The electrocatalytic epoxidation of alkenes at heterogeneous catalysts using water as the sole oxygen source is a promising safe route toward the sustainable synthesis of epoxides, which are essential building blocks in organic chemistry. However, the physicochemical parameters governing the oxygen-atom transfer to the alkene and the impact of the electrolyte structure on the epoxidation reaction are yet to be understood. Here, we study the electrocatalytic epoxidation of cyclooctene at the surface of gold in hybrid organic/aqueous mixtures using acetonitrile (ACN) solvent. Gold was selected, as in ACN/water electrolytes gold oxide is formed by reactivity with water at potentials less anodic than the oxygen evolution reaction (OER). This unique property allows us to demonstrate that a sacrificial mechanism is responsible for cyclooctene epoxidation at metallic gold surfaces, proceeding through cyclooctene activation, while epoxidation at gold oxide shares similar reaction intermediates with the OER and proceeds via the activation of water. More importantly, we show that the hydrophilicity of the electrode/electrolyte interface can be tuned by changing the nature of the supporting salt cation, hence affecting the reaction selectivity. At low overpotential, hydrophilic interfaces formed using strong Lewis acid cations are found to favor gold passivation. Instead, hydrophobic interfaces created by the use of large organic cations favor the oxidation of cyclooctene and the formation of epoxide. Our study directly demonstrates how tuning the hydrophilicity of electrochemical interfaces can improve both the yield and selectivity of anodic reactions at the surface of heterogeneous catalysts.

O 2 activation under mild conditions remains a weighty challenge for chemists. Herein we report a study of electrochemical O 2 reductive activation catalyzed by Fe III (F 20 TPP)Cl, by means of cyclic voltammetry and UV−vis spectroelectrochemistry in acidic solutions of N,N-dimethylformamide. Two parallel catalytic pathways have been evidenced occurring at different overpotentials. At high overpotential a classical electron−proton (EPT) pathway where protonation of Fe peroxo ultimately leads to the formation of high-valent Fe oxo species dominates. At low overpotential a proton−electron (PET) pathway involving a hydrosuperoxo species has been identified.solution, and evolution of Fe III OH 2 + and Fe III OO − species of Fe(F 20 TPP) (PDF) AUTHOR INFORMATION

Herein we report the first example of using scanning electrochemical microscopy (SECM) to quantitatively analyze O2 reductive activation in organic media catalyzed by three different Fe porphyrins. For each porphyrin, SECM can provide in one single experiment the redox potential of various intermediates, the association constant of FeII with O2, and the pKa of the FeIII(OOH−)/ FeIII(OO2−) couple. The results obtained can contribute to a further understanding of the parameters controlling the catalytic efficiency of the Fe porphyrin towards O2 activation and reduction.