Polymer-Anchored Cu(II) Complex as an Efficient Catalyst for Selective and Mild Oxidation of Sulfides and Oxidative Brom
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Polymer-Anchored Cu(II) Complex as an Efficient Catalyst for Selective and Mild Oxidation of Sulfides and Oxidative Bromination Reaction Sk. M. Islam • Anupam Singha Roy • Paramita Mondal • Noor Salam • Sumantra Paul
Received: 26 September 2012 / Accepted: 16 November 2012 / Published online: 1 December 2012 Ó Springer Science+Business Media New York 2012
Abstract A new polymer-anchored Cu(II) complex has been tested for the oxidation of sulfides and in oxidative bromination reaction with hydrogen peroxide as oxidant. Sulfides have been selectively oxidized to corresponding sulfoxides in excellent yields and in presence of KBr as bromine source, organic substrates have been selectively converted to mono bromo substituted compounds. The polymer-anchored Cu(II) catalyst could be easily recovered by simple filtration and reused more than six times without appreciable loss of its initial activity. Keywords Oxybromination Sulfide oxidation Polymer-anchored Cu(II) catalyst Potassium bromide Hydrogen peroxide
1 Introduction In the recent past, there has been an increasing interest in developing environmental friendly greener processes which are also economically viable. However, some problems such as excessive use of oxidants, corrosion, difficulty in recovery and separation of the catalyst from reaction mixtures are associated with homogeneous catalysts and make such systems environmentally unsuitable [1]. In recent years, the design and synthesis of catalytically active supported metal complexes have received considerable interest. Many effective and recyclable heterogeneous catalysts have been studied for the liquid phase oxidation [2, 3]. Various approaches have been focused on Sk. M. Islam (&) A. S. Roy P. Mondal N. Salam S. Paul Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, WB, India e-mail: [email protected]
the incorporation of metal-based catalysts onto or into inert supports by different methods, such as alumina [4], amorphous silicates [5], polymers [6], zeolites [7] and MCM-41 [8]. Application of polymer supported catalysts in oxidation reactions has been received attention in recent years due to their potential advantages over the homogeneous one [9–13]. The activity of polymer supported Schiff base complexes of transition metal ions varies with the type of Schiff base ligands, coordination sites and metal ions used in their formation. Selective oxidation of organic sulfides to sulfoxides is one of the key reactions in the domain of organic oxidation chemistry especially because of the potential use of sulfoxides as synthetic intermediates for construction of many chemically and biologically active molecules [14, 15]. The main synthetic route for the preparation of these valuable materials is via oxidation of the corresponding sulfides. There are several reagents available for this key transformation which is typically achieved using stoichiometric or catalytic amounts of both organic and inorganic reagents [16–18]. The use of ‘green oxidants’ such as molecular
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