Nano-MgO-ZrO2 mixed metal oxides: Characterization by SIMS and application in the reduction of carbonyl compounds and in multicomponent reactions

Article abstract of DOI:10.1039/c2ra22511e

A nano-sized Magnesia-Zirconia (nano-MgO-ZrO₂) catalyst was prepared by a simple ultradilution co-precipitation method and by using inexpensive precursors. The nano-MgO-ZrO₂ was extensively characterized by SIMS together with other analytical techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nano-MgO-ZrO₂ catalyst proved to be very efficient for the reduction of carbonyl compounds and multicomponent reactions under mild reaction conditions. The recyclability and reusability of the nano-MgO-ZrO₂ catalyst has been tested.

Full text of DOI:10.1039/c2ra22511e

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Nano-MgO–ZrO2 mixed metal oxides: characterization
by SIMS and application in the reduction of carbonyl
compounds and in multicomponent reactions3
Cite this: RSC Advances, 2013, 3,
3611
Manoj B. Gawande,*a Anuj K. Rathi,b Paula S. Branco,a T. M. Potewar,a
Alexandre Velhinho,c Isabel D. Nogueira,d Alexander Tolstogouzov,e C. Amjad
A. Ghummane and Orlando M. N. D. Teodoroe
A nano-sized Magnesia–Zirconia (nano-MgO–ZrO2) catalyst was prepared by a simple ultradilution co-
precipitation method and by using inexpensive precursors. The nano-MgO–ZrO2 was extensively
characterized by SIMS together with other analytical techniques such as X-ray diffraction (XRD) and
transmission electron microscopy (TEM). The nano-MgO–ZrO2 catalyst proved to be very efficient for the
reduction of carbonyl compounds and multicomponent reactions under mild reaction conditions. The
recyclability and reusability of the nano-MgO–ZrO2 catalyst has been tested.
Received 13th October 2012,
Accepted 4th January 2013
DOI: 10.1039/c2ra22511e
www.rsc.org/advances
acetate with tert-butyl hydroperoxide catalyzed by MoO3/TiO2
oxide,8c and the determination of the effect of the phosphate
Introduction
Mixed metal oxides (MMOs) represent one of the most
important and widely employed categories of solid catalysts,
either as active phases or supports. MMOs may be used either
by their acid/base or their redox properties and constitute the
largest family of heterogeneous catalysts.1–3 In addition to
catalytic applications, MMOs have played very important roles
in many areas such as in chemistry, physics, materials science,
and geochemistry.4–6 Due to their versatile applications, they
have great scope in various microelectronic devices, electrodes
and sensors.7 Nano-sized MMOs are attractive for a range of
applications due to their excellent chemical and thermal
stability, high porosity and large surface area. Therefore, great
efforts are dedicated to the optimization of new procedures
able to synthesize pure and mixed nano-sized metal oxides.
MMOs have been used for the selective reduction of the CLO
bond in a,b-unsaturated carbonyl compounds through hydro-
gen transfer reactions,8a the study of chemical structures and
performance of perovskite oxides,8b the epoxidation of allyl
ion on the textural and catalytic activity of titania–silica mixed
oxide,8d among other relevant applications in chemistry.8e–i
The reduction of carbonyl compounds to their correspond-
ing alcohols is an industrially important reaction, as alcohols
are important starting materials and intermediates for the
manufacture of a variety of chemicals.9 Although a number of
methods have been developed for the reduction of carbonyl
compounds employing homogeneous catalysts,10 the control
of the reaction rates is highly difficult.11 Moreover, the main
disadvantage of these reactions is that when homogeneous
catalysts are used, the metal can contaminate the product,
which is unacceptable e.g. in pharmaceutical syntheses.
Recently, prompted by stringent environment protection laws,
there has been an increased emphasis on the design, synthesis
and use of environmentally benign solid acid/base hetero-
geneous catalysts for organic transformations to reduce the
amount of toxic waste and by products from chemical
processes. The main advantage of a heterogeneous catalyst is
that, being a solid material, it is easy to separate from the gas
or liquid phase reactants and products after completion of the
reaction.
