Phytomanagement strategy leads to plant-derived catalysts for the sustainable synthesis of oxidized Hantzsch esters

Abstract

This study proposes a phytomanagement strategy to produce plant-derived eco-catalysts from Lolium perenne (ryegrass) and Trifolium incarnatum (clover), cultivated in contaminated or nutrient-rich soils from two French regions (Pompey and Bordeaux, respectively) and two Belgium sites (Duferco and Vieille Montagne, respectively), for the sustainable oxidation of Hantzsch esters and other substrates. Accumulating plants, cultivated in nutrient-rich or contaminated soils, provide catalysts enriched with transition metals like copper and zinc, supporting green chemistry principles by minimizing hazardous waste and fostering resource circularity. These catalysts were evaluated for the oxidation of Hantzsch esters to pyridines, pyridine-4(1H)-thione to pyridine-4-thiol, cyclohex-2-enone to substituted phenol, and dihydroquinoxaline to hydroxyquinoxaline. Results demonstrated substrate-dependent performance influenced by electronic effects, metal composition, and reaction parameters, with conversions reaching up to 95% for BIO-P2 and 89% for BIO-V catalysts, surpassing traditional oxidants such as KMnO₄. Solvent and catalyst loading optimizations further enhanced reaction efficiency, with acetonitrile identified as an appropriate solvent. This dual-purpose strategy combines environmental remediation with the development of efficient, plant-derived catalysts, offering a scalable, eco-friendly alternative for industrial and pharmaceutical oxidative processes while aligning with Sustainable Development Goals.