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Green Synthetic Alternatives to Organic Compounds and Nanomaterials
Citation:
VARMA, R. S. Green Synthetic Alternatives to Organic Compounds and Nanomaterials. Presented at 3rd Indo-US Workshop on Green Chemistry, Delhi, INDIA, January 07 - 09, 2008.
Impact/Purpose:
To inform the public.
Description:
A brief 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 from in situ generated reactive intermediates via enamines or using hypervalent iodine reagents will be described that can be adapted for parallel synthesis in multicomponent reactions (Biginelli and Ugi reactions). The eco-friendly nucleophilic substitution chemistry in water can be manipulated using microwaves to generate cyclic amines via double N-alkylation of primary amines or hydrazines by dihalides or tosylates. Greener protocols for the synthesis of pharmaceutically active heterocycles [namely N-aryl azacycloalkanes, isoindoles, and dihydropyrazoles, 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,3-dioxanes, pyrazoles, hydrazones and 3,4-dihydropyrimidin-2(1H)-ones, 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, and vitamin C which can function both as reducing and capping agents will be presented that allows synthesis of polypyrrole-wrapped Ag nanocables. Bulk and shape-controlled synthesis of noble nanostructures via MW-assisted spontaneous reduction of noble metal salts using -D-glucose, sucrose, and maltose will be described; MW method also 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; and SWNT, MWNT, and C-60. The strategy is extended to the formation of biodegradable carboxymethyl cellulose (CMC) composite films with noble nanometals; such metal decoration and alignment of carbon nanotubes in CMC is possible using MW approach which also enables the shape-controlled bulk synthesis of Ag and Fe nanorods in poly (ethylene glycol). The application of nano-sized MgO is demonstrated in a green synthesis of 2-amino-2-chromene derivatives in aqueous PEG.