Silica polymer nanocomposites functionalized with polyphosphoric acid: A mild catalyst for efficient one-pot synthesis of dihydropyrimidinones under environmentally benign conditions

Article abstract of DOI:10.1080/24701556.2016.1241268

An efficient, mild catalyst was employed for the synthesis of dihydropyrimidinones via condensation of aldehyde, ethyl acetoacetate, and urea/thiourea in the presence of silica polymer nanocomposite functionalized with polyphosphoric acid. The present met

Full text of DOI:10.1080/24701556.2016.1241268

ACCEPTED MANUSCRIPT
Silica polymer nanocomposites functionalized with polyphosphoric acid; a mild catalyst for
efficient one-pot synthesis of dihydropyrimidinones under environmentally benign conditions
Divya Sachdev1,*
1*National Institute of Food Technology Entrepeneurship and Management-Kundli
Email: Dr Divya Sachdev- divya19sachdev@gmail.com
Department of Agriculture and Environment Sciences
National Institute of Food Technology Entrepeneurship and Management
Kundli --Sonepat, Haryana
* Corresponding author
Abstract
An efficient, mild catalyst was employed for the synthesis of dihydropyrimidinones (DHPMs)
via condensation of aldehyde, ethylacetoacetate and urea/ thiourea in the presence of silica
polymer nanocomposite functionalized with polyphosphoric acid (PPA).The present
methodology offers an advantage of being mild and highly selective wherein a three component
reaction proceeds proficiently because of the synergistic role of the hydrophobic polymer and the
acidic sites functionalized on silica, which allows easy removal of water molecule formed during
the reaction.
1
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Keywords
Mesoporous silica, polyphosphoric acid, polymerization, wet-impregnation method,
heterogeneous catalyst, dihydropyrimidinones.
2
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Introduction
Discovery of Ordered mesoporous silica materials (OMS) have gained remarkable attention
[1-3],
because of their numerous interesting properties such as large surface area
uniform and
controllable pore size and flexibility of incorporating the active functional sites.
Functionalization of these materials by different organic-inorganic groups can be attained easily
and is advantageous for various applications such as ion-exchange, catalysis, adsorption,
chemical-optical sensors and drug delivery[4]. Majorly grafting and co-condensation are the two
indispensable routes for surface functionalization of OMS; however there is an alternate route
[5]
wherein a polymeric layer can be introduced before tethering an active moiety on the silica
.
Although various researchers have tried to incorporate the polymer directly on the silica surface
however in most of the cases, the structural order either collapsed completely or became
nonporous [6]. Therefore wet impregnation method was devised for better dispersal of the active
groups. This penetrating network of polymer introduces the degree of hydrophobiocity/
hydrophilicity while improving the strength and flexibility of the material which may tune the
material into a highly efficient catalyst[7].
In recent years, heterogeneous catalysts have been introduced to address the sustainability issues
and have emerged as an alternative approach in limiting the homogeneous acid catalysts which
are often highly toxic, environmentally hazardous[8], corrosive and produce lot of wastes.
Although, recent trends of organic transformations shows an extensive use of strong acidic
sites[9-11] however in the present state of art it would be desirable and significant to perform the
same organic transformations with a mild catalyst and decrease the nontoxic effects of the
3
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
catalyst [12-13]. Therefore the current methodology deals with the development of mild and
efficient catalyst which can be employed under sustainable and eco-friendly conditions for the
synthesis of DHPMs.
Various biologically active compounds especially DHPMs compounds act as a precursor for
antibacterial, antitumor, anticancer, anti-inflammatory drugs. So far several catalyst such as ionic
[18]
liquid[14-15], NiO2[16], supported iron[17], zeolites
silica-PPA[19], ZnO nanoparticles[20] and
[22]
various bronsted and lewis acid like dry acetic acid, boric acid [21]and alcoholic HCl
have
been employed for carrying out biginelli reaction. However many of these methods are
associated with side products resulting in difficult product isolation or needs highly acidic
environment. Therefore there is a need of developing a mild catalyst which is highly selective
and have no deteriorating effects on the environment, and in this context for the first time we
report the use of polyphosphoric acid (PPA) impregnated over hydrophobic polymeric layer
(SBA/PS/PPA) for the synthesis of DHPMs.
