Recyclable Multifunctional Ionic Liquids for Sustainable Electroorganic Oxidations

The study of electrochemical oxidations has wide-ranging implications, from the development of new electrocatalysts for fuel cells for energy conversion, to the synthesis of fine chemicals. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) has been used for decades as a sustainable, metal-free mediator for chemical oxidations and is now being used for electrochemical oxidations. We describe here a novel approach to TEMPO-mediated electrooxidations, in which the chemical input and waste generated during electrooxidations of alcohols are minimized by using a multifunctional room temperature ionic liquid (RTIL) to facilitate flow electrosynthesis. Our three-pronged approach involves the following: (1) the use of a recyclable alkylimidazolium-based RTIL to replace the electrolytes and volatile organic solvents typically used in TEMPO-mediated alcohol electrooxidations; (2) pairing alcohol oxidation at the positive electrode with electroreduction of the cationic component of the RTIL at the negative electrode to generate the base required for the electrosynthesis; (3) incorporation of the catalytic TEMPO moiety in our RTIL-based system. We demonstrate the possibilities offered by our strategy using a range of alcohols, illustrating the scope of reactions that can be driven using our strategy and demonstrating the opportunities offered by task-specific, multifunctional RTILs for electroorganic synthesis.