Highly efficient Beckmann rearrangement and dehydration of oximes

Article abstract of DOI:10.1016/j.tetlet.2004.11.116

Under mild conditions, Beckmann rearrangement of a variety of ketoximes could proceed in the presence of chlorosulfonic acid using toluene as a solvent with excellent conversion and selectivity. This procedure could also be applied in the dehydration of aldoximes for obtaining the corresponding nitriles.

Full text of DOI:10.1016/j.tetlet.2004.11.116

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 671–674
Highly efficient Beckmann rearrangement and
dehydration of oximes
Dongmei Li, Feng Shi, Shu Guo and Youquan Deng*
Centre for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, China
Received 10 November 2004; revised 19November 2004; accepted 24 November 2004
Available online 10 December 2004
Abstract—Under mild conditions, Beckmann rearrangement of a variety of ketoximes could proceed in the presence of chlorosulf-
onic acid using toluene as a solvent with excellent conversion and selectivity. This procedure could also be applied in the dehydration
of aldoximes for obtaining the corresponding nitriles.
Ó 2004 Elsevier Ltd. All rights reserved.
1
7
1
. Introduction
tetrabutylammonium
perrhenate,
1
chlorosulfonic
acid–dimethyl formamide reagent, and antimony(V)
8
1
9
A great effort has been made to know, to lucubrate, and
to manufacture the amides and the transformation of
ketoximes to corresponding amides, known as the Beck-
mann rearrangement, is a common method, and is a
topic of current interest. As it is widely known, the
reaction generally requires relatively high reaction tem-
perature, strong acid, for example, concentrated sulfuric
salt, etc., as catalysts. Recently, the Beckmann rear-
2
rangement in supercritical water and ionic liquids
0
21
were also reported, however, the yield in supercritical
water was very low and the ionic liquid catalytic system
was very complicated. Therefore, the development of
simple, highly efficient, and highly selective Beckmann
rearrangement process was still highly demanded.
1
acid, which usually lead to large amounts of waste. On
these bases, milder conditions were tried and investiga-
tions on clean, simple, and highly efficient processes be-
came the chemists interesting undertaking. Needless to
say, vapor-phase Beckmann rearrangement was a very
important direction and many catalyst systems such as
At the same time, dehydration of oximes to nitriles is
also an important transformation in organic syntheses
and a number of methods have been developed
although the methods developed so far have their
own limitations. For example, the use of extremely
anhydrous reaction conditions, toxic, and hazardous
2
2
2
3
4
boria-hydroxyapatite, metal ilerite, supported oxide,
5
6
and zeolites including MCM-41, MCM-22, SAPO-
7
chemicals and the need of cumbersome work-up proce-
23–25
8
1
1, and MgCoAlPO-36 were reported. However, these
dures.
method is still continuing.
Therefore, the search for a more convenient
processes were mainly concentrated on the synthesis of
caprolactam and low selectivity or rapid decay of activ-
ity was generally resulted partially because of the high
reaction temperature. As for the liquid-phase process,
it usually proceeded under milder conditions and could
afford various amides, and good results have been ob-
We now wish to report a simple and efficient process for
Beckmann rearrangement of ketoximes to amides or
dehydration of aldoximes to nitriles using chlorosulfonic
acid in toluene, in which the mole ratio of chlorosulfonic
acid and oxime was 1:2 and it should be greener than the
sulfuric acid system currently used.
9
tained by using AlCl Æ6H O/KI/H O/CH CN, cyanuric
3
2
2
11
3
1
0
12
chloride/DMF, sulfamic acid, chloral, anhydrous
1
3
14
oxalic acid, solid metaboric acid, boron trifluoride
1
5
16
etherate,
O-alkyl-N,N-dimethylformamidium salt,
2. Results and discussion
Keywords: Beckmann rearrangement; Oxime; Dehydration; Chloro-
sulfonic acid; Catalysis.
The Beckmann rearrangement of a series of alkyl and
aryl ketoximes to corresponding amides was firstly con-
ducted (Scheme 1).
*
Corresponding author. Tel./fax: +86 931 4968116; e-mail: ydeng@
ns.lzb.ac.cn
0
040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.11.116

