Sulfamic acid as a cost-effective and recyclable catalyst for liquid Beckmann rearrangement, a green process to produce amides from ketoximes without waste

Article abstract of DOI:10.1016/j.tetlet.2004.03.017

Sulfamic acid (H₂NSO₃H) has been proved to be an efficient and green catalyst for liquid Beckmann rearrangement of ketoxime in dried acetonitrile. The use of basic neutralization agent has been avoided in this system due to its intrinsic zwitterionic property. Thus it is a green process for preparation of amide from ketoxime without producing any waste.

Full text of DOI:10.1016/j.tetlet.2004.03.017

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 3369–3372
Sulfamic acid as a cost-effective and recyclable catalyst for
liquid Beckmann rearrangement, a green process to produce
amides from ketoximes without waste
*
Bo Wang, Yanlong Gu, Cheng Luo, Tao Yang, Liming Yang and Jishuan Suo
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, China
Received 12 February2004; revised 5 March 2004; accepted 5 March 2004
2 3
Abstract—Sulfamic acid (H NSO H) has been proved to be an efficient and green catalyst for liquid Beckmann rearrangement of
ketoxime in dried acetonitrile. The use of basic neutralization agent has been avoided in this system due to its intrinsic zwitterionic
property. Thus it is a green process for preparation of amide from ketoxime without producing any waste.
Ó 2004 Elsevier Ltd. All rights reserved.
The conversion of ketoxime into corresponding amide,
known as the Beckmann rearrangement, is a common
method used in organic chemistry and is also a topic of
neat desired product, so that the reaction can lead to
large amounts of byproducts. Therefore, it is necessary
to develop a green, simple, and cost-effective catalytic
system for Beckmann rearrangement of ketoxime.
1
current interest. It accomplishes both the cleavage of a
carbon–carbon bond and the formation of a carbon–
nitrogen bond, and represents a powerful method
particularlyfor manufacturing e-caprolactam in the
chemical industry. The reaction generally requires high
reaction temperature and strong acidic and dehydrating
2 3
Sulfamic acid (NH SO H, SA) is a dry, nonvolatile,
nonhydroscopic, odorless, and white crystalline solid
with an outstanding physical property and stability. The
crystal can be kept in the laboratory for many years
without change. It is commerciallyavailable and is a
verycheap chemical. Recentl y, it is shown that SA has
the prospect to be used as a substitute for conventional
acidic catalytic materials. Last year, it has been used as
an efficient heterogeneous acid catalyst for ketal for-
1
media, thus, the application of sensitive substrates is
usuallyimpeded in this reaction. On these basis, mild
conditions were tried and several interesting variants
2;3
were developed. Recently, the Beckmann rearrange-
ment was reported to be accomplished in ionic liquids at
4
5
6
room temperature. Nevertheless, until now the occur-
mation or acetalation and deprotection of acetals.
Subsequently, we reported sulfamic acid catalyzed tet-
rence of mild conditions was onlyrelated to the use of
rather toxic solvents and expensive reagents. On the
other hand, the problem, which is almost common to all
conventional catalytic systems, is that it is very difficult
to separate the product from the solution containing
catalyst, because there exists on the inevitable interac-
tion of acidic catalyst with basic substrates (including
ketoximes and amides), and as a result, a large amount
of basic neutralization agent has to be used to obtain a
7
rahydropyranylation of hydroxy compounds, esterifi-
cation of cyclic olefins with aliphatic acids under
8
solvent-free conditions, and transesterification of
9
b-ketoesters in ionic liquids. In those homogeneous
liquid reactions, SA is recyclable and is easy to handle as
a catalyst owing to its immiscibility with common
organic solvents, and the unique catalytic features and
intrinsic zwitterionic propertyof SA is verydifferent
from the conventional acidic catalyst, which prompted
2 3
us to explore further applications of NH SO H as an
acidic catalyst in other carbon–carbon and carbon–
heteroatom forming reactions. We report herein, for the
first time, sulfamic acid catalyzed liquid Beckmann
rearrangement of ketoximes to produce corresponding
amides without producing anywaste (Scheme 1).
Keywords: Beckmann rearrangement; Sulfamic acid; Ketoxime;
Amide; Green synthesis.
*
Corresponding author. Tel.: +86-931-8277635; fax: +86-931-82770-
8; e-mail: limy@ns.lzb.ac.cn
8
0
040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.03.017

