Metal-free heterogeneous and mesoporous biogenic graphene-oxide nanoparticle-catalyzed synthesis of bioactive benzylpyrazolyl coumarin derivatives

Article abstract of DOI:10.1039/c7ra12550j

We report the preparation of graphene oxide nanoparticles (GONPs), a metal-free, heterogeneous, non-toxic, reusable and mesoporous green-(acid)-catalyst obtained by sugar carbonization through a micro-wave chemical synthesis method for the synthesis of bi

Full text of DOI:10.1039/c7ra12550j

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Metal-free heterogeneous and mesoporous
biogenic graphene-oxide nanoparticle-catalyzed
Cite this: RSC Adv., 2018, 8, 17373
synthesis of bioactive benzylpyrazolyl coumarin
derivatives†
b
T. A. J. Siddiqui,a Balaji G. Ghule,
Shoyebmohamad Shaikh,b
b
Pritamkumar V. Shinde,
Krishna Chaitanya Gunturu,a P. K. Zubaidha,a
c
de
bc
*
*
Je Moon Yun,
Colm O'Dwyer,
Rajaram S. Mane
c
*
and Kwang Ho Kim
We report the preparation of graphene oxide nanoparticles (GONPs), a metal-free, heterogeneous, non-
toxic, reusable and mesoporous green-(acid)-catalyst obtained by sugar carbonization through a micro-
wave chemical synthesis method for the synthesis of bio-active benzylpyrazolyl coumarin derivatives
(BCDs) under thermal conditions (50 ꢀC) in ethanol solvent. The obtained products were purified by re-
crystallization from ethanol, assuring usability of GONPs in multicomponent reactions (MCRs) that could
find wide application in the synthesis of a variety of biologically potent molecules of therapeutic
significance.
Received 18th November 2017
Accepted 3rd May 2018
DOI: 10.1039/c7ra12550j
rsc.li/rsc-advances
having high activity, is a continuing effort of censorious
importance.15,16 Based on abundant elements, nding alterna-
Introduction
tive metal-free hetero or homogeneous, selective or high
performance catalysts is alluring and important. The potential
of carbon materials (CMs) as heterogeneous catalysts could be
profound. The term “carbocatalysis” is used to denote the
utilization of metal-free carbon materials as direct/active cata-
lysts rather than inert catalysts. Certain carbonaceous materials
have intrinsic physicochemical properties such as exclusive
structure, gigantic surface area, good pore interconnectivity and
high chemical/thermal stability. The CMs such as activated
carbon, fullerene, single and multi-walled carbon nanotubes,
and graphene oxide (GO) etc., have been manifested as efficient
carbocatalyst. CMs offer new opportunities for the development
of advanced carbon-based nanocatalysts with much improved
catalytic performance, due to their peculiar molecular struc-
tures and optoelectronic properties. Among them, GO is highly
preferred due to its low-cost, 2D structure, rich chemical func-
tionality (solid-acid, solid-base, redox and defect sites) and
chemical stability and mechanical robustness. To date, several
metal-based catalytic organic transformations have been
replaced by GO-based carbocatalytic systems.17–21 To the best of
our knowledge, the majority of GO sheets reported were ob-
tained by the excruciating methods,22–24 typically carried out by
the use of fuming nitric acid, concentrated sulfuric acid,
potassium chlorate, potassium permanganate and hydrogen
peroxide etc. Furthermore, most of the experimental processes
generate waste gas, large amounts of acidic water and a little
nitrogen and sulphur as well as metal ion co-doped GO sheets,
New facets of conventional heterogeneous catalysts have stim-
ulated extensive efforts in nanochemistry methods for
preparing new catalytic materials with greater precision.1 The
most widely explored non-noble and platinum group catalytic
nanomaterials include transition metals, metal oxides,2 and
hybrid materials based on inorganic and enzymes3–7 where the
use of ultraviolet-visible irradiation is oen obligatory. The
development of metal-free green synthesis of ne chemicals
and pharmaceuticals8–10 to overcome the shortcomings of
transition metal-based catalysts (both heterogeneous and
homogenous)11,12 used in the catalytic process nds at niche
place in the industrial community.13,14 As such, the search for
catalysts that combine the toxicological benets of a metal-free
synthesis with the amenities of heterogeneous work-up, whilst
aSchool of Chemical Sciences, SRTM University, Nanded, India-431606
bCenter for Nanomaterials & Energy Devices, School of Physical Sciences, SRTM
University, Nanded, India-431606. E-mail: rajarammane70@srtmun.ac.in
cGlobal Frontier R&D Center for Hybrid Interface Materials, Pusan National
University, San 30 Jangjeon-dong, Geumjeong-gu, Busan, 609-735, Republic of
Korea. E-mail: kwhokim@pusan.ac.kr
dSchool of Chemistry, University College Cork, Cork T12 YN60, Ireland. E-mail: c.
