SOCl 2/β-cyclodextrin: A new and efficient catalytic system for Beckmann rearrangement and dehydration of aldoximes under aqueous condition

Article abstract of DOI:10.1080/00397911.2011.592747

A rapid and efficient synthesis of amides via Beckmann rearrangement of ketoximes and dehydration of aldoximes to corresponding nitriles with good to excellent yields has been carried out in the presence of SOCl ₂/β-cyclodextrin under aqueous conditions. The β-cyclodextrin has been recovered and reused. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2011.592747

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SOCl2/β-Cyclodextrin: A New and
Efficient Catalytic System for Beckmann
Rearrangement and Dehydration of
Aldoximes Under Aqueous Condition
Dipak Patil a & Dipak Dalal a
a Department of Organic Chemistry, North Maharashtra University,
Jalgaon, Maharashtra, India
Accepted author version posted online: 01 Feb 2012.Version of
record first published: 05 Sep 2012.
To cite this article: Dipak Patil & Dipak Dalal (2013): SOCl2/β-Cyclodextrin: A New and Efficient
Catalytic System for Beckmann Rearrangement and Dehydration of Aldoximes Under Aqueous
Condition, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 43:1, 118-128
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Synthetic Communications1, 43: 118–128, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.592747
SOCl2/b-CYCLODEXTRIN: A NEW AND EFFICIENT
CATALYTIC SYSTEM FOR BECKMANN
REARRANGEMENT AND DEHYDRATION OF
ALDOXIMES UNDER AQUEOUS CONDITION
Dipak Patil and Dipak Dalal
Department of Organic Chemistry, North Maharashtra University, Jalgaon,
Maharashtra, India
GRAPHICAL ABSTRACT
Abstract A rapid and efficient synthesis of amides via Beckmann rearrangement of ketox-
imes and dehydration of aldoximes to corresponding nitriles with good to excellent yields
has been carried out in the presence of SOCl2/b-cyclodextrin under aqueous conditions.
The b-cyclodextrin has been recovered and reused.
Keywords Beckmann rearrangement; b-cyclodextrin (b-CD); thionyl chloride (SOCl2)
INTRODUCTION
A great effort has been made to manufacture amides and transform ketoximes
to amides, known as the Beckmann rearrangement, a very important and useful
transformation in synthetic chemistry.[1] Conventional Beckmann rearrangement
usually requires relatively high temperature and large amounts of strongly acidic
and dehydrating media such as concentrated H2SO4 (forms ammonium sulfate as
by-product),[2a] and polyphosphoric acid,[2b] P2O5–methanesulfonic acid[2c] (leads
to large waste products, forms inorganic salts caused by neutralization, and is not
applicative to sensitive substrate). Consequently, research is being pursued to make
the process mild and catalytic. To avoid these harsh conditions, several methodologies
in liquid phase,[3–5] supercritical water,[6] ionic liquid,[7] and vapor phase[8] have been
developed. Many catalytic systems such as boria hydroxyapatite, metal ilerite, and
supported oxide and zeolite have been reported.8 However, these processes require
high reaction temperature (300 ꢀC) and low selectivity and can suffer from rapid decay
in the activity of catalyst. Various inorganic catalysts such as terpyridine ruthenium,[9a]
Received January 3, 2011.
Address correspondence to Dipak Dalal, Department of Organic Chemistry, North Maharashtra
University, Jalgaon, Maharashtra 425 001, India. E-mail: dsdalal2007@gmail.com
118

