N-rich Porous Organic Polymer as Heterogeneous Organocatalyst for the One-Pot Synthesis of Polyhydroquinoline Derivatives through the Hantzsch Condensation Reaction

Article abstract of DOI:10.1002/cctc.201702013

Incorporation of nitrogen functionality onto the high surface area porous polymeric network are very demanding in designing suitable heterogeneous organocatalyst having surface basicity. Here we report the synthesis of a new N-rich triazine based micropor

Full text of DOI:10.1002/cctc.201702013

Accepted Article
Title: N-rich porous organic polymer as heterogeneous organocatalyst
for the one-pot synthesis of polyhydroquinoline derivatives
through Hantzsch condensation reaction
Authors: Sabuj K Das, Sujan Mondal, Sauvik Chatterjee, and Asim
Bhaumik
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ChemCatChem
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N-rich porous organic polymer as heterogeneous organocatalyst
for the one-pot synthesis of polyhydroquinoline derivatives
through Hantzsch condensation reaction
Sabuj Kanti Das, Sujan Mondal, Sauvik Chatterjee,[a] and Asim Bhaumik*,[a]
[
a]
[a]
Abstract: Incorporation of nitrogen functionality onto the high
surface area porous polymeric network are very demanding in
designing suitable heterogeneous organocatalyst having surface
basicity. Here we report the synthesis of a new aminal-linked triazine
based microporous organic polymer (TrzMOP) through a simple and
efficient condensation pathway involving the reaction between 1,4-
bis(4,6-diamino-s-triazin-2-yl)-benzene (SL-1) and 2,5-thiophene
dicarboxaldehyde. The material has been characterized by using
powder XRD, FTIR spectroscopy, solid state magic-angle spinning
cutting agent (nifedipine, nicardipine, amlodipine) for factor IV
channel and modulation agonist-antagonist activities of calcium
channel (L-type calcium channel blocker).[
3-7]
Hence, synthesis
significant
of polyhydroquinoline derivatives are drawing
a
attention for last few decades. Extensive analysis of these
derivatives has revealed that they can play various important
medicinal functions such as vasodilator, bronchodilator,
antiatherosclerotic, antitumor, geroprotective, hepatoprotective,
neuroprotectant,
antidiabetic
agents.[8-11] Platelet
anti-
13
C
NMR, CHN analysis, FESEM, CO
2
-TPD and
N
2
aggregatory and cerebral antischemic activity in the treatment of
Alzheimer’s disease and chemosensitizing activity in tumor
therapy have been explored with these kind of compounds.[
Along with the above mentioned various important roles, from
the biological point of view, substituted 1,4-dihydropyridines
compounds are analogue of NADH coenzymes which have the
potential application for reductive amination by supplying
hydride.[14-15] All these advantages including medicinal and
biological importance, synthesis of this heterocyclic nucleus
have attracted huge attention to the synthetic chemists and a
large number of synthetic roots for the synthesis of valuable
molecules have been reported for last few decades.
adsorption/desorption techniques. This nitrogen-rich new porous
organic polymer showed very high catalytic efficiency for one-pot
proficient synthesis of polyhydroquinoline derivatives via microwave
assisted condensation reaction. As little as 8 mg of catalyst was
found to be effective under the optimum reaction conditions. In
addition, TrzMOP catalyzed synthesis of biologically active
polyhydroquinoline derivatives are very cost effective, scalable, less
time consuming, and environmentally benign compared to those of
currently used as heterogeneous catalysts.
