Keggin-type Bronsted dodecatungstophosphoric acid: A quasi homogenous and reusable catalyst system for liquid phase Beckmann rearrangement

Article abstract of DOI:10.1016/j.tetlet.2013.12.038

A variety of ketoximes, prepared from corresponding ketones, undergo Beckmann rearrangement using H₃PW₁₂O₄₀ (DTPA) in acetonitrile under reflux to yield N-substituted amides and lactams in good to excellent yields (72-96%). The present method provides an efficient, clean, eco-friendly, and simple synthesis. The catalyst is cheap, moisture tolerant, recoverable, and reusable without much loss of its activity.

Full text of DOI:10.1016/j.tetlet.2013.12.038

Tetrahedron Letters 55 (2014) 1136–1140
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Keggin-type Bronsted dodecatungstophosphoric acid: a quasi
homogenous and reusable catalyst system for liquid
phase Beckmann rearrangement
⇑
Gagandeep Kaur, Jaspreet Kaur Rajput , Priya Arora, Nisha Devi
Department of Chemistry, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar 144011, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A variety of ketoximes, prepared from corresponding ketones, undergo Beckmann rearrangement using
Received 28 August 2013
Revised 11 December 2013
Accepted 14 December 2013
Available online 19 December 2013
3
H PW12O40 (DTPA) in acetonitrile under reflux to yield N-substituted amides and lactams in good to
excellent yields (72–96%). The present method provides an efficient, clean, eco-friendly, and simple syn-
thesis. The catalyst is cheap, moisture tolerant, recoverable, and reusable without much loss of its
activity.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Beckmann rearrangement
H PW12O40 (DTPA)
3
Ketoximes
Quasi homogenous catalyst
N-substituted amides
Beckmann rearrangement, an acid induced rearrangement of
ketoximes to corresponding N-substituted amides and lactams, is
an important reaction in synthetic organic chemistry. Beckmann
rearrangement has gained much attention due to a broad range
Heteropoly acids (HPAs) belonging to a large family of polyoxo-
metalates containing metal oxygen cluster have gained attention
2
5–27
because of high Bronsted acidity and redox properties.
Among
various HPAs Keggin-type HPAs have cage type anionic form
1–3
nÀ
of applications such as in pharmaceuticals
and fiber produc-
[XM12
O
40
]
where X is the heteroatom (P or Si) and M is the ad-
4
–7
tion.
In addition, Beckmann rearrangement of steroid 17-oximes
denda atom (Mo or W), are more attractive for catalytic synthesis.
DTPA (H 40) is one of the strongest acids with high thermal
leads to formation of alkene nitriles which can be subsequently
converted into 18-norsteroids.8 It also plays an important role in
the synthesis of alkaloids and their derivatives like indophenazino
3
PW12O
28
stability decomposing at 465 °C. In the liquid phase catalysis,
DTPA has advantages such as low volatility, high acidity, activity,
flexibility, and low corrosiveness etc. with a disadvantage of sepa-
3
3
fused pyrrolo, azepine, indophenazino fused pyrrolo, diazepines
9
derivatives alkaloids. The various types of reagents are reported
ration from reaction mixture. In continuation of our work on catal-
10
11
29
in the literature such as sulfuric acid, silica sulfuric acid, cyan-
3
ysis, herein we report the use of H PW12O40 as a catalyst for
1
2
13
14
15
uric chloride, chloral, anhydrous oxalic acid, BDMS, boron
Beckmann rearrangement of ketoximes.
1
6
17
18
trifluoride etherate,
3
PEG–SO H,
PCl
5
,
[C
3
SO
3
Hmim][Cl]-
In our experimental protocol, we have optimized the conditions
for Beckmann rearrangement. When the synthesis is carried out
under these optimized conditions water is eliminated as side prod-
uct and catalyst is separated and reused (Theme 1). Whereas on
1
9
20
21
22
[
ZnCl
2
], propyl phosphonic anhydride, PhOP(O)Cl
2
,
Ti-mont,
bromodimethylsulfonium bromide-zinc chloride,2 and citric
3
2
4
acid. However, many of the methods/reagents suffer from draw-
backs such as (a) use of strong acids (b) disposal of reagents (c)
toxic reagents (d) corrosive nature (e) high temperature conditions
3
0
using the conventional method using PCl
5
,
POCl
3
and HCl are
is
produced as side products which are corrosive. Also the PCl
5
(
f) hazardous solvents and (g) formation of side products. So still
required in >1.5 equiv and normally cannot be recycled but is
recyclable in our case.
In this Letter we report the Beckmann rearrangement of ketox-
imes to corresponding N-substituted amides and lactams using
DTPA as a catalyst (Schemes 1–3).
there is a need of green, clean, simple, highly efficient, and
selective pathway using an inexpensive, moisture insensitive,
recoverable, and reusable catalyst.
Benzophenone oxime (1a) was chosen as the model substrate
for screening various reaction conditions. The product (2a) was
obtained in 65% yield in CH OH on refluxing (1a) with DTPA as a
3
⇑
Corresponding author. Tel.: +91 181 2690301 02x2208; fax: +91 181 2690320.
E-mail address: rajputj@nitj.ac.in (J.K. Rajput).
0
040-4039/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.12.038