We have previously shown that a MgO–ZrO2 catalyst has
applicability in various important organic reactions such as
cross-aldol condensation, N-benzyloxycarbonylation of
amines, reduction of aromatic nitrocompounds, and synthesis
of 1,5-benzodiazepines12 and N-benzyloxycarbonylation of
alcohols.13 Engaged with the development of sustainable
protocols,14 heterogeneous catalysis15 and nanomaterials,16
we herein report an extension of the application of the nano-
MgO–ZrO2 catalyst for the reduction of carbonyl compounds
aDepartment of Chemistry, Faculty of Science and Technology, Universidade Nova de
Lisboa, 2829-516 Caparica, Portugal. E-mail: mbgawande@yahoo.co.in,
m.gawande@fct.unl.pt; Fax: +351 21 2948550; Tel: +351 96 4223243
Tel: +351 21 2948300
bJubilant Chemsys Ltd., B-34, Sector-58, Noida-201301, New Delhi (India)
c
ˆ
ˆ
CENIMAT/I3N Departmento de Ciencias dos Materiais, Faculdade de Ciencias e
Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
dInstituto de Ciencia e Engenharia de Materiais e Superficies IST, Lisbon, Portugal
eCentre for Physics and Technological Research (CeFITec), Department of Physics,
Faculty of Science and Technology, Universidade Nova de Lisboa, 2829-516
Caparica, Portugal
Electronic supplementary information (ESI) available. See DOI: 10.1039/
3
c2ra22511e
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patterns of MZ, showing the presence of both substances in
the sample.
The TEM micrographs of MgO–ZrO2 are depicted below,
clearly indicating that the particles are in the nano-size range
(20–35 nm) (Fig. 2a and b). The scarcity of observed particles
notwithstanding, it was possible to measure a sufficiently high
number to build the histogram (Fig. 2c). In EDS spectra the
elements Zr, Mg and O were identified, the results being in
general agreement with the XRD spectrum, even if it should be
noted that the EDS signal in the TEM analysis concerns a
much smaller area. One of the EDS spectra acquired is
depicted in Fig. 2d. The copper peak is due to the instrument’s
grid.
Scheme 1 Reduction of carbonyl compounds by hydrogen transfer reactions
over nano-MgO–ZrO2 catalyst.
using isopropyl alcohol (IPA) as a hydrogen transfer reagent
(Scheme 1). In addition to the usually used techniques for the
characterization of solid matrixes such as XRD or TEM, we
engaged in a extensive chemical characterization of the nano-
MgO–ZrO2 catalyst surface by time of flight secondary mass
spectrometry (TOF-SIMS). The TOF-SIMS technique is widely
and successfully used to determine the elemental and
molecular composition of the surface and near-surface layers
of different catalysts.17
To produce a plain and conductive sample suitable for
SIMS analysis, the powder catalyst was pressed onto an ultra-
pure indium foil by Goodfellow (Huntingdon, UK). We used a
manual toggle pressing machine by Brauer (Milton Keynes,
UK). The sample was prepared by a reported procedure18 and
the TOF-SIMS analysis was performed by acquiring positive
and negative secondary ion spectra in the mass range of 0.5–
200 m/z.
Fig. 3 shows the results obtained from mass spectroscopy,
as applied to the MgO/ZrO2 powder catalyst when placed onto
a indium substrate.
