Solid supported microwave-assisted Beckmann rearrangement of ketoximes in dry media

Article abstract of DOI:10.1081/SCC-120037921

An AlCl₃-ZnCl₂ mixture supported on silica gel is found to be a new efficient medium for the Beckmann rearrangement in solvent-free conditions under microwave irradiation. The yields are good to excellent.

Full text of DOI:10.1081/SCC-120037921

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Solid Supported Microwave‐Assisted Beckmann
Rearrangement of Ketoximes in Dry Media
Firouz Matloubi Moghaddam a , Abbas Ali Rastegar Rad a & Hassan Zali‐Boinee a
a Department of Chemistry , Sharif University of Technology , P.O. Box 11365‐9516,
Tehran, Iran
Published online: 20 Aug 2006.
To cite this article: Firouz Matloubi Moghaddam , Abbas Ali Rastegar Rad & Hassan Zali‐Boinee (2004) Solid Supported
Microwave‐Assisted Beckmann Rearrangement of Ketoximes in Dry Media, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 34:11, 2071-2075, DOI: 10.1081/SCC-120037921
To link to this article: http://dx.doi.org/10.1081/SCC-120037921
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 11, pp. 2071–2075, 2004
Solid Supported Microwave-Assisted
Beckmann Rearrangement of
Ketoximes in Dry Media
*
Firouz Matloubi Moghaddam, Abbas Ali Rastegar Rad,
and Hassan Zali-Boinee
Department of Chemistry, Sharif University of Technology,
Tehran, Iran
ABSTRACT
An AlCl3–ZnCl2 mixture supported on silica gel is found to be a new
efficient medium for the Beckmann rearrangement in solvent-free con-
ditions under microwave irradiation. The yields are good to excellent.
Key Words: Beckmann rearrangement; Ketoxime; Microwave irradia-
tion; Solid support; Solvent-free.
*
Correspondence: Firouz Matloubi Moghaddam, Department of Chemistry, Sharif
University of Technology, P.O. Box 11365-9516, Tehran, Iran; E-mail: matloubi@
sharif.edu.
2071
DOI: 10.1081/SCC-120037921
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Moghaddam, Rad, and Zali-Boinee
INTRODUCTION
The rearrangement of ketoximes to the corresponding amides, known as
the Beckmann reaction, is a common method in organic chemistry[1] and is
a topic of current interest. This reaction generally requires high reaction temp-
¨
erature and a large amount of strong Bronsted acids, such as sulfuric acid and
dehydrating media and forms ammonium sulfate as by-product.[1] However,
with commonly used acid catalysts several problems such as difficultly in
separation, recovery, disposal of spent catalyst, corrosion, and high toxicity,
were encountered.
Various reagents such as KSF,[2] K-10,[3] FeCl3/SiO2,[4]and FeCl3/K-
10[5] as solid recyclable non-polluting and non-corrosive acids have been
used successfully.
The coupling of microwave irradiation with the use of catalysts on
mineral supported reagents, under solvent-free conditions, provide unique
chemical processes with special attributes such as enhanced reaction rates,
higher yields, greater selectivity, and ease of manipulation. Various improve-
ments for this reaction were also developed using K-10[3] or alumina[6] in dry
media under microwave irradiation.
Recently, we have developed a new and eco-friendly solid acid (AlCl3–
ZnCl2/SiO2), which could catalyze many organic reactions such as Fries
rearrangement[7] and hetero-Fries rearrangement.[8] The present work was
undertaken to find the efficiency of this solid catalyst for the Beckmann
rearrangement of ketoximes under microwave irradiation in solvent-free
condition (Sch. 1).
In order to explore the best reaction conditions, the p-methoxy-aceto-
phenone oxime was selected as a model molecule for this reaction. When
p-methoxy-acetophenone oxime was supported on the catalyst and subjected
to microwave irradiation in solvent-free condition for 5 min, the rearranged
product was obtained in excellent yield (92%) after conventional work-up.
Comparing of this result with conventional thermal condition for the same
substrate (958C, 7 hr, 65%) reveals the advantage of our methodology.
In a typical procedure, ketoxime (5 mmol) was supported on 0.5 g of the
catalyst and subjected to microwave irradiation for a given time (see Table 1).
After conventional work-up amides were obtained in good to excellent yields.
The results are summarized in Table 1.
Scheme 1.

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Beckmann Rearrangement of Ketoximes
2073
Table 1. Beckmann rearrangement of ketoximes with AlCl3–ZnCl2/SiO2 under
microwave irradiation.a
Reaction
time (min)b
Yield
(%)c
M.p. (8C)
[Lit.]
Entry
1
R1
R2
7
11.5
5
82
87
92
93
76
90
71
86
51
28
160–161
(162)[9]
2
3
CH3
CH3
110–113
(114)[9]
125–127
(130)[9]
4
CH3
4.5
7
135–138
(137)[9]
5
CH3
168–169
(168)[9]
6
CH3
7
150–152
(148.5)[9]
7
CH3
11
8
168–170
(172)[10]
8
CH3
175–177
(179)[9]
9
CH3
10.5
165–168
(167)[9]
10
–(CH2)5–
4.5
68–70 (71)[9]
aThe microwave oven used for this work was a National (1550 W) at 2450 MHz (100%
power), which was modified to a focused monomode system in our laboratory.
bThe reaction times were optimized after several experiments.
cYields refer to isolated products.
As in the conventional Beckmann rearrangement, electron-donating
groups on the aromatic ring facilitate the reaction to lead to better yields
(Entries 3–5) compared to electron-withdrawing groups (Entries 8, 9).
It should be noted that the catalyst could be reused for several runs by
simple filtration and activation.
In conclusion, AlCl3/ZnCl2 supported on silica gel has been shown to be
an efficient medium for the Beckmann rearrangement of ketoximes under
microwave irradiation in solvent-free condition. This method has the advan-
tages of (a) being a readily available medium; (b) the reaction is fast and

