Photocatalytic Partial Oxidation of 4-Vinylguaiacol to Vanillin over TiO₂: A Biomimetic Approach Inspired by Spirit Aging

Inspired by natural oxidative aging processes observed in traditionally matured distilled spirits, we developed a biomimetic photocatalytic approach for the partial oxidation of 4-vinylguaiacol (4-VG)—a ferulic acid-derived aromatic compound—to vanillin using titanium dioxide (TiO₂) under ultraviolet (UV) light. The choice of 4-VG as the reaction substrate is rooted in its documented transformation during long-term spirit aging, which we sought to replicate and accelerate under controlled catalytic conditions. By optimizing the pH of aqueous ethanol media, vanillin selectivity reached up to S = 36% under mild alkaline conditions. Mechanistic studies indicated that both β-hydrogen abstraction from ethanol and pH-enhanced radical propagation contribute to the efficient oxidation pathway. The photocatalytic performance was further evaluated in fermentation-derived multicomponent systems, where inhibitory effects from background silicate anions were identified, whereas low-concentration organic constituents had minimal impact. Ion exchange pretreatment successfully restored photocatalytic activity, underscoring the method’s robustness. Product characterization, including sensory validation, confirmed the formation of vanillin, thereby supporting the proposed reaction pathway. This biomimetic oxidation approach offers a sustainable and scalable route for the transformation of bio-derived aromatic compounds under mild, aqueous conditions using non-biological catalysis. It effectively accelerates a naturally slow transformation into a rapid photocatalytic reaction completed within hours.