Novel and green approach for the nanocrystalline magnesium oxide synthesis and its catalytic performance in Claisen-Schmidt condensation

Article abstract of DOI:10.1016/j.catcom.2013.03.012

Magnesium oxide is one of the most promising solid base material having catalytic applications. A novel, simple, efficient, inexpensive, additives free and green synthesis protocol for magnesium oxide nano-particles using concentrated solar energy has been reported. Using magnesium acetate and 1, 4-butanediol magnesium oxide nanoparticles in the range of 5-20 nm was prepared. The driving force for the nanoparticles synthesis was obtained by using concentrated solar energy as a dual energy source in the form of radiational and thermal effect. The resulting magnesium oxide nanoparticles are found to be excellent and reusable catalyst for the Claisen-Schmidt condensation under solvent free condition.

Full text of DOI:10.1016/j.catcom.2013.03.012

Catalysis Communications 36 (2013) 79–83
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Novel and green approach for the nanocrystalline magnesium oxide
synthesis and its catalytic performance in Claisen–Schmidt condensation
⁎
Aniruddha B. Patil, Bhalchandra M. Bhanage
Department of Chemistry, Institute of Chemical Technology, N. M. Parekh Marg, Matunga, Mumbai-400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Magnesium oxide is one of the most promising solid base material having catalytic applications. A novel, simple,
efficient, inexpensive, additives free and green synthesis protocol for magnesium oxide nano-particles using
concentrated solar energy has been reported. Using magnesium acetate and 1, 4-butanediol magnesium oxide
nanoparticles in the range of 5–20 nm was prepared. The driving force for the nanoparticles synthesis was
obtained by using concentrated solar energy as a dual energy source in the form of radiational and thermal effect.
The resulting magnesium oxide nanoparticles are found to be excellent and reusable catalyst for the Claisen–
Schmidt condensation under solvent free condition.
Received 4 February 2013
Received in revised form 7 March 2013
Accepted 8 March 2013
Available online 19 March 2013
Keywords:
Magnesium oxide
Nanoparticles
© 2013 Elsevier B.V. All rights reserved.
Crystal structure
Solar
Claisen–Schmidt condensation
1. Introduction
are no combustion products. In this work, we are reporting a novel,
green, additive free methodology for MgONPs using concentrated solar
Metal oxides are of immense interest to the scientists due to their
enhanced surface chemistry and high surface area. Magnesium oxide
(MgO) is one of the most significant metal oxides having variety of
applications in catalysis, refractory material industries, paint and super-
conductors [1–4]. The synthesis of nanomaterials can be achieved using
template-assisted [5], vapour–liquid–solid (VLS) [6], colloidal micellar
[7], sol-gel method, [8] and microwave [9] based methods. Convention-
ally, Magnesium oxide nanoparticles (MgONPs) are synthesized via
thermal decomposition of various magnesium salts [10,11]. However,
the aforesaid methodologies are not preferable due to the harsh reaction
conditions, the use of toxic reagents, high pressure, specialized equip-
ment setup and the use of conventional non-renewable energy sources.
Thus, the synthesis of MgONPs by green and inexpensive method with
its catalytic application is a subject of current work.
Solar energy being a greener source of energy differs from conven-
tional heating systems. Although, the sunlight associated with the pho-
tochemical conversion is not excluded completely, the solar energy used
in heating process might provide thermodynamic route to form stable
MgONPs. The concept of concentrated solar energy is advantageous in
the synthesis of nanomaterials due to the dual energy effect (radiation
and thermal) [12–14]. The flux of solar radiations along with developed
thermal energy speed up the reaction. Solar energy heating offers the
advantages like rapid heat transfer, volumetric and selective heating,
avoiding of sophisticated equipment and pollution free route as there
energy. This synthetic protocol is much simpler than previous reports,
avoiding complex and multistep reaction schemes, additives, conven-
tional energy source and expensive equipments.
In addition to the synthesis of nanoparticles the catalytic applicabil-
ity of synthesized nanoparticles was checked for the Claisen–Schmidt
condensation reaction. Till date, several magnesium oxide powders dif-
fering in size and surface area has been reported as a better catalyst for
the organic transformation, but very few reports available which deals
with the synthesis of oxide nanoparticles and study its catalytic activity
towards the condensation reactions.
Recently, Ganguly et al. reported a simple route for the synthesis
of magnesium oxide crystals having a high surface area with small
size and used for the Claisen–Schmidt condensation in which lower
conversion of benzaldehyde was obtained (58%) [15]. In view of this,
herein, we are reporting a novel and greener method for MgONPs syn-
thesis and its application as a catalyst for Claisen–Schmidt condensa-
tion to get higher conversion levels. The catalyst was also screened
for various derivatives of benzaldehyde and acetophenone with elec-
tron withdrawing and donating moieties. The catalyst could be reused
up to three consecutive recycles without significant loss in its catalytic
performance.
2. Experimental
2.1. Materials
⁎
Corresponding author. Tel.: +91 22 3361 1111/2222; fax: +91 3361 1020.
All commercial reagents and solvents were used directly as pur-
E-mail addresses: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
(B.M. Bhanage).
chased without further purification.
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.03.012

