. Conclusion
In summary, we have found a facile and efficient method for the
deprotection of oximes by silica sulfuric acid/SDS/paraformalde-
hyde in water under ultrasound irradiation. The present procedure
avoided the use of organic solvent during the reaction, and silica
sulfuric acid as catalyst can be recyclable.
Acknowledgements
The effect of amount of silica sulfuric acid and paraformalde-
hyde on the reaction yields under ultrasound irradiation was also
investigated. As shown in Table 1, in the absence of silica sulfuric
acid, acetophenone oxime was treated for 4 h at 50 °C, no product
was examined by TLC, whereas the amount of silica sulfuric acid
was 0.1 mmol, acetophenone was obtained in 78% yield within
the same time. By increasing the amount of silica sulfuric acid from
0.2 to 0.25 mmol, the reaction time required was shortened from 2
to 1.5 h. When decreasing the amount of paraformaldehyde from 2
to 1.5 mmol, longer reaction time was necessary to obtain the
same yield. Further addition of an amount of silica sulfuric acid
or paraformaldehyde had no effect on the deoximation of aceto-
phenone oxime under ultrasound irradiation. Thus the optimum
amount of silica sulfuric acid and paraformaldehyde was 0.25
and 2 mmol, respectively.
In order to verify the effect of ultrasound irradiation, we also did
the experiments under silent conditions. The deoximation of 1a
and 1c was carried out by stirring for 3 and 2.5 h at 50 °C, 2a and
2c were obtained in 92% and 94% yields, respectively. When under
ultrasound irradiation, 2a and 2c were obtained in 93% and 95%
yields with 1.5 and 1 h, respectively. It is apparent that deoxima-
tion of oximes can be finished in shorter time to get the same
yields under ultrasound irradiation. The reason may be the phe-
nomenon of cavitation produced by ultrasound [12].
From the results given above, the reaction conditions we chose
are as follows: oxime (1 mmol), silica sulfuric acid (0.25 mmol),
paraformaldehyde (2 mmol), sodium dodecylsulfonate (0.05
mmol), H2O (5 mL). Using this reaction system, we did a series of
experiments for deoximation of oximes under ultrasound irradia-
tion. The results are summarized in Table 2.
As shown in Table 2, deoximation of some oximes were carried
out in good yields with paraformaldehyde catalyzed by silica sulfu-
ric acid in the presence of SDS under ultrasound irradiation. The
different substituents in the benzene ring have some effects on
the yield. When ketoximes containing electron-donating group in
the benzene ring were used as substrates, ketones were obtained
Natural Science Foundation of Hebei Province (B2006000969),
China, supported the project.
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