![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20090507234438im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Alternative Chemical Synthetic Pathways
Center for Green Nanomaterials
Nanomaterials: Reducing Environmental and Human Health Risk and Avoiding Future Environmental Liability; Greener Syntheses of Nanomaterials and their Safer Applications as Polymer Nanocomposites for Chemical Catalysis and Environmental Applications
Solvent-Free Processes Using Mechanochemical Mixing or Supported Reagents; Accelerated Organic Syntheses via Activation by Microwave- and Ultrasound Irradiation in Eco-friendly Media
Solvent-free Mechanochemical and Microwave-Accelerated Reactions
Organic reactions under solvent-free conditions are advantageous
because of enhanced selectivity and efficiency, ease of manipulation,
and more importantly, because toxic and often volatile solvents
are avoided. Solvent-free approaches involve mechanochemical mixing
(grinding), microwave (MW) irradiation of neat reactants (undiluted),
or catalysis by the surfaces of inexpensive and recyclable mineral
supports, such as alumina, silica, clay, or ‘doped’
surfaces. These approaches are applicable to a wide range of cleavage,
condensation, cyclization, oxidation, and reduction reactions,
including convergent one-pot assembly of heterocyclic compounds
from in situ generated reactive intermediates such as
α-tosyloxyketones and enamines. The strategy is adaptable
to multi-component reactions (e.g. Ugi and Biginelli reactions)
for high-speed parallel synthesis of a library of biologically
active molecules. Recent results from our laboratory for the MW-expedited
approach include the synthesis of a wide variety of industrially
significant compounds and intermediates, namely enones, imines,
enamines, nitroalkenes, and oxidized sulfur species and their
demonstrated value in the concise synthesis of flavones, tetrahydroquinolones,
2-aroylbenzofurans, and thiazole derivatives, as well as the solventless
preparation of ionic liquids which have unique roles as catalysts.
MW irradiation, an unconventional energy source, has been used for a variety of organic transformations wherein chemical reactions are accelerated because of selective absorption of MW energy by polar molecules; non-polar molecules are inert to the MW dielectric loss. The MW application under solventless conditions enables rapid synthetic transformations at ambient pressure, thus providing unique chemical processes with special attributes such as ease of manipulation, enhanced reaction rates, and higher yields. The distinct advantage of this strategy, that reduces or prevents pollution ‘at-source,’ has been exemplified by efficient functional group transformations involving non-metallic hypervalent iodine oxidants and substitution of conventional metal-based reducing agents.
MW-Assisted Reactions in Water, Polyethylene Glycol (PEG) and
Ionic Liquids
The development of efficient and selective greener methods has
become a major focus of researchers worldwide and selection of
appropriate alternate eco-friendly reaction media has become an
integral part of this paradigm shift. Microwave (MW) irradiation
as an alternative energy source in conjunction with water as reaction
medium has proven to be a successful ‘greener’ chemical
approach. Recent examples include the aqueous N-alkylation of
amines by alkyl halides that proceed expeditiously in the presence
of aqueous sodium hydroxide 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 MW protocol. This double N-alkylation of primary amines
readily assembles two C-N bonds in a SN2-like heterocyclization
sequence which cannot be fully realized under conventional heating
conditions. The MW-assisted reaction proceeds in aqueous potassium
carbonate and leads to the formation of a variety of five-membered
heterocycles (e.g. isoindole, pyrazole and pyrazolidine) by condensation
of amines or hydrazines with alkyl 1,3-dihalides or -ditosylates.
Similarly, classical nucleophilic substitution reactions can be
revisited in aqueous medium by reacting alkyl halides or tosylates
with alkali azides to provide azides and thiocyanides in the absence
of a phase transfer catalyst. The protocol can be extended to
preparation of sulfones from sulfinate salts in aqueous medium.