12-13]
One-pot condensation of an aldehyde, β-ketoester and
ammonia in acetic acid or ethanol was first reported by Arthur
Hantzsch, in 1882. [2] A prolonged reaction time was required for
this process. Followed by this so many researchers have
reported advance methodology to reduce reaction time, increase
yield, minimise the drastic reaction conditions. Many research
Introduction
Multi-component reactions (MCRs) are very useful chemical
reactions where three or more starting materials take part in a
single step at a time in the presence of a suitable heterogeneous
catalyst to form a product, where most of the reactive atoms
contribute in the formation of the final product.[1] For being atom
economy and environmentally benign MCRs are very powerful
and proficient tool for the synthesis of fine chemicals. In addition,
MCRs reduce reaction time, minifies the reaction and purification
steps, save raw materials and there is no complexity to isolate
the product. Polyhydroquinoline synthesis through Hantzsch
condensation applying MCR procedure is an economically
favorable, time efficient, high yield and easily separable
pathway.[2]
groups used heterogeneous solid acid like sulfonated porous
nanomaterials,[16] p-toluenesulfonic acid (p-TSA),[17] ionic
liquids,[18-20]
,[21] HClO ,[22] metal triflates,
[23]
Yb(OTf) -SiO
3 4 2
[24]
[25]
vanadium ion doped titania nanoparticles, sulfonated CMP
etc. as efficient catalyst for the synthesis of polyhydroquinolines.
But no group ever used heterogeneous solid base as a catalyst
in the synthesis of polyhydroquinoline derivatives through the
[26]
Hantzsch reaction. Heravi et al. have employed morpholine as
a homogeneous organocatalyst for this reaction, but the catalyst
can’t be recycled for the sustainable operation.
Polyhydroquinoline derivatives are precursor to several
important class of drugs. Those possess a variety of biological
activities like treatment of cardiovascular diseases as the chain
Porous organic materials/polymers (POPs)[27] materials are
intensively studied over the years due to their wide range of
applications like gas storage,[28] separation,[29] energy
applications,[30-32]
photocatalysis[33]
and
heterogeneous
catalysis.[34-40,c,d] These versatile properties lead those materials
to perform different type of acidic,[ basic
selective[43] catalytic reactions. These POPs are generally
41]
[42]
as well as stereo
[
a]
S. K. Das, S. Mondal, S. Chatterjee, Prof. Dr. A. Bhaumik
Department of Materials Science
Indian Association for the Cultivation of Science
synthesized through the condensation polymerization reaction
between two reactive monomers in the presence of porogenic
solvent molecules.[ Thus the introduction of aminal-linkages
through the amine and triazine containing monomeric units can
2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India
E-mail: msab@iacs.res.in
44]
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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ChemCatChem
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offer great opportunities heterogeneous basic organocatalysis.
In comparison to the intensive usage of solid acid catalysts in
chemical technology, solid bases are not lagging far behind.
There are various solid bases that have been studied as
Spectroscopic analysis: To investigate the bonding
connectivity presence in the polymer network, the FTIR spectral
analysis has been done with both monomer units and TrzMOP
material from 4000 to 400 cm-1 which is represented in ESI,
Figure S1 and ESI, Figure S2. The attenuation intensity of the
heterogeneous catalyst for
a
wide variety of catalytic
successful
reactions.[45] Herein, we are demonstrating
a
sharp aldehydic C=O stretching peak at 1666 cm-1 and -NH
2
fabrication of new aminal-linked microporous triazine based
organic polymer (TrzMOP) by a simple condensation pathway.
We are exploiting the activity of newly developed porous
polymer TrzMOP as an efficient heterogeneous organo-catalyst
to synthesize polyhydroquinoline derivatives. To the best of our
knowledge first time we are reporting here microporous
heterogeneous solid base catalyzed one-pot proficient synthesis
of polyhydroquinoline derivatives under microwave irradiation
conditions (Scheme 1).
deformation band between 1650-1657 cm-1 confirms the
condensation reaction between two monomer units. The
-1
presence of a sharp IR band at 1540 cm in both the SL-1
monomer and TrzMOP material indicates the presence of
triazine moiety in the polymer. Absence of imine (-C=N)
-1
stretching band at 1620 cm and presence of a very broad band
at 3417 cm-1 in TrzMOP confirmes about the formation of (-CH-
NH-) bond.[46] FTIR spectrum of TrzMOP catalyst and recycled
catalyst after 7th cycle is displayed in ESI, Figure S3. Both of the
FTIR spectra remain unaltered which indicates no structural
breakage occurred during the catalytic reaction. The Solid state
13C
CP MAS NMR spectrum of TrzMOP material was
represented in Figure 1. The down field resonance signal
appeared at 166 ppm is due to the presence of carbon atom in
triazine ring. And the sp2 hybridized aromatic carbon atoms
(Phenyl and thiophene ring) adjacent to triazine ring gave the
resonance signals at 128, 141 ppm.[47] The Schiff base
condensation reaction can generate two type of C-N linkage like
aminal (-NH-CH-NH-) or iminal (-C=N-) linkage.[48,49] The signal
appeared at around 57 ppm is attributed to the formation of
aminal linkage in TrzMOP.