SOCl2/b-CYCLODEXTRIN
119
AlCl3 ꢁ 6H2O=KI=H2O=CH3CN,[5c] bromodimethylsulfoniumbromide–ZnCl2 in acet-
onitrile,[9b] HgCl2,[3c] metal lewis acid–Ga(OTf)3,[5e] [RhCl(cod)]2, Au=Ag cocatalytic
system,[9c] and triphosphazene in HIIP or acetonitrile[3a] have been tried. The
other reagents include cyanuric chloride=dimethylformanide,[5a,5d] anhydrous oxalic
acid,[9d] and chlorosulfonic acid in toluene.[3b] However, some of these processes
require hazardous high-cost solvents such as dichloromethane, dimethylformanide,
acetonitrile, and toluene with high reaction times. Therefore, the development of a
simple, highly efficient, and selective Beckmann rearrangement process is still highly
in demand.
At the same time, dehydration of aldoximes to nitriles is also an important
transformation in organic synthesis and a number of methods have been
developed.[10] Many methods using SOCl2 for dehydration of aldoximes to nitriles
have been reported including silica gel=SOCl2,[10i] SOCl2–benztriozole,[10j] and
Na2CO3=SOCl2.[10l] However, the methods developed so far have their own limita-
tions, for example, extremely anhydrous reaction conditions, toxic and hazardous
chemicals, and cumbersome workup procedures.[11] Therefore, the search for more
convenient methods still continues.
RESULTS AND DISCUSSION
Rama Rao[12] reported that b-cyclodextrin-mediated water reactions are very
useful from both economic and environmental points of view and because flammable
anhydrous organic solvents and toxic and expensive reagents are not needed. Apart
from being nontoxic, b-cyclodextrin (b-CD) is also considered metabolically safe[13]
because of its efficient catalytic activity. Herein we present our results on highly
selective SOCl2=b-cyclodextrin-catalyzed Beckmann rearrangement and dehydration
of aldoximes to corresponding nitriles (Scheme 1). As the Beckmann rearrangement
usually requires electrophilic activation of the oxime hydroxy group, we hypothe-
sized that b-CD may facilate the transformation of ketoximes to amide or dehy-
dration of aldoximes by hydrogen bonding with b-CD hydroxyl groups by
supramolecular interaction. The hydrogen bonding with oxygen may also force
the departure of the leaving group and accelerate the rate of migration or rate of
dehydration.
To explore the best reaction condition, the 4-bromoacetophenone oxime was
selected as a model molecule under various reaction conditions (Table 1).
The effect of temperature for this reaction has been studied, and it was found
that at lower temperature (entry 1, Table 1), the rate of migration was very slow,
requiring long reaction time and leading to the side product identified as 4-bromo
acetophenone. Increase in temperature favors the rate of migration, and the best
Scheme 1. b-CD mediated Beckmann rearrangement or dehydration of aldoximes.

120
D. PATIL AND D. DALAL
Table 1. Screen of reaction conditionsa
Yield (%)b
Entry
Temp. (ꢀC)
Time (h)
A
B
1
2
3
4
Rt
40
60
80
12
30
38
47
85
68
53
50
—
2.45
0.5
0.41
aReaction conditions: To a solution of 4-bromoacetophenone oxime in acetone, SOCl2 was added drop-
wise at 0–10 ꢀC. Then a clear solution of b-CD dissolved in distilled water (10 ml) was added at room
temperature and stirred at the given temperature. Molar ratio of oxime–SOCl2–b-CD ¼ 5:6:0.5.
bIsolated yield.
result was found at 80 ꢀC (entry 4, Table 1, 85%). The reactions were also carried out
by varying the amount of catalyst (shown in Table 2) at 80 ꢀC. When we increased
the amount of catalyst from 0.5 to 5 mmol, no yield improvement was observed.
When same reaction was carried out at 80 ꢀC without b-CD catalyst, formation of
amide and the carbonyl compound takes place. The efficiency of catalyst has been
studied for the structurally diverse ketoxime[14] (Table 3). Oximes were readily pre-
pared in quantitative yields by reaction of corresponding carbonyl compounds with
NH2OH ꢁ HCl (in sodium acetate=ethanol.) The reactions were found to be complete
Table 2. Transformation of ketoximes to amides using different amounts of catalyst at 80 ꢀCa
Entry
Catalyst (mmol)
Time (min)
Yield (%)b
1
2
3
4
5
6
0.5
1
25
25
28
30
40
35
85
84
84
80
80
41
2
4
5
–
aA molar ratio of oxime–SOCl2 ¼ 5:6 was used.
bIsolated yield.

SOCl2/b-CYCLODEXTRIN
121
Table 3. Catalytic conversions of various ketoximes to amide using SOCl2=b-CD as catalysta
Entry
1
Amide
Time (min)
Yield (%)b
5
86
2
3
8
88
85
25
4
20
90
5
6
15
20
91
93
7
18
94
aA molar ratio of ketoximes–SOCl2–b-CD ¼ 5:6:0.5.
bIsolated yield after column chromatography.
Table 4. Reuse of b-CD for entry 3 (Table 3)
Use
Yield (%)
Recovery of b-CD (%)
1
2
3
85
85
83
96
90
85

122
D. PATIL AND D. DALAL
Table 5. Catalytic dehydration of aldoximes to corresponding nitriles using SOCl2=b-CD as a catalysta
Entry
1
Nitrile
Time (min)
15
Yield (%)b
90
2
3
8
98
91
10
4
5
10
15
96
91
6
20
94
7
8
12
12
91
91
9
15
92
10
11
15
20
94
92
12
13
25
10
93
89
aMolar ratio of aldoximes–SOCl2–b-CD ¼ 5:6:0.5.
bIsolated yield after column chromatography.