odwyer@ucc.ie
eMicro-nano Systems Centre, Tyndall National Institute, Lee Maltings, Cork T12 R5CP,
Ireland
† Electronic supplementary information (ESI) available: Quantitative analysis data
of energy-dispersive X-ray spectroscopy spectrums, deconvolution of GONPs XPS
C1s peak, structural analysis data of 1H NMR, 13C NMR and mass spectra and
their respective spectra. See DOI: 10.1039/c7ra12550j
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collected and crushed in a mortar pastor to get smooth powder
ꢀ
and annealed at 450 C for 2 h. The sample formed is black in
appearance and smooth in nature. This black powder was
insoluble in water, ethanol, methanol, and benzene but,
partially soluble in dimethyl sulphoxide. The annealed powder
was collected and well characterized by the X-ray diffraction
(XRD, D8-Discovery Bruker, Cu Ka, 40 kV, 40 mA) pattern,
scanned from 20 to 80ꢀ. The Raman spectrum was recorded on
a WITec system within a Raman shi of 1000–2000 cmÀ1. Field-
emission scanning electron microscopy (FE-SEM, Hitachi, S-
4800, 15 kV), energy dispersive X-ray (EDX) analysis, and high-
resolution transmission electron microscopy (HR-TEM) along
with the selected area electron diffraction (SAED) pattern
(Technai F20) were used to observe the surface morphology,
grain size, and elemental conguration, respectively. X-ray
photoelectron spectroscopy (XPS, VG Scientic ESCALAB250)
was utilized to analyze the chemical composition and bonding
status. The Brunauer–Emmett–Teller surface area was obtained
using a Micrometrics ASAP2010 analyzer in a N2 environment
with proper moisture removal from the sample.
Scheme
1 A micro-oven-assisted chemical method used for
obtaining GONPs from market quality sugar.
implying the presence of environmental and health-related
issues with processing and use. Therefore, current scenarios
require the organic chemist to systematize the research in such
a way that it preserves the environment and to develop proce-
dures that are both eco-friendly and economically suitable. One
major objective is, therefore, to simplify and accommodate the
traditional procedures in a modern way with the aim of mini-
mizing pollution effects to the least.25,26 In continuation of
research on the synthesis of highly functionalized BCDs,27–30
here, we report an unveiling protocol for the preparation of the
GONPs which has specic area ꢁ5.15 m2 gÀ1, mean pore
diameter ꢁ4.6 nm with pore volume of ꢁ0.0876 cm3 gÀ1(ref. 31)
and their catalytic applications as novel and stable heteroge-
neous catalyst for the synthesis of BCDs. Environmental pres-
tige, economic soul and recyclability are the advantages of this
novel catalyst. In a nutshell, synthesis of microwave-mediated
GONPs on market quality sugar carbonation was carried out
by irradiating radiations at 400–500 W power for 10–15 min
General procedure for the preparation of benzylpyrazoly
coumarin derivatives
To a mixture of 20% of catalyst and 3 ml of ethanol as a solvent
was added phenyl hydrazine 1 (1 mmol), ethyl acetoacetate 2 (1
mmol), aromatic aldehyde (1 mmol) and 4-hydroxycoumarin 4
ꢀ
(1 mmol) and heated at 50 C. The clear reaction mixture was
stirred for the stipulated time and the mixture becomes turbid
as the reaction proceeds. Aer completion of the reaction
(monitored by TLC), the free-owing solid was dissolved in
dichloromethane to separate the heterogeneous catalyst by
simple ltration method. Aerwards, the ltrate was evaporated
under reduced pressure to obtain crude products as pale-yellow
solids. The products, thus, obtained was recrystallized from hot
ethanol to the get pure compounds as white or pale-yellow
solids. Yields were calculated aer recrystallization (Scheme
2). The isolated compounds were well characterized by 1H NMR,
13C NMR, and Mass spectrum and reported in supportive
information.
ꢀ
duration. The synthesized product was air-annealed at 450 C
for 2 h and the black-product was obtained i.e. GONPs
(Scheme 1). The GONPs were characterized for their structure,
morphology, grain-size, phase-purity, porosity, pore-size distri-
bution, elemental composition and catalytic activity.
