Efficient procedure for beckmann rearrangement of ketoximes catalyzed by sulfamic acid/Zinc chloride

Article abstract of DOI:10.1080/00397910903097286

The Beckmann rearrangement of a variety of ketoximes to corresponding amides catalyzed by sulfamic acid and zinc chloride was carried out in good yields at refluxing temperature in acetonitrile. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910903097286

This article was downloaded by: [University of California, San Diego]
On: 08 September 2013, At: 11:33
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Efficient Procedure for Beckmann
Rearrangement of Ketoximes Catalyzed
by Sulfamic Acid/Zinc Chloride
a
a
a
Ji-Tai Li , Xian-Tao Meng & Ying Yin
a
College of Chemistry and Environmental Science, Hebei University,
Key Laboratory of Analytical Science and Technology of Hebei
Province, Key Laboratory of Medical Chemistry and Molecular
Diagnosis, Ministry of Education, Baoding, China
Published online: 23 Apr 2010.
To cite this article: Ji-Tai Li , Xian-Tao Meng & Ying Yin (2010) Efficient Procedure for Beckmann
Rearrangement of Ketoximes Catalyzed by Sulfamic Acid/Zinc Chloride, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 40:10, 1445-1452,
DOI: 10.1080/00397910903097286
To link to this article: http://dx.doi.org/10.1080/00397910903097286
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“
Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

1
Synthetic Communications , 40: 1445–1452, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903097286
EFFICIENT PROCEDURE FOR BECKMANN
REARRANGEMENT OF KETOXIMES CATALYZED BY
SULFAMIC ACID/ZINC CHLORIDE
Ji-Tai Li, Xian-Tao Meng, and Ying Yin
College of Chemistry and Environmental Science, Hebei University,
Key Laboratory of Analytical Science and Technology of Hebei Province,
Key Laboratory of Medical Chemistry and Molecular Diagnosis,
Ministry of Education, Baoding, China
The Beckmann rearrangement of a variety of ketoximes to corresponding amides catalyzed
by sulfamic acid and zinc chloride was carried out in good yields at refluxing temperature in
acetonitrile.
Keywords: Amides; Beckmann rearrangement; cocatalyst; ketoxime; synthesis
INTRODUCTION
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
[
1,2]
of current interest.
a very important development, and a great number of vapor-phase Beckmann
Needless to say, vapor-phase Beckmann rearrangement was
[3]
rearrangement processes have been reported. As is widely known, the reaction
generally requires high temperature, strongly acidic conditions, and dehydrating
media. It leads to large amounts of by-products and cannot be used with sensitive
substrates. Milder conditions were tried, and investigations into clean, simple, and
highly efficient processes were conducted. Liquid-phase catalytic Beckmann
rearrangement usually proceeded under mild condition with high conversion and
[
4]
selectivity, and several methods for this rearrangement have been reported in the
literature. The cyclohexanone oxime could be transformed into e-caprolactam cata-
[
5]
[6]
lyzed by trialkyloxonium salts or P O in dimethylformamide (DMF) solutions,
2
5
but the yields of e-caprolactam were unsatisfactory. Beckmann rearrangements of
several ketoximes were performed in the catalytic media consisting of ionic liquid
[
7a]
[7b]
and PCl5
cyclohexanone oxime. One of the most serious shortcomings concerning the catalytic
or P O
. Excellent conversion and selectivity were achieved for
2
5
Received March 26, 2009.
Address correspondence to Ji-Tai Li, College of Chemistry and Environmental Science, Hebei
University, Key Laboratory of Analytical Science and Technology of Hebei Province, Key Laboratory
of Medical Chemistry and Molecular Diagnosis, Ministry of Education, 071002 Baoding, China.
E-mail: lijitai@hbu.cn
1
445

