The Prakash Lab

Our efforts in this area mainly emphasize the development of new reactions and reagents, which greatly benefit practicing synthetic organic chemists. Although our goal is not oriented towards target molecule synthesis, development of single step selective and stereoselective transformations is of immense value in general organic synthesis. We have developed many fluorination protocols based on pyridinium polyhydrogen fluorides (ionic liquids) as room temperature nucleophilic fluorinating agents. Many of the methods replace the use of highly toxic HF and elemental fluorine. Selective trifluoromethylations, difluoromethylations and difluoromethylenations have been achieved using the trifluoromethyltrimethylsilane (the Ruppert-Prakash Reagent). Related fluoroalkylations using sulfur-based reagents have shown great promise. Recent efforts involve fluoroalkylation and fluoroalkoxylations involving photoredox catalysis. Such methods have gained wide use in the area of small molecule-based drug discovery. Silicon reagents such as trialkylsilanes, trimethylsilyl nitrile and azide have been developed as useful synthons. A new ionic hydrogenation method using trialkylsilanes as reducing agent has resulted in general-purpose ether and sulfide synthesis method. We have adopted the method for the preparation of polymers and crown ethers. Increasingly, superacids serve as excellent high acidity medium for electrophilic reactions (so called superelectrophilic activation). Using CF₃SO₃H, CH₃SO₃H or BF₃-H₂O as a high acidity and non-oxidizing medium, a host of new reactions for deactivated aromatics such as iodination, acylation, nitration etc., are being developed. Use of solid strong acid catalysts such as Nafion-H^R (an ionomeric perfluoroalkane type sulfonic acid) are also being investigated.

Utilization of saturated hydrocarbons including methane as raw materials to synthesize value added compounds. Use of hydrocarbons and oxygenated hydrocarbons (particularly methanol) as fuels in direct oxidation fuel cells. Hydrocarbon isomerization, functionalization (nitration, carbonylation, hydroxylation, sulfuration, etc.,) and synthesis of polycyclic cage hydrocarbons. Polymerization of ethylene and α-olefins to polyolefins by aluminum subhalide chemistry. Polymerization of unusual monomers. Proton conducting polymer electrolytes for fuel cells and lithium ion batteries. Superacid facilitated upgrading of fossil fuels (such as coal, methane, etc.) to industrially useful feedstocks. Electrochemical reduction of anthropogenic carbon dioxide to formic acid, methanol and related derivatives. Development of CO₂ capture and carbon neutral energy cycles through the Methanol Economy^TM concept. Using methanol and formic acid as hydrogen storage media. Development of rechargeable aqueous batteries based on iron- nickel and organic redox flow materials.

These studies involve generation of reactive electrophilic intermediates such as carbocations, carbodications, halonium ions, diazonium ions, oxonium ions, acylium ions, thioacylium ions, nitrenium ions, silicenium ions and selenonium ions in low nucleophilicity highly acidic solvent systems and their characterization using low temperature broad-band nuclear magnetic resonance spectroscopy (¹H, ²H, ¹³C, ¹⁹F, ¹⁷O, ²⁹Si, ⁷⁷Se, ¹⁵N, ³⁵Cl, etc.,). Other techniques such as infrared and X-ray photoelectron spectroscopy are also employed to characterize their structures. Using the above methods, a wide variety of trivalent (classical) and bridged (non-classical) carbocations have been characterized along with some new aromatic cationic systems. Several empirical correlations to relate positive charge density and chemical shifts were developed. Other reactive intermediates studied include carbanions, including trifluoromethanide anion, and oxonium ylides. In conjunction with these studies a wide array of two-dimensional NMR techniques and special pulse sequences are routinely employed. Solid-state ¹³C NMR spectra of carbocation salts are also obtained using cross polarization magic angle spinning techniques (CPMAS). In this area ab initio and DFT calculations are routinely employed to delineate structure and energetics of complex carbocation structures. The minimized structures are also used in NMR chemical shift calculations.

Electrochemistry uses the controlled flow of electrons for generation of electricity, analytical measurements and drive chemical reactions. Our group has a longstanding history of working on electrochemistry such as developing the direct methanol fuel cell (DMFC), polymer membrane synthesis, organic flow batteries. Currently the group is interested in developing new catalysts for proton exchange and anion exchange membrane fuel cells, CO2 electroreduction, and electrochemical sensors. As well as probing new compounds that can serve as potential fuel sources in fuel cells.