These MW-assisted ‘greener’ and expeditious chemical
transformations circumvent the need for multi-step processes that
use expensive metal catalysts and accommodate reactive functional
groups because of mild reaction conditions, thus minimizing or
eliminating the formation of byproducts. Selected reactions using
polyethylene glycol (PEG), carbon dioxide, and ionic liquids as
reaction media or catalysts have been accomplished, where recycling
of catalysts have been demonstrated in our laboratory.
Nanomaterials
The heavy investment in the development and deployment of products
containing nanomaterials is now a worldwide phenomenon. The unique
physical and chemical properties of nanomaterials, such as different
conductivity, optical sensitivity, and reactivity, originate mainly
from factors such as small size, surface structure, chemical composition,
shape, solubility, or aggregation. These varied properties are
attractive for application in a variety of technology areas. Consequently,
nanomaterials are becoming widely used in varied applications
from cosmetics to semiconductors. Nanotechnology development and
production presents a unique opportunity to offer a more sustainable
approach to protect public health and the environment and prevent
future environmental liability. There is a great need for EPA
to provide manufacturers and users with the most up-to-date science
on the potential risk of these materials on human health and the
environment and robust information on how to prevent future environmental
liability.
Our Approach is to develop a scientifically based framework for greener preparation of these materials in a manner that renders the materials less mobile in the environment and reduces or eliminates the use and generation of hazardous substances, such as the hydrazine and borohydride reducing agents normally used in nanomaterials production. Three areas of opportunity are being exploited to engage green chemistry: (i) choice of solvent, (ii) the reducing agent employed, and (iii) the capping agent (or dispersing agent). The synthesis of nanometal/nanometal oxide/nanostructured polymers and their stabilization (through dispersant, biodegradable polymer) will involve the use of natural renewable resources such plant material extract, biodegradable polymers, and sugars, and finally microwave (MW) irradiation as an efficient and selective mode of activation.
Current results from our Center for Green Nanomaterials laboratories have shown that vitamins B1 and B2 or related benign materials can function both as reducing and capping agents and provide an extremely simple, one-pot, greener method to synthesize bulk quantities of nanospheres, nanorods, nanowires, and nanoballs of aligned nanobelts and nanoplates of the metals in water without the need of large amounts of insoluble templates. We have extended this non-conventional MW route to make these nanostructures via spontaneous reduction of gold, silver, platinum, and palladium nanostrutures with sugar solutions such as alpha-D-glucose, sucrose and maltose; a newer form of carbon-doped porous titania has been also prepared using dextrose that can be useful for visible-light induced photodegradation of pollutants. A facile MW method has been developed that accomplishes cross-linking reaction of poly (vinyl alcohol) (PVA) with metallic and bimetallic systems. Nanocomposites of PVA cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-Pt, Pt-Fe, Cu-Pd, Pt-Pd and Pd-Fe are prepared expeditiously by reacting respective metal salts with 3 wt % PVA under MW irradiation maintaining a temperature at 100 oC, a radical improvement over the literature methods to prepare cross-linked PVA. For the first time, we have accomplished a single-step bulk synthesis of leucoemealdine polyaniline nanofibers (completely reduced state) without the need of reducing agent, template, or seed at room temperature. The polyaniline nanofibers can reduce metal salts to generate novel nanocomposites which exhibit high thermal stability with broad decomposition temperatures, which could lead to a myriad of applications, such as energy storage systems, catalysis, fuel cell membranes, and nanodevices.
The long-term goal is to produce a “guide” for nanomaterial manufacturers to follow to limit risk to human health and the environment and prevent future clean-up of these materials if they are found to be toxic. In the short term, current research will also be extended to the use of other benign materials to synthesize nanometals/polymer nanostructures/nanopolymer composites and study their catalytic properties for various chemical and environmental remediation applications. These applications may range from catalysts to destroy noxious and toxic gases as CO, SOx, and NOx in automobile catalytic converters and power generation systems from burning of gasoline and coal to highly sensitivity sensors, water purification, membrane systems, adsorption of heavy metals, and antibacterial coatings.