Results and discussion
Experimental details
Chemicals
Fig. 1a shows the X-ray diffraction pattern of as-prepared
GONPs, which is in accordance with (002) and (100) planes of
graphitic carbon (JCPDF# 41-1487). The Raman shi spectrum
(Fig. 1b) reveals the presence of two characteristic bands of
carbon at 1352 cmÀ1 (D-band) for the sp3 conguration and
All the reagents were purchased from Merck and Spectrochem
and were used without further purication. The reaction was
monitored by TLC using 0.2 mm Merck silica gel 60 F254 pre-
coated plates, which were seen with UV light. Melting points
were measured by open capillary method.
Synthesis of GONPs through market quality sugar
Dry table-sugar was crushed in a mortar to form uniform
powder and then transferred into a glass beaker and heated
under 400–500 W power radiations for 4–6 times with each of 1–
2 min duration in a microwave oven. The formed charcoal was Scheme 2 Green synthesis of BCDs.
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1592 cmÀ1 (G-band) for the sp2 graphitic conguration. The
0.75 intensity ratio of the D-band over the G-band signies the
graphitic behavior of GONPs.32 The Fourier-transform infrared
(FTIR) spectrum of GONPs (Fig. 1c) conrms basal planes of sp2
carbon functionalized with hydroxyl (–OH), epoxide (C–O–C)
and carboxylic acid (–COOH) groups33,34 qualitatively demon-
strating the presence of GO rather other carbonaceous phases
such as graphite and graphene. The FTIR spectrum shows
broad and strong bands at ꢁ3390 and 1090 cmÀ1 which are
attributed to stretching vibrations and in plane bending vibra-
tion of –OH/H2O. A weak band at ꢁ2926 cmÀ1 corresponds to
the stretching vibrations of the C–H bond. Presence of the
featured bands at ꢁ1622 cmÀ1 and 1716 cmÀ1 conrms the
stretching of C]O. A relatively sharp band at ꢁ1205 cmÀ1 is
due to stretching of –C–O or bending of alkyl groups. Band
appeared at 618 cmÀ1 was assigned to CH deformation. The
eld-emission scanning electron microscopy image of GONPs
exhibits crystallites of irregular dimensions (Fig. 1d). The
globular GONPs are typically interconnected to one another at
the edges. The 72 : 28 composition ratio for carbon and oxygen
elements supports a GO composition (Fig. S1†). Fig. 1e and f
presents digital images of normal and high-resolution trans-
mission electron microscopy where, surprisingly, irregular
grains of 10–50 nm diameters are found. Selected area electron
diffraction pattern in Fig. 1f demonstrates the nanocrystalline
nature of GONPs.35,36 Consistent with X-ray diffraction results,
the interplanar distances of ꢁ0.38 nm (inset of Fig. 1f) and
ꢁ0.28 nm for lattice fringe widths of the (002) and (100) planes,
respectively, are corroborated.
A steep-rise in the nitrogen/adsorption curve is observed
aer a relative pressure (p/po) > 0.3, signifying (Fig. 1g) the
mesoporous nature of GONPs. Correspondingly derived
surface-area and micro-pore surface-area of GONPs are 5.15 and
33.12 m2 gÀ1, respectively. The pore-size distribution curve
(Fig. 1h) of GONPs reveals a total specic pore-volume and
Fig. 1 (a) X-ray diffraction pattern, (b) Raman spectrum (concluding
graphitic nature), (c) FTIR spectrum, (d) FE-SEM, (e) TEM (showing
interconnected and irregular signature), (f) HR-TEM (inset shows
0.38 nm interplanar spacing of (002) plane), (g) adsorption–desorption
isotherm, and (h) pore-size distribution curve (confirming the meso-
porous character) of GONPs.
average pore-diameter of 0.0876 cm3 gÀ1 and 46.13 A, respec-
˚
tively. The deconvoluted high resolution C1s photoemission
peak from GONPs by XPS is shown in Fig. S2.† The calibration of
carbon C1s core-level of adventitious was 284.6 eV, corre-
sponding to the sp2 carbon phase. The C1s peaks were tted
with three contributions: sp2 (284.6 eV), C–O (286.8 eV), C]O
(288.9 eV), respectively.
