Acidity in methanol-water

The different factors influencing acidity of solutes in methanol-water (aci dity of the solute, basicity and dielectric constant of the solvent, and sp ecific solute-solvent interactions) are discussed. General thermodynamic mo dels and preferential solvation models are used to establish linear relatio nships between the acidity pK values of a family of compounds in any methan ol-water mixture and the pK values of the compounds in water. The parameter s (slope and intercept) of the relationships are related with solvent compo sition for the most common families of compounds (phenols, carboxylic acids , amines and pyridine derivatives). These equations allow accurate calculat ion of the pK values of any member of these families at any methanol-water mixture from the pK value of the compound in water, or conversely estimatio n of the pK value in water from pK values measured in methanol-water mixtur es. Some examples of prediction, including chromatographic retention of aci d-base compounds, are presented. (C) 2001 Elsevier Science B.V. All rights reserved.