Synthesis and tribological properties of a sulfur nitrogen-containing heterocyclic borate ester

2-(2-benzothiazolylthio) ethanol (BTE) was synthesized using 2-mercapto benzothiazole as raw material and then a sulfur nitrogen-containing heterocyclic borate ester (SNHB) lubricant additive was synthesized using BTE as raw material. The structures of BTE and SNHB were characterized by FTIR and elemental analysis. The solubility of BTE and SNHB in rapeseed oil were tested and the thermal stabilities of them were studied by thermal analysis. The hydrolytic stabilities of SNHB were also determined. The friction reducing, anti-wear and load-carrying capacities of BTE and SNHB were investigated by four-ball test. The surface morphology and the elemental composition of the tribofilms were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The results revealed that the synthesized products were the target compounds of BTE and SNHB, and they completely dissolved in the rapeseed oil and thus had good oil soluble properties. The decomposition temperature of SNHB and BTE ranged from 270.50℃ to 396.01℃, and from 253.04℃ to 326.83℃, respectively. Both SNHB and BTE had good thermal stability, and SNHB was better. SNHB was not hydrolyzed over 7 days, while triisopropyl borate (a commercially available borate product) was hydrolyzed completely within 10 min, so SNHB had better hydrolytic stability under the same experimental conditions. SNHB exhibited superior tribological performances to BTE under different test loads and additive concentrations. © 2016, Chemical Industry Press. All right reserved.