A Cooperative Research and Development Agreement (CRADA) has been signed with CEM, a leading microwave equipment manufacturer, and developmental efforts on sustainable processes are pursued with researchers worldwide.
Recent Publications (selected from 255 peer-reviewed papers):
Novel Mercury Oxidant and Sorbent for Mercury Emissions Control From Coal-Fired Power Plants.
J.-Y. Lee, Y. Ju, S.-S Lee, T.C. Keener, and R.S. Varma: Water Air Soil Pollution, (2008).
Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2: Catalytic Polymerisation of Aniline and Pyrrole.
M.N. Nadagouda and R.S. Varma: J. Nanomaterials, 2008, 782358 (2008).
Microwave-Assisted Shape-Controlled Bulk Synthesis of Ag and Fe Nanorods in Poly(ethylene glycol) Solutions.
M.N. Nadagouda and R.S. Varma: Crystal Growth and Design, 8, 1: 291–295 (2008).
Noble Metal Decoration and Alignment of Carbon Nanotubes in Carboxymethyl Cellulose.
M.N. Nadagouda and R.S. Varma: Macromolecular Rapid Commun., 29, 2: 155–159 (2008).
Greener and Expeditious Synthesis of Bio-Active Heterocycles Using Microwave Irradiation.
V. Polshettiwar and R.S. Varma: Pure Applied Chem., 80 (2008).
Greener and Rapid Access to Bio-Active Heterocycles: Room Temperature Synthesis of Pyrazoles and Diazepines in Aqueous Medium.
V. Polshettiwar and R.S. Varma: Tetrahedron Lett., 49: 397 (2008).
Rapid Access to Bio-Active Heterocycles: One-Pot Solvent-Free Synthesis of 1,3,4-Oxadiazoles and 1,3,4-Thiadiazoles.
V. Polshettiwar and R.S. Varma: Tetrahedron Lett., 49 (2008).
An Efficient and Chemoselective Cbz-Protection of Amines Using Silica-Sulfuric Acid at Room Temperature.
M.B. Gawande, V. Polshettiwar, R.S. Varma, and R.V. Jayaram: Tetrahedron Lett., 48: 8170 (2007).
Nanosized Magnesium Oxide as Catalyst for the Rapid and Green Synthesis of Substituted 2-Amino-2-Chromenes.
D. Kumar, V.B. Reddy, B.G. Mishra, R.K. Rana, M.N. Nadagouda, and R.S. Varma: Tetrahedron, 63, 15: 3093–3097 (2007).
Vapor Phase Mercury Sorption by Organic Sulfide Modified Bimetallic Iron-Copper Nanoparticle Aggregates.
A. Makkuni, R.S. Varma, S.K. Sikdar, and D. Bhattacharyya: Ind. Eng. Chem. Res., 46, 4: 1305–1315 (2007).
A Greener Synthesis of Core (Fe, Cu)-Shell (Au, Pt, Pd, and Ag) Nanocrystals Using Aqueous Vitamin C.
M.N. Nadagouda and R.S. Varma: Crystal Growth and Design, 7: 2582 (2007).
Microwave-Assisted Shape-Controlled Bulk Synthesis of Noble Nanocrystals and Their Catalytic Properties.
M.N. Nadagouda and R.S. Varma: Crystal Growth and Design, 7, 4: 686–690 (2007).
Microwave-Assisted Synthesis of Cross-Linked Poly (Vinyl Alcohol) Nanocomposites Comprising Single-Wall Carbon Nanotubes (SWNT), Multi-Wall Carbon Nanotubes (MWNT), and Buckminsterfullerene (C-60).
M.N. Nadagouda and R.S. Varma: Macromolecular Rapid Commun., 28: 842 (2007).
Preparation of Novel Metallic and Bimetallic Cross-Linked Poly (Vinyl Alcohol) Nanocomposites Under Microwave Irradiation.
M.N. Nadagouda and R.S. Varma: Macromolecular Rapid Commun., 28, 4: 465–472 (2007).
