p-Nitrophenolate: A Probe for Determining Acid Strength in Ionic Liquids

In order to obtain an acidity scale in room-temperature ionic liquid solutions, the protonation equilibrium of sodium p-nitrophenolate in [bm(2)im][NTf(2)] and in [bmpyrr][NTf(2)], at 298 K, has been studied by means of spectrophotometric titration. Carboxylic acids differing in both structure and in water solution strength have been used. Data collected indicate that in the analyzed ionic liquid solutions carboxylic acids are less dissociated than in water solution. Furthermore, by virtue of a mutual interaction, the studied equilibrium seems to be affected by both the nature of the ionic liquids and the carboxylic acids.