Ion-association vis á vis hydrophobic effect in novel ionic liquids-tetraalkylphosphonium/polyisobutylenesuccinimide-tethered tetraalkylammonium diarylphosphates/thiophosphates: Synthesis and application

Abstract

A comprehensive study using conventional 1H, 31P NMR as well as advanced PFGSE-DOSY NMR on structurally unique ionic liquids (ILs) having, in one hand, both phosphorus based counter ions called tetraalkylphosphonium diarylphosphate (PP)/diarylthiophosphate (PTP), and on the other hand polyisobutylenesuccinimide-tethered tetraalkylammonium diarylphosphate (PIBSI-P)/diarylthiophosphate (PIBSI-TP) has been carried out in order to establish their structures and interactions between the counter ions in chloroform solution. It has been noticed that the ion association increases significantly by increasing the cationic alkyl chain length in PP and moderately in PTP owing to stronger hydrophobic interactions. However in polymeric ionic liquids (POILs), PIBSI-P and PIBSI-TP, it is the hydrophobic effect of the long chain PIB backbone which dominates the course, effect of cationic alkyl chain length was not much observed. The ILs were synthesized either from an anion exchange reaction between tetraalkylphosphonium bromides and diarylphosphate/thiophosphate (former) or from a reaction of same diarylphosphate/thiophosphate with tetraalkylammonium bromide derived from polyisobutylene succinic anhydride (PIBSA) (later). The synthetic procedure is very simple, efficient and high yielding. The developed ILs are found to be effective for application as lubricant additive.