1446
J.-T. LI, X.-T. MENG, AND Y. YIN
Scheme 1. Beckmann rearrangement of ketoximes to corresponding amides.
Beckmann rearrangement, not only in ionic liquids but also in industrial manu-
facturing, is that there is no an effective way to separate the e-caprolactam product
from the catalysts. Inevitably, volatile hydrogen chloride as by-product is produ-
[
7c]
[8]
ced.
To overcome these problems, some catalysts such as cyanuric chloride,
[10]
[9]
p-toluenesulfonic acid, and BF ꢀ OEt were used for the rearrangement to give
amides in excellent yields, but a long reaction time was required. Although Beckmann
rearrangement catalyzed by RuCl3
corresponding amide in good yields, the catalyst was expensive. In addition, the
Beckmann rearrangements without solvent
developed, but high reaction temperatures were required.
3
2
[11]
[12]
or [RhCl(cod)] =CF SO
could give the
2
3
3
[
13,14]
[15]
and with supercritical water were
Sulfamic acid (NH SO H) is a commercially available and cheap chemical that
3
2
[
16]
is recyclable and easy to handle as a catalyst
owing to its immiscibility with
common organic solvents, unique catalytic features, and intrinsic zwitterionic
property that are different from conventional acidic catalysts. Recently, Wang
et al. reported that Beckmann rearrangement of ketoxime catalyzed by NH SO H
2
3
alone was carried out in 47–96% yield under refluxing CH CN, but the reactions
3
[
17]
were completed in 6–8 h.
Beckmann rearrangement of ketoximes to amides using sulfamic acid=zinc chloride
Herein we report a simple and efficient process for
under reflux conditions in acetonitrile (Scheme 1).
RESULTS AND DISCUSSION
A large number of organic reactions can be carried out in greater yield, shorter
reaction time, and milder conditions under ultrasonic irradiation than at classical
conditions, and the Beckmann rearrangement using ultrasonic irradiation has been
[
18]
reported.
by NH SO H under ultrasonic irradiation. No acetanilide was obtained for a long
Initially, we did the rearrangement of acetophenone oxime catalyzed
2
3
reaction time. Although the formation of acetanilide was observed when ZnCl2
was added, the yield was still poor under ultrasonic irradiation. In the presence of
sulfamic acid and zinc chloride under reflux conditions, the Beckmann rearrange-
ment of acetophenone oxime was completely carried out within a short time.
The effect of the different catalysts on the Beckmann rearrangement of aceto-
phenone oxime was observed. Representative results are shown in Table 1. The results
suggested that ZnCl (Table 1, entry 2) can further increase the catalytic activity of
2
NH SO H. Some Lewis acids (Table 1, entries 3–6) were inert or less active. There-
2
3
fore, less expensive ZnCl was the best choice as a cocatalyst for NH SO H.
2
2
3
The effect of the solvent was also investigated. When acetonitrile and 1,2-
dichloroethane were used as solvents, the acetanilide was obtained in 98% and 67%

BECKMANN REARRANGEMENT OF KETOXIMES
1447
Table 1. Effect of the different catalysts and solvents on the Beckmann rearrangement of acetophenone
a
oxime
Entry
Solvent
MeCN
MeCN
Catalyst
—
Isolated yield (%)
1
2
3
4
5
6
7
8
9
48
98
50
41
23
7
ZnCl
CoCl
FeCl
MnCl
MgCl
2
MeCN
2
MeCN
3
MeCN
2
MeCN
2
1,2-Dichloroethane
Toluene
CCl
ZnCl
ZnCl
ZnCl
ZnCl
ZnCl
2
67
55
23
12
—
2
4
2
2
2
1
1
0
1
Dioxane
THF
a
Reaction conditions: acetophenone oxime (1 mmol), sulfamic acid (0.5 mmol), Lewis acids (0.2 mmol),
solvent (3 mL), reflux, 2 h.
yields respectively (Table 1, entries 2 and 7), whereas when toluene, tetrachloro-
methane, dioxane, and tetrahydrofuran were used, the yields of acetanilide were very
poor (Table 1, entries 8–10) or no product was found (Table 1, entry 11). It shows that
solvent plays an important role in this reaction, and acetonitrile is the most suitable
solvent.
The effect of the amounts of NH SO H and ZnCl on the Beckmann
3
2
2
rearrangement of acetophenone oxime in acetonitrile was tested. The results were
summarized in Table 2. As shown in Table 2, when the amount of ZnCl was
2
0
0
2
.2 mmol, the rearrangement gave the acetanilide in 98% yield in the presence of
.3 mmol NH SO H (Table 2, entry 9), whereas acetanilide was obtained in
0–81% yield by changing the amount of NH SO H from none to 0.2 mmol
2
3
2
3
(Table 2, entries 6–8). Further addition of an amount of ZnCl or NH SO H had
2 2 3
Table 2. Effect of the ratio of NH
a
2
SO
3
H and ZnCl
2
on the Beckmann rearrangement of acetophenone
oxime in acetonitrile
Catalyst (mmol)
SO
Entry
NH
2
3
H
ZnCl
2
Time (h)
Isolated yield (%)
1
2
3
4
5
6
7
8
9
0.5
0.5
0.5
0.5
0.5
0
0
2
2
2
2
2
5
3
2
2
2
48
74
82
98
98
20
54
81
98
97
0.1
0.15
0.2
0.25
0.2
0.2
0.2
0.2
0.2
0.1
0.2
0.3
0.4
1
0
a
Acetophenone oxime: 1 mmol; acetonitrile: 3 mL; reflux.