Scheme 1. Multi-component reactions for the synthesis of polyhydroquinone
derivatives using TrzMOP as catalyst.
Results and Discussion
Triazine based tetra armed amine compound (SL-1) was
synthesized from terepthalonitrile in basic medium under
microwave irradiation for 10 min (Scheme 2). Then the Schiff
base condensation has been carried out between SL-1 and 2,5-
thiophenedicarboxaldehyde to synthesize porous organic
polymer (TrzMOP) catalyst (Scheme 3). Elemental analysis of
TrzMOP material reveals C, H, N and S content in the polymer
are 51.3 %, 4.2 %, 32.4 % and 7.3 % respectively.
166
128
57
141
2
50
200
150
100
50
0
Chemical shift (ppm)
Scheme 2. The synthetic scheme of polyhydroquinone derivatives.
Figure 1. 13C CP MAS NMR of polymeric network TrzMOP.
Porosity and surface area analysis: The nitrogen
adsorption/desorption analysis was performed to analyze the
specific surface area with architectural rigidity and permanent
2
porosity of TrzMOP. The N adsorption/desorption isotherm of
TrzMOP and recycled TrzMOP matrix were represented in
Figure 2 and ESI, Figure S4 which displayed the features of both
type I and IV isotherms according to IUPAC nomenclature.[47] At
the very low pressure region isotherm shows a sharp increase of
adsorbed
N
2
volume which indicates the presence of
microporosity in the polymeric material. Further, at very high
pressure region a small hysteresis loop together with large
nitrogen uptake suggested the existence of mesoporosity in this
material. This type of typical isotherm was generated probably
due to the disordered packing[48] of very small size polymer
Scheme 3. Synthetic scheme of porous organic polymer TrzMOP.
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ChemCatChem
10.1002/cctc.201702013
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particles as observed in the electron microscopic images (Figure
(
(
a)
c)
(b)
(d)
3). This nitrogen adsorption-desorption isotherm suggested the
Brunauer-Emmett-Teller (BET) surface area of TrzMOP material
2
-1
-1
0
as 792 m g with total pore volume 1.27 cc g at P/P 0.9913.
High surface area and pore volume of this porous polymer
suggested its huge scope in heterogeneous catalysis. Non local
density functional theory has been employed in this
adsorption/desorption isotherms to obtain the pore size
distribution (PSD) of TrzMOP and this is shown in the inset of
Figure 2. PSD plot suggested peak pore width of TrzMOP was
1.55 nm. Other peaks at 2.8, 4.7 and 8.2 could be attributed to
the presence of interparticle mesopores in TrzMOP material.
During the course of catalytic reactions organic catalyst TrzMOP
showed retention of structural integrity as seen from the FTIR
spectrum (ESI: Figure S3). Further, after using this TrzMOP
material for seven consecutive catalytic cycles the BET surface
2
-1
area of the material was 785 m g . This confirmed that surface
nanostructure of TrzMOP is quite stable and the catalyst can be
reused for several reaction cycles.
Figure 3. FESEM & HRTEM images of TrzMOP.
Thermal stability and PXRD analysis: Thermal stability of the
porous organic network is important to explore their potential in
catalysis.. To investigate the thermal stability of TrzMOP porous
polymer and the used catalyst after the reaction the
thermogravimetric analysis was performed at 10 C/min ramp
under N
2
flow in the temperature range of 25-800 oC. TGA
9
8
7
6
5
4
3
2
1
00
00
00
00
00
00
00
00
00
0
Adsorption
Desorption
o
profile diagram is shown in Figure 4. The polymeric network of
o
the organic catalyst is thermally stable upto 400 C. The sharp
weight loss below 100 °C can be assigned due to the surface
adsorbed water molcucles or trapped solvents in the porous
networks. The TGA profile diagram of recycled catalyst is also
very similar to that of the unused catalyst, which suggested high
structural stability and huge scope of TrzMOP as a recyclable
catalyst. The wide angle powder X-ray diffraction pattern of
TrzMOP material is shown in ESI, Figure S6. A broad peak
0
5
10 15 20
Pore Width (nm)
0.0
0.2
0.4
0.6
0.8
1.0
appeared between 2θ value of 20 to 30 degree as a
characteristic PXRD pattern of amorphous material.[50]
Relative pressure [P/P0]
1
00
2
Figure 2. N adsorption/desorption isotherm and pore size distribution of
TrzMOP.
