Ce/SiO2 composite as an efficient catalyst for the multicomponent one-pot synthesis of substituted pyrazolones in aqueous media and their antimicrobial activities

Article abstract of DOI:10.1016/j.molcata.2015.11.004

We describe here the preparation and characterization of a Ce/SiO₂ catalyst and its application in an eco-friendly and convenient synthesis of pyrazolone derivatives via one-pot multicomponent reaction of 2-naphthol, aldehydes, phenylhydrazine

Full text of DOI:10.1016/j.molcata.2015.11.004

Accepted Manuscript
Title: Ce/SiO2 composite as an efficient catalyst for the
multicomponent one-pot synthesis of substituted pyrazolones
in aqueous media and their antimicrobial activities
Author: Adinarayana Murthy Akondi Mannepalli Lakshmi
Kantam Rajiv Trivedi Jagadeesh Bharatam Sahitha Phani
Babu Vemulapalli Suresh K. Bhargava Sudheer Kumar
Buddana Reddy Shetty Prakasham
PII:
S1381-1169(15)30144-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.11.004
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Journal of Molecular Catalysis A: Chemical
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26-9-2015
6-11-2015
9-11-2015
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Ce/SiO2 composite as an efficient catalyst for the multicomponent one-pot synthesis of
substituted pyrazolones in aqueous media and their antimicrobial activities
Adinarayana Murthy Akondi,a Mannepalli Lakshmi Kantam,*a,b Rajiv Trivedi,*a Jagadeesh
Bharatam,c Sahitha Phani Babu Vemulapalli,c Suresh K Bhargava,d,e Sudheer Kumar
Buddana,f and Reddy Shetty Prakashamf
aInorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology,
Hyderabad 500007, India, mlakshmi@iict.res.in; trivedi.iict@gov.in, Fax: +91-40-2716-
0921; Tel: +91-40-2719-3510
bDepartment of Chemical Sciences, Tezpur University, Napaam 784028, Assam, India. E-
mail: mlk@tezu.ernet.in
cCentre for NMR and Structural Chemistry; CSIR-Indian Institute of Chemical Technology,
Hyderabad 500007, India.
dRMIT-IICT Research Centre, CSIR-Indian Institute of Chemical Technology, Hyderabad
500007, India.
eAdvanced Materials & Industrial Chemistry Group, School of Applied Sciences, RMIT
University, Melbourne, Australia.
fBioengineering and Environmental Sciences, CSIR-Indian Institute of Chemical Technology,
Hyderabad 500007, India.

Graphical Abstract

Highlights
► Multicomponent reactions provide a convenient platform to construct complex
polycyclic structural scaffolds.
► Ce-SiO2 composite as a selective and reusable solid catalyst for the synthesis of
polysubstituted pyrazolones.
► Eco-compatibility and aqueous medium protocols are added advantages of the
reaction.
► New Pyrazolone derivatives exhibit good to promising antimicrobial activity.

ABSTRACT
We describe here the preparation and characterization of a Ce/SiO2 catalyst and its
application in an eco-friendly and convenient synthesis of pyrazolone derivatives via one-pot
multicomponent reaction of 2-naphthol, aldehydes, phenylhydrazine and ethyl acetoacetate
under aqueous media. The catalyst was prepared using sol-gel method and characterized by
XRD, XPS, UV-DRS, SEM, TEM and surface area analysis. 2D-NMR technique was utilized
to ascertain the pyrazolone tautomer. The new compounds were evaluated for anti-microbial
activity and exhibited good to promising activity against most of the tested bacterial and
fungal strains.
Keywords: Ce-SiO2 catalyst, One-pot synthesis, Aqueous media, Substituted pyrazolones,
antimicrobial activity.
1. Introduction
N-heterocyclic compounds are found extensively in biologically active pharmaceuticals
and natural products such as hormones, vitamins, alkaloids and are also present in fine and
speciality chemicals [1]. The pyrazolone nucleus is one of the most interesting and
promising heterocyclic scaffolds that occur in many drugs and synthetic products [2].
Pyrazolone moieties are important components in many of the non-steroidal anti-
inflammatory drugs (NSAIDs) however, in recent times they have also displayed versatile
role in the treatment of cerebral ischemia and cardiovascular diseases [3]. The pyrazolone
moiety has gained increasing attention due to its diverse pharmacological properties such as
analgesic [4, 5], antitubercular [6], antifungal [7], antibacterial [8], anti-inflammatory [9, 10],
antioxidant [11] and antitumor activities [12]. The ease of preparation and rich biological
activities of pyrazolone framework makes it an interesting template for organic,
combinatorial and medicinal chemistry [13-16].
The multicomponent reaction (MCR) strategy offers significant advantages over
conventional multistep synthesis due to its flexible, convergent and atom economic nature
[17-19]. These reactions represent environmentally friendly processes by virtue of reduced
number of steps, lower energy consumption and minimized waste production [20, 21].
Diversified arrays of valuable heterocyclic ensembles can easily be constructed using such
multicomponent reactions [22]. The adducts obtained from such reactions often display