672
D. Li et al. / Tetrahedron Letters 46 (2005) 671–674
O
S
O
by GC–MS, it could be known that their main byprod-
OH
ucts were the corresponding ketones and only trace
amounts of dimeric oxime were observed (ꢀ0.1%).
Much better results could be obtained if aryl ketoximes
were used as substrates in Beckmann rearrangement
reaction. The conversions of acetophenone oxime and
its derivatives, for example, p-methyl acetophenone
oxime, p-methoxyl acetophenone oxime, m(p)-amino
acetophenone oxime, and m(p)-nitro acetophenone
oxime, all nearly 100% with selectivities >98% (entries
4–10). No obvious different activities exhibited between
m-amino (nitro) acetophenone oxime and p-amino
(nitro) acetophenone oxime although it was reported
previously that acetophenone oxime with p-position
HO
Cl
O
N
R
N
H
R1
R
R1
toluene
Scheme 1.
As it was shown in Table 1, moderate to good results
were obtained over Beckmann rearrangement of acetone
oxime, cyclopentanone oxime, and cyclohexanone oxime
entries 1–3). The conversion of these oximes all nearly
00%, however, the selectivities were only 43%, 64%,
and 72%, respectively. Based on the qualitative analysis
(
1
Table 1. Results of Beckmann rearrangement of ketoximes to amides in toluene
Entry
Oximes
Products
Conversion (%)
Selectivity (%)
OH
N
O
43
1
ꢀ99
N
H
OH
N
O
2
ꢀ99
64
NH
OH
N
O
N
3
4
ꢀ99
ꢀ99
72
98
OH
O
N
N
H
OH
O
N
5
6
7
8
9
ꢀ99
ꢀ99
ꢀ99
ꢀ99
ꢀ99
ꢀ99
ꢀ99
99
99
N
H
OH
O
N
H CO
3
N
H
H CO
3
OH
O
N
H N
2
98
N
H N
2
H
OH
O
N
H N
2
H2N
98
N
H
OH
O
N
O2N
99
N
O N
2
H
OH
O
N
O N
2
1
1
0
1
O2N
98
N
H
OH
O
N
ꢀ100
N
H

D. Li et al. / Tetrahedron Letters 46 (2005) 671–674
673
substitutes were more active than that with m-position
3. Conclusions
1
0
substitutes. As to the Beckmann rearrangement of
benzophenone oxime, a symmetrical oxime, its conver-
sion reached to ꢀ100% and no by-product was detected
after reaction except the desired amide (entry 11).
In conclusion, a simple and easily reproducible tech-
nique was developed for the Beckmann type or dehydra-
tion reaction of oximes, especially for aryl oximes, to
corresponding amides and nitriles. The method seems
to be convenient with respect to other reports and could
be used as a valid alternative.
The chlorosulfonic acid in toluene was also an efficient
and versatile alternate system for the dehydration of
aldoximes to nitriles (Scheme 2).
Under the same conditions, treatment of the aldoximes
with chlorosulfonic acid in toluene afforded the corre-
sponding nitriles rapidly and quantitatively (Table 2).
Excellent results over aryl aldoximes with different
substituted groups, for example, methoxyl, nitro, and
hydroxyl, were obtained, which conversions and selec-
tivities all nearly 100% (entries 1–6). Not as the low
selectivities obtained in Beckmann rearrangement reac-
tion of alkyl ketoximes, nearly 100% of conversion
and selectivity were achieved for the dehydration of
heptaldehyde oxime (entry 7).
4. Experimental
All solvents and reagents were A.R. and the aryl oximes
were recrystallized by ethanol/water before using to
remove the ketones/aldehydes because the hydrolysis
of aryl oximes usually occurred.
General procedure: for each reaction, the oxime
(12 mmol, 0.88 g ꢀ 2.36 g) and toluene (3 ml) were
charged into a 50 ml two mouth round-bottom flask
equipped with a magnetic stirrer and condenser. Then
the reactor was heated to 90 °C and chlorosulfonic acid
(
0.4 ml, 6 mmol) was added drop-wise to the mixture
from the other mouth of the round-bottomed flask.
The reaction was further reacted for 0.5 h and then the
resulted mixture was cooled to room temperature. In
order to achieve the isolated yields, 12 mmol of sodium
hydroxide was added to the resulted mixture to neutral-
ize the acid. Then adequate toluene was added to com-
pletely dissolve the product for analysis. Quantitative
O
S
O
OH
HO
Cl
N
R
N
R
H
toluene
Scheme 2.
Table 2. Results of dehydration of aldoximes to nitriles in toluene
Entry
Oximes
Products
Conversion (%)
99
Selectivity (%)
98
OH
H
N
1
N
OH
H
N
2
H CO
3
N
99
99
H CO
3
OH
H
N
N
3
4
99
99
99
99
OCH3
OCH3
OH
N
O N
2
N
O N
2
H
OH
H
N
O N
2
5
O2N
N
99
99
OH
H
N
N
6
7
99
99
99
99
OH
OH
OH
H
N
N

674
D. Li et al. / Tetrahedron Letters 46 (2005) 671–674
analyses were conducted with a HP 6890 GC equipped
with a FID detector. Qualitative analyses were con-
ducted with a HP 6890/5973 GC–MS with a chemstation
containing a NIST mass spectral database.
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Acknowledgements
This work was financially supported by the Natural Sci-
ence Foundation of China (No. 20233040).
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