Experimental
Synthesis of SBA-15
All the chemicals were procured from Sigma-Aldrich and used without further purification. The
synthesis of SBA-15 is carried out using Pluronic (P123) (EO20PO70EO20,MW = 5800,
Aldrich) as the surfactant and tetra ethoxy ortho-silicate (TEOS) as a silica source, respectively.
In a typical synthesis batch with TEOS, 3 g of P123 was dissolved in 100 g of distilled water and
5.9 g of conc. HCl (35%). After stirring for 1 h, 7.3 g of TEOS was added at 35C while
maintaining the molar ratio of P123: H2O: HCl: TEOS ratio as 1: 5562.9: 86.29: 42.51 and
4
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
continued stirring for 24 h[23]. Subsequently the mixture was heated for 24 h at 100C under
static conditions in a closed polypropylene bottle. The solid product obtained after the
hydrothermal treatment was filtered and dried at 80C. The template was removed by
calcinations at 550C for 6 h.
Synthesis of PPA functionalized silica polymer nanocomposite (SBA/PS/PPA)
The synthesis methodology of polymer supported silica (SBA/PS) involves the incorporation of
vinyl monomers (chlorostyrene and divinyl benzene), cross linkers and radical initiators into the
SBA-15 mesopore walls via the wet-impregnation method [7,23-24] and equilibrated under reduced
pressure to achieve a uniform distribution. The monomers adsorbed on the mesopore walls were
subsequently polymerised with temperature programmed heating. Typically, for 30 wt% polymer
loading of polymer on SBA-15, 0.114 g of chlorostyrene (80 mol%), 0.0358 g divinylbenzene
(20 mol%), 0.0065 g of AIBN, a,a9-azoisobutyronitrile (3% relative to the total vinyl group)
were dissolved into 2 ml of solvent (dichloromethane). The resulting mixture is impregnated
uniformly into the SBA-15 framework. After impregnating the solution, the sample was heated
to 40C to remove the dichlorobenzene and subjected to freeze--vacuum--thaw to remove the
residual solvent and air. The sample was sealed in a pyrex tube and subjected to controlled
temperature programming for polymerization. The temperature scheme follows 45C for 24 h,
60C for 4 h, 100C, 120C and 150C for 1 h [23-24]. Finally the polymer was washed with
ethanol to remove excess of monomers. Samples with 10, 20 and 30 wt% polymer loading were
also synthesized under similar conditions and named as SBA/PS. The role of polymer is to make
the surface more hydrophobic. Different amounts (5, 10, 20, 30 wt%) of PPA were incorporated
5
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
on SBA/PS using ethanol as a solvent. Typically for 20wt% incorporation of PPA, 600mg of
PPA was dissolved in 1g of SBA/PS using 5 ml of ethanol. After the impregnation, the solution
was kept for 2h at reflux temperature. The resulting mixture was cooled, filtered and washed
with excess solvent to remove the residual PPA and dried at 80C for 12h. Finally the samples
were named as SBA/aPS/xPPA, where a and x represents the wt% of polymer and PPA
incorporated respectively. Similarly PPA of (5, 10. 20, 30 wt%,) was impregnated over SBA-15
without surface modification and named as SBA/xPPA (imp) where “imp” stands for
impregnation[24]
.
Synthesis of DHPMs
A mixture of ethyl acetoacetate (1 mmol), aryl aldehyde (1 mmol), urea or thiourea (1.5 mmol),
and catalyst in solvent ethanol (15 mL) were heated under reflux for the appropriate time. The
progress of the reaction was monitored by TLC. After completion of the reaction, the catalyst
was filtered under hot condition. The product was extracted from the unreacted reactants by
washing with hexane. Finally the product was separated and the yield was calculated. The
products formed were confirmed by authentic samples prepared according to the reported
methods.
