Room temperature ionic liquids and their mixtures: Potential pharmaceutical solvents

Room temperature ionic liquids (RTILs) are organic salts which are liquids at ambient temperature. Composed of relatively large asymmetric organic cations and inorganic or organic anions, they have generated interest as ‘green’ solvents. Here we report on the solvency of alkyl imidazolium salts (PF6−Br−Cl−) for poorly water-soluble model drugs, albendazole and danazol, indicating their potential application as pharmaceutical solvents/cosolvents. The solubility of albendazole, for example, is increased by more than 10,000 times by 1-butyl-3-methylimidazolium hexaflourophosphate ([bmim]PF6−). Ionic liquids can be water-miscible or water-immiscible. The aqueous miscibility of a poorly water-miscible RTIL such as of [bmim]PF6− can be improved by the inclusion of a second more miscible RTIL (e.g. 1-hexyl-3-methylimidazolium bromide ([hmim]Br−)). The extent of improvement in water miscibility was found to correlate with the hydrophilicity of the second RTIL. This ability to modulate RTILs’ aqueous miscibility increases their usefulness as pharmaceutical solvents.