Synthesis of Thermally Stable Carboxymethyl Cellulose/Metal Biodegradable Nanocomposite Films for Potential Biological Applications.
M.N. Nadagouda and R.S. Varma: Biomacromolecules, 8: 2762–2767 (2007).
Room Temperature Bulk Synthesis of Silver Nanocables Wrapped With Polypyrrole.
M.N. Nadagouda and R.S. Varma: Macromolecular Rapid Commun., 28, 21: 2106–2111 (2007).
Green Approach to Bulk and Template-Free Synthesis of Thermally Stable Reduced Polyaniline Nanofibers for Capacitor Applications.
M.N. Nadagouda and R.S. Varma: Green Chem., 9: 632 (2007).
Expeditious Oxidation of Alcohols to Carbonyl Compounds Using Iron (III) Nitrate.
V. Namboodiri, V. Polshettiwar, and R.S. Varma: Tetrahedron Lett., 48: 8839 (2007).
Biginelli Reaction in Aqueous Medium: A Greener and Sustainable Approach to Substituted 3,4-Dihydropyrimidin-2(1H)-Ones.
V. Polshettiwar and R.S. Varma: Tetrahedron Lett., 48, 41: 7343–7346 (2007).
Greener and Sustainable Approaches to the Synthesis of Pharmaceutically Active Heterocycles.
V. Polshettiwar and R.S. Varma: Current Opinion Drug Discovery and Development, 10, 6: 723–737 (2007).
Polystyrene Sulfonic Acid Catalyzed Greener Synthesis of Hydrazones in Aqueous Medium Using Microwaves.
V. Polshettiwar and R.S. Varma: Tetrahedron Lett., 48, 32: 5649–5652 (2007).
Tandem Bis-Aldol Reaction of Ketones: A Facile One-Pot Synthesis of 1,3-Dioxanes in Aqueous Medium.
V. Polshettiwar and R.S. Varma: J. Org. Chem., 72, 19: 7420–7422 (2007).
Tandem Bis-Aza-Michael Addition Reaction of Amines in Aqueous Medium Promoted by Polystyrenesulfonic Acid.
V. Polshettiwar and R.S. Varma: Tetrahedron Lett., 48: 8735 (2007).
‘Greener’ Chemical Syntheses Using Mechanochemical Mixing or Microwave and Ultrasound Irradiation.
R.S. Varma: Green Chem. Letters and Reviews, 1 (2007).
Clean Chemical Synthesis in Water 
R.S. Varma: Invited Review in Organic Chemistry Highlights, February 1 (2007).
Greener Organic Syntheses Under Non-Traditional Conditions Using Microwave and Ultrasound Irradiation and Mechanochemical Mixing.
R.S. Varma: NATO-ASI, Green Chemistry Series, edited by P. Tundo (2007).
Thermally Stable Nanocrystalline TiO2 Photocatalysts Synthesized Via Sol-Gel Methods Modified With Ionic Liquid and Surfactant Molecules.
H. Choi, Y.-J. Kim, R. Varma, and D. Dionysiou: Chemistry Materials, 18, 22: 5377–5384 (2006).
Dextrose-Templated Microwave-Assisted Combustion Synthesis of Spongy Metal Oxides.
M.N. Nadagouda and R.S. Varma: J. Smart Materials Structures, 15: 1260–1265 (2006).
Green and Controlled Synthesis of Gold and Platinum Nanomaterials Using Vitamin B2: Density-Assisted Self-Assembly of Nanospheres, Wires, and Rods.
M.N. Nadagouda and R.S. Varma: Green Chem., 8: 516–518 (2006).
Greener Organic Syntheses Under Non-Traditional Conditions.
R.S. Varma, Indian J. Chemistry, 45B,
2305 (2006).
Solvent-free Facile Synthesis of α-Tosyloxy β-Keto
Sulfones Using [Hydroxy(tosyloxy)iodo]benzene.