pronounced biological activities [23]. The multicomponent reactions can be conducted in
organic as well as aqueous media. Most often the organic media becomes the choice of
solvent due to its ability to form single phase by dissolving all the components. Organic
processes conducted in an environmentally benign reaction media are always preferred by the
industry [24, 25]. Moreover, the water based MCRs for the constructions of bioactive
heterocycles are currently gaining much interest [26]. Water, a readily available natural
resource, has a huge potential as a media for chemical reactions. Water being non-hazardous,
environment friendly, non-inflammable and inexpensive medium can be adopted to avoid the
unwanted side reactions caused by the organic solvents [27-29]. According to recent reports
in the literature, it has been demonstrated that organic reactions performed in water as a
solvent are faster and display novel reactivity profiles [30]. In order to comply by the basic
principles of green chemistry such as “minimization of waste” and “replacement of
stoichiometric to catalytic reactions” [31], the focus of our research interest lies in the
development of selective and reusable solid catalysts for the synthesis of heterocyclic
molecules [32-35]. In continuation of this theme, we herein wish to report the synthesis of
pyrazolone scaffolds through multicomponent reaction in water medium.
Cerium salts are frequently used for catalysis and their effectiveness can be endorsed by
their moderate to low toxicity, ease of handling, reasonable cost and convenient usage as one-
electron redox system. However, their use in stoichiometric amounts often impediment the
economic and environmental aspects. Therefore, the use of heterogenized version of Ce salts
is a preferable choice for green organic transformations. Silica is extensively used as a
support due to its high specific surface area, greater flexibility and thermal durability. Silica
supported active species in well-dispersed form provides a suitable environment for various
applications over a wide range of temperatures [36]. The insoluble solid catalysts tend to
minimize the waste generated due to catalyst separation and disposal. They can be easily
incorporated into an economically attractive continuous flow processes for the industry [37].
There are quite a few conventional and catalytic methods for the synthesis of 2-aryl-5-
methyl-1H-pyrazol-3(2H)-ones. Literature reports have indicated the use of ultrasound,
microwave and thermal modes of synthesis. Among them, a four component reaction
catalysed by PTSA [38] and copper iodide [39] catalyst has been utilized recently. Such
reactions often involve high catalyst loading, elongated reaction time, drastic reaction
conditions and formation of non-desirous side products. The intrinsic reaction conditions
preferably utilize strong acidic media, high reaction temperatures and stoichiometric ratios

resulting in tedious work-up, operational complexity and waste generation. Thus, there is
tremendous scope for the development of new greener synthetic protocols to assemble such
frameworks.
In an earlier work, we have reported the synthesis of Ce-MCM-41 catalyst and its
application in the multicomponent reaction which demonstrated a promising anti-microbial
activity against many microbes [40]. We describe here, in continuation with our on-going
research, the preparation of a new cerium–silica composite (Ce–SiO2) and its application in
the multicomponent reactions. The inherent properties of Ce-SiO2 catalyst such as
environmental compatibility, reusability, greater selectivity, operational simplicity, non-
corrosiveness, low cost and ease of isolation makes this catalyst useful to carry out the
reaction. This new solid acid catalyst was successfully employed in the one-pot preparation
of a series of 2-aryl-5-methyl-1H-pyrazol-3(2H)-ones in water. These pyrazolone derivatives
were further screened for their antimicrobial activities. A simple method for the synthesis of
pyrazolone derivatives by using benzaldehyde, phenyl hydrazine, ethyl acetoacetate and 2-
naphthol is shown in Scheme 1.
2. Experimental methods
2.1. General remarks
The Thin Layer Chromatography (TLC) was performed on Merck silica gel 60 F254
plates using ethyl acetate and hexane as eluting agents. Thin layer chromatography plates
were visualized by exposure to UV-light/iodine and/or by immersion in an acidic staining
solution of phosphomolybdic acid followed by heating on a hot plate. Purification of
products was carried out by column chromatography using silica gel and a mixture of ethyl
acetate and hexane as eluting agents. All the products were characterized by Mass, 1H and
13C-NMR spectroscopy. The NMR spectra of samples were acquired on a Bruker Avance
300 MHz, 500 MHz and 700 MHz spectrometer using TMS as an internal standard in CDCl3
and Me2SO-d6. Mass spectra were acquired on a Thermo LCQ fleet ion trap mass
spectrometer. High resolution mass spectra were acquired on a Q STAR XL Hybrid
LC/MS/MS system, Applied Biosystems, USA. FT-IR data were acquired on a Thermo
Nicolet Nexus 670 FT-IR spectrometer with DTGS KBr detector. XPS spectra were recorded
on a Kratos AXIS 165 with a dual anode apparatus using the Mg Kα anode. X-ray powder
diffraction data was collected on a Siemens/D-5000 diffractometer using Cu Kα radiation.
Pore size distribution measurements were executed on Auto sorb-1 instrument (Quanta