TrzMOP
TrzMOP-Recycled
8
6
0
0
Microscopic analysis: The morphological and nanostructural
features of the porous polymer have been analyzed through field
emission scanning electron microscopy (FESEM) and high
resolution transmission electron microscopic (HRTEM)
techniques. The FESEM images of TrzMOP polymer have been
represented in the Figure 3a and 3b. The FESEM images show
spherical morphology. The average particle diameter is found to
be between 15-25 nm. The HRTEM images of TrzMOP before
and after catalysis were displayed in the Figure 3c and 3d and
ESI, Figure S5 respectively. HRTEM analysis also confirms the
sphere like particle morphology and with average particle size of
ca. 19.04 nm for this porous organic polymer. After 7th catalytic
reaction cycles we did not observe any morphological
deformation.
40
2
0
0
0
150
300
450
600
750
o
Temperature ( C)
Figure 4. Thermogravimetric (TG) plot of TrzMOP and recycled TrzMOP
catalysts.
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Basicity measurement: Prior to base catalyzed reaction
Table 1. TrzMOP catalyzed synthesis of polyhydroquinoline derivatives
basicity of TrzMOP material has been estimated. To investigate
through Hantzsch reaction.
the surface basicity, temperature programmed desorption (TPD)
TON[a]
Entry
1
Ar-CHO
-Ph
Product
Yield (%)
o
o
of CO
2
has been performed in the range of 25-350 C and a
84 (80 C)
300.00
332.14
350.00
350.36
o
o
93 (100 C)
broad peak with desorption maxima at 64 C was observed (ESI,
o
9
8 (120 C)
Figure S7). The Lewis basicity measured from CO
2
-TPD profile
o
9
8.1 (140 C)
suggested total basic strength of 0.35 mmol g-1
which can be
,
considered as mild surface basicity for this porous polymer
material.[51] Further, to understand the total base strength of the
TrzMOP catalyst, we have carried out the acid-base titration,
which suggested the total basic strength of 0.6445 mmol/g (ESI,
Section 1). Since the interaction of N-sites of the TrzMOP
network with the acidic CO molecules are not strong enough,
2
the basic strength estimated from this titration method is
considered as the correct quantification of surface basic sites
2
3
4-CH
3
-Ph-
96
342.86
339.28
328.57
342.86
325.00
342.86
4-CH
3
O-Ph-
95
92
96
91
96
2
over CO -TPD measurement.
4.
2
3,4,-(OMe) -Ph-
Heterogeneous Catalysis
TrzMOP material was used to examine catalytic performance in
four-component one-pot Hantzsch coupling synthesis of
polyhydroquinoline derivatives. The scope and generality of this
catalytic reaction is illustrated with various substituted aldehydes
5.
6
4-OH-Ph-
(
Table 1). We started our exploration with an optimization study
for the catalytic activity of TrzMOP in single step reaction
between benzaldehyde (1 mmol), dimedone (1 mmol) and ethyl
acetoacetate (1 mmol) with variation in the amount of
ammonium acetate as well as TrzMOP. The reaction was
carried out in ethanol under microwave irradiation and
benzaldehyde and ethyl acetoacetate are selected as the model
reactants for the synthesis of corresponding polyhydroquinoline
derivatives.
