Poly(4-vinylpyridine)-supported dual acidic ionic liquid: A novel heterogeneous catalyst for the synthesis of β-Acetamido ketones

Article abstract of DOI:10.1080/15533174.2013.768647

Asupported dual acidic ionic liquid catalystwas easily prepared from its startingmaterials and used as an environmentally friendly heterogeneous catalytic system for the synthesis of β-acetamido ketones from the four-component condensation of an aromatic aldehyde with acetophenone, acetyl chloride, and acetonitrile at room temperature. This catalyst was also applied as an efficient catalyst for the synthesis of α-aminophosphonates. The catalyst favorably combines the properties of ionic liquids and advantages of solid supports and is recoverable without loss in its catalytic activity. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2013.768647

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Synthesis and Reactivity in Inorganic, Metal-Organic,
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Poly(4-vinylpyridine)-Supported Dual Acidic Ionic
Liquid: a Novel Heterogeneous Catalyst for the
Synthesis of β-Acetamido Ketones
Kaveh Parvanak Boroujeni a & Giti Seyfipour a
a Department of Chemistry , Shahrekord University , Shahrekord , (115) , Iran
Accepted author version posted online: 15 Aug 2013.
To cite this article: Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2013): Poly(4-
vinylpyridine)-Supported Dual Acidic Ionic Liquid: a Novel Heterogeneous Catalyst for the Synthesis of β-Acetamido Ketones,
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2013.768647
To link to this article: http://dx.doi.org/10.1080/15533174.2013.768647
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Poly(4-vinylpyridine)-Supported Dual Acidic Ionic Liquid: a Novel Heterogeneous
Catalyst for the Synthesis of β-Acetamido Ketones
Kaveh Parvanak Boroujeni*, Giti Seyfipour
Department of Chemistry, Shahrekord University, Shahrekord (115), Iran
E-mail: parvanak-ka@sci.sku.ac.ir; Fax: 0098-381-4424419
Abstract
A supported dual acidic ionic liquid catalyst was easily prepared from its starting materials and
used as an environmentally friendly heterogeneous catalytic system for the synthesis of β-
acetamido ketones from the four-component condensation of an aromatic aldehyde with
acetophenone, acetyl chloride, and acetonitrile at room temperature. This catalyst was also
applied as an efficient catalyst for the synthesis of α-aminophosphonates. The catalyst favourably
combines the properties of ionic liquids and advantages of solid supports and is recoverable
without loss in its catalytic activity.
Keywords poly(4-vinylpyridine)-supported ionic liquid, β-acetamido ketones; α-
aminophosphonates, aldehydes, multi-component reactions
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INTRODUCTION
In recent years, ionic liquids have received considerable interest as eco-friendly catalysts in
green synthesis because of their unique properties.[1] One type is Brønsted acidic ionic liquids.
These ionic liquids are of special important because they possess simultaneously the proton
acidity and the characteristic properties of ionic liquid. Among them, SO3H-functionalized ionic
liquids with a hydrogen sulfate counteranion are of particular value as a class of dual acidic ionic
liquids, because the existence of both SO3H functional groups and hydrogen sulfate
counteranions can enhance their catalytic acidities.[2–4] However, despite having the widespread
application in organic synthesis, most of them suffer from one or more of the following
drawbacks such as laborious work-up procedures, difficulty of recovery and recycling, disposal
of spent catalyst, difficult to handle, and corrosion problems. Thus, these shortcomings make
them a prime target for heterogenisation.[5–8]
β-Acetamido ketones are important synthons for a variety of biologically or
pharmacologically important compounds.[9,10] These are precursors of 1,3-amino alcohols present
in antibiotic nikkomycins or neopolyoxines.[11] One-pot condensation of an aldehyde with an
enolisable ketone, acetyl chloride, and acetonitrile is the most convenient method for the
preparation of β-acetamido ketones. Several types of catalysts were introduced previously for
this purpose such as CoCl2,[12] zeolite Hβ,[13] silica sulfuric acid,[14] Sc(OTf)3, Yb(OTf)3, and
CuCl2,[15] CeCl3.7H2O,[16] ZrOCl2.8H2O,[17] FeCl3,[18] La(OTf)3,[19] polyaniline-sulfate salt,[20]
cellulose sulfuric acid,[21] and H5PW10V2O40.[22] Except a few, many of the above methods suffer
from the drawbacks such as generation of environmentally perilous waste material, tedious
work-up, high reaction temperature, long reaction times, unsatisfactory yields, complicated
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operations, the reaction has to be carried out under an inert atmosphere, and the use of moisture-
sensitive, expensive, hazardous, difficult to handle or unreusable catalysts. In view of these, the
search for finding a cost effective, mild, and simple protocol specially using green and eco-
friendly catalysts for the synthesis of β-acetamido ketones is still relevant.