80
A.B. Patil, B.M. Bhanage / Catalysis Communications 36 (2013) 79–83
2.2. Preparation of MgO nanoparticles
operating voltage 200 kV). TGA and DTA analysis was done by Perkin
Elmer STA 6000 model. Field Emission Gun-Scanning Electron Micros-
copy (FEG-SEM) analysis was done by Tescan MIRA 3 model with
beam SE detector at 15.0 kV. Electron dispersive X-ray Spectral analysis
(EDAX) for elemental analysis was recorded with a JEOL JSM-7600 F.
In a typical synthesis of MgONPs, a mixture of 1.0 g magnesium
acetate and 5 mL 1,4-butanediol were taken in a 50 mL round bottom
flask fitted with air condenser (Fig. 1). This mixture was irradiated
under solar radiations concentrated by ‘Fresnel lens (1 × 1 ft)’ for
6 h with manual stirring for one minute after an interval of 30 min
irradiation. As the solar effect is spatial and temporal to protect the
repeatability each experiment was carried out in the time interval of
9.30 am to 3.30 pm (6 h) at noon time in summer days (the surface
temperature went up to 120 °C). After irradiation, 5 mL methanol was
added to the reaction mass and then subjected for high speed centrifu-
gation at 10000 rpm for 20 min to separate white mass. The separated
mass was then subjected for calcinations at 400 °C for 5 h to get nano-
crystalline MgO. The same protocol was repeated in absence of concen-
trated solar energy using only thermal heating.
2.4. Typical procedure for Claisen–Schmidt condensation
In a 25 mL seal tube benzaldehyde 0.127 g (1.2 mmol) and
acetophenone 0.120 g (1 mmol) with 0.004 g (0.1 mmol, 10 mol %)
of MgONPs were added under solvent free condition. The sealed
tube was preferred for the reaction as it avoids the evaporation loss.
The reaction mixture was stirred for 4 h at 140 °C. The reaction progress
was monitored using GC analysis (Perkin Elmer, Clarus 400). After com-
pletion of the reaction, ethyl acetate (10 mL) was added to the reaction
mixture and the mixture was centrifuged for 20 min at 10000 rpm to
separate the catalyst. After three equal extractions the reaction solvent
was dried over Na2SO4 and evaporated under vacuum, followed by col-
umn chromatography using silica gel, (100–200 mesh size) with petro-
leum ether/ethyl acetate (PE–EtOAc, 95:05) as eluent, gave the pure
chalcone. The products are known and were confirmed by GC-MS
(Shimadzu GC-MS QP 2010) Reaction Scheme 1.
All the experiments were conducted at the author’s laboratory
located at Mumbai (Geographic location: Bombay, India, Asia. Geo-
graphic Coordination: 19° 2′ 0″ North, 72° 51′ 0″ East). The energy
input measured by the pyranometer DWR 8101 which was recorded
at 565 W m-2
.
2.3. Characterization of MgO nanoparticles
3. Result and discussion
The X-ray crystallographic pattern was obtained by XRD mini flex
Rigaku model using Cu Kα = 1.54 Å ranging from 0° to 80°with a
scanning rate of 2° per min. The IR spectrum was recorded by using
DigilabFts 7000 spectrophotometer. The particle size and morphology
analysis along with the selected area electron diffraction (SAED) was
done by Transmission electron microscopy (Philips model CM 200, at
3.1. Characterization of prepared magnesium oxide
Present work is focused on the development of a greener approach
for the synthesis of MgONPs using solar energy. Earlier reports on the
synthesis of MgONPs are associated with a higher driving force which
Fig. 1. Schematic representation of reaction setup with finally obtained white colour MgONPs powder (inset).

