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

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(n)MIm] 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 (Lambda(0)) and ion association constants (K-A) were calculated. The results show that the Lambda(0) and K-A values of ionic liquid are affected by the alkyl chain length of cation and the concentration of ASA. The values of Lambda(0) and K-A decrease as the alkyl chain length of cation and ASA concentration increase. The K-A was also used to calculate the standard Gibbs energy (Delta G(A)(0)) 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 Delta G(A)(0) and stronger interaction between [BMIM] Br and ASA.