In a continuation of our work on the synthesis and application of poly(vinylpyridine)-
supported reagents and catalysts in organic reactions,[23] herein, we now report the synthesis of
poly(4-vinylpyridine-co-1-sulfonic acid butyl-4-vinylpyridinium)hydrogen sulfate ([P4VPy-
BuSO3H]HSO4) from the reaction of poly(4-vinylpyridine) (P4VPy) with 1,4-butane sultone,
followed by the reaction with H2SO4. [P4VPy-BuSO3H]HSO4 was used as a polymer catalyst for
the synthesis of β-acetamido ketones from coupling of an aromatic aldehyde with acetophenone,
acetyl chloride, and acetonitrile (Scheme 1).
EXPERIMENTAL
Material and Techniques
Chemicals were either prepared in our laboratory or were purchased from Merck
and Fluka. Reaction monitoring and purity determination of the products were
accomplished by GLC or TLC on silica-gel polygram SILG/UV254 plates. Gas
chromatography was recorded on Shimadzu GC 14-A. IR spectra were obtained by a
Shimadzu model 8300 FT-IR spectrophotometer. NMR spectra were recorded on a
Bruker Advance DPX-300 spectrometer. The Leco sulfur analyzer was used for the
measurement of sulfur in catalyst. Melting points were determined on a Fisher-Jones
melting-point apparatus and are uncorrected. Thermal gravimetric analysis (TGA) were
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o
performed by a Stanton Redcraft STA-780 with 20 C/min heating rate in N2. The shape and
surface morphology of the samples were examined on a scanning electron microscope (SEM)
(Hitachi S-3400N, Japan).
Preparation of [P4VPy-BuSO3H]HSO4
In a round bottomed flask (50 mL) equipped with a reflux condenser, 1 g of the P4VPy (2%
o
DVB) was added to 1,4-butane sultone (1.5 mL) and the mixture was stirred at 100 C for 30 h,
filtered, washed with distilled water (20 mL), and dried at 80 oC overnight. Afterwards, H2SO4 (3
M, 5 mL) was added to the obtained resin and the mixture was stirred at room temperature for 2
o
h, filtered, washed with distilled water (20 mL), and dried at 80 C overnight to give [P4VPy-
BuSO3H]HSO4.
Typical experimental procedure
To a solution of an aromatic aldehyde (1 mmol), acetophenone (1mmol), acetyl chloride (2
mmol), and acetonitrile (4 mL) was added [P4VPy-BuSO3H]HSO4 (0.07 mmol), and the
resulting mixture was magnetically stirred at room temperature. The progress of the reaction was
monitored by TLC. After the completion of the reaction, the catalyst was filtered off and the
filtrate poured into ice-water (25 mL). The precipitated solid was filtered, washed with ice-water,
and recrystallized from ethyl acetate/n-hexane to give the pure product.
RESULTS AND DISCUSSION
[P4VPy-BuSO3H]HSO4 was prepared by the procedure shown in Scheme 2. At the first stage,
commercially available P4VPy (2% divinylbenzene) was reacted with 1,4-butane sultone to give
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the poly(4-vinylpyridine-co-1-sulfonate butyl-4-vinylpyridinium) ([P4VPy-BuSO3]) as a pale
yellow solid. [P4VPy-BuSO3] was analyzed by elemental analysis to quantify the percentage
loading of the sulfonate moiety by measuring the sulfur content, giving 0.9 mmol sulfonate
moiety per gram. In a second step, the [P4VPy-BuSO3] was further treated with H2SO4 to form
[P4VPy-BuSO3H]HSO4 as a white cream solid. The acidic site loading in [P4VPy-BuSO3H]HSO4
obtained by means of acid–base titration was found to be 1.7 mmol/g.[24]
For comparison, FT-IR spectra of the P4VPy, [P4VPy-BuSO3], and [P4VPy-BuSO3H]HSO4
were presented in Fig. 1. As can be seen in the spectrum of [P4VPy-BuSO3H]HSO4 new peaks
appeared at 1160, 1200, and 1220 cm-1, which can be assigned to S=O stretching vibration.[8]
Also, a new peak appeared at 1645 cm-1 which is ascribed to the C-N (pyridine-CH2-) bond
absorption. This observation confirms the N-alkylation of pyridine ring.