1
448
J.-T. LI, X.-T. MENG, AND Y. YIN
SO H=ZnCl
Table 3. Beckmann rearrangement catalyzed by NH
2
3
2
under refluxing in acetonitrile
Isolated
ꢁ ꢁ
[lit.]
Entry
Substrate
Time (h)
2
Product
yield (%) Mp ( C) Mp ( C)
[
19]
A
98
99
114–116
150–152
113
151
[19]
B
C
0.75
2
[20]
174–176 175–177
92
99
[20]
117–119 125–127
D
1
[19]
162
E
F
1
3
3
96
30
17
163–165
153–155
211–213
[8]
155
[21]
214
G
[22]
154–156 153–155
H
I
1.5
1.5
96
90
[23]
128–130 132–134
[
[
19]
21]
J
2
2
70
65
39–40
69–71
40
K
72
[24]
30
L
2
57
29–31

BECKMANN REARRANGEMENT OF KETOXIMES
1449
no effect on the yield of acetanilide (Table 2, entries 5 and 10). Thus, the optimum
amount was NH SO H (0.3 mmol) and ZnCl (0.2 mmol).
Compared with the reaction catalyzed by NH SO H alone, the present pro-
2
3
2
2
3
cedure can give greater yield in less time. For example, the Beckmann rearrangement
of acetophenone oxime catalyzed by NH SO H was carried out in 96% yield under
2
3
[17]
reflux for 6 h, whereas in the present procedure, treatment of acetophenone oxime
under reflux for 2 h in acetonitrile afforded acetanilide in 98% yield.
From these results, the reaction conditions we chose are as follows: ketoxime
(1 mmol), NH SO H (0.3 mmol), ZnCl (0.2 mmol), and acetonitrile (3 mL) with
refluxing temperature.
2 3 2
To explore the generality and scope of the Beckmann rearrangement catalyzed
by NH SO H=ZnCl , representative ketoximes were examined (Table 3). As shown
2
3
2
in Table 3, excellent yields were obtained with aromatic ketoximes, which contain
electron-donating substituents (Table 3, entries 1a–e, 1 h, 1i). When aliphatic ketox-
ime was used as substrate, the rearrangement provided moderate yield (Table 3,
entries 2j–l). Unfortunately, the reaction of aromatic ketoximes containing strong
electron-withdrawing substituents in the benzene ring gave the desired amides in
poor yield (Table 3, entries 2f, 2 g). It is clear that sulfamic acid=zinc chloride has
good catalytic activity for the Beckmann rearrangement of a variety of ketoximes,
especially for aryl ketoximes containing electron-donating substituents.
The specific zwitterionic feature of sulfamic acid avoided the use of basic
neutralization agent on the Beckmann rearrangement, and sulfamic acid and all
the solvents were recyclable. The only by-product confirmed was ketone, which is
derived from the deoximation of ketoxime. This procedure is significant from the
viewpoint of avoiding pollution.
In summary, we have found a facile and efficient method for the Beckmann
rearrangement of ketoximes to corresponding amides by using sulfamic acid=zinc
chloride. The present procedure has many advantages such as mild conditions, excel-
lent yields, and inexpensive and recyclable catalyst.
EXPERIMENTAL
The starting materials, ketoximes, were prepared according to method reported
[25]
in literature, and melting points are uncorrected.
General Methods
Sulfamic acid (0.3 mmol) and zinc chloride (0.2 mmol) were added to a solution
ꢁ
of ketoxime (1 mmol) in acetonitrile (3 mL). The mixture was heated to reflux (90 C)
for the period as indicated in Table 3. The progress of the reaction was monitored by
thin-layer chromatography (TLC). After the completion of the reaction, the reaction
was dispersed into 10 mL cooled diethyl ether to precipitate sulfamic acid. The
resulting suspension was filtered to recycle sulfamic acid. The filtrate was evapo-
rated, and the residue was dissolved in ethyl acetate and washed with a small amount
of water. The combined organic layer was dried over anhydrous magnesium sulfate
and filtered. Ethyl acetate was evaporated under reduced pressure to give the crude
product, which was separated by column chromatography on silica (200–100 mesh),