A.B. Patil, B.M. Bhanage / Catalysis Communications 36 (2013) 79–83
81
3.2. Evaluation of catalytic activity of MgONPs
The catalytic activity of isolated MgONPs was checked for the
Claisen–Schmidt condensation. Conventionally, the Claisen–Schmidt
reaction has been explored in the presence of aqueous or alcoholic
KOH as the catalyst. In toluene/aqueous biphasic conditions with
10% KOH, a conversion percentage of only 15% was observed after
24 h which increased to 98% in 2 h with 50% aqueous KOH [16].
On account of the separation issue of homogeneous catalyst, het-
erogeneous catalysts are preferred due to their easy work up and
regenerability. In study of MgONPs as a catalyst, aerogel synthesized
MgO gives 98% conversion of benzaldehyde after 12 h [17] whereas
conventionally prepared MgO gives 60% conversion after 15 h [17].
Though, several magnesium oxide powders differing in size and sur-
face area reported better catalytic activity, so far very few reports
are available to synthesize the oxide nanoparticles and study its cata-
lytic activity towards the condensation reaction. Our method offers a
simple route to synthesize MgONPs with high surface area and small
sized crystals showing excellent catalytic performance offering up to
96% yield of the desired product.
The reaction was carried out at 140 °C for 4 h at 10 mol % MgONPs
loading under a solvent free condition. At these conditions benzalde-
hyde and acetophenone undergo smooth conversion providing an
excellent isolated yield (81%) of the desired product. Encouraged by
these results the efficiency of the present protocol was further ex-
tended for the of various benzaldehyde and acetophenone derivatives
(Table 1). Initially benzaldehyde derivatives were screened wherein
an electron withdrawing fluoro and cyno group shows excellent yield
under optimized parameters (entries 2, 4). However, electron donating
group such as methoxy and dimethyl amine providing 79% and 84%
yield of the desired products respectively (entries 3, 5).
Reaction Scheme 1. MgONPs catalysed Claisen–Schmidt condensation reaction.
is not possible to achieve under normal solar radiations. Therefore,
the synthesis was carried out under the concentrated solar energy
and the radiations were concentrated by the ‘Fresnel lens’ (Fig. 1).
Compared to the conventional heating method the concentrated
solar energy concept was found to be very effective because of its
dual energy nature (radiation and thermal). In the synthesis, reaction
mass was kept under concentrated solar radiations. After the desired
time interval we obtained gel mass. In order to check the necessity and
effect of concentrated solar energy for the synthesis, parallel run was
carried out under natural sunlight wherein even after prolonged time
we didn’t obtain thick gel mass. Methanol was added to the gel mass
to get white precipitate. The obtained precipitate was centrifuged and
then subjected for calcinations.
After calcinations step we obtained milky white powder (Fig. 1(A)
[inset]). This visual observation gives one point of evidence to sup-
port MgO nanoparticle synthesis. The XRD pattern Fig. 2(A) shown
four characteristics sharp peaks at 2θ of 37, 43, 62 and 78, readily
assigned to the planes (1 1 1), (2 0 0), (2 2 0), (0 2 2) can be indexed
to the standard pattern of the pure cubic phase of MgO and confirming
the crystalline nature of the product (JCPDS: 75-0447). Using Scherrer's
equation: D = 0. 9λ/βcosθ (where D is the average crystalline size, λ
is the wavelength of Cu Kα, β is the full width at half maximum of the
diffraction peak, and θ is the Bragg's angle) the average crystalline size
of MgONPs is calculated to be around 14
1 nm. The TEM analysis
Several derivatives of acetophenone were also tested and they gave
excellent results. It was observed that electron withdrawing chloro
derivative gave 78% yield of the desired product (entry 6) and electron
donating methyl group gave 81% yield of the desired product (entry 7).
The probable reason for better catalytic activity can be attributed to the
nanoparticles having smaller particle size in the range of 5–20 nm. We
also investigated the reusability of the MgONPs catalysts (Fig. 4). After
reaction, the catalyst was separated by centrifugation, washed several
times with acetone, dried at 200 °C for 4 h, and reused. No substantial
change in catalytic activity was observed with respect to fresh catalyst
even after third recycle.
showed nanoparticles with variable shape predominantly in spherical
ranging 5–20 nm (Fig. 2(B)). However, SAED pattern reveals to the
crystalline nature of synthesized MgONPs (Fig. 2(B) [inset]).
A typical TGA-DTA profile is shown in Fig. 3(A), corresponding to
MgONPs. The FEG-SEM image giving three dimensional idea of syn-
thesized MgONPs which is another point of evidence about the size
and shape of nanocrystalline material (Fig. 3(B)). The FT-IR spectra
were recorded for prepared MgONPs (Fig. 3(C)) and the peaks at
456 cm−1 is the stretching vibrations of the bond between Mg and
O.The elemental detection was done by EDAX analysis showing the
presence of Mg and O elements in the desired ratio of MgO, whereas
the carbon content is due to the carbon coating (Fig. 3(D)). When the
same synthesis protocol was applied using conventional thermal
heating we obtained MgO nanoclusters (see supporting information
Fig. 1).
4. Conclusion
In summary, we have successfully demonstrated green protocol
for synthesis of MgONPs using solar energy for the first time. The
Fig. 2. (A) XRD pattern of synthesized MgONPs. (B) TEM image with SAED pattern (inset) of synthesized MgONPs.

