Catalysis Communications
Short Communication
γ-Maghemite-silica nanocomposite: A green catalyst for diverse
aromatic N-heterocycles
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Pranab Ghosh , Amitava Mandal, Raju Subba
Natural Products and Polymer Chemistry Laboratory, Department of Chemistry, University of North Bengal, Raja Rammohunpur, Darjeeling, West Bengal 734 013, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 May 2013
Received in revised form 22 June 2013
Accepted 24 June 2013
Available online 29 June 2013
γ-Maghemite-silica nanocomposite has been applied as a green catalyst to synthesize variety of aromatic
N-heterocycles under solvent free conditions. Characterization was done by modern analytical tools (UV,
IR, AAS, DSC, EDXRF, powdered XRD, EPR, Mössbauer and TEM). Mild reaction conditions and recyclability
have made the present protocol both environmentally and economically viable.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
γ-Maghemite-silica
Nanocomposite
Solvent free
Pyrazine
Quinoxaline
Benzimidazole
1. Introduction
benzimidazoles etc. form the origin of many life saving drugs and
lead research. Therefore, their synthesis is a subject of huge impor-
The role of iron based magnetic substances in daily life is enormous
[1]. Sixteen pure phases of iron oxides, hydroxides or oxy-hydroxides
are characterized to date [2]. These are essential materials for many
industrial applications [3] and catalysis [4]. During the course of
chemical reactions these paramagnetic nanoparticles always try to
deform and aggregate resulting in a concomitant change in the thermal
and chemical stability [5]. One way to prevent the aggregation is by
surface modification [4,5] or immobilization of these magnetic nano-
particles using appropriate capping agents like polymers. At higher
temperature polymeric capping agents always try to decompose
resulting deformation/easy aggregation. Immobilization of metallic
oxide nanoparticles at the pore surfaces of mesoporous silica is of
considerable technological importance [4,6].
Among all the elements widely distributed in nature, iron is not only
ubiquitous but also one of the most versatile transition metals and
important redox center for life and natural transformation processes
[7]. With respect to sustainable chemistry and following nature's princi-
ples, iron is the ideal metal for generating environmentally benign
heterogeneous catalyst system for future generations because of its
role in nature, availability, low toxicity and cost effectiveness.
tance over the decades.
Classically pyrazines were prepared by the condensation between
diamines and diols in vapor phase under diverse catalyzing
conditions [9–16]. However, the most difficult task in this series is
the aromatization of the intermediates that had generally been
achieved at elevated temperature by high loading of the catalysts.
On the other hand, quinoxaline derivatives were synthesized conven-
tionally by a microwave assisted cyclodehydration–condensation of
aryl 1,2-diamines with 1,2-dicarbonyls in MeOH/AcOH [17]. Catalysts
used are HClO4–SiO2 [18], ceric(IV)ammoniumnitrate [19], Yb(OTf)3
[20] and H6P2W18O62, 2H2O [21]. Leaving acid or base catalyzed
syntheses, at present a number of rare metal catalyzed synthetic
methods are available for benzimidazole derivatives [22–29].
But difficulties in preparation, handling of inherently toxic organo-
metallics, cumbersome product isolation from the homogeneous cata-
lysts and waste disposal problems have made the existing systems
incompatible under the aspect of sustainable synthesis [6,24–32].
These approaches would be significantly improved if we could
move away from (i) precious metals, (ii) homogeneous catalysis and
employ more earth abundant metals for heterogeneous catalyst
generation.
Aromatic N-heterocycles are widespread in nature and are indis-
pensable for almost all life systems [8]. Pyrazine, quinoxaline,
During the preceding decade, emphasis had given towards the
development of environmentally friendly/sustainable ways to a myriad
of materials. Clean technology requires the practice of environmentally
affable surface catalysts, typical solid heterogeneous catalysts that can
be easily recycled. With the beginning of solid phase organic synthesis
and the combinatorial synthetic approaches for ‘druglike’ molecules
⁎
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1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.