D. Kumar, M.S. Sundaree, G. Patel, V.S. Rao and R.S. Varma: Tetrahedron
Lett., 47, 8239 (2006).
Microwaves in Green and Sustainable Chemistry.
C.R. Strauss and R.S. Varma in “Microwave Methods in
Organic Synthesis”, a series in Topics in Current
Chemistry, Eds: Larhed / Olofsson, Springer-Verlag, Heidelberg,
266, pp199-231 (2006).
A Facile One-Pot Synthesis of β-Keto Sulfones from Ketones
Under Solvent-Free Conditions.
D. Kumar, S. Sundaree, V.S. Rao and R.S. Varma: Tetrahedron
Lett., 47, 4197 (2006).
Organic Synthesis Using Microwaves and Supported Reagents.
R.S. Varma and Y. Ju in “Microwaves in Organic Synthesis,
2nd Edition” A. Loupy (Ed.), Wiley-VCH, Weinheim, Chapter
8, pp 362-415 (2006).
Development of Cost-Effective Noncarbon Sorbents for Hgo
Removal from Coal-Fired Power Plants.
J.-Y. Lee, Y. Ju, T.C. Keener and R.S. Varma: Environ. Science
& Technology, 40, 2714 (2006).
Microwave Effects in Organic Synthesis: Mechanistic and Reaction
Medium Considerations.
A. Loupy and R.S. Varma: Chimica Oggi (Chemistry Today),
24, 36 (2006).
Aqueous N-Heterocyclization of Primary Amines and Hydrazines
with Dihalides: Microwave-assisted Syntheses of N-Azacycloalkanes,
Isoindole, Pyrazole, Pyrazolidine and Phthalazine Derivatives.
Y. Ju and R.S. Varma: J. Org. Chem., 71,
135 (2006).
Process Intensification: Oxidation of benzyl Alcohol Using a Continuous
Isothermal Reactor under Microwave Irradiation.
R.J.J. Jachuck, D.K. Selvaraj and R.S. Varma: Green Chem.,
8, 29 (2006).
Microwave-assisted Preparation of 1-Butyl-3-methylimidazolium
Tetrachlorogallate and its Catalytic Use in Acetal Formation Under Mild
Conditions.
Y.-J. Kim and R.S. Varma: Tetrahedron Lett., 46,
7447 (2005).
Efficient Trost’s γ-Addition Catalyzed by Polymer-Supported
Triphenylphosphine in Aqueous Media.
R. Skouta, R.S. Varma and C.J. Li: Green Chem., 7,
571 (2005).
Tetrahaloindate(III)-based Ionic Liquids in the Coupling Reaction
of Carbon Dioxide and Epoxides to Generate Cyclic Carbonates: H-Bonding
and Mechanistic Studies.
Y.-J. Kim and R.S. Varma: J. Org. Chem., 70,
7882 (2005).
Microwave-assisted Cyclocondensation of Hydrazine Derivatives
with Alkyl Dihalides or Ditosylates in Aqueous Media: Syntheses of Pyrazole,
Pyrazolidine, and Phthalazine Derivatives.
Y. Ju and R. S. Varma: Tetrahedron Lett., 46,
6011 (2005).
Solventless Reactions (SLR).
R.S. Varma and Y. Ju in “Microwaves in Organic Synthesis,”
C.A.M. Afonso and J.G. Crespo (Eds.), Wiley-VCH Verlag, Weinheim,
Chapter 2.2, pp 53-87 (2005).
An Efficient and Simple Aqueous N-Heterocyclization of
Aniline Derivatives: Microwave-assisted Synthesis of N-Aryl Azacycloalkanes.
Y. Ju and R.S. Varma: Organic Letters, 7,
2409 (2005).
Microwave-assisted Preparation of Imidazolium-Based Tetrachloroindate
and their Application in the Solvent-free Tetrahydropyranylation of Aromatic
Alcohols.
Y.-J. Kim and R.S. Varma: Tetrahedron Lett., 46,
1467 (2005).
