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).
Selected publications 12.