chrome, USA) using by nitrogen physisorption. The particle size and external morphology of
the samples were observed on a Philips TECNAI F12 FEI transmission electron microscopy
(TEM). SEM-EDX was performed on a Hitachi SEM S-520, EDX-Oxford Link ISIS-300
instrument. Diffuse reflectance UV/Vis spectra for samples as KBr pellets were recorded on
a GBC Cintra 10e UV-VIS spectrometer in the range 200 to 800 nm with a scan speed 400
nm per minute. The melting points were measured in open capillary tubes and are
uncorrected.
2.2. Synthesis of Ce–SiO2 composite by the sol–gel method
In a Becker cup, adapted with a magnetic stirrer, were placed 5 mL of ethanol, 2 mL of
deionized H2O and 3 drops of conc. HCl. Next, 5.0 mmol of anhydrous CeCl3 was added in
one portion. The mixture was vigorously stirred until total dissolution (ca. 15 min). To this
clean homogeneous solution 20 mmol of TEOS was added in one portion in a continuous
flow. This fresh mixture was stirred continuously for an additional 20 minutes. The magnetic
stirrer bar was removed and the flask was covered with a clock glass and left to rest until the
formation of a glass material (ca. 5 days). After this, the glass material was triturated in a
mortar and the light yellow solid was subjected to the thermal treatment at 180 °C during 24
hours. After this time, the material was washed with 20mL of ethanol followed by 20 mL of
deionized H2O. The material was subjected again to the thermal treatment at 100 °C for
additional 24 hours.
2.3. General procedure for synthesis of 2-phenyl-5-methyl-1H-pyrazol-3(2H)-ones
To a mixture of phenylhydrazine (1 mmol) and ethyl acetoacetate (1 mmol) in water (4
ml) (stirred at room temperature for 10-15 min), aromatic aldehyde (1 mmol), 2-naphthol (1
mmol) and Ce-SiO2 (0.9 mol %) were added and heated to reflux for appropriate times
(monitored by TLC). After completion of the reaction, the heterogeneous catalyst was
recovered from the reaction media by simple filtration. The filtrate was evaporated to afford
the crude solid product which was later purified by column chromatography. The solid
catalyst was washed with hot ethanol and then dried in oven to reuse. The spectral data for
some selected compounds are given below.

