Tris(dialkylamino)cyclopropenium dialkylphosphate ionic liquids as lubricants.

Six new tris(dialkylamino)cyclopropenium dialkylphosphate ionic liquids (ILs), [C 3 (NR 2 ) 3 ]BEHP (NR 2 = NEt 2 , NBuMe, NPr 2 , NBu 2 , NHex 2 , NDec 2 ; BEHP = bis(2-ethylhexyl)phosphate), were prepared and characterised as potential lubricants. Thermophysical and thermochemical properties of these ILs were investigated, namely: viscosity, density, conductivity, miscibility, thermal stability and phase transitions. Miscibility studies indicated that [C 3 (NEt 2 ) 3 ]BEHP would not be suitable due to its water solubility and hexane immiscibility. [C 3 (NDec 2 ) 3 ]BEHP was not investigated as a lubricant due to its low purity (the chloride salt of this cation is also hexane miscible). Of the other four, [C 3 (NHex 2 ) 3 ]BEHP was found to exhibit significantly less wear for pin-on-disk test conditions than the standard phosphonium [P 6,6,6,14 ]BEHP IL. The amount of wear was found to generally decrease with increasing molecular weight.