3,4,-(OH)
2
-Ph-
7
4-CN-Ph-
The impact of temperature was studied by carrying out the
model reaction in presence of TrzMOP under microwave
o
irradiation. We began our study at 80 C and then temperature
8
9
3-NO
2
-Ph-
-Ph-
90
90
321.43
321.43
was raised to 100 and 120 oC under the identical reaction
conditions. The product yield has been improved from 84 to
9
1
8 % (Table 1, entry 1). Upon further increase in temperature to
40 ºC no significant increase in yield was observed. To achieve
4-NO
2
the optimal amount of NH
treated with different amount of NH
shown in Table 2. Our experimental data suggested that the
reaction using 2 mmol of NH OAc was found to be the best for
4
OAc, the model catalytic reaction was
4
OAc and the results are
4
the synthesis of polyhydroquinoline derivatives. On the basis of
literature precedents,[18,52] polar solvents are much better than
the non-polar solvent and we choose ethanol as the reaction
medium for its fast reaction rate, high yield, economic viability
and environmental acceptability.
1
0
4-Cl-Ph-
4-Br-Ph-
95
94
339.28
335.71
257.14
11
The catalytic efficiency of TrzMOP in four component Hantzsch
condensation reaction was evaluated with different catalyst
loading for a fixed amount of aldehyde. In absence of TrzMOP a
very less amount of reaction yield (<2%) was obtained. But use
of just 1 mg of catalyst is enough to run the reaction forward.
Reaction product yield was gradually increased from 51% to
72
12
2-thienyl-
98 % up on use of 8 mg and then there was no significant
[a]TON: Turn Over Number= moles of substrate converted per mole of active
site of the catalyst.
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10.1002/cctc.201702013
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improvement of yield with high catalyst loading (Figure 5a). We
optimized the reaction time to get maximum yield of product.
4
Table 2. Effect on product yield with variation of added NH OAc.
Entry
NH
4
OAc (mmol)
Product yield (%)
1
2
3
4
1
1.5
2
88
95
98
98
2.5
Table 3. Comparative study of methods for synthesis of polyhydroquinolene.
Entry
Catalyst
Silica Sulfuric Acid
SBA-15 supported solid acids
p-TSA
Nature of Catalyst
Acidic (heterogeneous)
Acidic (heterogeneous)
Acidic (homogeneous)
Ionic liquid
Reaction Condition
Yield (%)
Reference
o
1
2
3
4
Solvent free (60 C, 45min)
93
92
93
95
16
17
18
19
o
Solvent free (110 C, 2h)
EtOH (RT, 2h)
Solvent free (90 C, 10min)
o
[hmim]BF
4
(homogeneous)
Ionic liquid
o
5
([(CH
2
)
4
SO HMIM][HSO
3
4
])
EtOH (78 C, 57min)
90
20
(homogeneous)
6
7
8
9
Yb(OTf)
HClO -SiO
Sc(OTf)
V-TiO
3
Acidic (homogeneous)
Acidic (heterogeneous)
Acidic (homogeneous)
Nanoparticle
Solvent free (RT, 5 h)
Solvent free (90 C, 8 min)
90
95
93
85
21
22
23
24
o
4
2
3
EtOH (RT, 4h)
Solvent free (80 C, 10 min)
o
2
(
heterogeneous)
o
1
1
0
1
SPPN
Morpholine
Acidic (heterogeneous)
EtOH (120 C, MW, 5 min)
96
95
25
26
Solvent free (RT, 60 min)
Basic (homogeneous)
o
1
2
3
TrzMOP
EtOH (120 C, 10 min)
57
This Work
This Work
Basic (heterogeneous)
Basic (heterogeneous)
o
EtOH (120 C, 30 min)
79
o
1
TrzMOP
EtOH (120 C, MW, 10 min)
98
1
00
(b) 100
well as heterocyclic aldehyde. As seen from Table 1, we
achieved good to excellent yields (72-98%) in most of the cases.
TON of the TrzMOP catalyst are obtained 257.14 - 350.36,
shown in Table 1 and calculation is represented in ESI, Section
2. All the polyhydroquinoline products were characterized by H-
NMR spectroscopy (ESI, Figure S8 to S19).
