Thiourea-Mediated Cu Surface Boosting Highly Efficient Synthesis of Phenylhydroxylamine under High Current Density

Phenylhydroxylamine (PHA) is a key intermediate in pharmaceutical and organic synthesis, yet its highly selective synthesis has remained a persistent challenge. This difficulty primarily stems from the inherent instability of PHA itself and the tendency of nitrobenzene reduction to produce multiple products, often leading to over-reduction to the thermodynamically more stable aniline. Herein, we present a green electrocatalytic strategy that achieves highly selective reduction of nitrobenzene to PHA through the synergistic interaction between thiourea and copper, which demonstrates exceptional performance with a Faradaic efficiency of 95% and a yield of 90% under high current density. Mechanistic studies demonstrate that thiourea forms a dynamic "proton-electron buffer layer" on copper foam surfaces, which not only modulates proton-electron coupling kinetics to enhance PHA synthesis but also weakens PHA adsorption to promote its desorption. This method has been successfully extended to the synthesis of other hydroxylamines and accomplishes gram-scale production in the laboratory, which provides a sustainable platform for the electrochemical synthesis of hydroxylamines and offers new insights into modern green synthetic chemistry.