Characterization details
PXRD pattern was recorded on Hecus X-Ray Systems S3 Model using Cu Kα radiation (k =
1.5404 A). Nitrogen adsorption--desorption isotherms were measured by using Quantachrome
NOVA series. Prior to the measurements, the materials were outgassed at 80°C under vacuum
for 12 h. The specific surface area was calculated by the BET method and the pore size
6
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
distribution was calculated from the desorption isotherms by the Barrett--Joyner--Halenda (BJH)
31
method. Solid state NMR P of samples was recorded on AV500S - 500 MHz High Resolution
Multinuclear FT-NMR Spectrometer at 121.4 MHz with a 5mm CP/MAS probe and magic
spinning frequency of 5 KHz and adenosine triphosphate was chosen as a standard. The IR
spectra of samples (as KBr pellets) were recorded using a Schimadzu FTIR spectrophotometer in
the range of 400--4000 cm1. The number of acidic sites on the catalyst surface was determined
by titration method. Microstructural characterization was conducted using Tecnai G2 F30 S-Twin
(FEI; Super Twin lens with Cs = 1.2 mm) instrument operated at an accelerating voltage at 300
kV, having a point resolution of 0.2nm and lattice resolution of 0.14nm. Program Digital
Micrograph (Gatan) was used for image processing. Scanning Electron Microscopy was used to
confirm the structural morphology of PPA functionalized silica polymer nanocomposites, Energy
Dispersive X-ray Analysis (EDX, Oxford INCA250 energy, UK) was also performed. The TEM
samples were prepared by drying a droplet of PPA functionalized silica polymer nanocomposites
on a carbon grid. EDX was also performed.
Results and Discussion
Characterization of PPA functionalized silica polymer nanocomposites (SBA/PS/PPA)
Powder X-ray diffraction pattern (PXRD) of SBA/PS/PPA samples (Figure.1) at low angles is
similar to SBA-15 materials. The diffraction peaks at (100), (110), and (200) planes can be
indexed to reflections comprising of two dimensional hexagonal p6mm symmetry indicating that
the materials possess ordered mesoporous structure. However an increase in intensity of the
SBA/PS/PPA compared to SBA-15 indicates a uniform coating of the polymer on the mesopore
7
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
wall [7,25-26]. Solid State NMR, P31of SBA/PS/PPA (Figure.2) exhibits different peaks centered at
-0.3 and -10.85 ppm indicating the distinct nature of phosphorus incorporated inside the silica
framework. The peak in the spectra clearly indicates the presence of PPA over the polymeric
surface[27]
.
N2 adsorption-desorption isotherms were measured at -196C using a Quantachrome AS-1MP
volumetric adsorption analyzer showed a type IV adsorption isotherm (Figure 3) indicating the
mesoporous nature of the samples according to the IUPAC classification. A sharp capillary
condensation step at relatively high pressure with an H1 hysteresis loop indicates the presence of
large mesopores with narrow pore size distributions[25,28]. The surface area, pore volume and
pore diameter decreased with the incorporation of polymer and PPA too, indicating that the PPA
has been incorporated inside the SBA framework. All the structural parameters are included in
Table 1.
FT-IR spectrum of the SBA/PS/PPA samples (Figure.4) showed the vibrational frequencies
similar to PPA, clearly demonstrating the uniform nature of PPA that sustained on the polymeric
surface of SBA-15 mesopores. Moreover the acidity of SBA/PS/PPA was determined by titration
method, wherein the number of acidic sites for SBA/PS/PPA (30%), SBA/PS/PPA (20%) and
SBA/PS/PPA(10%) was found to be 38.5mmol/g,27.36 mmol/g and 13.51 mmol/g respectively.
SEM images along with EDX (Figure.5) indicate uniform morphology of silica polymer
nanocomposites functionalized with polyphosphoric acid. HR-TEM images of SEM/PS/PPA
along with EDX (Figure.6) indicate the presence of the polymer coating and PPA incorporation
8
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
on the mesoporous material. The detailed characterization of SBA/PS/PPA has also been
mentioned in our recent publication [4,24-25]
.
Catalytic Studies
Synthesis of DHPMs were optimized on their respective model reactions (Scheme1,where R =
H).Various parameters were studied to obtain the suitable conditions for the synthesis of DHPMs
compounds[29]. Varied conditions were optimized for the synthesis of different compounds
formed via Biginelli reaction.
