An electrochemical pipette with thin-layer design for rapid electrosynthesis and mechanistic study of the catalytic reactions
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Abstract
In the past few decades, electrochemical organic synthesis has emerged as a transformative approach to modern organic synthesis. Electrochemical methods enable unique reaction pathways for both direct (electrode-driven) and mediated (redox-catalyst-assisted) systems through controlled electron transfer, access to reactive intermediates, and transformations that are inaccessible to conventional methods. However, traditional electrochemical reaction setups depend on mass transport, and extended electrolysis times limit their application in organic synthesis. Therefore, developing an electrochemical design that is independent of mass transfer, and facilitating fast electrolysis is essential for advancing the field of electrochemical organic synthesis. In this study, we fabricated an electrochemical cell that confines the electrolysis volume to a thin layer of solution, comparable to the thickness of the diffusion layer. The fabricated thin layer electrode (TLE) is independent of mass transfer and allows electrolysis to be performed within minutes owing to its high surface (A)/ volume (v) ratio. The utility of the TLE electrode for parallel electrosynthesis applications was benchmarked using N-hydroxyphthalimide (NHPI) mediated electrochemical C-H functionalization. Rapid electrolysis and generation of microscale volumes make TLE suitable for application in drug metabolism. The application of TLE in drug metabolism has been demonstrated through the oxidative metabolism of acetaminophen under mild basic and acidic conditions. The formation of an N-acetyl-p-benzoquinone imine metabolite (NAPQI) during acetaminophen oxidation and its subsequent chemical reactions during electrolysis were successfully studied. Moreover, the integration of a microelectrode with TLE (combined TLE) enabled the real-time monitoring of redox-active intermediates formed during rapid electrosynthesis. Real-time studies of electrocatalytic cycles allow for a better understanding of electrocatalytic mechanisms and their resting states. The utility of this combined TLE for mechanistic studies of electrochemical synthesis was demonstrated using a Ni-catalyzed biaryl coupling reaction. This approach allowed the real-time monitoring of both closed- and open-shell nickel species generated during nickel-catalyzed biaryl coupling reactions under catalytic conditions. Studying both the closed- and open-shell nickel species generated during the catalysis cycle using spectroscopic methods is challenging. Therefore, this approach assists in understanding the unreported trends in Ni speciation, concentration profiles of key intermediates under different reaction conditions, and reaction progress.
Table of Contents
Introduction -- Materials and methods -- Evaluation of the thin layer electrode and its' broader applications -- Direct analysis of ni-catalyzed reductive biaryl coupling using TLE-µE
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Ph.D (Doctor of Philosophy)