Voltammetry and chronoamperometry-based reactivity screening of water-insoluble microparticles is demonstrated for a mediated reaction. The solid-solid 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated electrolytic conversion of diphenylcarbinol to benzophenone is investigated by employing TEMPO and its derivatives (4-carboxy-TEMPO, 4-methoxy-TEMPO, 4-amino-TEMPO, 4-acetamido-TEMPO) in alkaline carbonate buffer at pH 11. Chronoamperometry experiments reveal (at least) two reaction stages with (i) a high onset current (ca. 30 s) with nucleation and growth of product and (ii) a first-order transport-controlled reaction (ca. 5 min) leading to bulk conversion. It is shown that the type of TEMPO derivative and the pH (but not the TEMPO concentration) affect the reaction rate. The 4-acetamido-TEMPO derivative is the most effective mediator.
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- Organic electrosynthesis
- Solid-state electrolytic conversion