Fig. 2 shows TGA curves of P4VPy and [P4VPy-BuSO3H]HSO4. A weight loss was observed
o
in each case around 100 C due to the loss of moisture. In the case of [P4VPy-BuSO3H]HSO4,
o
the second weight loss started at about 200 C is mainly assigned to the decomposition of alky-
sulfonic acid groups and hydrogen sulphate counteranions. In TGA curves of P4VPy and
o
[P4VPy-BuSO3H]HSO4 the last weight losses were observed at about 350 C and 420 C,
o
respectively, which are attributed to the degradation of polymer backbone.
An attempt was made to investigate the morphology of [P4VPy-BuSO3H]HSO4 catalyst using
scanning electron microscopy (SEM). The SEM images of P4VPy and [P4VPy-BuSO3H]HSO4
are provided in Fig. 3. In the SEM photograph of [P4VPy-BuSO3H]HSO4, it can be seen that the
[P4VPy-BuSO3H]HSO4 surface is uniform and in this catalyst the pores of P4VPy are filled with
alky-sulfonic acid groups and hydrogen sulphate counteranions.
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The catalytic activity of [P4VPy-BuSO3H]HSO4 was studied in the synthesis of β-acetamido
ketones by the condensation of aldehydes with acetophenone, acetyl chloride, and acetonitrile at
room temperature (Table 1). The optimum molar ratio of [P4VPy-BuSO3H]HSO4: aldehyde:
acetyl chloride was found to be 0.07:1:2. Various types of substituted benzaldehydes were
smoothly converted into the corresponding β-acetamido ketones (entries 1-8). Salicylaldehyde
afforded the corresponding product without any acetylation of hydroxyl group (entry 9).
Aliphatic aldehydes did not yield the desired product (entry 10). The reaction of benzaldehyde
with acetophenone and acetonitrile in the absence of acetyl chloride failed to produce the
corresponding product. This observation indicated that the presence of acetyl chloride is
necessary in this reaction. Also, the reaction of benzaldehyde with acetophenone, acetyl chloride,
and benzonitrile (instead of acetonitrile) led to the formation of the corresponding β-benzamido
ketone in 88% yield after 1 h. This demonstrates that in this reaction, nitrile acts as a nucleophile
according to the mechanism proposed in Scheme 3. We believe that [P4VPy-BuSO3H]HSO4
activates the aldehyde group for nucleophilic attack as well as facilitating enolization of
acetophenone.
Recently, we used polystyrene-supported Al(OTf)3 as a polymer catalyst for the synthesis of
α-aminophosphonates by the condensation of amines and aldehydes with diethyl phosphite.[25]
Along this line, in this study, we observed that [P4VPy-BuSO3H]HSO4 is also an effective
catalyst for the synthesis of α-aminophosphonates (Scheme 4).
[P4VPy-BuSO3H]HSO4 recovered after a reaction can be washed with water and used again
at least five times without appreciable change in its efficiency (Scheme 5).
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A comparison of the present procedure, using [P4VPy-BuSO3H]HSO4, with selected
previously known protocols is collected in Table 2. As it is seen in addition to having the general
advantages attributed to the solid supported catalysts, [P4VPy-BuSO3H]HSO4 has a good
efficiency compared to other recently reported catalysts
CONCLUSION
In conclusion, we have synthesized [P4VPy-BuSO3H]HSO4 as a polymer-supported dual
acidic ionic liquid. [P4VPy-BuSO3H]HSO4 can act as an efficient catalyst for the synthesis of β-
acetamido ketones and α-aminophosphonates. The significant advantages of this methodology
are high yields, short reaction times, simple work-up procedure, and easy preparation and
handling of the catalyst. In addition, the use of this catalyst has resulted in a reduction in the
unwanted and hazardous waste that is produced during conventional homogeneous processes.
Finally, this solid catalyst can be recovered unchanged and used again.
ACKNOWLEDGEMEBNTS
The author thanks the Research Council of Shahrekord University for partial support of this
work.
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24. 1 gr of dry [P4VPy-BuSO3H]HSO4 was added to 10 mL aqueous solution of NaCl (2 M) and
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O
NHAc
O
O
[P4VPy-BuSO3H]HSO4 (0.07 mmol)
+
Ar
Ph
Ar
H
CH3
Ph
CH3CN / CH3COCl / r.t.
SCH. 1.
O
n
n
n
S
O
H2SO4
O
HSO4
CH2(CH2)3SO3H
100oC / 30 h
N
N
CH2(CH2)3SO3
r.t. / 2 h
N
P4VPy (2% DVB)
[P4VPy-BuSO3H]HSO4
[P4VPy-BuSO3]
SCH. 2.