Aqueous and Vapor Phase Mercury Sorption by Inorganic Oxide Materials
Functionalized with Thiols and Poly-Thiols
A. Makkuni, L.G. Bachas, D. Bhattacharyya, R.S. Varma and S.K.
Sikdar: Clean Technologies and Environmental Policy,
7, 87 (2005).
Polythiol-Functionalized Alumina Membranes for Mercury Capture
V. Smuleac, D.A. Butterfield, S.K. Sikdar, R.S. Varma, D. Bhattacharyya:
J. Membrane Science, 251, 169 (2005).
Water as a Reaction Medium for Clean Chemical Processes.
W. Wei, C.C.K. Keh, C.-J. Li and R.S. Varma: Clean Technologies and
Environmental Policy, 7, 62 (2005).
Microwave-assisted Preparation of Cyclic Ureas from Diamines in
the presence of ZnO.
Y.J. Kim and R.S. Varma: Tetrahedron Lett., 45,
7205 (2004).
Hydrodechlorination of Chlorinated Benzenes in a Continuous Microwave
Reactor.
U.R. Pillai, E. Sahle-Demessie and R.S. Varma: Green Chem.,
6, 295 (2004).
Microwave-assisted Cu(I) Catalyzed Solvent-free Three Component
Coupling of Aldehyde, Alkyne and Amine.
Y. Ju, C.-J. Li and R.S. Varma: QSAR and Combinatorial Science,
23, 891 (2004).
Microwave-induced, solvent-free transformations of benzoheteracyclanones
by HTIB (Koser’s reagent).
T. Patonay, A. Lévai, É. Rimán and R.S. Varma:
ARKIVOC (2004).
Aqueous N-Alkylation of Amines Using Alkyl Halides: Direct
Synthesis of Tertiary Amines under Microwave Irradiation.
Y. Ju and R.S. Varma: Green Chemistry, 6,
219 (2004).
An Expeditious Synthesis of 1-Aryl-4-Methyl-1,2,4-Triazolo[4,3a]Quinoxalines
Under Solvent-free Conditions Using Iodobenzene Diacatate.
D. Kumar, K.V.G. Chandra Sekhar, H. Dhillon, V.S. Rao and R.S. Varma:
Green Chemistry, 6, 156 (2004).
Three Component Coupling of Aldehyde, Alkyne and Amine Catalyzed
by Silver in Ionic Liquid.
Z. Li, C. Wei, L. Chen, R.S. Varma and C.-J. Li: Tetrahedron
Lett., 45, 2443 (2004).
Ionic Liquids Catalyst for the Alkylation of Isobutane with 2-Butene.
K. Yoo, V.V. Namboodiri, P.G. Smirniotis and R.S. Varma: J.
Catal., 222, 511 (2004).
Ruthenium-Catalyzed Tandem Olefin Migration–Aldol and Mannich-Type
Reactions in Ionic Liquid.
X.-F.Yang, M. Wang, R.S. Varma and C.-J. Li: J. Mol. Cat.
A Chemical, 214, 147 (2004).
Preparation, Characterization and Activity of Al2O3
Supported V2O5 Catalysts.
E.P. Reddy and R.S. Varma: J. Catal., 221,
93 (2004).
Microwave Technology: Chemical Applications.
R.S. Varma: Kik-Othmer On-line Encyclopedia of Chemical Technology,
5th Edn. (2004).
Expeditious Synthesis of Ionic Liquids Using Ultrasound and Microwave
Irradiation.
R.S. Varma in “Ionic Liquids as Green Solvents. Progress and
Prospects,” R. Rogers and K. R. Seddon (Eds.), ACS Symposium
Series 856, American Chemical Society, Washington, D. C., Chapter 7, pp
82-92 (2003).
Alternate Routes for Catalyst Preparation: Use of Ultrasound and
Microwave Irradiation for the Preparation of Vanadium Phosphorus Oxide
Catalyst and their Activity for Hydrocarbon Oxidation.