A comparative study of the catalyst (Table 2) was done wherein careful analysis of the results
indicates that the polymer coating has a profound role in the activity and selectivity of the
product DHPMs. The catalytic activity was measured in respect to the variations in polymer and
PPA content. Although there was no pronounced difference in the catalytic behavior with
increase in the polymer content in SBA/PS/PPA but maximum yield was achieved with 30 wt%
polymer indicating that the polymer creates the hydrophobic surface which ultimately enhances
the diffusion of the products and leads to higher conversion. Varied amount of PPA from (10 to
30 wt %) impregnated over SBA/PS(30)/PPA gave 92% conversion with 98% selectivity of the
product DHPMs[23]. However only 74% conversion with 92% selectivity of DHPMs over
SBA/PPA alone was obtained, this may be due to higher surface area and better dispersion of
acidic active sites on SBA/PS/PPA than SBA/PPA. It is important to mention here that only 54%
conversion and 70% selectivity was obtained on homogeneous PPA, indicating the need of
heterogenization of PPA. The best catalyst SBA/PS/PPA (30) was selected for further studies.
9
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
The variations in the catalyst weight showed an increasing trend with respect to the catalyst
SBA/PS(30)/PPA. The conversion of DHPMs increased linearly with increase in the wt of
catalyst (Figure.7) up to 100mg but with further increase in the weight, there was a drop in
conversion, indicating that the active centers might have been blocked by the reactants or the
product formed inhibits the access of reactants to the catalyst to undergo further reaction.
In order to chose the medium the reaction was performed in various solvents such as ethanol,
methanol, acetonitrile, chloroform, dichloromethane, toluene, ethylacetate and the best results
were obtained in ethanol solvent with (92%) conversion; 86% yield and 98% selectivity of the
dihydropyrimidinone product; this may be due to better stabilization of enol form of
[30-31]
ethylacetoacetate
in the presence of polar solvent (scheme 2). Hence ethanol was chosen
for further optimization of the synthesis of dihydropyrimidinone.
Furthermore, the higher rate of conversion and selectivity of DHPMs was achieved at 60°C in 6
h (Figure. 8) which remained consistent till 80°C but further increase in temperature led to drop
in conversion to ~80%. Moreover with further increase in temperature does not induce changes
in the selectivity of DHPMs and a favorable temperature was chosen for the reaction.
A probable mechanism(Scheme2) for the synthesis of DHPMs showed that the reaction
progresses in a very smooth manner wherein an intermediate (a, schiff base synthesized from
urea and benzaldehyde) could not be detected on a Thin layer chromatography (TLC) which may
be due to the unstable nature of aliphatic schiff base (B) formed in step 2. Subsequently the
ethanol stabilized enol form of ethylacetoacetate (acting as a nucleophile) reacts with Schiff base
(an electrophilic transition state). SBA/PS/PPA plays a vital role in controlling the rate of the
10
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
reaction by constantly removing the water from the reaction (water repelling property due to
hydrophobicity), thereby resulting in an enhanced acidity and regeneration of catalyst during the
course of the reaction. In order to see the reusability of the catalysts, the catalyst after the
completion of reaction, was filtered thoroughly first with methanol, water and then with
acetone[29]
.
The catalyst was dried at 120°C and subjected for fresh reaction. Recycling of the catalyst was
repeated for 5 cycles without any significant loss in the activity and selectivity indicating the
non-leaching behavior of the acidic contents from the catalyst during the course of the
reaction[29]. The optimized conditions were employed for the synthesis of other substituted
DHPMs and it was observed that the yield of DHPMs increased in presence of electron donating
groups on aldehydes (Table3).
Conclusion
A novel mild acidic functionalized catalytic system SBA/PS/PPA that allowed the precise
control of the polymeric moiety along with the successful dispersion of polyphosphoric acid was
successfully employed for the synthesis of DHPMs with high yield and selectivity. The plausible
mechanism clearly depicts the role of the SBA/PS/PPA catalyst in an increased rate of formation
of the product DHPMs. This can be attributed to the combination of hydrophobicity, textural
properties and the presence of bronsted acidic sites.
11
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Acknowledgements
DS thanks Department of Science and Technology for financial support via DST-Fast track
project SB/FT/CS-011/2013. I would like to acknowledge the support of Dr Ajit Kumar, Vice
Chancellor, NIFTEM. Thanks are due to Delhi University for conducting SEM and adsorption
isotherm, IISc-Bangalore for SSNMR, of the samples.
12
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
References
[1]
276, 923.
Feng, X.; Fryxell, G.; Wang, L.-Q.; Kim, A. Y.; Liu, J.; Kemner, K. Science 1997,
[2]
Al-Sharab, J. F.; Mikmeková, E.; Das, S.; Goswami, A.; El-Sheikh, S. M.; Ismail,
A. A.; Hesari, M.; Maran, F.; Asefa, T. Microsc. Microanal. 2014, 20, 1900.
[3]
[4]
Han, Y.; Zhu, Y.; Zhang, D. Adv.Hierach.Nanostruct.Mat. 2014, 1.