Py-BuSO3H(HSO4)
CH3
O
OCOCH3
OCOCH3
O
CH3
O
CH3COCl
N
Ar
Ar
Cl
H
H
Ar
H
Ar
O
N
CH3
Ar
NCCH3
O
CH3
Py-BuSO3H(HSO4)
O
O
O
O H
CH3
CH3
CH3
O
Ph
Ar
Ph
Ar
H
Ph
O
hydrolysis
H2C
Ph
Ar
N
N
OH
O
N
CH3
SCH. 3.
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O
Cat.
PhHN
H
P(OEt)2
PhCHO
HPO(OEt)2 (1.2 mmol) / PhNH2 (1 mmol)
(1 mmol)
Ph
Cat.: [P4VPy-BuSO3H]HSO4 (0.07 mmol) / CH3CN / r.t. / 0.7 h
PS-Al(OTf)3 (0.1 mmol) / r.t. / 0.9 h
(94 %)
(92 %)
O
Cat.
CHO
(1 mmol)
PhHN
P(OEt)2
HPO(OEt)2 (1.2 mmol) / PhNH2 (1 mmol)
H
CH2CH2CH3
Cat.: [P4VPy-BuSO3H]HSO4 (0.07 mmol) / CH3CN / r.t. / 1 h
PS-Al(OTf)3 (0.1 mmol) / r.t. / 1.5 h
(92 %)
(91 %)
SCH. 4.
O
O
O
NHAc
[P4VPy-BuSO3H]HSO4 (0.07 mmol)
Ph
Ph
H
+
CH3
Ph
Ph
CH3CN (3 mL) / CH3COCl (2 mmol) / r.t. / 0.4 h
Run No.
Isolated yield (%)
1
2
3
4
5
94
94
93
90
90
SCH. 5.
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FIG. 1. FT-IR spectra of P4VPy (A), [P4VPy-BuSO3] (B), and [P4VPy-BuSO3H]HSO4 (C).
FIG. 2. TGA curves of P4VPy (A) and [P4VPy-BuSO3H]HSO4 (B).
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FIG. 3. SEM photographs of P4VPy (A), [P4VPy-BuSO3H]HSO4 (B) and [P4VPy-
BuSO3H]HSO4 after five uses (C).
TABLE 1
Synthesis of β-acetamido ketones using [P4VPy-BuSO3H]HSO4.
Entry
Ar
Ph
Time (h)
0.4
Yield (%)a
Mp (oC) (Lit. (Ref.))
104-106 (103-105)[9]
111-113 (112)[17]
1
94
94
92
94
92
93
92
90
90
–
2
4-CH3C6H4
4-CH3OC6H4
4-ClC6H4
0.5
3
0.5
111-113 (110-112)[17]
148-150 (144-146)[22]
149-151 (148-150)[18]
105-106 (101-103)[22]
155-157 (154)[17]
4
0.4
5
4-BrC6H4
0.4
6
3-BrC6H4
0.4
7
4-NO2C6H4
2-NO2C6H4
2-HOC6H4
CH3CH2CHO
0.3
8
0.4
194-196 (191-192)[17]
131-133 (129-131)[22]
–
9
0.5
10
1
aIsolated yields. All products are known compounds and were identified by comparison
of their physical and spectral data with those of the authentic samples.
TABLE 2
Comparison of the catalytic activity of [P4VPy-BuSO3H]HSO4 against other reported
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catalysts for the coupling of benzaldehyde with acetophenone, acetyl chloride, and
acetonitrile.
Entry
Catalyst
Temp. (°C)
Time (h)
Yield (%)
64[12]
87[13]
91[14]
82[15]
96[16]
90[17]
88[18]
87[19]
90[20]
97[21]
80[22]
94
a
1
2
CoCl2
80
28
80
r.t.
r.t.
r.t.
r.t.
85
80
80
80
r.t.
1
8.5
1
Zeolite Hβa
Silica sulfuric acid
Sc(OTf)3
3
4
30
7
5
CeCl3.7H2O
ZrOCl2.8H2O
FeCl3
6
5
7
8
b
8
La(OTf)3
4
9
Polyaniline-sulfate salt
Cellulose sulfuric acidc
H5PW10V2O40
1
10
11
12
1
0.7
0.4
[P4VPy-BuSO3H]HSO4
aWith 4-chlorobenzaldehyde instead of benzaldehyde.
bWith 4-fluorobenzaldehyde instead of benzaldehyde.
cWith dimedone instead of benzaldehyde.
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