U.R. Pillai, E. Sahle-Demessie, and R.S. Varma: Appl. Cat.
A General, 252, 1-8 (2003).
Nontraditional ‘Greener’ Alternatives to Synthetic
Organic Transformations Using Microwaves.
R.S. Varma in “Green Chemistry: Environment Friendly
Alternatives,” R. Sanghi and M.M. Srivastava (Eds.),
Narosa Publishing House, New Delhi, India, Chapter 6, pp 93-105
(2003).
Aldol and Mannich-type Reactions via in situ Olefin Migration
in Ionic Liquid.
X.-F. Yang, M. Wang, R.S. Varma, and C.-J. Li: Org. Lett.,
5, 657 (2003).
Ultrasound-assisted Epoxidation of Olefins and α,Β-Unsaturated
Ketones Over Hydrotalcites Using Hydrogen Peroxide.
U.R. Pillai, E. Sahle-Demessie and R.S. Varma: Synth. Commun.,
33, 2017 (2003).
Advances in Green Chemistry: Chemical Syntheses Using Microwave Irradiation R.S. Varma: Book published by AstraZeneca Research Foundation India, Bangalore, India, [85 Reaction schemes, ~300 references], (2002)
Feature article: Environmentally Friendlier Organic Transformations
on Mineral Supports Under Non-traditional Conditions.
U.R. Pillai, E. Sahle-Demessie, and R.S. Varma: J. Material
Chem., 12, 3199-3207 (2002).
Organic Synthesis Using Microwaves and Supported Reagents.
R.S. Varma in "Microwaves in Organic Synthesis,"
A. Loupy (Ed.), Wiley-VCH, Weinheim, Chapter 6, pp 181-218 (2002).
An Efficient and Ecofriendly Oxidation of Alkenes Using Iron Nitrate
and Molecular Oxygen.
U.R. Pillai, E. Sahle-Demessie, V.V. Namboodiri and R.S. Varma:
Green Chemistry, 4, 495 (2002).
Nafion-catalyzed Preparation of benzhydryl Ethers.
M.A. Stanescu and R.S. Varma: Tetrahedron Lett., 43, 7307
(2002).
An Improved Preparation of 1,3-Dialkylimidazolium Tetrafluroborate Ionic
Liquids Using Microwaves.
V.V. Namboodiri and R.S. Varma: Tetrahedron Lett., 43,
5381 (2002).
Solvent-free Sonochemical Preparation of Ionic Liquids.
V.V. Namboodiri and R.S. Varma: Organic Letters, 4, 3161
(2002).
Direct Formation of Tetrahydropyranols via Catalysis in Ionic Liquid.
C.C.K. Keh, V.V. Namboodiri, R.S. Varma, and C.-J. Li: Tetrahedron
Lett., 43, 4993 (2002).
Iron-catalyzed Solvent-free of Alcohols and Phenols into Diphenylmethyl
(DPM) Ethers.
V.V. Namboodiri and R.S. Varma: Tetrahedron Lett., 43,
4593 (2002).
Microwave-Expedited Olefin Epoxidation Over Hydrotalcites Using Hydrogen
Peroxide and Acetonitrile.
U.R. Pillai, E. Sahle-Demessie, and R.S. Varma: Tetrahedron
Lett., 43, 2909 (2002).
Selective Oxidation of Styrene to Acetophenone in Presence of Ionic
Liquids.
V.V. Namboodiri, R. S. Varma, E. Sahle-Demessie and U. R. Pillai:
Green Chemistry, 4, 170 (2002).
Clay and Clay-supported Reagents in Organic Synthesis.
R.S. Varma: Tetrahedron Report Number 598, Tetrahedron,
58, 1235-55 (2002).
Microwave-assisted Preparation of Dialkylimidazolium Tetrachloroaluminates
and Their Use as Catalysts in the Solvent-free Tetrahydropyranylation
of Alcohols and Phenols.