G. Kaur et al. / Tetrahedron Letters 55 (2014) 1136–1140
1137
-
Cl-
-
POCl
3
-HCl
-
HCl
R
H
2
O
R
C
NO
PCl
C
N
R'
t)
R'
4
l
en
l-
iv
a
u
C
q
1.5e
R
,
R'
R
H
N
>
2O
(
H
l5
C
R
C
C
NOH
P
C
N
R'
R'
H3
O
H2
O
PW1
O
O4
P
W1
2
H
2
O
0
R
2
R
(
5
40 3-
m
C
o
N
l%
C
NOH
2
)
H PW12O
40
R'
R'
3
-
H O
2
Recyclable
Theme 1.
R=C
6
H
5
, R'= C
6
H
5
We observed that electron withdrawing substituent like –Cl
Table 2, entries 2, 6) attached to the ketoxime favors the Beck-
R
DTPA (0.05mmol)
Refluxing, CH CN
R'
H
R=4-Cl-C H , R'= C H
6
4
6 5
(
C
O
R=C H , R'= CH
C
N
R
6
5
3
R'
3
R=4-Cl-C
R=2-OH-C
R=4-OCH
R=4-CH -C
R=4-NO -C
6
H
4
, R'= CH
3
mann rearrangement while electron donating substituents like –
OH, –CH –OCH (Table 2, entries 7–9) retard the rearrangement.
O
6
H
4
, R'= CH
, R'= CH
, R'= CH
, R'= CH
3
-C
6
H
4
3
3
3
3
3
2
6
H
4
3
3
The thiophene containing ketoxime (Table 2, entry 11) afforded
the desired product in lesser time with high yield, whereas pyri-
dine containing ketoximes gave no product even after refluxing
for 12 h (Table 2, entry 12). This happens as protonation of pyridine
nitrogen retards the migration process. The turn over frequency
has been calculated for all the products (Table 2, entries 1–12).
All the products were obtained with good chemoselectivity and
6
H
4
Scheme 1. Synthesis of N-substituted amides and lactams from corresponding
ketoximes via Beckmann rearrangement.
DTPA (0.05mmol)
O
n = 0,1
n
1
13
C
NOH
characterized by FT-IR, H NMR, and C NMR spectroscopic tech-
niques. From our studies it is proposed that catalyst plays the role
of Bronsted acid during the conversion of oxime to amide.
To check the efficiency of our synthetic protocol, it was com-
pared with the reported methods/reagents. Cyanuric chloride12
n
3
Refluxing, CH CN
NH
Scheme 2. Synthesis of N-substituted amides and lactams from corresponding
ketoximes via Beckmann rearrangement.
(
0.034 mmol) afforded caprolactam in 30% yield after 2 h at
2
2
21
X
O
60 °C. Ti mont (0.068mmol), PhOP(O)Cl
(3mmol) afforded cap-
X
NOH DTPA (0.05mmol)
n=0, X=S, R''=CH
n=1, X=N, R''=CH
3
2
2
H
N
CH
3
C
n
rolactam in 74% yield after 20 h at 90 °C and in 33% yield after 12 h
at room temperature respectively. It appears that our protocol and
catalyst DTPA are superior for Beckmann rearrangement reaction
(Table 3). The other catalysts employed for this rearrangement
are corrosive, moisture sensitive, expensive, require harsh reaction
conditions, lower yield, and are not recyclable.
n
3
Refluxing, CH CN
R''
R''
Scheme 3. Synthesis of N-substituted amides and lactams from corresponding
ketoximes via Beckmann rearrangement.
catalyst (Table 1, entry 1). The yield of (2a) increased to 89% using
We tried to recover our catalyst (DTPA) used in the present pro-
tocol by using organic solvents and the compatibility of product
and catalyst ended with dichloroethane (DCE). The product was
first dissolved in DCE (2–3 ml) by leaving the catalyst as such in
reaction RBF and the clear solution of product was transferred by
syringe to another flask. The whole process was repeated twice.
Then the catalyst containing flask was dried at 50 °C and catalyst
was reused. To make the separation environmentally benign, water
was also used to recover the catalyst. The final product was insol-
uble in water and the catalyst was soluble. The procedure em-
ployed for recovery of catalyst was carried out in two steps.
Firstly water (2–3 ml) was added to reaction RBF and stirred for
2 min. In the second step the reaction product was filtered which
provided the clear solution containing the catalyst. The addition
of water and washing of product was repeated three times. Then
the catalyst containing water in RBF was evaporated under vacuum
at 70 °C which leaves behind the catalyst in RBF. Further the cata-
lyst was dried in an oven for 30 min and reused. Then the weight of
the catalyst was determined. It was observed that catalyst recovery
was almost constant. The reusability of catalyst was checked by
carrying out the repeated reaction using recovered catalyst and
ketoxime (Fig. 1). Catalyst was used up to five times without much
loss of its activity (small decrease due to catalyst loss during
extraction).
CH
ether, DMF, ethyl acetate, and toluene did not effectively improve
the yield (Table 1, entries 2–6). CH CN was found to be the best
solvent for the present protocol. This may be because the solvent
3
CN (Table 1, entry 8). But other solvents like acetic acid, diethyl
3
3
1
3
CH CN stabilizes the nitrilium ion formed during the reaction.
It was observed that on increasing or decreasing the catalyst
loading other than 0.05 mmol, the yield decreased (Table 1, entries
7
–13).
The reaction was also investigated at different temperatures
Table 1, entries 14, 15), but no significant changes were observed.
(
Even under microwave irradiation the yield was less (Table 1, en-
tries 16, 17). In the absence of the catalyst, no product was isolated
(Table 1, entry 18) on refluxing even after 24 h.
Subsequently, the reaction was also investigated using other
HPAs such as H SiW12O40 and H PMo12O40, but they gave poor
4 3
results compared to DTPA catalyst (Table 1 entries 19, 20).
Under the optimized reaction conditions (ketoxime (5 mmol),
3
DTPA (0.05 mmol), CH CN, refluxing) a series of N-substituted
amides and lactams was studied to establish the scope and limita-
tions of this method (Table 2). To our delight a wide range of
substituted ketoximes derived from various aromatic, aliphatic,
cyclic, and heterocyclic ketones gave desired products in good to
3
4
excellent yield (Schemes 1–3 Table 2, entries 1–12).

