Electrochemical quinuclidine-mediated C–H activation: Intermediates and mechanism

Abstract

• Hydrogen Peroxide is the terminal oxidant in the reaction. • Quinuclidine is oxidized by hydrogen peroxide to quinuclidine N -oxide. • 1,1,1,3,3,3-hexafluoropropan-2-ol is consumed during oxygen reduction and oxidation to 1,1,1,3,3,3-hexafluoroacetone. • 0.1 M 1,1,1,3,3,3-hexafluoropropan-2-ol is optimal for quinuclidine’s oxidation. The reaction mechanism of quinuclidine mediated C–H oxidation of unactivated C–H bonds has been elucidated. In-situ cathodically generated H 2 O 2 was shown to diffuse to the anode where it is oxidized and participates in the ketonization reaction. Further oxidation of H 2 O 2 to H 2 O, O 2 and H + leads to glassy carbon surface degradation. Oxidation of quinuclidine was shown be kinetic-diffusion control limited and shown to be irreversible at 0 and 1 M 1,1,1,3,3,3-hexafluoroisopropan-2-ol solutions, and quasi-reversible at 0.1 M. Competing side reactions of quinuclidine with hexafluroisopropanol and hydrogen peroxide were identified that lead to decreased reaction efficiency, which explains why quinuclidine needs to be used stoichiometrically.