A highly efficient antioxidant based on boron and a Schiff base bridged phenolic diphenylamine: synthesis, crystal structure and thermal and antioxidant properties

摘要

Antioxidants can effectively protect vegetable‐oil‐based lubricants against oxidative degradation and prolong their service life. A novel compound, ( E )‐4‐({3,5‐di‐ tert ‐butyl‐2‐[(diphenylboranyl)oxy]benzylidene}amino)‐ N ‐phenylaniline (BSPD) or {2‐[(4‐anilinophenyl)iminomethyl‐κ N ]‐4,6‐di‐ tert ‐butylphenolato‐κ O }diphenylboron, C 39 H 41 BN 2 O, was synthesized by a one‐pot reaction of the Schiff base bridged phenolic diphenylamine 2,4‐di‐ tert ‐butyl‐6‐{ N ‐[4‐(phenylamino)phenyl]carboximidoyl}phenol (SPD) with phenylboronic acid. The corresponding single‐crystal X‐ray study revealed that the B atom in BSPD has a typical tetrahedral geometry, and the N , O ‐chelated six‐membered ring adopts a chair conformation. According to thermogravimetric analysis, the 5% weight‐loss temperature of BSPD increases to 328?°C and the 95% weight‐loss temperature is up to 414?°C. More importantly, the antioxidant capability of BSPD in vegetable oil is much better than that of commercial antioxidants [diphenylamine (DPA) and 2,6‐di‐ tert ‐butyl‐4‐methylphenol (BHT)] and unmodified SPD.