Tris-imidazolium and benzimidazolium ionic liquids: a new class of biodegradable surfactants

Based on imidazolium and benzimidazolium, two series of novel tris-cationic ionic liquid surfactants containing ester groups were synthesized simply from readily available starting materials in high yields. Biodegradability and surfactants properties of the tris-imidazolium and tris-benzimidazolium ionic liquids were investigated. Some compounds showed assembly behaviour in the pure form (i.e. absence of solvent) and in the presence of polar or nonpolar solvents. These surfactants are effectively reducing the surface tension of water in the range of 28-31 mN m(-1). Through using the 'Closed-Bottle Test' OECD 301D, the incorporation of alkyl or phenyl side chains with ester groups in the same molecule significantly improved the biodegradation compared to sodium n-dodecyl sulphate (SDS) as a reference. The aliphatic alkyl side chain, i.e., butyl, hexyl, octyl, decyl and dodecyl, in both imidazolium and benzimidazolium ionic liquids have marked increasing biodegradation and phase behaviour results compared to aromatic side-chains.