4-((2-hydroxynaphthalen-1-yl)(3,4,5-trimethoxyphenyl)methyl)-5-methyl-2-phenyl-1H-
pyrazol-3(2H)-one:
Yellow solid, mp 128-130 °C; 1H NMR (300 MHz, CDCl3): 8.02 (t, 1H, J = 7.2 Hz, Ar-H),
7.80 (d, 1H, J = 7.9 Hz, Ar-H), 7.64 (d, 1H, J = 8.9 Hz, Ar-H), 7.47 (t, 1H, J = 7.5 Hz, Ar-H),
7.33 (t, 1H, J = 7.4 Hz, Ar-H), 7.18 (d, 2H, J = 7.7 Hz, Ar-H), 7.04 (d, 1H, J = 8.8 Hz, Ar-H),
6.90 (t, 2H, J = 7.5 Hz, Ar-H), 6.80 (t, 1H, J = 7.2 Hz , Ar-H), 6.32 (s, 2H, Ar-H), 5.97 (s,
1H, CH), 3.69 (S, 3H, OCH3), 3.52 (s, 6H, OCH3), 2.13 (s, 3H, CH3); 13C NMR (176 MHz,
CDCl3): δ 154.0, 152.8, 146.8, 136.4, 136.2, 135.1, 133.5, 129.4, 129.2, 129.1, 128.8, 126.5,
126.3, 122.7, 122.1, 121.6, 120.9, 120.4, 119.5, 106.8, 104.7, 60.7, 56.0, 36.3, 11.4; HRMS:
m/z Calcd. for C30H29N2O5 [M+H]+ : 497.2071; Found, 497.2050 (Rel. Int.100%). FT-IR
(KBr) ν cm-1 : 3063, 2929, 1593, 1499, 1457, 1414, 1370, 1321, 1233, 1125, 1002, 821, 750,
691, 542.
4-((6-bromobenzo[d][1,3]dioxol-5-yl)(2-hydroxynaphthalen-1-yl)methyl)-5-methyl-2-phenyl-
1H-pyrazol-3(2H)-one:
White solid, 178-179 °C; 1H NMR (300 MHz, CDCl3+Me2SO-d6): 11.0 (bs, 1H, NH), 9.89
(bs, 1H, OH), 7.94 (d, 1H, J = 8.9 Hz, Ar-H), 7.80 (d, 1H, J = 7.7 Hz, Ar-H), 7.69-7.72 (m,
3H, Ar-H), 7.41 (t, 3H, J = 7.5 Hz, Ar-H), 7.21-7.31 (m, 1H, Ar-H), 7.16-7.19 (m, 2H, Ar-H),
7.09 (d, 1H, J = 8.7 Hz, Ar-H), 6.71 (s, 1H, Ar-H), 6.01 (m, 2H, CH2, CH), 5.98 (s, 1H,
CH2), 1.86 (s, 3H, CH3); 13C NMR (126 MHz, Me2SO-d6): δ 163.3, 153.3, 148.4, 146.5,
146.3, 137.1, 134.7, 133.5, 128.8, 128.6, 128.5, 126.3, 124.4, 122.6, 122.2, 119.4, 118.6,
118.2, 113.8, 112.2, 110.6, 107.0, 101.6, 38.2, 11.3; HRMS: m/z Calcd. for C28H22BrN2O4
[M+H]+ : 529.0757; Found, 529.0740 (Rel. Int.100%). FT-IR (KBr) ν cm-1: 3450, 3062,
2906, 2797, 1732, 1598, 1550, 1501, 1475, 1411, 1373, 1312, 1249, 1158, 1104, 1038, 933,
859, 832, 813, 783, 748, 720, 686, 628, 570.
2.4. Evaluation of antimicrobial activity by plate method
Well plate method was followed for both antibacterial and antifungal activities for
measuring the zone of inhibition by compounds against selected test organisms. Six bacterial
strains which include three gram negative bacteria such as Salmonella typhi, Salmonella
paratyphi, Pseudomonas aeruginosa and three gram positive bacteria such as Bacillus
subtilis, Micrococcus luteus and Streptococcus mutans. While, Candida albicans and
Trichoderma viride strains were used for determination of antifungal activity. Initially all the

above bacterial strains were grown in nutrient broth for 24 hours at 37oC and fungal strains
were grown in Czapek dox broth. All the synthesized compounds were diluted with DMSO
to get final concentration of 1 mg/ml. Medium and the Petri plates were initially sterilized at
121oC for 15 min. Under sterilized environment, the agar medium was poured into plates.
After solidification, 60 µl of test inoculum was spread on the plates using sterile spreader.
Wells were made with sterile cork borer and in each well exactly 100 µl of sample were
loaded. Control and standard were also placed in separate wells in each plate. The plates were
first incubated for 20 – 30 min at 4oC to allow the compounds to diffuse into the agar, and
then subsequently incubated for 24 h at 37oC for antibacterial and 48 h for antifungal activity.
Zone diameters were expressed in mm using calibrated scale. Experiment was performed in
triplicate and average values were reported to minimize the deviations.
3. Results and discussion
Water, as a reaction media, enhances the synthetic efficiency of a multicomponent
reaction while conserving the environmental benefits [41] and the use of such protocol can
thus establish an ideal green synthetic reaction condition. Knoevenagel condensation
reactions, often utilized for the construction of polyfunctional compounds, can be
conveniently performed under aqueous environments. These polyfunctional compounds can
be combined with other complexity-generating reactions such as inter- or intramolecular
Diels–Alder, Michael addition reactions, etc., thereby forming different diverse heterocyclic
structures [42]. Herein, the emphasis is focused on conducting a complex multi-component
reaction in the presence of a solid acid catalyst under aqueous media to obtain poly-
substituted pyrazolones. These pyrazolone derivatives will be screened for their antibacterial
and antifungal activity in the hope of discovering new structural leads serving as
antimicrobial agents.
3.1. Characterization of ceria–silica composite
Taking into account our interest to explore the ability of cerium (IV) compounds as
Lewis acid catalysts [43-45], we decided to synthesize a new Ce–SiO2 composite based on
the sol–gel method [46]. Thus, requisite amounts of cerium chloride and
tetraethylorthosilicate were taken under appropriate reaction conditions to yield the Ce-SiO2
composite. The glassy composite was crushed and heated to give a fine pale yellow powder.
Textural properties like BET specific surface area, pore volume, and average pore diameter
of Ce-SiO2 have been assessed from N2 adsorption–desorption isotherm measurements. The

