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

Abstract

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‐κN]‐4,6‐di‐tert‐butylphenolato‐κO}diphenylboron, C39H41BN2O, 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.

Research Progress of Antioxidant Additives for Lubricating Oils

“…The OIT value of BSPD in epoxidized soybean oils is 1.20, 2.0, and 8.4 times higher than SPD1, diphenylamine, and 2,6-di-tert-butyl-4-methylphenol, respectively. As a result, the synthesized BSPD has good thermal stability and antioxidant properties [128], while the antioxidant properties of SSPD-BF1 and SSPD-BF2 additives are superior to diphenylamine and traditional ZDDP at high temperatures [127]. Furthermore, this additive type has good anti-friction ability because of the introduction of B and F elements in the molecule regardless of the aniline structure.…”

“…This phenomenon is attributed to the small steric hindrance of the imine group, allowing radicals to easily capture hydrogen. In addition, Wang et al [127,128] even introduced B and F elements into SPD and SSPD molecules to prepare BSPD, SSPD-BF1, and SSPD-BF2 compounds, as shown in Figure 16. TGA indicated that the weight loss phenomenon of BSPD occurs at relatively high temperatures, and the corresponding temperatures for BSPD at 5% and 95% weight loss are 328 and 414 • C, respectively.…”

The Impact of Trace Elements on Osteoarthritis

“…On the other hand, some boron-compounds, such as calcium fructoborate, boric acid or borax, show promising antioxidant properties. Supplementation of boric acid or borate can improve antioxidant defense mechanism, stimulating activities of superoxide dismutase, glucose-6-phosphate dehydrogenase, catalase, glutathione peroxidase and glutathione-S-transferase enzymes, detoxifying reactive oxygen species and reactive nitrogen, reducing oxidative stress, and lowering DNA damage and lipid peroxidation ( 36 ). Furthermore, it has been found that the addition of calcium fructoborate to human diets has beneficial effects on various anti-inflammatory processes.…”

Preparation and performance evaluation of an ester‐bridged antioxidant used as multifunctional additive in ester oil

“…The intramolecular synergisms of phenol and amine groups with or without the sulfur atom were reported and exhibited high-antioxidant effectiveness in lubricating oils. 14,[18][19][20][21][22][23] The International Lubricant Standardization and Approval Committee (ILSAC) introduced the GF-5 performance standards, which strictly limits the sulfur content in motor oils. Pursuing low-sulfur or even non-sulfur antioxidants was the development trend of lubricants, according to the environmental protection requirements.…”

“…A number of amine antioxidants have been investigated and found to improve the antioxidation capacity of ester oils 16,17 ; however, the toxicity of amine derivatives was not eco‐friendly. The intramolecular synergisms of phenol and amine groups with or without the sulfur atom were reported and exhibited high‐antioxidant effectiveness in lubricating oils 14,18–23 . The International Lubricant Standardization and Approval Committee (ILSAC) introduced the GF‐5 performance standards, which strictly limits the sulfur content in motor oils.…”