Hydrophobic and polar ionic liquids

By designing both the cation and anion to give rise to hydrophobicity and polarity, we have created a new class of ionic liquids that are both hydrophobic and polar. These comprise one component of ionic liquid-water biphasic systems having strong hydrogen bonding characteristics in the presence of water. A series of alkylphosphonium phosphonate-type ILs had differing affinities with water, manifested in their phase behaviour with water according to the hydrophobicity of the cations. In particular, ethylphosphonate salts coupled with tetra-n-hexylphosphonium and tri-n-hexyl-n-octylphosphonium cations had lower critical solution temperature behaviour after mixing with water. Moreover, tetra-n-octylphosphonium ethylphosphonate and n-butylphosphonate exhibited stable phase separation and higher hydrogen bonding characteristics even after mixing with water.