3370
B. Wang et al. / Tetrahedron Letters 45 (2004) 3369–3372
O
organic solvents. For example, the treatment of ace-
tophenone oxime with sulfamic acid in acetonitrile
afforded the acetanilide in a selectivityof 98% with a
nearlycomplete conversion whereas the same reaction in
toluene give a mixture of acetophenone and acetanilide
in a ratio of 3:1 with a conversion of 60% of oxime
OH
N
H
2
NSO
3
H
R
1
N
H
R
2
CH
3
CN
R
1
R
2
Scheme 1. Sulfamic acid catalyzed liquid Beckmann rearrangement of
ketoximes.
(entries 2 and 3). Although all other polar organic sol-
vents are effective media for sulfamic acid catalyzed
Beckmann rearrangement, acetonitrile is proved to be
the best (entries 4–6). Chloride based imidazolium ionic
liquids, such as 1-butyl-3-methylimidazolium chloride
Initially, acetophenone oxime has been used as a sub-
strate to test the feasibilityof sulfamic acid used as a
catalyst for Beckmann rearrangement. Thus, treatment
of acetophenone oxime with sulfamic acid at 90 °C in
dried acetonitrile afforded a 96% yield of acetanilide
after 6 h of reaction. Better catalytic activity of sulfamic
acid was obtained with 10% of catalyst than with 5% or
without anycatal ys t (Table 1, entries 1–3). The only
by-product being confirmed is acetophenone, which is
derived from the deoximation of acetophenone oxime.
Subsequential experiments revealed that both 6 h and
(
[BMIm]Cl), has been used as a novel solvent for sul-
9
famic acid catalyst in our previous work. Unfortu-
nately, Beckmann rearrangement of acetophenone
oxime does not effectuallyproceed in [BMIm]Cl (entry
7
).
Since avoiding the production of waste in the product
separation procedure was the aim for developing a new
catalytic system, the isolation of acetanilide was also
attempted. It has alreadybeen manifested that sulfamic
acid was comprised not of the aminosulfonic acid form,
9
0 °C are necessaryto complete the reaction. When 4 h
or 60 °C is used, the yield of acetanilide is only 34.0%
and 30.0%, respectively(entries 4 and 5).
þ
ꢀ
but rather of H NSO zwitterionic units byboth X-ray
3
Table 2 shows the effects of different solvents on the
reaction of acetophenone oxime catalyzed by sulfamic
3
10
and neutron diffraction techniques. So, sulfamic acid is
immiscible with diethyl ether, and it can be precipitated
from the reaction mixture bydispersing it in a large
amount of diethyl ether. After filtration, a neat product
can be obtained byconcentrating the filtrate and fol-
lowed bythe elution of acetone using a chromatographic
column. Most importantly, no interaction was happen-
ing between the ketoximes and amides with sulfamic acid
catalyst, as a result, the neutralizing agent that is abso-
lutelynecessaril ,y can be avoided. This procedure is
significant from the viewpoint of avoiding pollution. The
separation procedure is shown schematicallyin Figure 1.
It appears that all solvents and catalyst are recyclable
and no waste is produced in Beckmann rearrangement of
acetophenone oxime over the sulfamic acid catalytic
system. Thus, the sulfamic acid/dried acetonitrile system
represents a substantial improvement over previous
acid at 90 °C. In CCl , the conversion of the substrate
4
proves to be quite high, almost 90%, but the selectivity
to acetanilide is only4% after 6 h (entry1). In contrast
to nonpolar organic solvents, high reaction rate and
improved selectivityare the features obtained in polar
Table 1. Sulfamic acid catalyzed Beckmann rearrangement of ace-
tophenone oxime in dryacetonitrile
H
OH
N
N
H
2
NSO
3
H
3
CH CN
O
a
EntryCat./oxime
%)
Temperature
(°C)
Time
(h)
Yield
(
11
1
2
3
4
5
10
5
90
90
90
60
90
6
6
6
6
4
96
27
0
methods, wherein an excess of bases (such as ammonia
water, Na CO , etc.) is required to affect the product
2
3
b
––
10
10
separation would produce a large amount of wastes at
the same time.
30
34
a
GC yield.
Without catalyst.
Table 3 shows the results of Beckmann rearrangement
of various ketoximes over H NSO H in dried aceto-
2 3
b
nitrile. It has shown that aryl ketoximes have higher
activitythan the others, and acetophenone oxime has
the best result among the oximes in this sulfamic acid
system (entry 1–4). Cyclohexanone oxime and cyclo-
pentanone oxime also provide moderate yields (entries 5
and 6). Using short chain aliphatic ketoximes, acetone
oxime, and butanone oxime, 47% and 53% of yields of
product is achieved bythis method (entries 7 and 8). It is
seen that the sulfamic acid/dried acetonitrile system has
good activityfor the Beckmann rearrangement of a
varietyof ketoximes, especiallyfor ar yl ketoximes.
Table 2. Sulfamic acid catalyzed Beckmann rearrangement of ace-
a
tophenone oxime in different solvents
b
c
EntrySolvent
Conversion (%)
Selectivity(%)
1
2
3
4
5
6
7
CCl
Toluene
4
90
60
99
85
92
70
––
4
25
98
76
50
25
––
3
CH CN
NMP
DMF
DEC
[BMIm]Cl
a
2 3
The reuse abilityof H NSO H was studied in this sys-
tem. The catalyst can be so easily separated by dis-
persing the reaction mixture in diethyl ether, that
Reaction conditions: 0.6 g (4.42 mmol) acetophenone oxime, 0.042 g
0.44 mmol) sulfamic acid, 90 °C, 6 h.
Conversion of acetophenone oxime.
Selectivityto acetanilide.
(
b
c
2 3
the recoveryand reuse of H NSO H could be very