specific surface area of the Ce/SiO2 composite, analysed through BET method, was found to
be 197 m2g-1. The sample showed isotherm of type IV having inflection around P/P0 =0.7–
0.85. The BJH analysis showed a pore diameter of 66.4 Å and a pore volume of 0.9 cm3g-1,
for Ce-SiO2 composite, suggesting a mesoporous material (Fig. 1) [47, 48].
The chemical purity of the sample as well as their stoichiometry was analysed by EDAX
studies. The EDAX spectrum (Fig. 2) showed the presence of cerium, oxygen and silicon as
the only elementary components. The wide angle powder X-ray diffraction (XRD) patterns
of ceria–silica sample are shown in Fig. 3. Peaks observed at 2θ = 28.6, 32.8, 47.5, 56.3 and
76.7 degrees in both the samples (Fig. 3a and 3b) are attributed to the (111), (200), (220),
(311) and (331) reflection planes of typical face-centred cubic CeO2 [49, 50]. These
diffraction peaks clearly specify that Ce(III) ion incorporated in the silica framework has
been oxidized to more stable Ce(IV) species during sol–gel synthesis and calcination process
in presence of air. The similar diffraction patterns in both fresh and used (after 5th cycle)
samples relate to framework similarity in the catalysts.
XPS technique has been used to understand the chemical nature of cerium in silica
matrix and interaction between supported CeO2 with silica frameworks. Fig. 4a and 4b
shows Ce 3d and Si 2p electron core level X-ray photoelectron spectra of Ce-SiO2 composite.
The XPS signal, at binding energies 887.45 eV and 905.25 eV (Fig. 4a), can be assigned to
the Ce 3d5/2 and Ce 3d3/2 respectively [51-53]. The only peak near BE value ca. 103 eV in Si
2p XPS spectra (Fig. 4b) corresponds to the presence of SiO2 species in the catalyst. The
UV-vis absorbance of Ce-SiO2 originates from a charge transfer transition from
(ligand→metal) O 2p to Ce 4f and the spectrum (Fig. 5) displays two absorption peaks with
intensity maxima around 220 and 330 nm which can be attributed to the presence of two
different types (tetra-coordinated and hexa-coordinated) of Ce4+ species [47, 48, 50].
The SEM and TEM images of the Ce/SiO2 composite after five cycles (Fig. 6) did not
show any substantial changes in the morphology of the catalyst, which specifies that the
integrity of the catalyst is preserved throughout the recycling studies. The above studies thus
endorse a stable structure of the catalyst and cerium is tightly bound to the support, which in
turn facilitates efficient recycling (Fig. 7). The ICP-AES analysis revealed that the
concentration of Ce in both fresh (4.54 wt. % Ce) and after 5th cycle catalyst (4.48 wt. % Ce)
was almost similar. This denotes that Ce is tightly bound to the support and no leaching of
the catalyst occurs upon it reuse.

3.2. Optimization studies
In the first series of experiments, the effect of the catalyst loading, the nature of the
solvent, the optimum reaction time and temperature were examined. The four component
reaction conducted on a 1 mmol scale reaction of benzaldehyde, 2-naphthol, phenyl
hydrazine and ethyl acetoacetate at reflux temperature, under catalyst free conditions, formed
trace amount of the product (Table 1, entry 1). To enhance the yield of the product and to
optimize the reaction conditions, a number of alternative cerium based catalysts, preferably
various cerium salts and different loadings of Ce-SiO2 were investigated (Table 1).
Heterogeneous Ce-SiO2 composite exhibited better catalytic activity among various cerium
catalysts under aqueous conditions (Table 1, entry 5).
Further, different loadings of Ce-SiO2 were examined under given reaction conditions.
The increase in the amount of Ce-SiO2 from 0.3 to 0.9 mol% shortened the reaction time as
well as enhanced the yield of product from 62% to 92% (Table 1, entries 5-9). An increase in
the catalyst quantity had no significant effect on reaction time and the yield of product (Table
1, entry 10). A gradual increase in the reaction temperature from 60°C to 80°C to reflux
temperature hastened the reaction to give the desired product in optimum yield (Table 1,
entries 7, 8 and 9). The effect of solvents such as H2O (Table 1, entry 9), CH3CN (Table 1,
entry 11), CH3OH (Table 1, entry 12), EtOH (Table 1, entry 13) and toluene (Table 1, entry
14) was also examined at reflux temperatures and it was observed that the best result were
obtained in the presence of water as a solvent. Catalytic amount of pure SiO2 did not show
valued effect on the reaction system emphasizing the role of cerium metal as a crucial species
in the Ce/SiO2 composite (Table 1, entry 15).
The optimized reaction conditions were then extended for a series of different aldehydes
(1a–p) to assess the versatility of the Ce/SiO2 catalysis. The results are summarized in Table
2. The reaction progressed almost with same ease with aromatic, heterocyclic and aliphatic
aldehydes. Various functional groups such as nitro (NO2), halo (X), hydroxyl (OH), methoxy
(OCH3) and methyl (CH3) were tolerated. No significant change in the yield was observed
when more than one substituent was present in the phenyl ring (Table 2, entries 9-12 and 15).
Hence, electronic and steric factors played a negligible role in this protocol.