SOCl2/b-CYCLODEXTRIN
123
Table 6. Reuse of b-CD for entry 2 (Table 5)
Use
Yield (%)
Recovery of b-CD (%)
1
2
3
98
94
90
94
90
86
within 5–25 min. As usual, here only migration of the aryl group was observed. The
naphthalene and diphenyl compounds also show good results (entries 4–7). In our
results, the electronic effect of substituents on aromatic ring was not more
pronounced.
The starting oximes used in the present study are mostly a mixture of syn and
anti isomers, but we obtained a majority of single amide isomer as the product,
which is favored based on migratory aptitude (except for entry 7). The equilibrium
among involved isomers is faster than rearrangement, so the product composition is
determined by the relative rates of migration of involved groups and is independent
of the stereochemistry of starting oximes. On prolonged heating at 80 ꢀC there was
no further dehydration of amide to nitrile or hydrolysis of amide to acid and amine.
The reaction was also carried out in the absence of SOCl2 for a prolonged time but
the starting oximes were isolated. The catalyst was quantitatively recovered and
reused up to three cycles (Table 4).
With promising results in hand for the formation of amide from ketoximes, we
next tested for the aldoximes to examine the generality of this reaction under identical
conditions. Aldoximes were found to undergo dehydration to furnish the correspond-
ing nitriles in good to excellent yields and within short reaction time (Table 5,
8–25 min.). On comparison of the overall reactivity of aldoximes and ketoximes in
our results with respect to time and yields, aldoximes were found to be more reactive.
The effect of substituent on aromatic ring like nitro, halide, hydroxyl, methoxy, and
methyl was found to be less on reaction efficiency and selectivity. It is noteworthy that
protection of indole (entry 6, table 5) and hydroxyl group on substrate is not necessary
as demonstrated by reaction of 4-hydroxy benzaldehyde oxime (entry 7, table 5). The
same reaction proceeds much slowly when reaction carried out in acetonitrile at similar
condition affording side product (monitor by TLC) which was undetectable. Not only
aromatic aldoximes were efficiently converted to aromatic cyano compounds but het-
erocyclic (entry 6) as well as aliphatic aldoxime (entry 13) could also be employed as a
good substrate with similar selectivity to affords the corresponding nitriles. Com-
pounds entry 1, 4, 8, 11 were isolated in 90, 96, 91 and 92% yields in shorter reaction
time while using a literature procedure[14] these compounds were isolated in 82, 87,
82 and 85% yields in 1 hr. reaction time. Furthermore catalytic activity of recovered
catalyst (b-CD) was examined. As shown in Table 6, the yield of 3-nitro benzonitrile
in second and third use of catalyst not found to be decreasing much more. In each case
almost >86% of b-CD was easily recovered by liophilization of aqueous layer. How-
ever when these reactions were carried out in presence of simple oligosaccharides such
as glucose or dextrose, the reaction was completed in 30 min. and 20 min. with yields
only 45% and 55% for 4-bromoacetophenone oxime and 4-nitrobenzaldehyde oxime
respectively. It confirms that cyclodextrin may form complex with oxime, thus yields