Dubey, A.; Sachdev, D.; Srivasatava, N. M. Advanced Materials Letters 2013, 4,
39.
[5]
[6]
Wight, A.; Davis, M. Chem. Rev. 2002, 102, 3589.
Clippel, F.; Dusselier, M.; Van de Vyver, S.; Peng, L.; Jacobs, P. A.; Sels, B. F.
Green Chem. 2013, 15, 1398.
[7]
Choi, M.; Kleitz, F.; Liu, D.; Lee, H. Y.; Ahn, W.-S.; Ryoo, R. J. Am. Chem. Soc.
2005, 127, 1924.
[8]
[9]
Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem. Int. Ed. 2005, 44, 7852.
Macquarrie, D. J.; Tavener, S. J.; Harmer, M. A. Chem. Commun. 2005, 2363.
[10] Liu, F.; Kong, W.; Wang, L.; Yi, X.; Noshadi, I.; Zheng, A.; Qi, C. Green Chem.
2015, 17, 480.
13
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
[11] Hodgson, G. K.; Impellizzeri, S.; Hallett-Tapley, G. L.; Scaiano, J. C. RSC Adv.
2015, 5, 3728.
[12] Qian, D.; Zhang, J. Beilstein J.Org.Chem. 2011, 7, 808.
[13] Boeck, F.; Blazejak, M.; Anneser, M. R.; Hintermann, L. Beilstein J.Org.Chem.
2012, 8, 1630.
[14] Sharma, N.; Sharma, U. K.; Kumar, R.; Sinha, A. K. RSC Adv. 2012, 2, 10648.
[15] Ramos, L. M.; Ponce de Leon y Tobio, A. Y.; dos Santos, M. R.; de Oliveira, H.
C.; Gomes, A. F.; Gozzo, F. C.; de Oliveira, A. L.; Neto, B. A. The J.Org.Chem. 2012, 77,
10184.
[16] Lal, J.; Sharma, M.; Sahu, P. K.; Agarwal, D. D. Proc.Nat.Acad.Sci.A-Ph.Sci.
2013, 83, 187.
[17] Girija, D.; Naik, H. B.; Kumar, B. V.; Sudhamani, C.; Harish, K. Arab.J.Chem.
2014.
[18] Moosavifar, M. Comp.R.Chemie. 2012, 15, 444.
[19] Zeinali‐Dastmalbaf, M.; Davoodnia, A.; Heravi, M. M.; Tavakoli‐Hoseini, N.;
Khojastehnezhad, A.; Zamani, H. A. ChemInform 2011, 42.
[20] Handore, K. N.; Bhavsar, S. V.; Pande, N.; Chhattise, P. K.; Sharma, S. B.;
Dallavalle, S.; Gaikwad, V.; Mohite, K. C.; Chabukswar, V. V. Polym-Plast.Tech.Eng. 2014, 53,
734.
14
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
[21] Tu, S.; Fang, F.; Miao, C.; Jiang, H.; Feng, Y.; Shi, D.; Wang, X. Tetrahedron
Lett. 2003, 44, 6153.
[22] Zeinali‐Dastmalbaf, M.; Davoodnia, A.; Heravi, M. M.; Tavakoli‐Hoseini, N.;
Khojastehnezhad, A.; Zamani, H. A. ChemInform 2011, 42, no.
[23] Sachdev, D.; Dubey, A. Catal. Lett. 2011, 141, 1548.
[24] Sachdev, D.; Wilson, G. R.; Sharma, A. New J. Chem. 2015.
[25] Sachdev, D.; Dubey, A. Catal. Commun. 2013, 39, 39.
[26] Che, S.; Liu, Z.; Ohsuna, T.; Sakamoto, K.; Terasaki, O.; Tatsumi, T. Nature
2004, 429, 281.
[27] Errede, L.; Newmark, R. A.; Hill, J. R. Macromol. 1986, 19, 651.
[28] Han, Y.-J.; Kim, J. M.; Stucky, G. D. Chem. Mater. 2000, 12, 2068.
[29] Naik, M. A.; Sachdev, D.; Dubey, A. Catal. Commun. 2010, 11, 1148.
