Optimizing Vanillin Production From Guaiacol-Type Precursors: An Integrated Experimental and Computational Approach

Aromatic aldehydes hold significant value in food additives and the valorization of biorefineries. This study investigated the oxidative conversion of five guaiacol-type compounds-eugenol, isoeugenol, ferulic acid, 4-ethyl-2-methoxyphenol, and 2-methoxy-4-propylphenol-to vanillin in sodium hydroxide and nitrobenzene solutions. We thoroughly examined the effects of temperature, oxidant, and C4 substituents on vanillin yield. Our results demonstrate that at 180°C for 1 h, eugenol and isoeugenol, both possessing alkenyl functional groups, exhibited exceptionally high vanillin yields of 90.8% and 91.7%, respectively. In contrast, 4-ethyl-2-methoxyphenol and 2-methoxy-4-propylphenol, featuring saturated side chains, yielded significantly lower amounts of vanillin, at 36.8% and 24.7%, respectively. Further density functional theory calculations confirmed that the alkenyl side chain and strong structural symmetry of the C4 substituent in guaiacol-type compounds lead to lower reaction energy barriers, thereby facilitating the reaction.