1
138
G. Kaur et al. / Tetrahedron Letters 55 (2014) 1136–1140
Table 1
Optimization of various reaction conditions for compound 2a
OH
O
N
C
C
Catalyst
NH
Solvent, Temperature
1a
2a
Entry
Catalyst (mmol)
Solvent
CH OH
EtOAc
Toluene
DMF
Reaction conditions
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
.
.
.
.
.
.
.
.
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
H
3
PW12
PW12
PW12
PW12
PW12
PW12
PW12
O
O
O
O
O
O
O
40 (0.05)
40 (0.05)
40 (0.05)
40 (0.05)
40 (0.05)
40 (0.05)
40 (0.02)
40 (0.05)
40 (0.1)
40 (0.15)
40 (0.2)
40 (0.25)
40 (0.3)
3
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
Refluxing
65
75
72
72
70
78
82
89
77
75
71
71
70
78
84
76
CH
(C
3
COOH
2
H
5 2
) O
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
PW12
O
O
.
PW12
PW12
PW12
PW12
PW12
PW12
PW12
PW12
PW12
0.
1.
2.
3.
4.
5.
6.
7
8.
9.
0.
O
O
O
O
O
O
O
O
Refluxing
40 (0.05)
40 (0.05)
40 (0.05)
40 (0.02)
Stirring at room temperature (30 °C)
Heating at 60 °C
Microwave irradiation
Microwave irradiation
Refluxing (24 h)
Refluxing
70
—
No reaction
75
80
H
H
3
PMo12
O
4
(0.05)
4
SiW12
O
40 (0.05)
Refluxing
The bold values specify the optimization reaction conditions.
Table 2
Beckmann rearrangement of various ketoximes (1a–1l) to corresponding N-substituted amides (2a–2l)a
S. no.
Reactant (1a–1l)
Product (2a–2l)
Time
Turn over frequency
Yield (%)
Mp (°C) (obs.)
Mp (°C) (lit.)
b
À1
(
min)
TOF (h
)
OH
O
N
N
H
1
.
65
92.59
89
161–164
16232
2
a
1
a
OH
O
N
N
H
2
.
65
92.59
88
186–189
16632
Cl
Cl
2
b
1
b
OH
O
N
NH
3
4
.
.
120
120
50
50
89
84
69–70
35–39
68–7018
2
c
1
c
N
OH
O
NH
39.533
1
d
2
d