1450
J.-T. LI, X.-T. MENG, AND Y. YIN
eluted with petroleum ether or the mixture of petroleum ether and ethyl acetate
(
V=V ¼ 3=1). The authenticity of the product was established by their melting points
compared with that reported in the literature.
ACKNOWLEDGMENT
The Natural Science Foundation of Hebei Province (B2006000969), China,
supported the project.
REFERENCES
1. Smith, M. B.; March, J. Advanced Organic Chemistry, 5th ed.; John Wiley & Sons: New
York, 2001.
2
. (a) Narasaka, K.; Kusama, H.; Yamashita, Y.; Sato, H. Beckmann rearrangement
catalyzed by the combined use of tetrabutylammonium perrhenate(VII) and trilfluoro-
methanesulfonic acid. Chem. Lett. 1993, 489–492; (b) Ikushima, Y.; Sato, O.; Sato, M.;
Hatakeda, K. A.; Arai, M. Innovations in chemical reaction processes using supercritical
water: An environmental application to the production of e-caprolactam. Chem. Eng. Sci.
2003, 58, 935–941; (c) Srinvas, K. V. N. S.; Reddy, E. B.; Das, B. Highly convenient and
efficient one-pot conversions of aldehydes into nitriles and ketones into amides using
HY-zeolite. Synlett 2002, 625–627.
. (a) Mao, D.; Chen, Q.; Lu, G. Vapor-phase Beckmann rearrangement of cyclohexanone
3
oxime over B
2
O
Bhagwat, V. V.; Ramana, C. V.; Gurjar, M. K. Silica-supported MoO
3
=TiO
2
-ZrO
2
. Appl. Catal. A 2003, 244, 273–282; (b) Dongare, M. K.;
: A mild hetero-
3
geneous catalyst for the Beckmann rearrangement and its application to some sugar
derived ketoximes. Tetrahedron Lett. 2004, 45, 4759–4762; (c) Ko, Y.; Kim, M. H.;
Kim, S. J.; Seo, G.; Kim, M. Y.; Uh, Y. S. Vapor-phase Beckmann rearrangement of
cyclohexanone oxime over a novel tantalum pillared-ilerite. Chem. Commun. 2000,
829–830; (d) Izumi, Y.; Sato, S.; Urabe, K. Vapor-phase Beckmann rearrangement of
cyclohexanone oxime over boria-hydroxyapatite catalyst. Chem. Lett. 1983, 1649–1652.
. (a) Nguyen, M. T.; Raspoet, G.; Vanquickenborne, L. G. A new look at the classical
Beckmann rearrangement: A strong case of active solvent effect. J. Am. Chem. Soc.
4
1
997, 119, 2552–2562; (b) Furuya, Y.; Ishihara, K.; Yamamoto, H. Cyanuric chloride
as a mild and active Beckmann rearrangement catalyst. J. Am. Chem. Soc. 2005, 127,
1240–11241; (c) Zhu, M.; Cha, C. T.; Deng, W.-P.; Shi, X. X. A mild and efficient
catalyst for the Beckmann rearrangement, BOP-Cl. Tetrahedron Lett. 2006, 47, 4861–
863; (d) Li, D.; Shi, F.; Guo, S.; Deng, Y. Highly efficient Beckmann rearrangement
1
4
and dehydration of oximes. Tetrahedron Lett. 2005, 46, 671–674.
5. Izumi, Y. Catalytic Beckmann rearrangement of oximes in homogeneous liquid phase.
Chem. Lett. 1990, 2171–2174.
6
. Sato, H.; Yoshioka, H.; Izumi, Y. Homogeneous liquid-phase Beckmann rearrangement
of oxime catalyzed by phosphorous pentaoxide and accelerated by fluorine-containing
strong acid. J. Mol. Catal. A. Chem. 1999, 149, 25–32.
7. (a) Peng, J.; Deng, Y. Catalytic Beckmann rearrangement of ketoximes in ionic liquids.
Tetrahedron Lett. 2001, 42, 403–405; (b) Ren, R. X.; Zueva, L. D.; Ou, W. Formation
2 5
of e-caprolactam via catalytic Beckmann rearrangement using P O in ionic liquids.
Tetrahedron Lett. 2001, 42, 8441–8443; (c) Gui, J.; Deng, Y.; Hu, Z.; Sun, Z. A novel
task-specific ionic liquid for Beckmann rearrangement: A simple and effective way for
product separation. Tetrahedron Lett. 2004, 45, 2681–2683.

