Isopentane Disproportionation in Lewis Acidic Chloroaluminate Ionic Liquid
Jiande Mai1,2, David E Ryan1,2, Wei Zhang1,2
1Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99354, United States.
Ionic liquids catalyze alkane disproportionation via carbenium ions. Two kinetic regimes were observed, with the initial carbenium ion concentration significantly impacting isopentane conversion.
Area of Science:
- Catalysis
- Ionic Liquids
- Organic Chemistry
Background:
- Lewis acidic chloroaluminate ionic liquids can catalyze hydrocarbon conversions.
- Carbenium ions are key intermediates in alkane disproportionation reactions.
Purpose of the Study:
- To investigate the catalytic activity of ionic liquids in alkane disproportionation.
- To elucidate the kinetic regimes and mechanisms governing this reaction.
Main Methods:
- Utilized Lewis acidic chloroaluminate ionic liquid in dichloromethane.
- Initiated reaction with tert-butyl chloride (TBC) as a carbenium ion precursor.
- Analyzed reaction kinetics and intermediates using 1H NMR and DFT calculations.
Main Results:
- Identified two kinetic regimes: transient (0-5 min) and steady-state (>5 min).
- Transient regime dominated isopentane conversion, controlled by initial carbenium ion concentration.
- Steady-state regime showed slower rates influenced by carbenium ion concentration, ionic liquid concentration, and temperature.
Conclusions:
- Deprotonation of carbenium ion-pairs reduces concentration and reaction rate.
- Kinetic modeling revealed rate constants for hydride transfer, deprotonation, and alkene protonation.
- The study highlights the potential of mild Lewis acid-catalyzed hydrocarbon conversions.
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