%0 Journal Article
%T An Efficient Protocol for the Green and Solvent-Free Synthesis of Azine Derivatives at Room Temperature Using BiCl3-Loaded Montmorillonite K10 as a New Recyclable Heterogeneous Catalyst
%A K. Ravi
%A B. Krishnakumar
%A M. Swaminathan
%J ISRN Organic Chemistry
%D 2012
%R 10.5402/2012/595868
%X A new BiCl3-loaded montmorillonite K10 catalyst has been prepared by solid dispersion method and was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and cyclic voltammetry (CV) measurements. BiCl3 loaded K10 (BiCl3-K10) has been used as solid acid catalyst for the synthesis of azine derivatives from benzophenone hydrazone and ketones/aldehydes by simple physical grinding. This BiCl3-K10 gives an excellent yield with short reaction time and is an inexpensive, easily recyclable catalyst for this reaction. 1. Introduction Commercially available BiCl3 had been widely used as a Lewis acid catalyst for aldol reaction [1], hetero Diels-Alder reaction [2], ring opening of epoxides with aromatic amines [3], deoxygenative allylation of substituted benzylic alcohols with allyltrimethylsilane [4], and for three-component synthesis of ¦Â-amino carbonyl compounds [5]. But BiCl3 is highly hygroscopic and difficult to handle as it is toxic and causes irritation to the gastrointestinal and respiratory tract. In addition, this catalyst cannot be reused. Bismuth chloride is to be loaded on a support material for easy handling and utilization. Clays function as efficient catalysts for various organic transformations due to their Bronsted and Lewis acidities in their natural and ion-exchanged forms [6]. Commercially available montmorillonite K10 (Mont K10) clay is one such material that can fulfill these requirements. Mont K10 is an environmentally benign and economically feasible solid catalyst that offer several advantages, such as ease of handling, non-corrosiveness, low cost, and regeneration. Its high surface area (250£¿m2£¿g£¿1) makes it as a useful and active catalyst. Its structural feature [7] and synthetic potential [8] have been extensively studied. Mont K10 is a layered alumino-silicate with a dioctahedral layer sandwiched between two tetrahedral layers. Due to strong catalytic activity as solid acid, Mont K10 clay has been used extensively as a catalyst for many organic transformations [9¨C12]. Azines, R1R2C=N¨CN=CR1R2, have attracted great attention in organic synthesis as they are good synthons for obtaining various heterocyclic compounds [13, 14]. These compounds constitute an important class of compounds with unexpected biological activities [15, 16]. The usual method for the preparation of azines involves treatment of carbonyl compounds with hydrazine hydrate and acetic acid in ethanol [17]. A number of methods have been reported for the synthesis of azines under various conditions [18¨C21], but most of them require
%U http://www.hindawi.com/journals/isrn.organic.chemistry/2012/595868/