V. V. Namboodiri and R.S. Varma: Chem. Commun., 342 (2002).
Solvent-free tetrahydropyranylation (THP) of alcohols and phenols and
their regeneration by catalytic aluminum chloride hexahydrate.
V. V. Namboodiri and R.S. Varma: Tetrahedron Lett., 43,
1143 (2002).
Solid-state Synthesis of Heterocyclic Hydrazones Using Microwaves Under
Catalyst-free Conditions.
M. Ješelnik, R.S. Varma, S. Polanc, and M. Kocevar: Green
Chemistry, 4, 35 (2002).
Solvent-Free Preparation of Ionic Liquids Using a Household Microwave
Oven.
R.S. Varma and V. V. Namboodiri: Pure Applied Chem., 73,
1309 (2001).
Catalyst-free Reactions Under Solvent-free Conditions: Microwave-assisted
Synthesis of Heterocyclic Hydrazones Below the Melting Points of Neat
Reactants.
M. Ješelnik, R.S. Varma, S. Polanc, and M. Kocevar: Chem.
Commun., 1716 (2001).
Solvent-free Reduction of Aromatic Nitro Compounds with Alumina-supported
Hydrazine Under Microwave Irradiation
A. Vass, J. Dudás, J. Toth and R.S. Varma: Tetrahedron
Lett., 42, 5347 (2001).
Microwave Organic Synthesis.
R.S. Varma in "McGraw-Hill Yearbook of Science and Technology
2002",
pp 223-225, McGraw-Hill, New York, NY (2001).
Microwave Accelerated Solvent-Free Chemical Reactions.
R.S. Varma: AMPERE (Association for Microwave Power in
Europe for Research and Education), p 3 (2001).
Microwave-Accelerated Suzuki Cross-coupling Reaction in Polyethylene
Glycol (PEG).
V.V. Namboodiri and R.S. Varma: Green Chemistry, 3, 146
(2001).
Highly Diastereoselective Michael Reaction Under Solvent-free Conditions
using Microwaves: Conjugate Addition of Flavanone to its Chalcone Precursor
T. Patonay, R.S. Varma, A. Vass, A. Lévai and J. Dudás:
Tetrahedron Lett., 42, 1403 (2001).
An Expeditious Solvent-Free Route to Ionic Liquids Using Microwaves.
R.S. Varma and V.V. Namboodiri: Chem. Commun., 643 (2001).
Solvent-Free Accelerated Organic Syntheses Using Microwaves.
R.S. Varma: Pure Applied Chem., 73, 193 (2001).
Environmentally Benign Organic Transformations Using Microwave Irradiation
Under Solvent-Free Conditions.
R.S. Varma in "Green Chemistry: Challenging Perspectives,"
P.T. Anastas and P. Tundo (Eds.), pp 221-244, Oxford University
Press, Oxford (2000).
Solid State Oxidation of Thiols to Disulfides Using Ammonium Persulfate
.
R.S. Varma, H.M. Meshram and R. Dahiya: Synth. Commun.,
30, 1249 (2000).
Expeditious Solvent-Free Organic Syntheses Using Microwave Irradiation.
R.S. Varma in "ACS Symposium Series No. 767/ Green Chemical Syntheses
and Processes" P.T. Anastas, L. Heine and T. Williamson (Eds.), Chapter
23,
pp 292-312, American Chemical Society, Washington DC (2000).
Microwave-accelerated Three-component Condensation Reaction on Clay:
Solvent-free Synthesis of Imidazo[1,2-a] annulated Pyridines, Pyrazines
and Pyrimidines.
R.S. Varma and D. Kumar: Tetrahedron Lett., 40, 7665 (1999).
Contact Information:
| Primary Investigator: | Dr. Rajender Varma (513) 487-2701 varma.rajender@epa.gov |
| Fax: | (513) 569-7677 |
| Postal Address: | 26 West Martin Luther King Drive Mail Stop 443 Cincinnati, Ohio 45268 |