In the positive mode (Fig. 3a), we detected the isotopic
peaks of the main components and their oxy-hydrated
compounds, namely, Mg+, MgO+, MgOH+, Zr+, ZrH+, ZrO+,
+
ZrOH+, ZrO2 and ZrO2H+, along with some surface contam-
inations (Na+, Al+, K+, Ca+), implanted and re-sputtered
analysis ions (Ga+) and ions originating from the substrate
(In+). The intensity of MgOH+ (m/z 41) is higher than that of
MgO+ (m/z 40). In the negative mode (Fig. 3b), the isotopic
peaks of zirconium oxides and hydroxides with the most
abundant peaks at m/z 122 (90ZrO22) and m/z 123 (90ZrO2H2
+
91ZrO22) were registered. At the low-mass part of the spectrum,
we detected different hydrocarbons and halogens (F2, Cl2);
oxygen-containing ions of the analysis (GaO2 and GaO22) and
substrate (InO2 and InO22) species were also found. In
addition to the abovementioned ions, trace amounts of
glycerol were also identified via the discrete series of foremost
characteristic peaks at m/z 93 [M + H]2, m/z 185 [2M + H]2 (not
shown), and m/z 277 [3M + H]2.18c We suspect the presence of
some glycerol contamination in our vacuum chamber due to
the memory effect.
Results and discussion
The XRD spectrum of MgO–ZrO2 is depicted in Fig. 1. Cubic
ZrO2 and MgO phases (according to JCPDS files 49–1642 and
45–0946, respectively) were observed in powder diffraction
The modification (degradation) of the surface of the
catalyst under ion-beam sputtering was studied by measuring
four successive positive mass spectra. Each spectrum was
collected after short-run Ga+ pre-sputtering of the sample in
the continuous mode. The relative magnesium (zirconium)
intensity RIMg(Zr) was estimated as
IMg(Zr)
RIMg(Zr)
~
(1)
I
MgzIZr
where IMg(Zr) is the peak intensity (sum of all isotopes) of the
corresponding element integrated within ¡0.5 m/z.
In Fig. 4 the magnesium and zirconium intensities versus
the relative gallium calculated intensity is presented
IGa
RIGa
~
(2)
I
GazIMgzIZr
where IGa is the peak intensity (sum of all isotopes) of Ga+
analysis ions integrated within ¡0.5 m/z.
One can see in Fig. 4 that the Mg+ relative intensity tends to
decrease (with corresponding growth of Zr+ intensity) under
Fig. 1 XRD spectrum of nano-MgO–ZrO2.
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Fig. 2 a) TEM image of nano-MgO–ZrO2 at 50 nm, b) TEM image of nano-MgO–ZrO2 at 20 nm, c) histogram of nano-MgO–ZrO2, d) TEM-EDS profile of nano-MgO–
ZrO2.
Fig. 3 Mass spectra of positive (a) and negative (b) secondary ions of MgO/ZrO2
Fig. 4 Relative magnesium and zirconium intensities versus the relative Ga+
powder catalyst placed onto In substrate. The time of the spectra acquisition
was 5 min.
content onto the surface of catalysts.
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the continuous Ga+ irradiation, i.e. as data is gathered from
regions increasingly deeper in the sample. It means that the
near-surface region of the catalyst is enriched by Mg. We did
not find data on sputter rates of magnesia and zirconia in the
literature. However, the sputter rates of aluminum and
hafnium oxide films are rather similar,19 and with a high
degree of certainty we are able to ignore the effect of
preferential ion-beam sputtering of our samples.
The fact that Mg is preferably found near the surface of the
nano-particles is a strong indication that these possess a
zirconia-rich core, whereas MgO is mainly present as an
adhered deposit at the surface. Whether such deposit assumes
the form of a continuous layer, or if magnesia is present over a
discrete number of loci, could not be ascertained by the
experimental techniques used in this study. However, the
literature provides examples of systems prepared via techni-
ques similar to the ultra-dilution co-precipitation technique
possessing a discontinuous deposit structure.20
Table 1 Optimization of reactions conditionsa
No Catalyst
Base
—
KOH 24
—
KOH
KOH
KOH
KOH
KOH
Time (h) Isolated Yield 2ad (%)
1
2
3
4
5
6
7
8
9
—
—
24
NR
NR
Nano-MgO-ZrO2
Nano-MgO-ZrO2
Nano-MgO-ZrO2
Nano-MgO-ZrO2
Nano-MgO
Nano-ZrO2
24
4
4
4
4
4
4
NR
42b
68c
92
4613
2513
6014b
Normal MgO-ZrO2 KOH
a
Reaction conditions: acetophenone (1 mmol), KOH (2 mmol), IPA
b
c
(3 mL), temp. 80 uC, catalyst (30 mg). 10 mg catalyst used. 20 mg
catalyst used. NR. No reaction.
