Synergy and isosterism design of a phosphorus-free lubricating additive

Abstract

Thirty-one hydrazides were selected as isosteres and other analogs when five phosphates were used as templates by an isosteric exchange from phosphate group (PO4) to hydrazide group (CONHN). Their tribological properties of the lubricant modified with 1% hydrazide or phosphate additives were tested under 98 N load in three base oils, respectively. About 40% of the isosteres showed an acceptable deviation of ±5% relative to the template. The phosphate template molecules and hydrazide isosteres have better tribological properties in triisodecyl trimellitate than trimethylolpropane trioleate or di(2-ethylhexyl) adipate. Especially, most of the other hydrazide analogs have better antiwear property because of the same CONHN group as the isostere. CoMFA and CoMSIA models were used to discuss the dependency of molecular structure. The models show that the higher the structural similarity between the base oil and the additive, the more synergy the molecular force field in a lubricant, which may ameliorate the antiwear or friction-reduction properties. Surface analysis of the worn disc specimen also shows similarity between a template and an isostere by Scanning Electron Microscopy, EDS, and Raman spectra.