Sustainable Iron Catalysis for Chemodivergent Oxidation of Lignin‐Based Vanillyl Alcohol: Selective Access to Vanillin and Vanillic Acid

Abstract

Abstract

Sustainable development has driven intensive research on the oxidation of lignin‐derived phenolics for fine‐chemical production. Selective catalysis, particularly chemodivergent catalysis, plays a crucial role in synthetic chemistry. In this context, chemoselective oxidation of lignin‐based vanillyl alcohol to vanillin or vanillic acid, key aroma compounds with broad industrial relevance, has garnered particular interest. Employing iron as a base‐metal catalyst is particularly attractive because it is plentiful, inexpensive, and environmentally benign. A tridentate NNN‐ligand was used to synthesize the corresponding FeCl 2 ( 1 ) and FeBr 2 ( 2 ) complexes. Complex 2 displayed high catalytic efficiency for the selective peroxidative oxidation of vanillyl alcohol to the corresponding aldehyde, vanillin. The catalytic activity of complex 1 is slightly lower. Complex 2 also demonstrated remarkably high efficiency (TOF: 100 000 h −1 ) for the selective peroxidative oxidation of vanillyl alcohol to the corresponding carboxylic acid, vanillic acid, in deep eutectic solvent. This example highlights the chemodivergent oxidation of a biomass‐model alcohol into aldehyde and carboxylic acid enabled by green reaction media. Evidence suggests that the reaction follows a radical‐mediated route. Sustainable merits were examined using CHEM21 green metrics toolkit. Low E ‐factor (4.39) and excellent Eco‐scale score (89) indicate sustainable oxidation of vanillyl alcohol with minimized waste.