Solubility of pharmaceutical compounds in ionic liquids

The solubility of N-acetyl-L-cysteine, coumarin and 4-hydroxycoumarin in alternative solvents was studied in this work. The solid-liquid equilibrium (SLE) measurements have been performed using a dynamic (synthetic) method. Melting points and enthalpies of fusion of the pharmaceutical compounds were acquired using a differential scanning calorimetry (DSC). The solubility of N-acetyl-L-cysteine and 4-hydroxycoumarin in trifluoromethanesulfonate ionic liquids was found to be significantly higher than in the studied bis(trifluoromethylsulfonyl)amide ionic liquids while coumarin exhibited the opposite behaviour. The solid-liquid phase equilibria were described using the six different correlation equations which revealed a good description with an acceptable standard deviation temperature range. Moreover, the solubility data were used to calculate the 1-octanol/water partition coefficients of the studied drugs. Coumarin has a high partition coefficient, which is considered to be favourable for a rapid absorption of compounds once they are in an aqueous solution. N-acetyl-L-cysteine showed opposite results for the system with 1-octanol/water. (C) 2013 Elsevier B.V. All rights reserved.