The amount of oxygen in the GONPs can be explained by
bonding of oxygen to the defected carbon bonds. The above-
mentioned measurements have provided evidence that our
microwave-assisted product is structurally close to GO. Taking
into consideration the importance of carbon-based mate-
rials,35,36 the catalytic behaviour of the prepared GONPs was
studied for the synthesis of BCDs.
Design and development of interweaved molecular scaffolds
for the biological applications have fascinated much attention
as these moieties exhibit wide-ranging and improved bio-
activities. It is anticipated that the integration of the 3-benzyl
coumarin and pyrazolone moieties leading to benzylpyrazolyl
coumarin scaffolds could be fascinating and benecial from
a biological point of view.27–30 Amongst few earlier reports for
this scaffold, the use of glacial acetic acid in water under reux
conditions along with molecular motif of scaffold explored by
single X-ray crystallographic analysis27 and metal containing
catalysts were explored.28–30 Natural carbon was demonstrated
as an alternative to metal and metal oxide-based catalysts due to
its worldwide natural abundance, stability, inexpensiveness and
non-toxic signature.19,20 As part of our interest in exploring
environmentally benign GONPs and other materials as green-
catalysts for the synthesis of several biologically important
heterocyclic compounds, we report a facile one-pot MCR for the
synthesis of various BCDs in ethanol solvent using GONPs
derived from natural sugar. The effects of solvent, catalyst
amount, reaction duration and molar-ratio of the raw material
on the yield of BCDs were studied systematically. The synthesis
of BCDs 4-[(4-hydroxy-2-oxo-2H-chromen-3-yl)-phenylmethyl]-5-
methyl-2-phenyl-1,2-dihydro-pyrazol-3-one with high percent
yield by one-pot four-component condensation reactions is one
of the major objectives of this work. These four-components i.e.
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Table 1 A Four-component reactions was done with different derivatives of aldehydes in the presence of catalytic amount of GONPs
Paper
Sr. no
Aromatic aldehydes
Time (h)
Product (BCDs)
Yield (%)
1
6
90
2
3
4
5
5
8
3
4
93
87
90
93
6
10
93
7
8
9
8
86
87
86
10
7
10
10
88
phenylhydrazine (1), ethyl acetoacetate (2), aromatic aldehyde Furthermore, the optimization study of this four-component
(3) and 4-hydroxycoumarin (4) react in the presence of GONPs as reaction was studied in different solvents (Table 2). The best
a heterogeneous acid catalyst by using ethanol solvent at 50 ꢀC. results were obtained in ethanol solvent, while water as solvent
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results in a sticky product with unreacted starting material. The
For nanostructured carbon materials like GONPs, the weak
reaction without GONPs catalyst could not provide the product adsorption sites are characteristically placed with their basal
even aer 10 h under identical conditions (see entry 1 of Table planes consisting of the hexagonal arrangement of carbon
2). The optimized yield of the product (5) was obtained in atoms, while the high energy sites are typically associated at the
ethanol as a solvent medium using 20% of GONPs as catalyst edges, which are oen saturated with hydrogen atoms attached
(see 10 entry of Table 2). As envisaged, the GONPs displayed to heteroatoms. The edge hydrogen atoms can be replaced by
excellent catalytic properties due to their considerable surface other heteroatoms, e.g. oxygen and/or nitrogen, to provide
area, abundant active sites and unique chemical/physical strong chemical relativities for redox or acid–base reactions.37
properties. The functional groups (hydroxy, epoxide and The GONPs catalyzed Knoevenagel condensation and Michael
carboxyl etc.) as seen in FTIR studies endow suitable acidity and addition reaction supports the present mechanistic pathway in
oxidizing properties providing high tenability of ethanol solvent the synthesis of BCDs.38,39 As we mentioned before GONPs
towards polar organic substrates and reagents. The ethanol which has specic area ꢁ5.15 m2 gÀ1, mean pore diameter
solvent polarity created ambient conditions for good conver- ꢁ4.6 nm with pore volume of ꢁ0.0876 cm3 gÀ1(ref. 31) and this
sion, which was further optimized for the reaction purity, yield surfaces of the GONPs play an important role in these MCRs.
