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MICROWAVE IRRADIATION IN BENIGN SYNTHESIS OF ORGANIC MOLECULES, NOBLE NANOMETALS AND NANOCOMPOSITES
Citation:
VARMA, R. S. MICROWAVE IRRADIATION IN BENIGN SYNTHESIS OF ORGANIC MOLECULES, NOBLE NANOMETALS AND NANOCOMPOSITES. Presented at 13th China National Conference on Microwave Power Application & International Forum on Industrial Microwave Power Economization, Changsha, CHINA, November 14 - 16, 2007.
Impact/Purpose:
To inform the public.
Description:
A brief historic account of reactions involving microwave (MW) exposure 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. Examples of multicomponent reactions that can be adapted for rapid parallel synthesis include solventless synthesis of dihydropyrimidine-2(1H)-ones (Biginelli reaction) [4], imidazo[1,2-a]annulated pyridines, pyrazines, and pyrimidines (Ugi reaction) [5]. The eco-friendly nucleophilic substitution chemistry in water [6,7] can be manipulated using microwaves to generate cyclic amines via double N-alkylation of primary amines or hydrazines by dihalides or tosylates [8]. The protocol circumvents running multi-step reactions to assemble N-aryl azacycloalkanes, isoindoles, and dihydropyrazoles etc. and tolerates a variety of sensitive functional groups. Our simple greener aqueous one-pot method synthesizes bulk quantities of nanospheres, nanorods, nanowires, and nanoballs of aligned nanobelts of the metals without the need for large amounts of insoluble templates (9). A bulk and shape-controlled synthesis of noble nanostructures with various shapes such as prisms, cubes, and hexagons occurs via MW spontaneous reduction of noble metal salts using an aqueous solution of -D-glucose, sucrose, and maltose (10). A general MW method has also been developed that accomplishes 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 (11); and single-wall carbon nanotubes (SWNT), multi-wall carbon nanotubes (MWNT), and Buckminsterfullerene (C-60) (12) in various shape forms such as spheres, dendrites, and cubes. The strategy is now extended to formation of biodegradable carboxymethyl cellulose (CMC) composite films with noble nanometals that may find potential biological applications (13)