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.