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Moghaddam, Rad, and Zali-Boinee
solvent-free; (c) the catalyst could be reused for several runs; (d) the ease of
work-up.
EXPERIMENTAL
All solvents and reagents were used as obtained from commercial
sources. The oximes were prepared according to standard methods[9] and
their purities were established before utilization by spectroscopic methods
and melting point.[11]
Preparation of the Support
.
To 100 g of SiO2 (70–230 mesh) : AlCl3 6H2O: ZnCl2 (5 : 2.3 : 1.28 w/
w/w), was added 150 mL of water and the product well mixed to give a
gel-like material. The water was evaporated in vacuo and the gel left to
stand at 1208C overnight. The resulting solid granules were ground and further
activated by heating to 2308C in vacuo. The catalyst was stored under dry
conditions.
Beckmann Rearrangement (General Procedure)
To a solution of ketoxime (5 mmol) in dry CH2Cl2 (15 mL), 0.5 g catalyst
was added. After mixing well and the solvent was evaporated under reduced
pressure. The residue was subjected to microwave irradiation for the given
time (Table 1). After the reaction course, the resulting mixture was extracted
by CH2Cl2 or acetone (2 Â 10 mL), then filtered and the solvent was evapo-
rated. The residue was then recrystallized from a suitable solvent (n-PrOH
or EtOH). Products were known and gave satisfactory spectroscopic data
compared with those of authentic samples.[12]
REFERENCES
1. (a) Gawly, R.E. Org. React. 1988, 35, 1 and references therein;
(b) Smith, M.B.; March, J. Advanced Organic Chemistry, 5th Ed.; John
Wiley & Sons: New York, 2001; 1415 and references therein.
2. Meshram, H.M. Clay catalyzed facile Beckmann rearrangement of keto-
ximes. Synth. Commun. 1990, 20, 3253.

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Beckmann Rearrangement of Ketoximes
2075
3. Bosch, A.I.; De la Cruz, P.; Diez-Barra, E.; Loupy, A.; Langa, F. Micro-
wave assisted Beckmann rearrangement of ketoximes in dry media.
Synlett. 1995, 12, 1259.
4. Pai, S.G.; Bajpai, A.R.; Deshpande, A.B.; Samant, S.D. Beckmann
rearrangement of substituted diaryle ketoximes using FeCl3 impregnated
montmorillonite K10. Synth. Commun. 1997, 27, 379.
5. Khadilkar, B.M.; Upadhyaya, D.J. Studies in Beckmann rearrangement of
substituted benzophenone and acetophenone oximes. Synth. Commun.
2002, 32, 1867.
6. Touaux, B.; Texier-Boullet, F.; Hamelin, J. Synthesis of oximes, conver-
sion to nitrile oxides and their subsequent 1,3-dipolar cycloaddition reac-
tions under microwave irradiation and solvent-free reaction conditions.
Heteroatom. Chem. 1998, 9, 351.
7. Matloubi Moghaddam, F.; Ghffarzadeh, M.; Abdi-Oskui, S.H. Tandem
fries reaction-conjugate addition under microwave irradiation in dry
media; one-pot synthesis of flavanones. J. Chem. Res. 1999, 9, 575.
8. Matloubi Moghaddam, F.; Dekamin, M.G. Thia-fries rearrangement of
aryl sulfonates in dry media under microwave activation. Tetrahedron
Lett. 2000, 41, 3479.
9. Furniss, B.S.; Hannaford, A.J.; Rogers, V.; Smith, P.W.G.; Tatchell, A.R.
Qualitative organic analysis; physical constant of organic compounds. In
Vogel’s Textbook of Practical Organic Chemistry, 4th Ed.; Longman:
London & New York, 1978; Chapters VII and VIII, 1113, 1194, 1222.
10. (a) Simons, J.H.; Randal, D.; Archer, S. Hydrogen fluoride as a conden-
sing agent. VII. The acylation of aromatic compounds. J. Am. Chem.
Soc. 1939, 61, 1795; (b) Lovern, M.L.; Henry, R.H. Synthesis of ketone
derivatives of biphenyl by the Friedel–Crafts reaction. J. Am. Chem. Soc.
1941, 63, 1939.
11. Weste, R.C.; Grasselli, J.G. Handbook of Data on Organic Compound,
2nd Ed.; 1989; CRC Press Inc., Boca Raton, Florida, 33431.
12. WWW.aist.go.jp/RIODBS/SDBS/sdbs/owa/sdbs_sea.ere_frame-sea.
Received in Poland December 10, 2003

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