G. Kaur et al. / Tetrahedron Letters 55 (2014) 1136–1140
1139
Table 2 (continued)
S. no. Reactant (1a–1l)
Product (2a–2l)
Time
min)
Turn over frequency
Yield (%)
Mp (°C) (obs.)
Mp (°C) (lit.)
b
À1
(
TOF (h
)
OH
H
N
N
O
C
CH3
CH3
5.
6.
7.
140
125
150
42.91
48.07
40
89
113–115
11332
2
e
1
e
OH
H
N
N
O
C
CH3
CH3
96
79
177–181
169–172
—
Cl
2
f
Cl
1
f
OH
H
N
N
O
C
CH3
CH3
—
OH
OH
2
g
1
g
OH
H
N
N
O
C
CH3
CH3
8
.
.
160
130
37.59
46.29
72
78
129–132
149–151
130–13218
H3CO
H3CO
2h
1
h
OH
H
N
N
O
C
CH3
CH3
9
15233
2
i
1
i
OH
H
N
O
N
C
CH3
1
0.
O2
N
130
46.29
92
208–210
—
2
j
O2N
S
1
j
NOH
S
H
N
1
1.
2
O
65
92.59
82
—
—
—
—
—
2
k
1
N
k
NOH
–
1
720
—
2
l
1
l
a
Conditions: Reactant (5 mmol), DTPA (0.05 mmol), CH
TOF: Turn over frequency (moles of reactant converted/moles of catalyst (DTPA) Â reaction time (h)).
3
CN (5 ml), reflux.
b
In conclusion, an efficient, eco-friendly, simple, and clean
Supplementary data
synthesis of N-substituted amides and lactams has been achieved
successfully with excellent conversion.
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
12.038.
Acknowledgements
1
We are thankful to SAIF, PU Chandigarh, for FT-IR, H NMR and
Reference and notes
1
3
C NMR and one of the authors (G.K.) and (P.A.) are thankful to
MHRD and NIT Jalandhar for providing the research fellowship.
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1
140
G. Kaur et al. / Tetrahedron Letters 55 (2014) 1136–1140
Table 3
Comparative study of the present synthetic protocol with the reported methods/reagents
S. no.
Ketoxime
Catalyst (amount)
Reaction conditions
Time (h)
Yield (%)
1
6
1
2
3
4
5
6
7
8
9
.
.
.
.
.
.
.
.
.
1c
1c
1c
1c
1c
1c
1c
1c
1c
1a
Boron trifluoride etherate (1mmol)
Dichloromethane/room temperature
Acetonitrile/refluxing
Solvent free/100–110 °C
Dried dioxane/room temperature
Ionic liquid/80 °C
Ionic Liquid/60 °C
Benzonitrile/90 °C
3
CH CN/room temperature
Acetonitrile/refluxing
Acetonitrile/refluxing
10
6
12
24
3
58
85
64
73
60
30
74
33
89
89
1
7
PEG–SO
3
H (0.6mmol)
1
4
Anhydrous oxalic acid (2.5mmol)
Silica sulfuric acid (0.63mmol)
BDMS (0.2mmol)
Cyanuric chloride (0.034mmol)
Ti-mont (0.068mmol)
1
1
1
5
1
2
2
2
2
20
12
2
2
1
PhOP(O)Cl
2
(3mmol)
DTPA(0.05mmol) [present work]
DTPA (0.05mmol) [present work]
1
0.
1
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13
FT-IR,
H
NMR,
cm : 3343(N–H stretch), 1655 (C@O stretch), 3051 (C–H stretch of Ar). 1
NMR (400 MHz, DMSO, d ppm): 10.1(1H, s, NH), 7.6–7.0 (5H, m, Ar–H), 8.0–7.4
and C NMR spectroscopic techniques. Spectral data:
1
1
1
1
1
1
1
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Benzanilide (entry 1): white crystalline solid, mp 161–164 °C. FT-IR (KBr)
À1
H
13
(
1
5H, m, Ar–H). C NMR (400 MHz, DMSO, d ppm): 164.8, 135.9, 134.2, 132.2,
29.0, 129.0, 128.9, 128.9, 127.5, 127.5, 124.4, 121.6, 121.6.
2
009, 20, 651–655.