Synthetic and Mechanistic Organic Chemistry
Professor Olah's research spans a wide range of synthetic and mechanistic organic
chemistry. But most notably, his work on the chemistry of carbocations earned
him the 1994
Nobel Prize in Chemistry.
Carbocations and Onium Ions
Olah and his group have developed a wide variety of superacids which possess
such low nucleophilicity toward carbocations that they can be prepared and directly
observed as long lived species in these media. Higher valency Lewis acid fluorides
such as SbF5, TaF5, combined with Brønsted acids
such as HF or FSO3H results in superacids that are billions of times
stronger than sulfuric acid. When they are used as solvents in ion-generating
reactions, the lifetimes of carbocations and onium ions (halonium, oxonium,
etc.) are sufficiently long to allow them to be examined by a variety of chemical
and spectroscopic techniques (13C NMR 1H NMR, IR, ESCA,
Ionic Organic Reactions and Their Intermediates
As a continuation of earlier work on carbocations and their reactions, newer
studies emphasize the investigation and reactions of onium ions and ylides.
New types of oxonium, halonium and other onium ions were prepared and studied.
The role of electrophilic (protic) solvation of the non-bonded electron pairs
in oxonium ions (superelectrophilic activation) is widely explored, allowing
new applications in alkylation, acylation and related reactions. The structures
of the intriguing dicationic intermediates are also explored using ab initio
and DFT calculational methods.
Hydrocarbon Chemistry - Methane and Carbon Dioxide Conversion. Methanol
Acid catalyzed conversion of hydrocarbons, such as cracking, isomerization,
alkylation, oligo-and polycondensation, etc. are of fundamental significance.
Their fundamental chemistry is systematically studied using methods developed
in connection with studies of carbocations and their reactions. Novel environmentally
benign catalyst systems are developed to overcome difficulties connected with
acids such as hydrofluoric or sulfuric acid. New chemical additives are explored
to improve diesel fuels and make them cleaner burning and less polluting. The
use of methane and its oxygenates is studied in superacidic direct oxidation
fuel cell systems. The direct electrophilic conversion of methane to higher
hydrocarbons and derived products offers a viable alternative to Fischer-Tropsch
chemistry. Until recently, the utilization of methane as a chemical building
block was limited to free radical reactions (combustion, nitration, chlorination,
etc.) and various stoichiometric organometallic insertion reactions. Studies
are carried out on the superacid- catalyzed oxidative condensation of methane
to higher hydrocarbons, as well as the selective, electrophilic catalytic conversion
of methane to its monosubstituted derivatives including methyl halides and methyl
alcohol. Further condensation to ethylene, propylene and derived hydrocarbons
over bifunctional acidic-basic catalysts gives easy access to the whole range
of hydrocarbons essential to our everyday life. Mechanistic aspects of the above
chemistry of methane, particularly the importance of pentacoordinate CH5+-type
carbocation intermediates, are now being evaluated. The reductive recycling
of excess atmospheric carbon dioxide (one of the major greenhouse gases causing
global warming) to methanol and through it to useful fuels and hydrocarbons
is extensively studied. This represents a new approach called the methanol economy
for energy storage, efficient fuels and synthetic hydrocarbons beyond the exhaustion
of out non-renewable fossil fuel sources. Environmentally benign alkylation
methods have also been developed. New direct oxidation fuel cell technology
using methanol and related fuels are also being explored.
Synthetic Reagents and Methods
A continued research program centers on developing new, more selective and
more convenient synthetic reagents and methods. Representative reagents already
developed include: nitronium tetrafluoroborate (for nitration), pyridinium polyhydrogen
fluoride and cyanuric fluoride (for fluorinations), dialkylhalonium salts, alkyl
fluoride-Lewis acid halide complexes (for alkylation), formyl fluoride and formic
anhydride (for formylation), UF6 (for oxidation), carbocation salts
(for Friedel-Crafts reactions and initiation of polymerization), iodotrimethylsilane
(for various organic transformations) and perfluoroalkyltrimethylsilanes (for
G.A., Molnár A. Hydrocarbon Chemistry, 2nd revised ed.
Wiley Interscience, New York (2003).
G. A. Oil and Hydrocarbons in the 21st Century, a chapter in
Chemical Research-200 and Beyond: Challenge and Visions, Barkan, P. (Ed.),
Oxford University Press, New York (1997).
G.A. Prakash, G.K.S. (Eds.) Across Conventional Lines. Selected papers of
G. A. Olah, World Scientific Publ. (2003).
G. A., Prakash, G. K. S., Mathew, T., Marinez, E. R. Superacid Catalyzed
Selective Formylation-Rearrangement of Isoalkanes with Carbon Monoxide to
Branched Ketones, Angew.Chem. Int. Ed. Engl. 39, 2547 (2000).
H., Reinbold, J., Bertau, M., Voss, T., Martin, H-D., Mayer, B., Heinze,
J., Neschchadin, D., Gescheidt, G., Prakash, G. K. S., and Olah, G. A. s-Bishomoconjugation
(s-Bishomoaromaticity) in 4C/3(2) e Cations- "Scope and Limitations",
Angew. Chem. Inst. Ed., 40, 911 (2001).
G. and Olah, G. A. Calculational Study of the Protonation of BXH2
and BX2H (X = F and Cl). Structures of BXH3+
and BX2Hv+ and Their Dihydrogen Complexes BXH5+
and BX2H4+, Inorg. Chem., 40, 2453 (2001).
Dialkyl Ether/Poly(Hydrogen Fluoride) Complexes: Dimethyl Ether/Poly(Hydrogen
Fluoride), A New, Convenient, and Effective Fluorinating Agent, I. Bucsi,
B. Török, A. Iza Marco, G. Rasul, G. K. S. Prakash, G. A. Olah,
J. Am. Chem. Soc., 124, 7728-7736, (2002).
Chemoselective Carboxylation of Aromatics to Arylcarboxylic Acids with Superelectrophilically
Activated Carbon Dioxide-Al2C6/Al System, G. A. Olah, B. Török,
J.P. Joschek, I. Bucsi, P.M. Esteves, G. Rasul and G.K.S. Prakash, J. Am.
Chem. Soc., 124, 11379-11391, (2002).
(III) Trifluoromethanesulfonate: A Water Tolerant, Reusable Lewis Acid Catalyst
for Friedel-Crafts Reactions, by G. K. S. Prakash, P. Yan, B. Török,
I. Bucsi, M. Tanaka and G. A. Olah, Catalysis Letters, 85, 1 (2003).
Mechanistic Concept of Electrophilic Aromatic Nitration: Convergence of
Computational Results and Experimental Data, P. M. Esteves, J. E. de M.
Carneiro, S. P. Cardoso, A. G. H. Barbosa, K. K. Laali, G. Rasul, G. K.
S. Prakash and G. A. Olah, J. Am. Chem. Soc., 125, 4836-49, (2003).
G.A The Methanol Economy, Chem. Eng. News 81, P 5 (No. 38), (2003)
G.A. After Oil and Gas: Methanol Economy, Catal. Letters. 93 1 (2004)