Electrochemically Controlled One-Electron Oxidation Coupled to Consecutive Hydrogen Atom Transfer of Caffeine

Caffeine (CAF) undergoes a one-electron oxidation in acetonitrile to form a cation radical, with variable scan rate CV experiments indicating that the lifetime of the cation radical improves as the trace water content of the solvent is decreased. Electrochemical oxidation (and chemical oxidation with NOSbF₆) of CAF in CH₃CN leads to the generation of the protonated CAF cation as the long-term product in high yield, whose structure is confirmed by single-crystal X-ray crystallography and NMR spectroscopy. The protonated cation is able to be electrochemically reduced back to CAF under electrolysis conditions. The formation of the protonated cation involves the initial one-electron oxidation of CAF to form the cation radical, which undergoes a hydrogen atom abstraction reaction. Digital simulations of the CV data show that the rate and equilibrium constants for the hydrogen atom abstraction step are k_f=1.0×10²Lmol^-1s^-1 and K_eq=1.0×10².