d
The effect of reaction time was inspected for the reduction
of acetophenone; notably nano-MgO–ZrO2 gives almost quan-
titative yield of 2a in 92% within 4 h; however within 5 h time,
the yield of 1-phenylethanol has not increased further (93%).
Therefore, the reaction time of 4 h was optimal for the
reduction of acetophenone to 1-phenyl ethanol (Fig. 5).
In all cases the reaction was completed within 4–6 h with
remarkably high yields (89–93%). As depicted in Table 2,
selective reduction of 4-methoxyacetophenone (entry 4) is
possible to afford the corresponding alcohol in excellent yield
(93%) although with a slightly longer reaction time. Moreover,
high yields can also be attained for 4-chloroacetophenone and
4-bromoacetophenone reduction (Table 2, entries 2 and 3),
with no evidence of dehalogenation. The effectiveness of this
protocol is comparable to some existing protocols22 with the
main advantages of being recyclable for several runs and the
nanocatalysts being prepared from inexpensive precursors.
Catalytic activity of MgO–ZrO2 for carbonyl
compound reduction
The catalytic activity of the nano-MgO–ZrO2 catalyst was tested
in the reduction of carbonyl compounds (Scheme 2). For
optimization of reactions conditions, we chose acetophenone
(1, R = H) as the substrate for the reduction under different
reaction conditions.
No reactions occur in the absence of catalyst, either with or
without base (Table 1, entry 1 and 2). As we increased the
amount of catalyst from 10, 20 and 30 mg, we observed the
yield of reaction increasing to 42, 68 and 92% respectively
(Table 1, entries 4 to 6). The wt% of nano-MgO–ZrO2 catalyst
also affects the reaction rate. It was observed that component
oxides such as MgO and ZrO2 also gave moderate yield of the
corresponding products; nevertheless, nano-MgO–ZrO2 is the
most effective nanomaterial among them. This could be due to
a prominent feature of the active Mg–Zr mixed oxides, which
can be found to originate from the co-operative action of both
the basic (O22) and acidic sites (Mg2+ and Zr 4+) located in a
neighbour at the surface.21 Even current (micro-size) MgO–
ZrO2 has less catalytic activity in terms of yield of the product
(Table 1, entry 9).
Table 2 Nano-MgO–ZrO2 catalyzed ketone reductiona
Entry Carbonyl compound (1) Products (2)
Time (h) Yield (%)
1
4
92
2
3
4
4.5
89
The catalytic activity of the nano-MgO–ZrO2 was further
explored for various other carbonyl compounds (Table 2).
4.5
6
90
93
92
5
4
a
Reaction conditions: carbonyl compound (1 mmol), KOH (1.5
Scheme 2 Aromatic carbonyl group reduction over nano-MgO–ZrO2.
3614 | RSC Adv., 2013, 3, 3611–3617
mmol), 80 uC, IPA (3 mL), 30 mg of catalyst.
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Fig. 5 Time dependency of carbonyl group reduction of acetophenone.
Fig. 6 Reusability study for the catalytic activity of nano-MgO–ZrO2 catalyst.
A base supported Oppenauer oxidation mechanism should
be involved (Scheme 3). This type of oxidation is known to be
conducted among others using heterogeneous catalysts (e.g.
alumina, zeolites).23 Both carbonyl compound (ketone) and
the alcohol (IPA) are bound to the catalyst (I). The alcohol is
bound as the alkoxide. Coordination of the ketone to the
catalyst activates it for the hydride transfer from the alkoxide
followed by alcoholysis.