3.3. Catalyst Recycling
The catalyst recycling experiment was done using the model reaction of benzaldehyde,
2-naphthol, phenyl hydrazine and ethyl acetoacetate and 0.9 mol% of the catalyst in H2O at
reflux temperature. After completion of the reaction, the catalyst was easily separated by
filtration and washed with hot ethanol, dried under oven and reused in the subsequent
reaction. In addition, the absence of any leached cerium in the ICP-AES analysis of the
filtrate confirmed that the catalytic process was completely heterogeneous. Almost
quantifiable catalyst could be recovered from each run. The reusability of the catalyst was
tested up to 5 successive runs (Fig. 7), with only marginal decrease in catalytic activity
(Table 2, entry 1). It was found that the catalyst maintained good activity for a minimum of
five cycles. The TEM images of the catalyst after five cycles (Fig. 6c and 6d) showed that
the structure of the catalyst does not alter during the course of study. The catalyst was further
reused for the 6th and 7th cycle. A drastic change in the recovery amount and yields (78% and
59% respectively for 6th and 7th cycles) of the desired product was observed due to loss of
catalyst activity. Moreover, a change in the catalyst morphology (as evident from the TEM
analysis) was also observed on further recycling experiments (See supplementary
information).
3.4. 2D NMR studies
The structure of the final product was unequivocally established from the extensive 1D-
(1H and 13C) and 2D- (1H-1H DQFCOSY, 1H-1H ROESY, 1H-13C multiplicity edited HSQC,
1H-15N HSQC and 1H-13C HMBC) NMR spectroscopy analysis of selected compound 8o
(Fig. 8). The NMR spectra were acquired on Bruker Avance 500 MHz (for 1H) and 700 MHz
(for 1H) spectrometers and are referenced to δ 2.50 ppm and δ 39.51 ppm in DMSO-d6
solvent for 1H and 13C, respectively. The chemical shift values are presented in ppm (parts
per million) units. The existence of NH form of the final product among the three possible
CH, OH and NH forms (Fig. 9), was unambiguously confirmed from the observed
characteristic 1H- 15N HSQC cross peak between N-3/H-3 (Fig. 10a) and noe cross peak
between CH3/NH protons (Fig. 10b). In the 1H NMR spectrum of compound 8o, the NH and
OH protons appear as broad singlets at 11.0 and 9.89 ppm, respectively. The chiral proton
(H-7) gives a singlet at 6.00 ppm and show HSQC correlation with carbon (C-7) at 38.19
ppm (see SI). Furthermore, the H-7 proton shows HMBC correlations with C-6, C-13, C-1'',
C-8, C-4, and C-1 at 107.0, 113.8, 118.6, 134.7, 148.4 and 163.3 ppm, respectively (see SI).

