Novel arylindane diols as sustainable primary antioxidants from lignin†

Synthetic phenolic antioxidant additives are commonly used to prevent oxidative degradation in various materials, but they present significant challenges due to their non-renewable origins and potential health risks. This study explores the synthesis of novel arylindane diols—specifically diisoeugenol (DiE) and diisoallylsyringol (DiAS)—and evaluates their potential as safer and more sustainable alternatives. Using zeolite catalysis, a highly selective pathway for synthesizing DiE through the dimerization of the lignin-derived monomer isoeugenol (IE) was demonstrated. The synthesis of DiAS and diisoallylphenol (DiAP) enabled further exploration of how structural differences, such as o-methoxy groups, affect the physicochemical and toxicological properties of these arylindanes. The antioxidant activity of the compounds was tested using ABTS and DPPH assays, revealing strong radical-scavenging capabilities. Furthermore, oxidation onset temperature (OOT) measurements in polypropylene (PP) formulations containing these antioxidants showed improved thermal stability, matching or surpassing that of commercial antioxidants. Toxicological evaluations, including cytotoxicity tests on human gingival fibroblasts and an estrogenic activity (EA) screening using the CALUX assay, indicated low levels of EA and cytotoxicity. These results highlight the potential of DiE and DiAS as effective, renewable, and safe lignin-derived antioxidants for industrial applications.