The reaction between benzaldehyde, ammonium acetate,
methyl acetoacetate and 5,5-dimethylcyclohexane-1,3-dione,
performed in the presence of nano-MgO–ZrO2 under mild
conditions, allowed us to obtain methyl 2,7,7-trimethyl-5-oxo-
4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (3) in
95% yield.
In conclusion, we have investigated the surface properties
In order to prove that the reaction is heterogeneous, a
standard leaching experiment was conducted by the filtration
method. The model reaction of acetophenone (Table 2, entry
1) proceeded for 15 min in the presence of a nano-MgO–ZrO2
at 80 uC. The reaction mixture was then filtered under suction
to remove the catalyst. The filtered reaction mixture was then
stirred without catalyst for 12 h. Notably, no formation of
corresponding product was observed even after 12 h, indicat-
ing that no homogeneous catalyst was involved. The reusa-
bility of the catalyst was tested for the reduction of
acetophenone. Under the established conditions the catalyst
was filtered off after completion of the reaction and the
reaction mixture was washed with water, followed by ethyl
acetate, and then dried at 120 uC for 3 h, before being reused
for the next cycle. The catalytic activity was maintained
practically constant with only a slightly decrease even after
the fifth cycle (Fig. 6).
of
a MgO–ZrO2 nano-catalyst by SIMS techniques, and
observed that MgO is supported on ZrO2. Furthermore, the
catalytic activity of nano-MgO–ZrO2 was investigated, for the
reduction of carbonyl compounds by a simple procedure. In
addition, the applicability of nano MgO–ZrO2 was explored for
four component reactions under benign conditions. This
developed green protocol offers several advantages such as
use of a heterogeneous and reusable catalyst, high reaction
rates, operational simplicity and mild reaction conditions.
Experimental
All commercial reagents were used as received unless other-
wise mentioned. For analytical and preparative thin-layer
chromatography, Merck, 0.2 mm and 0.5 mm Kieselgel GF 254
percoated were used, respectively.
To explore the catalytic activity of nano-MgO–ZrO2, we
tested it in the multicomponent reaction depicted in
Scheme 4.
Synthesis of nano-MgO–ZrO2
In a typical experiment, for the preparation of MgO–ZrO2 an
appropriate amount of magnesium nitrate [Mg(NO3)2?6H2O]
(3.10 g) and zirconium oxychloride [ZrOCl2?8H2O] (8.11 g) were
dissolved together in a 2 L flask with 1 L deionized water.
Dilute ammonia solution was added drop wise with vigorous
stirring (RPM-5 000) until the precipitation was complete
(around 6 to 8 h at pH = 10.0). The resultant precipitate was
filtered and washed with distilled water until it was free from
chloride ions. The residue was dried for 24 h at 383 K in an
oven and the obtained precipitate of metal hydroxides was
heated in a porcelain crucible progressively to 873 K for 10 h
(ESI ).
3
Characterization nano-MgO–ZrO2
After calcination, the nano-MgO–ZrO2 catalyst was character-
ized by various analytical and spectroscopic techniques. The
Scheme 3 Proposed mechanism for the reduction of acetophenone.
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X-ray powder diffraction pattern was obtained using
a
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Scheme 4 Synthesis of methyl 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (3).
conventional powder diffractometer (Philips 1050) using
graphite monochromatized Cu-Ka radiation operating in
Acknowledgements
˜
ˆ
This work has been supported by Fundaçao para a Ciencia e
Tecnologia through grants nos. PEst-C/EQB/LA0006/2011 and
PEst-C/CTM/LA0025/2011. Manoj B. Gawande also thanks the
PRAXIS program for the award of research fellowship SFRH/
BPD/64934/2009.