[30] Markov, P.; Shishkova, L.; Zdravkova, Z. Tetrahedron Lett. 1972, 13, 4017.
[31] Powling, J.; Bernstein, H. J. Am. Chem. Soc. 1951, 73, 4353.
15
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table1. Structural Parameters of functionalized mesoporous silica nanocomposites.
Materials
Surface area
(m2/g)
Pore Volume
(cm3/g)
Pore Size
(nm, #9)
SBA-15
678
391
1.2
7.4
4.7
SBA/PPA(30)
0.43
SBA/PS(30)
312
221
114
0.59
0.46
0.20
4.0
3.8
2.8
SBA/PS(30)/PPA(30)
SBA/PS(30)/PPA(10)
16
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table 2 Effect of varied catalyst on the conversion of DHPMs
Catalyst*
DHPMs
Conversiona(%)
54 (48%)
74 (70%)
70 (67%)
66 (65%)
92 (86%)
82 (77%)
76 (70%)
bSelectivity(%)
PPA
70
SBA/PPA(30)
SBA/PPA(20)
SBA/PPA (10)
SBA/PS/PPA (30)
SBA/PS/PPA(20)
SBA/PS/PPA(10)
92
92
92
98
96
98
aethyl acetoacetate -1 mmol, benzaldehyde -1 mmol, urea-1.5 mmol, catalyst-100mg solvent-
ethanol Temperature- 60°C. %Conversion as indicated from the authentic samples.* ()
parenthesis indicates the percentage loading
bselectivity of the product only () parenthesis in the (%) conversion column indicates (%)
isolated yield.
17
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Table 3 Effect of substituent on the yield of DHPMs
Substituted
aldehydes
X
O
a %yield
CHO
CHO
86
O
O
O
92
75
65
OMe
CHO
Cl
CHO
NO2
18
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
CHO
S
80
OH
CHO
S
50
Cl
aConditions as indicated in Table 2
19
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
40000
35000
30000
25000
20000
15000
10000
5000
SBA-15
SBA/PS/PPA
0
-5000
0
1
2
3
4
5
2 theta (degrees)
Fig 1: PXRD pattern of mesoporous silica and functionalized mesoporous silica (a) SBA-15
(b) SBA/PS/PPA
20
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Fig2: 31P spectra of mesoporous silica polymer nanocomposites functionalized with PPA
(SBA/PS/PPA).
21
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
40
SBA/PS(30)
SBA/PS(30)/PPA(30)
35
30
25
20
15
10
5
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/Po)
Fig 3: Nitrogen adsorption-desorption isotherms of SBA/PS and SBA/PS/PPA.
22
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
90
PPA
SBA/PS/PPA
80
70
60
50
40
30
20
10
0
Polymeric C
C=C
O-H stretching
-10
-20
Si-O stretching
4000
3500
3000
2500
2000
1500
1000
500
wavelength cm-1
Fig.4: FT-IR spectra of polyphosphoric acid and functionalized mesoporous silica (a) PPA
(b) SBA/PS/PPA.
23
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Fig 5 SEM showing uniform morphology of Polyphosphoric acid functionalized silica
polymer nanocomposites (SBA/PS/PPA) with EDX
24
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Fig.6 TEM image of polyphosphoric acid functionalized silica polymer nanocomposite
(SBA/PS/PPA) with EDX.
25
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
100
(%) dihydropyrimidinone
80
60
40
20
0
0
20
40
60
80
100
120
wt of catalyst (mg)
Fig.7 Effect of catalyst weight on the conversion of DHPMs. (Conditions as given in Table
2)
26
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
100
(% conversion)
80
60
40
20
0
20
40
60
80
100
Temperature (oC)
Fig.8 Effect of [19]reaction temperature on the conversion of DHPMs. (Conditions as given
in Table 2)
27
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
R
CHO
SBA/PS/PPA
Ethanol
(NH2)2C=X
Et2OC
H3C
CH3COCH2COOEt
+
+
NH
R
Urea
Ethylacetoacetate
Aryl aldehyde
N
H
X
X= O, S
DHPMs
Scheme 1. Biginelli Reaction
28
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Scheme2 Plausible reaction mechanism for the synthesis of DHPMs (Conditions as given in
Table 2)
29
ACCEPTED MANUSCRIPT