Highly Selective Synthesis and Superior Antioxidant Performance of Cardanol-Derived Unsymmetrical Hindered-Phenol Additives

Using bio-based cardanol as raw material, the influence of alkylating agents and catalysts on the Friedel–Crafts alkylation was investigated. Screening of alkylating agents and catalysts enabled the efficient synthesis of the unsymmetrical-hindered phenol antioxidant 2-tert-butyl-5-pentadecylphenol (SAC, i.e., Saturated Alkylated Cardanol), which was evaluated as a novel lubricant antioxidant. The structure of SAC was characterized by mass spectrometry, infra-red spectroscopy, and nuclear magnetic resonance, and its thermal stability and antioxidant performance were studied in depth. The results show that SAC has superior antioxidant performance compared to market-available 2,6-di-tert-butylphenol and 3,5-di-tert-butyl-4-hydroxyphenylpropenoic acid octyl ester hindered phenol antioxidants. Through molecular simulation technology, the intrinsic reasons for SAC's superior antioxidant performance were further explained. The study indicates that the green SAC antioxidant has great potential to replace traditional mineral-based additives, providing a new choice and practice for efficient and environmentally friendly lubricating oil additives. Graphical Screening alkylating agents and catalysts for Friedel-Crafts alkylation enables highly selective synthesis of unsymmetrical hindered phenol SAC from bio-based cardanol. SAC outperforms commercial hindered phenol antioxidants (26P, T501, T512) in antioxidation and thermal stability, with its mechanism clarified by molecular simulation, offering a green lubricant additive.