Bragg–Brentano (h/2h) geometry. Transmission Electron
Microscopy (TEM) experiments were performed on a Hitachi
8100 microscope with a Rontec standard EDS detector and
digital image acquisition. All samples were prepared by
evaporating dilute suspensions on a carbon-coated film. To
produce a plain and conductive sample suitable for SIMS
analysis, the powder catalyst was pressed onto an ultra-pure
indium foil by Goodfellow (Huntingdon, UK). We used a
manual toggle pressing machine by Brauer (Milton Keynes,
UK). TOF-SIMS analysis was performed by acquiring positive
and negative secondary ion spectra in the mass range of 0.5–
200 m/z with an upgraded VG Ionex IX23LS TOF-SIMS set-up
based on the Poschenrieder design. A focused liquid Ga+ gun
in the pulsed mode (6 kHz/40 ns) was used as a source of the
analysis ions. The beam current in the continuous mode at 14
keV was ca. 15 nA with a raster size of 300 6 300 mm2 (128 6
128 pixels, 10 kHz). The sample potential was ¡5 kV. Vacuum
during the experiments was maintained in the range of (2–3)
6 1029 mbar in the analytical chamber.
References
1 (a) C. Mercier and P. Chabardes, Stud. Surf. Sci. Catal.,
1993, 78, 677; (b) Y. Izumi, N. Natsume, H. Takamine,
I. Tamaoki and K. Urabe, Bull. Chem. Soc. Jpn., 1989, 62,
2159–2164; (c) K. Tanabe and W. F. Holderich, Appl. Catal.,
A, 1999, 181, 399–434; (d) B. M. Reddy and A. Khan, Catal.
Rev. Sci. Eng., 2005, 47, 257–296.
2 (a) H. H. Kung, Transition Metal Oxides: Surface Chemistry
and Catalysis, Stud. Surf. Sci. Catal, Elsevier, Amsterdam,
1989, Vol. 45, pp. 1–277; (b) V. E. Henrich and P. A. Cox, The
Surface Science of Metal Oxides, Cambridge University Press,
Cambridge, UK, 1994; (c) C. Noguera, Physics and Chemistry
at Oxide Surface, Cambridge university press, Cambridge,
UK, 1996; (d) S. U. Sonavane, M. B. Gawande, S.
S. Deshpande and R. V. Jayaram, Catal. Commun., 2007,
8, 1803–1806.
3 M. B. Gawande, R. K. Pandey and R. V. Jayaram, Catal. Sci.
Technol., 2012, 2, 1113–1125 and references cited therein.
4 M. J. Guittet, J. P. Crocombette and M. Gautier-Soyer, Phys.
Rev. B: Condens. Matter, 2001, 63, 125117–6.
5 F. S. Galasso, Structure, Properties and Preparation of
Perovskite-Type Compounds, Pergamon Press, Oxford, 1969.
6 L. G. Tejuca, J. L. G. Fierro and J. M. D. Tascon, Adv. Catal.,
1989, 36, 237–328.
Reduction of carbonyl compounds (1)
Carbonyl compound 1 (10 mmol), IPA (10 mL), KOH (20 mmol)
and nano-MgO–ZrO2 (30 mg with respect to 1), were stirred at
80 uC for an appropriate time. After completion of the reaction
(monitored by TLC) the catalyst was separated by simple
filtration. The resultant product was extracted with ethyl
acetate from the reaction mixture. Then the organic solvent
was evaporated in vacuo. The crude product was purified by
column chromatography on silica gel using n-hexane and ethyl
acetate as eluent. All compounds are well characterized and
well reported in the literature.
7 Jin Huang and Qing Wan, Sensors, 2009, 9, 9903–9924.
8 (a) S. U. Sonavane and R. V. Jayaram, Synlett, 2004, 1, 146–148;
(b) M. A. Pena and J. L. G. Fierro, Chem. Rev., 2001, 101,
1981–2017; (c) H. Kanai, Y. Ikeda and S. Imamura, Appl. Catal.,
A, 2003, 247, 185–191; (d) S. K. Samantaray and K. Parida, Appl.
