Conductometric Analysis of some Ionic Liquids, 1-Alkyl-3-methylimidazolium Bromide with Aspirin in Acetonitrile Solutions

Abstract

In recent years, ionic liquids have been used in pharmaceutical processes. Therefore, having a deep insight into the ion association behavior of ionic liquids in the presence of a drug is of particular importance. So, in this work, the molar conductivities of the ionic liquids, 1-alkyl-3-methylimidazolium bromide, [C_nMIm]Br (n = 4, 6 and 8) in various concentrations of aspirin (ASA) in acetonitrile (MeCN) solutions are determined in very diluted region of ILs, (molality less than 0.01 mol kg^-1) and at 298.15 K. The obtained conductivity data were analyzed by low concentration Chemical Model (lcCM) of conductance equation. Using this model the limiting molar conductivities (L₀) and ion association constants (<em>K_A</em>) were calculated. The results show that the L₀ and <em>K_A</em> values of ionic liquid are affected by the alkyl chain length of cation and the concentration of ASA. The values of L₀ and <em>K_A</em> decrease as the alkyl chain length of cation and ASA concentration increase. The <em>K_A</em> was also used to calculate the standard Gibbs energy ( ) of ion-pairing association. In general, 1-butyl-3-methylimidazolium bromide, [BMIM]Br, has the low values of ion-pair formation and the high negative values of and stronger interaction between [BMIM]Br and ASA.