Synthesis and Physical Properties of Choline Carboxylate Ionic Liquids

A series of choline carboxylate ionic liquids (ILs) have been synthesized by neutralization of choline hydroxide solution with acetic, propanoic, butanoic, pivalic, and hexanoic acids. The salts so obtained were characterized by NMR spectroscopy, thermal methods, and elemental analysis. Key physical properties (density, viscosity, and refractive index) were measured for the propanoate, butanoate, and hexanoate salts at temperatures from (293.15 to 353.15) K. The densities were used to estimate the molecular volumes, standard entropies, crystal lattice energies, and thermal expansion coefficients. All five choline carboxylates were found to have cytotoxicities (IC50 values) above 10 mM toward the human breast cancer cell line, MCF-7, indicating they are much less toxic than common imidazolium-based ILs.