Catalysis Communications
Short Communication
Nanomagnetic double-charged diazoniabicyclo[2.2.2]octane dichloride
silica as a novel nanomagnetic phase-transfer catalyst for the aqueous
synthesis of benzyl acetates and thiocyanates
⁎
Jamal Davarpanah, Ali Reza Kiasat
Chemistry Department, College of Science, Shahid Chamran University, Ahvaz 61357-4-3169, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 June 2013
Received in revised form 24 July 2013
Accepted 26 July 2013
Available online 2 August 2013
Nanomagnetic double-charged diazoniabicyclo[2.2.2]octane dichloride silica hybrid (Fe3O4@SiO2/DABCO) was
used as an efficient and magnetically recoverable phase-transfer catalyst (PTC) for nucleophilic substitution reac-
tions of benzyl halides for the synthesis of benzyl acetates and thiocyanates in good to excellent yields at 100 °C in
water. No evidence for the formation of by-products, for example, isothiocyanate or benzyl alcohol was observed
and the products were obtained in pure form without further purification. The catalyst was easily separated with
the assistance of an external magnetic field from the reaction mixture and reused for several consecutive runs
without significant loss of its catalytic efficiency.
Keywords:
Organic–inorganic hybrid silica
Magnetite composite
© 2013 Elsevier B.V. All rights reserved.
Double-charged hybrid silica
nucleophilic substitution reactions
nucleophilic substitution reactions
1. Introduction
toxic than their metallic counterparts, and they still have high saturation
magnetization and superparamagnetic behavior, among which magne-
Hybrid xerogel materials, where the organic component is bonded
to a polymeric silica skeleton framework, have attracted significant at-
tention over the last decade. In this context, single- and double-charged
silica-based hybrid xerogels containing the 1-azonia-4-azabicyclo
[2.2.2]octane, DABCO, chloride group have recently drawn particular
interest [1–4].
tite is a very promising choice due to its already proven biocompatibility.
In addition, previous investigations have shown that magnetite has rel-
atively high LD50 values (400 mg/kg in rats) and polymer-coated mag-
netite has not shown any acute or subacute toxicity in animal studies
[13,14].
Phase-transfer catalysis (PTC) is a very useful technique, which is
widely used in the synthesis of dyes, pharmaceutics/perfumes,
flavorants, agricultural chemicals, monomers, and polymers, and it
has been widely used for organic synthesis, particularly for nucleo-
philic substitution [15–18]. The design of efficient and recoverable
phase-transfer catalysts has become an important issue for reasons
of economic and environmental impact, in recent years. In particular,
immobilization of the phase-transfer catalyst on a support has con-
siderable advantages, including easy catalyst recovery and product
isolation, and employment of a continuous flow method owing to
the three-phase nature of the system, which make the technique at-
tractive for industrial applications. Although many phase-transfer
catalysts are known, quaternary salts formed from ammonia are
practically important and used in many of organic reactions. Its
high polarity and ability to solubilize both organic and inorganic
compounds can result in enhanced reaction rates and can provide
higher selectivity compared with conventional methods [19–22].
Considering these facts and taking all this into account, we decided
to use supported nanomagnetic double-charged diazoniabicyclo[2.2.2]
octane dichloride silica hybrid (Fe3O4@SiO2/DABCO) as an efficient
nanomagnetic phase transfer system for organic transformation.
Ionic liquids (ILs) have been widely used in organic synthesis and cat-
alytic reactions as solvents and catalysts. The practical utility of ILs as a
catalyst in aqueous media could be extended further if it can be rendered
water insoluble. The chemical industry still prefers to use heterogeneous
catalyst systems because of the ease of separation, thus supported ILs are
highly desirable [5]. Immobilization of ILs on solid supports has been
suggested as an alternative way of getting around the problems.
Due to the high surface area to volume ratios, superparamagnetic
properties and biocompatibility, magnetic nanoparticles (MNPs) can
effectively improve the loading and catalytic efficiency of immobilized
catalysts. They often encompass the desirable features of both organic
and inorganic compounds [6–11]. More than these, they can be easily
separated by the simple application of an external magnetic field,
which may optimize operational costs and enhance a product’s purity
[12]. Iron oxides, magnetite (Fe3O4), and maghemite (γ-Fe2O3) are by
far the most used magnetic nanoparticles because they are much less
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