82
A.B. Patil, B.M. Bhanage / Catalysis Communications 36 (2013) 79–83
Fig. 3. (A) TGA and DTA pattern of synthesized MgONPs. (B) FEG-SEM Image of synthesized MgONPs. (C) FT-IR spectrum of synthesized MgONPs. (D) EDS pattern of synthesized
MgONPs.
essential driving force for the synthesis was obtained by concentrat-
ing the radiation delivering thermal and radiational effect. The MgO
Table 1
nanoparticles obtained are in the range of 5–20 nm. Furthermore,
MgONPs were successfully applied as a catalyst in Claisen–Schmidt
condensation reaction for the synthesis of chalcones and its deriva-
tives under solvent free condition. In addition, the catalyst was reused
for three more consecutive recycles.
Magnesium oxide nanoparticles (MgONPs) catalysed Claisen–Schmidt condensation.a
Entry Aldehyde
Acetophenone Product
Yield (%)b
81
1
2
3
80
79
Acknowledgements
The authors express their appreciation towards DAE-ICT and DST,
India for DST-Nanomission Project SR/NM/NS-1097/2011 giving finan-
cial support.
4
5
85
84
6
7
70
75
a
Reaction conditions: benzaldehyde (1.2 mmol), acetophenone (1.0 mmol), catalyst
(10 mol%), Time (4 h), Temperature (140 °C).
b
Isolated yield.
Fig. 4. Recycle study MgONPs catalysed Claisen–Schmidt condensation reaction.

A.B. Patil, B.M. Bhanage / Catalysis Communications 36 (2013) 79–83
83
[9] K.D. Bhatte, D.N. Sawant, K.M. Deshmukh, B.M. Bhanage, Particuology 10 (2011)
384–387.
Appendix A. Supplementary data
[10] E. Alvarado, L. Torres-Martinez, A. Fuentes, P. Quintana, Polyhedron 19 (2000)
2345–2351.
[11] Y. Ding, G. Zhang, H. Wu, N. Hai, L. Wang, Y. Qian, Chemistry of Materials 13
(2001) 435–440.
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2013.03.012.
[12] A.B. Patil, S.R. Lanke, K.M. Deshmukh, A.B. Pandit, B.M. Bhanage, Materials Letters
79 (2012) 1–3.
[13] A.B. Patil, D.S. Patil, B.M. Bhanage, Journal of Molecular Catalysis. A 365 (2012)
146–153.
[14] A.B. Patil, D.S. Patil, B.M. Bhanage, Materials Letters 86 (2012) 50–53.
[15] A. Ganguly, P. Trinh, K. Ramanujachary, T. Ahmad, A. Mugweru, A. Ganguli, Journal of
Colloid and Interface Science 353 (2011) 137–142.
References
[1] H. Heidari, M. Abedini, A. Nemati, M. Amini, Catalysis Letters 130 (2009) 266–270.
[2] C. Yan, D. Xue, The Journal of Physical Chemistry. B 109 (2005) 12358–12361.
[3] S. Bian, Z. Ma, Z. Cui, L. Zhang, F. Niu, W. Song, Journal of Physical Chemistry C 112
(2008) 11340–11344.
[4] M. Climent, A. Corma, S. Iborra, M. Mifsud, Journal of Catalysis 247 (2007) 223–230.
[5] Y. Han, J. Kim, G. Stucky, Chemistry of Materials 12 (2000) 2068–2069.
[6] J. Hu, T. Odom, C. Lieber, Accounts of Chemical Research 32 (1999) 435–445.
[7] C. Chen, C. Chao, Z. Lang, Chemistry of Materials 12 (2000) 1516–1519.
[8] T. Athar, A. Hakeem, W. Ahmed, Advanced Science Letters 7 (2012) 27–29.
[16] Y. Wang, J. Ye, X. Liang, Advanced Synthesis and Catalysis 349 (2007) 1033–1036.
[17] B. Choudary, M. Kantam, K.V.S. Ranganath, K. Mahendar, B. Sreedhar, Journal of
the American Chemical Society 126 (2004) 3396–3397.