Application of the Baheʹs pseudolattice theory to water–1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) mixtures at 298.15 K: Part II. Acidity scales

Molten salts at room temperature and their mixtures with water or molecular solvents are excellent candidates for future replacement of most of organic solvents used in many industrial processes. To make this possible and to allow efficient application, it is necessary to determine physico-chemical parameters (such as the acidity scales) for these reaction media. This work follows a study of the autoprotolysis constants (Ks) of water–1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) mixtures at 298.15 K over the composition range of 0–77.43 vol.% bmimBF4 [I. Bou Malham, P. Letellier, M. Turmine, Talanta 72 (2007) 155–164]. In this second analysis, we determined the values of the dissociation constant (pKa) of various conjugate acid–base pairs for the same water–bmimBF4 mixtures, to establish acidity scales for each medium. These data can be used to produce proton buffer solutions and thus to control the acidity level of water–ionic liquid (IL) mixtures. We compare the values of pKa for acid–base pairs in water–bmimBF4 mixtures with published values for water–methanol mixtures.