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, etc.).

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 economy

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 perfluoroalkylations).

References

 

1.	Olah, G.A., Molnár A. Hydrocarbon Chemistry, 2nd revised ed. Wiley Interscience, New York (2003).
2.	Olah, 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).
3.	Olah, G.A. Prakash, G.K.S. (Eds.) Across Conventional Lines. Selected papers of G. A. Olah, World Scientific Publ. (2003).
4.	Olah, 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).
5.	Prinzbach, 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).
6.	Rasul, 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).
7.	Stable 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).
8.	Efficient 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).
9.	Gallium (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).
10.	Unified 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).
11.	Olah. G.A The Methanol Economy, Chem. Eng. News 81, P 5 (No. 38), (2003)
12.	Olah. G.A. After Oil and Gas: Methanol Economy, Catal. Letters. 93 1 (2004)