Catal., A, 2001, 220, 9; (e) S. D. Jackson and J. S. J. Hargreaves,
Metal Oxide Catalysis, Wiley-VCH, 2008, ISBN-10: 3527318151;
(f) G. Mestl, Top. Catal., 2006, 38, 69–82; (g) J. Kaspar,
P. Fornasiero and M. Graziani, Catal. Today, 1999, 50,
285–298; (h) R. Di Monte and J. Kaspar, Top. Catal., 2004, 28,
47–57; (i) R. Di Monte and J. Kaspar, J. Mater. Chem., 2005, 15,
633–648 and references cited therein.
Synthesis of methyl 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-
hexahydroquinoline-3-carboxylate (3)
A solution of benzaldehyde (5 mmol), 5,5-dimethylcyclohex-
ane-1,3-dione (5 mmol), ammonium acetate (10 mmol), methyl
acetoacetate (5 mmol), and nano-MgO–ZrO2 (30 mg) in ethanol
(3 mL) was stirred at room temperature for 20 min. After
terminus of the reaction monitored by TLC (n-hexane and
ethyl acetate; 70 : 30), the catalyst was filtered. To the solution
was added ethyl acetate (10 mL). The organic layer was washed
with saturated NaHCO3 (aq) and brine, dried with anhydrous
Na2SO4, and concentrated to dryness. The crude mixture was
purified by crystallization in ethanol and the methyl 2,7,7-
trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-car-
boxylate 3 was obtained in 95% yield.
9 (a) R. C. Larock, Organic Transformations, VCH, New York,
1989, p. 411; (b) G. W. Kabalka and R. S. Varma, Comprehensive
Organic Synthesis, ed. B. M. Trost and I. Fleming, Pergamon
Press, Oxford, 1991, vol. 8, pp. 363; (c) F.-Z. Su, L. He, J. Ni,
3616 | RSC Adv., 2013, 3, 3611–3617
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
Y. Cao, H.-Y. He and K.-N. Fan, Chem. Commun., 2008,
3531–3533.
Tetrahedron Lett., 2012, 53, 3857–3860; (f) M. B. Gawande, P.
S. Branco, I. D. Nogueira, C. A. A. Ghumman, N. Bundaleski,
A. Santos, O. M. N. D. Teodoro and R. Luque, Green Chem., 2013,
DOI: 10.1039/c3gc36844k.
10 (a) E. J. Creyghton, J. Huskens, J. C. Van der Waal and
H. Van Bekkum, 1997, Heterogeneous catalysis and fine
chemicals IV, Elsevier, Amsterdam, pp. 531–537; (b) Y. Ishii,
T. Nakano, A. Inada, Y. Kishigami, K. Sakurai and
M. Ogawa, J. Org. Chem., 1986, 51, 240–242.
17 (a) F. De Smet, M. Devillers, C. Poleunis and P. Bertrand, J.
Chem. Soc., Faraday Trans., 1998, 94, 941–947; (b) J. Grams,
´
J. Goralski and P. Kwintal, Int. J. Mass Spectrom., 2010, 292,
11 D. J. Pasto, J. Am. Chem. Soc., 1979, 101, 6852–6857.
12 M. B. Gawande, P. S. Branco, K. Parghi, J. J. Shrikhande, R.
K. Pandey, C. A. A. Ghumman, N. Bundaleski, O. M. N. D. Teodoro
and R. V. Jayaram, Catal. Sci. Technol., 2011, 1, 1653–1664.
13 M. B. Gawande, S. N. Shelke, A. Rathi, P. S. Branco and R.
K. Pandey, Appl. Organomet. Chem., 2012, 26, 395–400.
14 (a) M. B. Gawande and P. S. Branco, Green Chem., 2011, 13,
1355–3359; (b) M. B. Gawande and R. V. Jayaram, Catal.
Commun., 2006, 7, 931–935; (c) S. N. Shelke, G. R. Mhaske, V.
