Unveiling Electroorganic Reactions by Tracking Intermediates via Spectroelectrochemistry in a Thin-Layer Electroanalysis Microchip

Monitoring reaction intermediates provides crucial information about synthetic reaction mechanisms. In this sense, UV–Vis spectroelectrochemistry (SEC) can be a useful tool for investigating organic electrosynthesis reactions. While there have been recent applications in the field of electrocatalytic studies, cases in organic electrosynthesis are comparatively rare. Organic electrosynthesis, driven by electrochemical cues followed by chemical transformations, requires precise monitoring of events occurring in the solution phase near the electrode surface. However, conventional bulk cuvette cells lack the ability to exclusively observe these events, as the majority of signals from the bulk solution arising from the thick cell pathlengths, while minor signals from the diffusion layer are of utmost importance for investigation. Utilizing the thin-layer electroanalysis microchip (TEAM) as a UV–Vis SEC cell with a pathlength of a few tens of micrometers, we demonstrate comprehensive analyses of the electrochemical azidation of alkenes as a model reaction. Stable and sensitive in situ monitoring of the key intermediate, TEMPO–N3 charge transfer complex, was enabled by the uniform concentration profile in a thin-layer cell. Tracking the intermediate’s absorbance change revealed its potential-dependent behavior and provided insights into its reaction kinetics. Furthermore, rapid reagent screening for different synthetic conditions was achieved with sub-microliter volumes through in situ concentration profiling. This work demonstrates that UV–Vis SEC analysis using TEAM can provide intuitive and complementary mechanistic insights into electroorganic reactions, as well as synthetic implications for the rational design of organic electrosynthesis, effectively addressing challenges such as mass transfer interference and iR drops that are often encountered in conventional SEC cells.