BECKMANN REARRANGEMENT OF KETOXIMES
1451
8
9
. Luca, L. D.; Giacomelli, G.; Porcheddu, A. Beckmann rearrangement of oximes under
very mild conditions. J. Org. Chem. 2002, 67, 6272–6274.
. Xiao, L. F.; Xia, C. G.; Chen, J. p-Toluenesulfonic acid mediated zinc chloride: Highly
effective catalyst for the Beckmann rearrangement. Tetrahedron Lett. 2007, 48, 7218–7221.
1
0. Anilkumar, R.; Chandrasekhar, S. Improved procedures for the Beckmann rearrange-
ment: The reaction of ketoxime carbonates with boron trifluoride etherate. Tetrahedron
Lett. 2000, 41, 5427–5429.
1
1
1
1. De, S. K. RuCl -catalyzed facile conversion of arylalkyl ketoximes to amides. Synth.
3
Commun. 2004, 34, 3431–3434.
2. Arisawa, M.; Yamaguchi, M. Rhodium-catalyzed Beckmann rearrangement. Org. Lett.
2001, 3, 311–312.
3. Sharghi, H.; Sarvari, M. H. One-step Beckmann rearrangement from carbonyl com-
2 3 3 3
pounds and hydroxylamine hydrochloride in Al O =CH SO H (AMA) as a new reagent.
J. Chem. Res. 2001, 446–449.
1
4. (a) Chandrasekhar, S.; Gopalaiah, K. Beckmann reaction of oximes catalysed by chloral:
Mild and neutral procedures. Tetrahedron Lett. 2003, 44, 755–756; (b) Chandrasekhar, S.;
Gopalaiah, K. Beckmann rearrangement of ketoximes on solid metaboric acid: A simple
and effective procedure. Tetrahedron Lett. 2002, 43, 2455–2457.
1
5. (a) Ikushima, Y.; Hatakeda, K.; Sato, O.; Yokoyama, T.; Arai, M. Acceleration of
synthetic organic reactions using supercritical water: Noncatalytic Beckmann and pinacol
rearrangements. J. Am. Chem. Soc. 2000, 122, 1908–1918; (b) Sato, O.; Ikushima, Y.;
Yokoyama, T. Noncatalytic Beckmann rearrangement of cyclohexanone–oxime in super-
critical water. J. Org. Chem. 1998, 63, 9100–9102; (c) Boero, M.; Ikeshoji, T.; Liew, C. C.;
Terakura, K.; Parrinello, M. Hydrogen bond–driven chemical reactions: Beckmann
rearrangement of cyclohexanone oxime into e-caprolactam in supercritical water. J.
Am. Chem. Soc. 2004, 126, 6280–6286.
16. (a) Wang, B.; Yang, L. M.; Suo, J. S. Ionic liquid–regulated sulfamic acid: Chemoselective
catalyst for the transesterification of b-ketoesters. Tetrahedron Lett. 2003, 44, 5037–5039;
(
b) Wang, B.; Yang, L. M.; Suo, J. S. Solvent-free tetrahydropyranylation of alcohols with