(
a)
9
8
7
6
5
4
0
0
0
0
0
0
8
6
4
2
0
0
0
0
0
1
9
8 %
98 %
98 %
97 %
97 %
96 %
95 %
1
00%
0%
60%
8
30
0
2
4
6
8
10
0
2
4
6
8 10 12 14 16
4
0%
0%
0%
Catalyst Loading (mg)
Time (min)
2
Figure 5. (a) Reaction profile of TrzMOP catalyst at variable catalyst loadings
a). Reaction conditions: benzaldehyde (1 mmol), t = 10 min, T=120 oC,
microwave irradiation, NH OAc (2.0 mmol), ethyl acetoacetate (1 mmol),
1
2
3
4
5
6
7
(
Catalytic Run
4
dimedone (1.0 mmol) and EtOH (2 mL). Yield of reaction against time (b).
Figure 6. Recycling efficiency of the TrzMOP catalyst in the multi-component
reaction.
o
Reaction conditions: benzaldehyde (1 mmol), T=120 C, microwave irradiation,
4
NH OAc (2.0 mmol), ethyl acetoacetate (1 mmol), dimedone (1 mmol),
TrzMOP catalyst (8 mg), and EtOH (2 mL).
A comparative study (Table 3) was done for this reaction with
other reported catalysts, both homogeneous and heterogeneous,
to show the catalytic efficiency of TrzMOP. This reaction was
mostly reported with acidic catalysts with very high yield, upto
95%. Morpholine, the only basic moiety used as homogeneous
catalyst for the same reaction, shows 95% product yield.
TrzMOP, however, shows 98% yield for this one pot MCR. A
controlled reaction has been carried out under same condition in
absence of microwave irradiation. We achieved comparatively
low yield (Table 3, entry 12) of the product when the heating
source is changed from microwave to oil-bath. To explore the
Under the identical reaction condition product yield was
increased from 39% to 98% with increasing reaction time from 1
to 10 min. There is no considerable change in yield was
observed at longer reaction times (Figure 5b).
In order to investigate the versatility and generality of this
catalytic process we have taken a series of other aldehydes to
achieve the corresponding polyhydroquinoline derivatives and
this method has the ability to tolerate a variety of functional
groups with electron rich and electron-deficient substituents as
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recyclability of TrzMOP catalyst, it was separated from the
reaction mixture through centrifugation then the recovered
catalyst was thoroughly washed with hot methanol and THF,
scope to explore for the reactions involving various structurally
analogous aldehydes for the synthesis of a wide range of
polyhydroquinoline derivatives.
o
well dried under vacuum at 120 C for 6h. Recovery and
reusability of TrzMOP catalyst were evaluated with the reaction
of benzaldehyde (1 mmol), dimedone (1mmol), ethyl Experimental Section
acetoacetate (1mmol), and ammonium acetate under optimized
reaction condition. We reused the catalyst up to 7 consecutive
Materials. Terephthalonitrile, 2,5-thiophenedicarboxaldehyde
cycles and it was noticed that upto 3rd catalytic run the reaction
yield remained same such as fresh catalyst (figure 6). After the
and dicyandiamide were purchased from Sigma Aldrich.
Ammonium acetate was procured from Merck, India, ethyl
aceoacetate from Loba chemicals and dimedone from from TCI.
The organic solvents viz. dimethylsulphoxide (DMSO) and 2-
methoxyethanol were used as received from Spectrochem, India
and ethanol from Bengal Chemicals. All reactions were
performed without further purification.
7th cycle the product yield was declined by 3%.
A
reasonable pathway for the
formation
of
polyhydroquinoline derivatives have been proposed in scheme 4.
On the basis of the above explanations and the literature
precedents polyhydroquinoline is formed through Hantzsch-like
Conjugate addition mechanism. In presence of basic surface
sites of TrzMOP cyclization of enamine to the corresponding
enone product takes place. The mechanism is gone through
either step I or step II. According to step I conjugate addition of
enamine intermediate (A) with enone product (B) and according
to step II conjugate addition of enamine intermediate (C) with
enone product (D) leads to the formation of polyhydroquinoline
derivatives followed by cyclization.
Characterization techniques. To check crystalline nature of the
material powder X-Ray diffraction patterns of the porous
polymers was analyzed by using a Bruker AXS D-8 Advanced
SWAX diffractometer using Cu-Kα (λ = 0.15406 nm) radiation.
