Electrosynthesis of p ‐Hydroxybenzoic Acid From Phenol and CO 2

ABSTRACT P ‐hydroxybenzoic acid ( p ‐HBA), with wide applications in food preservatives, pesticides, pharmaceuticals, and liquid crystalline polyether, is currently synthesized via the Kolbe–Schmitt reaction using anhydrous phenolate (PhO − ) and carbon dioxide (CO 2 ). However, this reaction typically suffers from poor selectivity, and requires high temperature/pressure, strongly base, and metal/organic cations for selectivity control. Herein, we report a new method for the electrosynthesis of p ‐HBA from phenol (PhOH) and CO 2 by iodine mediation, achieving 61% yield and 90% selectivity without strong bases and metal cations under ambient temperature and pressure conditions. Mechanism studies indicated that PhOH was first selectively iodinated by iodine cations (I + ) generated at the anode to form p ‐iodophenol (HOPh‐I). Subsequently, HOPh‐I and CO 2 were respectively activated on Ag catalyst with abundant grain boundaries (GB‐Ag) through single‐electron reduction, and then underwent radical coupling processes to produce p ‐HBA. Notably, this electrochemical method also successfully converted various oxygen‐containing and nitrogen‐containing aromatic compounds, including the typical structural units of lignin and its derivatives, into valuable carboxylic acids. This innovative electrochemical approach overcomes the inherent limitations of the traditional Kolbe–Schmitt reaction, offering a promising strategy for the sustainable utilization of CO 2 and biomass resources.