1–6; (c) N. Kruse and S. Chenakin, Low Energy Ion Scattering
and Secondary Ion Mass Spectrometry, in Characterization of
Solid materials and Heterogeneous Catalysts, ed. M. Che and
J. C. Vedrine, 2012, Wiley, Weinheim, pp. 453–510.
18 (a) C. A. A. Ghumman, O. M. T. Carreira, A. M. C. Moutinho,
A. Tolstogouzov, V. Vassilenko and O. M. N. D. Teodoro,
Rapid Commun. Mass Spectrom., 2010, 24, 185–190; (b) C. A.
A. Ghumman, A. M. C. Moutinho, A. Tolstogouzov and O.
M.N. D. Teodoro, Rapid Commun. Mass Spectrom., 2011, 25,
997–999; (c) F. H. Field, J. Phys. Chem., 1982, 86, 5115–5123.
19 (a) D. R. Baer, M. H. Engelhard, A. S. Lea, P. Nachimuthu,
T. C. Droubay, J. Kim, B. Lee, C. Mathews, R. L. Opila, L.
V. Saraf, W. F. Stickle, R. M. Wallace and B. S. Wright, J.
Vac. Sci. Technol., A, 2010, 28, 1060–1072.
20 (a) G. K. Pradhan and K. M. Parida, Intern. J. Engin. Sci. and
Techn, 2010, 2, 53–65; (b) M. Zhang, T. An, X. Hu, C. Wang,
G. Sheng and J. Fu, Appl. Catal., A, 2004, 260, 215–222; (c)
M. Zhang, G. Sheng, J. Fu, T. An, X. Wang and X. Hu, Mater.
Lett., 2005, 59, 3641–3644.
´
D. B. Bonifacio and M. B. Gawande, Bioorg. Med. Chem. Lett.,
2012, 22, 5727–5730; (d) M. B. Gawande, V. Polshettiwar, R.
S. Varma and R. V. Jayaram, Tetrahedron Lett., 2007, 48,
8170–8173.
15 (a) M. B. Gawande, S. S. Deshpande, S. U. Sonavane and R.
V. Jayaram, J. Mol. Catal. A: Chem., 2005, 241, 151–155; (b) M.
B. Gawande, S. S. Deshpande, J. R. Satam and R. V. Jayaram,
Catal. Commun., 2007, 8, 576–582.
16 (a) M. B. Gawande, A. Velhinho, I. D. Nogueira, C. A.
A. Ghumman, O. M. N. D. Teodoro and P. S. Branco, RSC Adv.,
2012, 2, 6144–6149; (b) M. B. Gawande, A. Rathi, I. D. Nogueira, C.
A. A. Ghumman, N. Bundaleski, O. M. N. D. Teodoro and P.
S. Branco, Chem Plus Chem, 2012, 77, 865–871; (c) M. B. Gawande,
A. Rathi, P. S. Branco, I. D. Nogueira, A. Velhinho, J. J. Shrikhande,
U. U. Indulkar, R. V. Jayaram, C. A. A. Ghumman, N. Bundaleski
and O. M. N. D. Teodoro, Chem.–Eur. J., 2012, 18, 12628–12632; (d)
M. B. Gawande, H. Guo, A. K. Rathi, P. S. Branco, Y. Chen, R.
S. Varma and D. L. Peng, RSC Adv., 2013, 3, 1050–1053; (e) U.
U. Indulkar, S. R. Kale, M. B. Gawande and R. V. Jayaram,
21 K. Yamaguchi, K. Ebitani, T. Yoshida, H. Yoshida and
K. Kaunda, J. Am. Chem. Soc., 1999, 121, 4526–4527.
22 (a) F.-Z. Su, L. He, J. Ni, Y. Cao, H.-Y. He and K.-N. Fan, Chem.
Commun., 2008, 3531–3533; (b) F. Alonso, P. Riente, F. Rodriguez-
Reinoso, J. Ruiz-Martinez, A. Sepffllveda-Escribano and M. Yus,
ChemCatChem, 2009, 1, 75–77.
23 E. J. Creyghton, S. D. Ganeshie, R. S. Downing and H. van
Bekkum, J. Mol. Catal. A: Chem., 1997, 115, 457–472.
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