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Green Chemistry and Organic Reactions

EPA researchers use a variety of approaches to develop greener organic reactions. The same researchers conduct related nanotechnology research.

Solvent-free Reactions

Organic reactions under solvent-free conditions offer enhanced selectivity and efficiency, ease of manipulation, and often avoid toxic and volatile solvents. Solvent-free approaches involve grinding, ultrasonic irradiation and microwave irradiation of undiluted reactants, or catalysis by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or doped aluminosilicates. These approaches are applicable to a wide range of cleavage, condensation, cyclization, oxidation and reduction reactions, and to the high-speed parallel synthesis of a library of biologically active molecules.

Microwave-accelerated Reactions

Microwave irradiation, an unconventional energy source, has been used for a variety of organic transformations wherein chemical reactions are accelerated because of the selective absorption of microwaves by polar molecules. The use of microwave irradiation under solventless conditions enables rapid synthetic transformations at ambient pressure, thus providing unique chemical processes with attributes such as ease of manipulation, enhanced reaction rates, and higher yields. Recent results from our laboratory for the microwave-expedited approach include the synthesis of a wide variety of industrially significant compounds and intermediates, namely enones, imines, enamines, nitroalkenes, and oxidized sulfur species. Microwave irradiation was also used in the solventless preparation of ionic liquids, which have unique roles as catalysts.

Microwave-assisted Reactions in Water and Other Solvents

Microwave irradiation with water as a reaction medium has been a successful greener chemical approach. Recent examples include the aqueous N-alkylation of amines to deliver tertiary amines. The synthesis of Ν-azacycloalkanes, an important class of building blocks in natural products and pharmaceuticals, can be achieved by a simple, efficient, and environmentally friendlier alternative using a microwave protocol in carbonated water. Similarly, classical nucleophilic substitution reactions can be revisited in an aqueous medium. These microwave-assisted, greener and expeditious chemical transformations circumvent the need for multi-step processes that use expensive metal catalysts, proceed under mild reaction conditions and minimize or eliminate the formation of byproducts. Selected reactions using polyethylene glycol, carbon dioxide, and ionic liquids as reaction media have also been accomplished.

Selected Recent Publications

Alternate Energy Input: Mechanochemical, Microwave and Ultrasound-assisted Organic Synthesis.
R. B. Nasir Baig and R.S. Varma: Chem. Soc. Reviews, 41, 1559-1584 (2012).

Microwave-Assisted Organic Synthesis and Transformations using Benign Reaction Media.
V. Polshettiwar and R.S. Varma: Acc. Chem. Res., 41, 629-639 (2008).

Additional Publications Selected from 330 Peer-reviewed Publications (PDF) (32 pp, 910 KB)

Contact

Rajender Varma
513- 487-2701
Fax: 513-569-7677
Mailing Address
U.S. EPA National Risk Management Research Laboratory
Andrew W. Breidenbach Environmental Research Center
26 West Martin Luther King Drive
Mail Code: Mail Stop 443
Cincinnati, Ohio 45268

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