Electrochemically Driven C-H Hydrogen Abstraction Processes with the Tetrachloro-Phthalimido-N-Oxyl (Cl₄PINO) Catalyst

The radical redox mediator tetrachloro-phthalimido-N-oxyl (Cl₄PINO) is generated at a glassy carbon electrode and investigated for the model oxidation of primary and secondary alcohols with particular attention to reaction rates and mechanism. The two-electron oxidation reactions of a range of primary, secondary, and cyclic alcohols are dissected into an initial step based on C-H hydrogen abstraction (rate constant k1, confirmed by kinetic isotope effect) and a fast radical-radical coupling of the resulting alcohol radical with Cl₄PINO to give a ketal that only slowly releases the aldehyde/ketone and redox mediator precursor back into solution (rate constant k2). In situ electrochemical EPR reveals Cl₄PINO sensitivity towards moisture. DFT methods are applied to confirm and predict C-H hydrogen abstraction reactivity.