B. Wang et al. / Tetrahedron Letters 45 (2004) 3369–3372
3371
9
6
0 ˚C
hours
disperse into
diethyl ether
H
N
H
2
NSO
+
3
H
2
3
H NSO H
OH
N
+
O
CH
3
CN
3
CH CN
Diethyl ether
+
CH CN
3
H
N
O
2
3
H NSO H
filtration
H
N
Diethyl ether
distillation
+
O
3
CH CN
sulfamic acid
to reuse
ether
elution with acetone
a chromatographic
column
H
N
O
Figure 1. Procedure of product separation in sulfamic acid catalyzed Beckmann rearrangement.
a
Table 3. Beckmann rearrangement of various ketoximes over sulfamic acid in dried acetonitrile
b
EntrySubstrate
Time (h)
Product
Yield (%)
HN
N
OH
N
1
6
8
96
95
O
OH
NH
2
3
4
O
N OH
OH
NH
NH
8
8
88
85
O
O
N
NH
OH
5
6
7
6
6
6
O
40
59
53
N
NH
N
O
OH
OH
O
O
N
NH
NH
OH
N
8
6
6
47
85
HN
N
OH
c
9
O
a
b
c
Reaction conditions: 4.42 mmol ketoxime, 0.042 g (0.44 mmol) sulfamic acid, 90 °C.
Yields of products of rearrangement.
Reuse for four time.

3372
B. Wang et al. / Tetrahedron Letters 45 (2004) 3369–3372
convenient. As shown in entry9, the yi eld of aceto-
phenone oxime onlydecreases a little after the reuse of
H NSO H for four times.
Organic Chemistry. 5th ed.; John Wileyand Sons: New
York, 2001; p 1415, and references cited therein.
. (a) Arisawa, M.; Yamaguchi, M. Org. Lett. 2001, 3, 311;
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The specific zwitterionic feature of sulfamic acid has
been proved to provide an efficient route for separating
corresponding products of Beckmann rearrangement of
ketoximes, and the sulfamic acid/dried acetonitrile sys-
tem also has made an improvement over previous
methods for producing corresponding amides in dried
acetonitrile. The use of basic neutralization agent has
been avoided, and all the solvents and catalyst are
recyclable and no waste is produced. Thus it is a green
process for the preparation of amide from ketoxime
without producing anywaste.
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oxime (4.42 mmol) in dried acetonitrile (5 mL), was
added sulfamic acid (0.42 g, 0.44 mmol) and the mixture
was heated at 90 °C for 6 h. And then the reaction
content was dispersed into 15 mL cooled diethyl ether,
so that the catalyst of sulfamic acid could be precipi-
tated out. After filtrating, the liquid content could be
analyzed by GC. The concentration of reactant and
product was directlygiven bythe s ys tem of GC chem-
station according to the area of each chromatograph
peak. The pure products could be obtained bythe dis-
tillation and then separating it on silica gel column using
acetone as eluent.
4
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2
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1
References and notes
(
1
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