Greener Synthetic Alternatives to Heterocycles, Nanomaterials and Nanocomposites
Dr. Rajender S. Varma, Sr. Scientist, Sustainable Technology Division, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH, USA.

Microwave (MW) expedited reaction of neat reactants or catalyzed by mineral support surfaces, such as alumina, silica, clay, or their 'doped' versions, for the rapid one-pot assembly of heterocyclic compounds [1] from in situ generated reactive intermediates via enamines [2] or using hypervalent iodine reagents [3] will be described that can be adapted for parallel synthesis in multicomponent reactions [4]. The eco-friendly nucleophilic substitution chemistry in water [5] can be manipulated using microwaves to generate cyclic amines via double N-alkylation of primary amines or hydrazines by dihalides or tosylates [6]. Greener protocols for the synthesis of pharmaceutically active heterocycles namely N-aryl azacycloalkanes, isoindoles, and dihydropyrazoles [6], 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,3-dioxanes [7a], pyrazoles, hydrazones [7b] and 3,4-dihydropyrimidin-2(1H)-ones [7c], catalyzed by basic water or polystyrene sulfonic acid (PSSA) in aqueous media or solid supported Nafion®NR50, or (P₄S₁₀/Al₂O₃) under solvent-free conditions will be described.

Aqueous preparation of nanoparticles using vitamins B₁ and B₂ [8a], which can function both as reducing and capping agents and the bulk and shape-controlled synthesis of noble nanostructures via microwave (MW)-assisted spontaneous reduction of noble metal salts using α-D-glucose, sucrose, and maltose [8b] will be presented. A general MW method has been developed that accomplishes the cross-linking reaction of poly (vinyl alcohol) (PVA) with metallic systems such as Pt, Cu, and In; bimetallic systems, namely Pt-In, Ag-Pt, Pt-Fe, Cu-Pd, Pt-Pd and Pd-Fe [9a]; and SWNT, MWNT, and C-60 [9b]. The strategy is extended to the formation of biodegradable carboxymethyl cellulose (CMC) composite films with noble nanometals [10]; such metal decoration and alignment of carbon nanotubes in CMC is possible using MW approach [11] which also enables the shape-controlled bulk synthesis of Ag and Fe nanorods in poly (ethylene glycol) [12].