and speed. Under optimized conditions in ethanol solvent, as The active sites i.e. hydroxy, carboxyl, epoxide etc.33,34 fulll the
high as 93% yield of BCD was obtained. Having set the reaction requirement of acidic sites for the reaction to occur in GONPs. A
conditions, the protocol was studied with
a variety of plausible reaction mechanism for the GONPs catalyzed
substituted benzaldehydes. Equimolar amounts of substituted synthesis of BCDs is given in Scheme 3. The carbonyl groups in
of phenyl hydrazine (1), ethyl acetoacetate (2), aromatic alde- the ethyl acetoacetate are initially activated by acidic functional
hyde (3), 4-hydroxycoumarin (4), and 20% of catalyst under groups of the catalyst to react with phenylhydrazine to form
ꢀ
thermal condition (50 C) in solvent ethanol (Scheme 2) have pyrazolone (I). Then, the activated aldehydes by acidic func-
provided a library of BCD (5) in good to excellent yields (86– tional groups of the catalyst react to form the Knoevenagel
93%) (Table 1). The reaction proceeded smoothly and tolerated product. Subsequently, during the Michael addition step,
electron withdrawing and electron donating substituted nucleophilic attack on (II) by tautomeric form of pyrazolone (I)
benzaldehydes.
affords the desired product (5) via intermediate (III). Alterna-
The reactions were consistently carried out at 1 mmol scale tively, there is another possible reaction pathway for the reac-
and no change of product yield was observed when scaled up to tion, via the formation of intermediate (IV) followed by reaction
the 10 mmol scale. It was encouraging to nd that the nal
products (5) could be isolated by simple ltration, avoiding any
requirement for chromatographic separation. This optimized
reaction condition was applied to different aldehydes to check
the general applicability and functional group tolerance. The
reaction proceeds well to give excellent yields of the product
without any column purication. The catalyst was easily
removed from the reaction mixture due to its heterogeneous
character. Furthermore, their purity was so high, no preparation
in an analytically pure form by single recrystallization using
ethanol as a solvent was necessary. The nal products were
conrmed by elemental analysis, IR, 1H NMR, 13C NMR and HR-
MS analytical and spectral techniques (SI-1).
Table
2 Optimization of catalyst with different solvents for the
synthesis of CBDs (5)
Catalyst
Sr. no. (%)
Temperature Time
Yield
(%)
Solvent
EtOH
(ꢀC)
(h)
1
No
catalyst
5
10
10
10
10
10
10
Reux
10
—
2
3
4
5
6
7
8
9
EtOH
MeOH
CH3CN
DCM
CHCl3
DMF
Reux
Reux
Reux
Reux
Reux
Reux
Reux
12
10
10
10
10
10
10
10
7
40
30
40
40
35
40
50
55
93
H2O
10
20
EtOH : H2O Reux
10
EtOH
50 ꢀ
C
Scheme 3 Plausible mechanism for the formation of BCDs.
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Acknowledgements
This work was supported by; (a) the Global Frontier Program
through the Global Frontier Hybrid Interface Materials
(GFHIM) of the National Research Foundation of Korea (NRF)
funded by the Ministry of Science, ICT & Future Planning 10
(2013M3A6B1078874), (b) Science Foundation Ireland under
grant no. 14/IA/2581 and by the Irish Research Council under
award GOIPD/2016/575, and (c) SFS would like to thank
University Grants Commission, New Delhi for awarding D. S.
Kothari Post-Doctoral Fellowship scheme (F.4-2/2006(BSR)/CH/
16-17/0015).
Fig. 2 Reproducibility test of GONPs for BCDs synthesis.
Notes and references
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was revealed that intermediates (II) and (IV) were very reactive
towards the subsequent reaction with pyrazolone and 4-
hydroxycoumarin respectively.27
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diate (II) or (IV) could not be measurably detected in current study.
Aer completion of the reaction, tautomerisation occurred in the
pyrazolone ring of product (5). This may exist in three tautomeric
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the synthesis of BCDs was carried out using the phases and active
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with acidic functional groups, (ii) the GONPs demonstrate
a superior catalytic performance with as high as 93–82% iso-
lated product yields, (iii) unveiling report of the biologically
important highly functionalized BCDs using a solid, metal-free,
nontoxic and reusable heterogeneous green/eco-friendly acid
catalyst. A facile one-pot multi-component protocol has been
demonstrated for the synthesis of biologically important, highly
functionalized BCDs. The reaction was performed in ethanol
solvent at 50 ꢀC using GONPs as a heterogeneous acid catalyst.
The products were puried by recrystallization from ethanol
and chromatography-free separation methods, where the use of
volatile and hazardous solvents, generally preferred, is avoided.
These GONPs should nd several applications in MCRs leading
to biologically potent molecules in the near future, which is
a topic of ongoing work.
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Conflicts of interest
There are no conicts to declare.
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