124
D. PATIL AND D. DALAL
of reaction increased to 85% and 91% respectively. Glucose or dextrose also not recov-
ered from aqueous layer quantitatively.
CONCLUSION
In conclusion we have described a highly efficient protocol for conversion of
ketoximes to amides and dehydration of aldoximes to nitriles using nontoxic and
inexpensive b-CD catalyst. The advantages of this protocol includes a simple reac-
tion setup with no specialized equipment, mild reaction conditions, good product
yields, very short reaction times, reusable catalyst, and no hazardous solvents.
EXPERIMENTAL
Chemicals required for the synthesis were obtained from Aldrich and Spectro-
chem. Melting points were taken in open capillary tubes and are uncorrected. Infra-
red (IR) spectra were recorded on a Shimadzu Fourier transform (FT)-IR
1
IRAffinity-1 using KBr. H NMR spectra were recorded with a Varian Mercury
at 300 MHz in CDCl3 with tetramethylsilane (TMS) as an internal standard. Mass
spectra were under electrospray ionization (ESI) mode, on a Thermo Finnigan
(Model- LCQ Advantage MAX) mass spectrometer.
Typical Procedure for Transformation of Oximes into Amide and
Nitriles
SOCl2 (6 mmol) was added dropwise to a solution of oxime (5 mmol) in acetone
(2 ml), with stirring at 0–10 ꢀC. Then a clear solution of b-CD (0.5 mmol) in distilled
water (10 ml) was added at room temperature and stirred at 80 ꢀC for the appropri-
ate time (monitored by TLC). The organic material was extracted in ethyl acetate
(3 ꢂ 20 ml). The aqueous layer was cooed to 0 ꢀC; in which b-CD reappeared as a
white solid. The obtained white solid mass was filtered, dried to recover b-CD,
and reused. The organic phase was dried over anhydrous Na2SO4, the solvent was
evaporated under reduced pressure, and the crude product purified by column chro-
matography using hexane-ethyl acetate as eluent to afford pure product.
The products were characterized by their physical constants, IR, NMR, mass
spectroscopy, and comparative TLC data, which were in good agreement with the
authentic samples.
N-p-Tolyacetamide
1
Mp 150 ꢀC (lit.[15] 149–151 ꢀC); IR (KBr) cmꢃ1: 3300, 2922, 1664; H NMR
(300 MHz, CDCl3): d 2.15 (s, 3H), 2.30 (s, 3H), 7.11 (d, 2H, J ¼ 8 Hz), 7.20 (brs,
1H), 7.36 (d, 2H, J ¼ 8 Hz); m=z ¼ 150 (M þ 1).
N-(Naphthalene-6-yl)acetamide
Mp 129–132 ꢀC, IR (KBr) cmꢃ1: 3284, 2983, 1668; 1H NMR (300 MHz, CDCl3):
2.23 (s, 3H), 7.39 ꢃ 7.45 (m, 4H), 7.76 ꢃ 7.79 (m, 3H), 8.17 (s, 1H); m=z ¼ 186 (M þ 1).

SOCl2/b-CYCLODEXTRIN
125
N-Phenylbenzamide
Mp 162 ꢀC (lit.[16] 162 ꢀC); IR (KBr) cmꢃ1: 3344, 1654, 1598; 1H NMR
(300 MHz, CDCl3): 7.07ꢃ7.96 (m, 10H), 10.2 (brs, 1H); m=z ¼ 198 (M þ 1).
4-Chloro-N-phenylbenzamide
1
Mp 200 ꢀC; IR (KBr) cmꢃ1: 3350, 1653, 1598; H NMR (300 MHz, CDCl3):
7.16ꢃ7.85 (m, 9H), 7.74 (s, 1H); m=z ¼ 232 (M þ 1).
4-Nitrobenzonitrile
1
Mp 148 ꢀC (lit.[16] 149 ꢀC); IR (KBr) cmꢃ1: 2223, 1348; H NMR (300 MHz,
CDCl3): 7.90 (d, 2H), 8.36 (d, 2H).
1H-Indole-3-carbonitrile
1
Mp 180–182 ꢀC (lit.[16] 179–182 ꢀC); IR (KBr) cmꢃ1: 3230, 2227; H NMR
(300 MHz, CDCl3): 7.26–7.80 (m, 5H), 8.68 (brs, 1H); m=z ¼ 143 (M þ 1).
4-Hydroxybenzonitrile
1
Mp 112 ꢀC (lit.[15] 113 ꢀC); IR (KBr) cmꢃ1: 3275, 2223; H NMR (300 MHz,
CDCl3): 6.09 (s, 1H), 6.93 (d, 2H), 7.56 (d, 2H); m=z ¼ 120 (M þ 1).
4-Methoxybenzonitrile
1
Mp 58 ꢀC (lit.[16] 57–59 ꢀC); IR (KBr) cmꢃ1: 2218, 1604; H NMR (300 MHz,
CDCl3): 3.88 (s, 3H), 6.98 (d, 2H), 7.60 (d, 2H); m=z ¼ 134 (M þ 1).
2-Chlorobenzonitrile
1
Mp 44 ꢀC (lit.[15] 43–46 ꢀC); IR (KBr) cmꢃ1: 3093, 2229; H NMR (300 MHz,
CDCl3): 7.34–7.69 (m, 4H).
4-Hydroxy-3-methoxybenzonitrile
1
Mp 84 ꢀC (lit.[15] 85–87 ꢀC); IR (KBr) cmꢃ1: 3226, 2225; H NMR (300 MHz,
CDCl3): 3.93 (s, 3H), 6.06 (s, 1H), 6.95–7.26 (m, 3H); m=z ¼ 150 (M þ 1).
ACKNOWLEDGMENT
We are thankful to the Department of Science and Technology, New Delhi,
India, for financial support.

126
D. PATIL AND D. DALAL
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