The methyl protons appear as a singlet at 1.86 ppm and the methyl carbon (C-5) appear at
11.3 ppm (see SI). Moreover, the methyl protons show HMBCs with C-6 and C-4 at 107.0
and 148.4 ppm, respectively (see SI).
3.5. A tentative mechanistic pathway for the multicomponent reaction
A tentative mechanism for the formation of compound 8 is proposed in Scheme 2. The
condensation of aldehyde (1), 2-naphthol (2), and 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one
(3) may occur by Knoevenagel condensation and Michael addition via two pathways
(Scheme 2) [38, 39]. As shown in Scheme 2, the solid acid catalyst Ce-SiO2 (≡ Ce (IV))
activates the reactants and the intermediates in this reaction. In the first pathway, the
intermediate 4 is formed by Knoevenagel condensation of 1 and 2 in the presence of Ce-SiO2,
followed by Michael addition of 3 to 4 to form product 8. In the second pathway, the
intermediate 5 is formed by Knoevenagel condensation of 1 and 3 in the presence of catalyst,
followed by Michael addition of 2 to 5 to form product 8.
3.6. Biological evaluation
Antimicrobial Activity
All the newly synthesized compounds were evaluated for in vitro antimicrobial activity
against gram-positive bacteria (B. subtilis, S. mutans and M. luteus) and gram negative
bacteria (P. aeruginosa, S. typhi and S. paratyphi) along with two fungal strains (C. albicans
and T. viride). Streptomycin sulphate and ketoconazole were used as standard drug,
respectively for antibacterial and antifungal activity evaluation. It was noticed that all tested
compounds (except 8l) showed promising antibacterial activity with either of the tested
bacterial strains. However, the antibacterial activity profile differed with type of bacterial
strain and nature of compounds. For example compounds 8d, 8e displayed superior inhibitory
activity on gram-positive bacteria Bacillus subtilis, Streptococcus mutans and Micrococcus
luteus respectively. In case of gram negative bacteria the 8e, 8g, 8i and 8k compounds
showed significant activity. The synthesized compounds showed good anti-bacterial activity
ranging from 10.5–27.5 mm zone (Table 3). Critical evaluation of antibacterial profile of the
synthesized compounds further indicated that all halogen and nitro substituted pyrazolone
derivatives showed considerably better antibacterial activity while tri substituted pyrazolone
derivative (8l) showed little or no biological activity with all test bacterial strains. In
addition, pyrazolone derivative (8m) revealed better activity profile compared to compound

8l but not similar to that of halogen and nitro substituted compounds. Further, inter species
difference in antibacterial activity for synthesized compounds also varied. For example
compound 8k (dinitro substituted pyrazolone derivative) denoted better antibacterial activity
with B. subtilis, M. luteus, S. typhi and S. paratyphi compared to S. mutans and P. aeruginosa
suggesting a bacterial strain specificity towards these synthesized compounds. The
compounds were also evaluated for antifungal activity (Table 3) and among the newly
synthesized compounds seven compounds (8d, 8e, 8g, 8i-8k and 8o) showed activity against
Candida albicans and three compounds (8e, 8i and 8k) showed activity against Trichoderma
viride. The antifungal profile of these synthesized compounds further suggested that
compound 8k (dinitro substituted pyrazolone derivative) has commercial importance as this
compound showed better activity than standard i.e., ketoconazole at similar concentration
(100 µg).
4. Conclusions
A new ceria–SiO2 composite prepared through the sol–gel method was successfully applied
as a heterogeneous Lewis acid catalyst in the synthesis of a series of 2-aryl-5-methyl-1H-
pyrazol-3(2H)-ones in good yields. All the newly synthesized compounds were assessed for
anti- microbial activity and showed promising activity against few of the bacterial and fungal
strains. Herein, we have demonstrated a greener approach for the multi-component reaction
using heterogeneous catalysis to prepare small molecules of biological interest.
Acknowledgment
R.T acknowledges the XIIth five year plan project IndusMagic, CSC-0123 of CSIR-IICT
for financial support. A.A.M thanks the Council of Scientific and Industrial Research, India
for the award of a Research Fellowship.

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Figure captions
Fig. 1. N2 adsorption–desorption isotherms of the Ce-SiO2 composite; inset: BJH pore size
distribution curve.
Fig. 2. The EDX spectra of the Ce-SiO2 composite.
Fig. 3. Powder XRD patterns of (a) fresh and (b) used Ce-SiO2 catalyst.
Fig. 4. XPS analysis showing (a) Ce 3d and (b) Si 2p core level spectra of the Ce-SiO2
composite.
Fig. 5. UV-DRS spectra of the Ce-SiO2 catalyst.
Fig. 6. SEM (a) fresh & (b) used and TEM (c) fresh & (d) used pictures of theCe-SiO2
catalyst.
Fig. 7. Recycling experiment of Ce-SiO2.
Fig. 8. Schematic representation of the characteristic 1H-13C HMBC correlations (shown as
red arrows) of the compound 8o.
Fig. 9. Tautomeric forms of pyrazolone 8.
Fig. 10. Expanded region of (a) 1H-15N HSQC (Heteronuclear Single-Quantum Correlation)
and (b) 1H-1H ROESY (Rotating frame Over Hauser Effect Spectroscopy) spectrum of
compound 8o(Avance 700 MHz, DMSO-d6, 25 °C).

