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cycloaddition reactions [12]. Non-symmetrical azines serve as educts for the preparation of fused tricyclic heterocy-clic systems by combined intra-intermolecular criss-cross cycloaddition [13]. Many methods have been designed to synthesize azines in the presence of catalysts such as sulfated anatase-titania [14], TiO 2-P 2 O 5 [15], tetrakis (N-methylpyridyl)porphinatoiron(III) pentachloride ([Fe III TMPyP]Cl 5) [16], and triphenylphosphine (PPh 3) [17]. Nanotechnology has gained a considerable importance in the recent times. Tungsten nanoparticles are attractive as functional materials [18] for surface metallization [19, 20]. New applications of tungsten hexachloride (WCl 6) as a cost-effective and widely available alternative would be interesting for us in recent years. To overcome disadvantages of Lewis acids, much effort has been devoted to develop heterogeneous supported catalysts based mont-morillonite K10 (Mont. K10) clay [21-26]. Montmoril-lonite K10 is a hydrophilic clay with a three-layered structure [27] belonging to the group of the smectites with an ideal chemical formula of (Al 2-y Mg y)Si 4 O 10 (OH) 2 ·nH 2 O [28, 29]. Natural occurrence of both Brønsted and Lewis acidic catalytic sites available in montmorillonite clay make it an effective catalyst [30-32]. Mont. K10 with a surface-active inorganic nature can be applied as efficient support for various transition metal salts and/or metal ions [33-38]. Green heterogeneous supports such as montmoril-lonite K10 clay have been widely used as inexpensive and noncorrosive solid acid catalyst in organic synthetic methodology and are gaining considerable importance from an environmental point of view [39, 40]. Montmorillonite K10 has been employed in several composite systems owing to large surface area, strong acidity, good efficiency, environment friendly nature, cation exchange capacity, selectiv-ity, cheapness, regeneration, and mild reaction conditions [41, 42]. We have developed new applications of tungsten Abstract In the present investigation, we have developed a novel technique to prepare azines using nano-WCl 6 loaded on Montmorillonite K10 clay as a highly active catalyst. A variety of aldehydes and ketones were efficiently converted to the corresponding azines using catalytic amounts of nanosized WCl 6 /Mont. K10 under mild conditions. The nanostructures of WCl 6 loaded on Mont. K10 as solid acid catalyst have been prepared by solid dispersion method. The advantages of this catalyst are rapid completion of the reactions, simplicity of performance, lack of pollution and mild and green reaction conditions. The morphologies, structure, and chemical components of parent and modified clay were successfully characterized using SEM, FT-IR, CV, XRD and EDX measurements.

Magnetic Fe 3 O 4 nanoparticles (MNPs) were prepared by a simple co-precipitation method using molar ratios of Fe 2+ : Fe 3+ ¼ 1 : 2 in ammonia solution, and subsequently were modified with tetraethyl orthosilicate (TEOS) via a modified StöberSt¨Stöber method and also with 3-aminopropyl triethylenesilane (APTES) via a silanization reaction. Then, a layer of TiO 2 shell was coated directly onto the silica coated magnetite core-shell nanoparticles (Fe 3 O 4 @SiO 2) followed by dispersion of a Ag nanoparticle layer on the surface of the TiO 2 shell. Also, the amino-silane coated magnetite nanoparticles (Fe 3 O 4-APTES) were successfully coated with polyethylene glycol (PEG) via the formation of covalent bonds between-NH 2 and-COOH to afford well-defined polymer-coated magnetic nanoparticles. Several transition metal nanoparticles (such as Cu, Ag, Co, Ni, Pb, Zn and Mn) were then loaded on the surface of Fe 3 O 4-APTES-PEG. We exhibit herein the synthesis and modification of magnetic nanoparticles as solid phase catalysts and their use in the reduction of nitroaromatics (nitrophenols, nitroanilines) in the presence of an excess amount of sodium borohydride (NaBH 4). The kinetic activity of the catalysts used in the reduction of nitroaromatic compounds was studied using UV-visible spectrophotometer. The reduction reaction followed first-order kinetics. Moreover, these magnetic core-shell nanocomposites showed convenient magnetic separability as well as quite good stability after five recycles.

Organosilane sulfonated graphene oxides (SSi-GO) have been synthesized by a two-step procedure involving the grafting of graphene oxide (GO) using 3-chloropropyltriethoxysilane (CCPTES) and subsequent oxidation using sulfanilic acid. It has been shown that organosilane sulfonated graphene oxide (SSi-GO) exhibits a superior catalytic performance to produce pyrimidines in the Biginelli and Biginelli-like reactions. This stronger acidity corresponds to the cooperative effects of the aryl sulfonic acid groups and other kinds of acid sites (carboxylic acids). However, the acidic functionalities bonded to the SSi-GO surface are stable under the catalytic reaction conditions resulting in its efficient reuse.

Some transition metal oxides supported on MWCNTs were prepared as novel heterogeneous catalysts using the facile processes. Then, the catalytic behaviour of transition metal oxide-MWCNT nanocomposites was investigated in the Biginelli one-pot cyclocondensation of aldehydes, b-dicarbonyl compounds and urea (thiourea) in solvent-free media under microwave irradiation as the energy source. The experimental results showed that TiO 2-MWCNTs were the most efficient nanocatalyst for the Biginelli reaction among the studied transition metal oxide-MWCNTs. This study provides new insights to develop this three components methodology using microwave-assisted dry media technology. The current catalytic process is an environmentally friendly, sustainable and economically acceptable synthetic tool because it operates under solvent-free conditions with high chemical efficiency, easy work-up procedures and feasible reusability of the nanocomposites.

Pt-MWCNTs nanocomposites are found to be an excellent and efficient catalyst to promote one-pot and three-component coupling reaction of isatoic anhydride, aldehyde and ammo-nium acetate or primary aromatic amine to produce 2,3-dihydroquinazolin-4(1H)-one derivatives under ultrasound irradiation. This novel method has the advantages such as short reaction times, convenient manipulation, excellent yields and the use of effective catalyst.

A supported carbon material is shown to be a highly efficient, eco-friendly and recyclable solid acid catalyst for the Biginelli reaction of aldehyde, b-ketoester and urea or thiourea under microwave irradiation in the absence of solvent. This method offers significant advantages such as efficiency, the excellent yield, avoidance of the organic solvents, mild reaction conditions, easy separation and simple operation. In addition, because of employing microwave as heating source and reducing use of organic solvents, this novel method emerges as a green-approach leading to less harmful residues. Furthermore, a mechanism was proposed to rationalize the reaction and the role of NiO-MWCNTs was also investigated in these transformations.