The Quantachrome Autosorb 1-C was used to obtain the
nitrogen adsorption/desorption isotherms of the TrzMOP
polymer at 77 K. Prior to N
2
sorption measurement of the
material, Solvent extraction was performed in Soxhlet apparatus
for 3 days with MeOH and activated for 24 h at 180 °C
temperature under vacuum to get rid of any adsorbed solvent
molecule occupied in the pore. Pore-size distribution of TrzMOP
material was calculated from adsorption isotherm by employing
Non-Local Density functional Theorem (NLDFT). To analyze the
bonding connectivity FTIR spectrum of the powder sample was
taken using Nicolet MAGMA-FTIR 750 Spectrometer Series II.
The liquid state 1H and 13C NMR spectra of the SL-1 and all
catalysis products were taken in a 400/500 MHz Bruker Advance
II spectrometer. The solid state 13C MAS NMR spectrum of the
polymer was obtained from 500MHz Bruker-Avance II
spectrometer at a mass frequency of 8 kHz using a 4 nm MAS
probe. To investigate the structural morphology as well as
particle size of the sample FE-SEM and HRTEM images were
taken from JEOL JEM 6700 and JEOL 1400 Plus respectively.
Thermal stability of the polymer network was investigated by
thermal analyzer TA-SDT Q-600 under nitrogen flow with
temperature ramp of 10 oC/min. Perkin Elmer 2400 Series II
CHN analyzer was used for elemental analysis of the TrzMOP
polymer. For determination of surface basicity of the material
Scheme 4: Probable mechanistic pathway for the TrzMOP catalyzed
synthesis of polyhydroquinolines.
Conclusions
CO
2
-TPD was analyzed by using a Micromeritics ChemiSorb
Here we have developed a new aminal-linked triazine based
microporous organic polymer having high BET surface area (792
2720 with a thermal conductivity detector.
2
-1
m g ) through simple condensation reaction between 1,4-
bis(4,6-diamino-s-triazin-2-yl)-benzene (SL-1) and 2,5-thiophene
dicarboxaldehyde. Owing to such high surface area and aminal
linkages, this porous polymer displayed excellent catalytic
activity and recycling efficiency as a heterogeneous basic
organocatalyst for the synthesis of polyhydroquinoline
derivatives. This protocol offers benefits such as clean reaction,
high yields of products, low catalyst loading, short reaction times,
high sustainability. Thus, this multicomponent reaction over
novel porous organic polymer based organocatalyst have huge
Synthetic procedure of 1, 4-Bis(4,6-diamino-s-triazin-2-yl)
benzene (SL-1). Following a literature procedure,[53] at first
terephthalonitrile (640mg, 5mmol), dicyandiamide (841mg,
10mmol) and KOH (100mg, 1.75 mmol) were taken into a
microwave (G-30) vial. 15 ml of 2-methoxyethanol solvent was
poured immediately into the vial and the reaction was carried out
at 195 ºC under microwave irradiation for 10 min (Scheme 2).
After cooling down, the reaction mixture was poured into in hot
water then filtered off under hot conditions and washed with
plenty of water followed by methanol and finally with acetone to
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ChemCatChem
10.1002/cctc.201702013
FULL PAPER
obtain 75 % yield. H and 13C NMR spectra with details of SL-1
1
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been
synthesized
using
54]
Schiff-base
condensation
[
polymerization method. The reaction was carried out with 2,5-
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with the MeOH and THF mixture (1:1) for 3 days and dried under
vacuum at 180 °C for 24 h to obtain guest free triazine based
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FULL PAPER
A
new aminal-linked microporous
Sabuj Kanti Das, Sujan Mondal, Sauvik
Chatterjee and Asim Bhaumik*
triazine based organic polymer
(
(
TrzMOP) with high BET surface area
792 m g ) has been synthesized and
2
-1
used as an efficient heterogeneous
basic organocatalyst for the synthesis
of polyhydroquinoline derivatives via
Hantzsch condensation reaction.
Page No.1 – 8
N-rich porous organic polymer as
heterogeneous organocatalyst for the
one-pot synthesis of
polyhydroquinoline derivatives
through Hantzsch condensation
reaction
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