Figure 1
Figure 2

Figure 3
Figure 4

Figure 5
Figure 6

Figure 7
Figure 8

Figure 9
Figure 10

Schemes
Scheme 1. General synthesis of 1H-3-pyrazolones
Scheme 2. Mechanistic considerations

Table 1. Screening of reaction parametersa
Entry
1.
2.
3.
4.
5.
6.
7.
8.
Catalyst
-
CeCl3
Ce(SO4)2
CeO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
Ce-SiO2
SiO2
loading
-
Solvent
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Temp (°C) Time (min) Yield (%)b
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
60
120
120
120
120
120
80
Traces
54
60
61
62
86
74
90
5 mol%
5 mol%
5 mol%
0.3 mol%
0.6 mol%
0.9 mol%
0.9 mol%
0.9 mol%
1.2 mol%
0.9 mol%
0.9 mol%
0.9 mol%
0.9 mol%
5 mol%
100
80
80
9.
H2O
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
35
35
90
90
90
90
100
92
91
58
55
60
53
Traces
10.
11.
12.
13.
14.
15.
CH3CN
MeOH
EtOH
Toluene
H2O
aReactions were performed using benzaldehyde, 2-naphthol, phenyl hydrazine and ethyl
acetoacetate in 1mmol scale.
bisolated yields after column chromatography.

Table 2. Synthesis of 1H-3-pyrazolones via Ce-SiO2 catalyst in H2Oa
TOFe
(min-
)
Time
(min)
Entry Aldehyde
Productb
Yield (%)c
1
92,92,90,89,8
9d
1.
8a 40
2.56
1.91
2.
8b 50
86
3.
8c 40
88
2.44
4.
5.
8d 55
83
84
1.67
1.69
8e 55

6.
8f 30
87
3.22
7.
8.
9.
8g 35
8h 35
8i 35
92
90
93
2.92
2.85
2.95
10.
8j 55
85
1.72

11.
8k 45
90
2.22
12.
13.
14.
15.
8l 60
92
87
92
91
1.70
1.75
2.92
2.89
8
55
m
8n 35
8o 35

16.
8p 40
92
2.56
aReaction conditions: aldehyde (1 mmol), 2-naphthol (1 mmol), phenylhydrazine (1mmol)
and ethylacetoacetate (1 mmol), Ce-SiO2 (0.9 mol%), Reflux, 35–60 min.
bAll products are characterized by NMR and mass spectroscopy.
cIsolated yields after column chromatography.
dYields from first to fifth cycle.
eTOF = TON/reaction time

Table 3. Anti-microbial activitya
P.
aerugino S. typhi paratyp
sa hi
18.5±0. 27.5±0. 13.5±0. 13.5±0.7 19.5±0. 19.5±0.
71 71 71 71 71
18.5±0. 29.5±0. 18.5±0. 14.5±0.7 19.5±0. 19.5±0.
71 71 71 71 71
19.5±0. 19±0.1. 14.5±0. 10.5±0.7 19.5±0. 20.5±0.
S.
Compou B.
S.
M.
C.
T.
nd
8d
8e
8g
8i
subtilis mutans luteus
albicans viride
14±0.00 0
1
15.5±0. 13.5±0.
1
71
71
13.5±0.
71
0
71
41
71
1
71
71
19.5±0.
71
16.5±0. 14.5±0.7 20.5±0. 19.5±0.
18.5±0. 10.5±0.
18±0.00
71
1
71
71
71
71
12.5±0. 15.5±0. 13.5±0.7
71 71
20.5±0.
71
12.5±0.
71
8j
17±0.00
16±0.00
0
1
22.5±0. 14.5±0. 21.5±0. 13.5±0.7
28.5±0. 21.5±0.
8k
8l
20±0.00 20±0.00
71
71
71
1
71
71
13.5±0.
71
10.5±0. 12.5±0.
0.00
0.00
0.00
0
0
71
71
10.5±0. 19.5±0. 11.5±0.7 12.5±0.
8m
8n
8o
8p
Stdb
12±0.00
15±0.00
0
0
0
0
71
71
1
71
20.5±0. 14.5±0. 18.5±0.
16.5±0.
71
12±0.00
20±0.00
71
71
71
16.5±0.
71
15.5±0. 11.5±0.7 15.5±0. 16.5±0.
13±0.00
13±0.00 0
71
1
71
71
15.5±0. 16.5±0. 13.5±0. 12.5±0.7 14.5±0.
71 71 71 71
16±0.00
0
0
1
21.5±0. 25.5±0.7 22.5±0. 21.5±0.
71 71 71
24.5±0.
71
25±0.00 26±0.00
25±0.00
1
azone of inhibition by compounds against selected test organisms.
bStreptomycin sulphate and ketoconazole were used as standard drug, respectively for
antibacterial and antifungal activity evaluation.