sulfamic acid as reusable catalyst. Synth. Commun. 2003, 33, 3929–3934.
7. Wang, B.; Gu, Y.; Luo, C.; Yang, T.; Yang, L.; Suo, J. Sulfamic acid as a cost-effective
and recyclable catalyst for liquid Beckmann rearrangement, a green process to produce
amides from ketoximes without waste. Tetrahedron Lett. 2004, 45, 3369–3372.
8. (a) Du, G.; Zhang, Q. The Beckmann rearrangement of acetophenonoxime under
ultrasonic irradiation. J. Hebei Univ. (Nat. Sci. Ed.) 1997, 38–40; (b) Zhou, H.; Huang,
W. Beckmann rearrangement of benzophenoneoxime under ultrasonic irradiation. J.
Anqing Teach. Coll. (Nat. Sci.) 2002, 8, 42–45.
1
1
1
9. Sardarian, A. R.; Shahsavari-Fard, Z.; Shahsavari, H. R.; Ebrahimi, Z. Efficient
Beckmann rearrangement and dehydration of oximes via phosphonate intermediates.
Tetrahedron Lett. 2007, 48, 2639–2643.
2
2
2
2
0. Moghaddam, F. M.; Rad, A. A. R.; Hassan, Z. B. Solid-supported microwave-assisted
Beckmann rearrangement of ketoximes in dry media. Synth. Commun. 2004, 34, 2071–2075.
1. K u¨ llertz, G.; Fischer, G.; Barth, A. Sekuedare D-isotopieeffekte bei der hydrolyse von
p-nitroacetanilid. Tetrahedron, 1976, 32, 759–761.
2. Newman, M. S.; Hung, W. M. An improved aromatization of a-tetralone oximes to N-
(
1-naphthyl)acetamides. J. Org. Chem. 1973, 38, 4073–4704.
3. (a) Banfield, J. E. Heterocyclic derivatives of guanidine, part II: Some derived products.
J. Chem. Soc. 1961, 2098–2106; (b) Nicanor, G.; Marcial, M. M.; Sebastian, R. M.;
Adelina, V. Dimethoxyethane as an alternative solvent for schmidt reactions: Preparation
of homochiral N-(5-oxazolyl)oxazolidinones from N-acetoacetyl derivatives of oxazolidi-
nones. Tetrahedron 1996, 52, 1609–1616.

1452
J.-T. LI, X.-T. MENG, AND Y. YIN
2
4. Thakur, A. J.; Boruah, A.; Prajapati, D.; Sandhu, J. S. Microwave-induced bismuth
trichloride–catalysed Beckmann rearrangement of oximes. Synth. Commun. 2000, 30,
105–2111.
2
2
5. (a) Li, J. T.; Li, X. L.; Li, T. S. Synthesis of oximes under ultrasound irradiation. Ultrason.
Sonochem. 2006, 13, 200–202; (b) Pan, Z. W.; Li, Y. X.; Xia, L. Synthesis of ethoxyamine
hydrochloride via acetoxime. Fine Chem. Intermediates 2007, 37, 17–21.