Ionization constants for water and for very weak organic acids in aqueous organic mixtures

A potentiometric method using a glass electrode has been applied to the determination of apparent ionization constants for water in binary mixtures of water with 11 organic solvents at 25°C. Further calculations with these apparent ionization constants permit evaluation of the acid ionization constant for some of the organic solvents as solutes in purely aqueous solvent by two different methods. Resulting values of pK _a derived from this work are: 1,2-propanediol (14.8 and 14.8), 2,3-butanediol (15.0 and 14.7), 1,3-butanediol (15.5 and 14.8), 1,4-butanediol (14.5 and 14.4), 2-butene-1,4-diol (14.0 and 13.9), 2-butyne-1,4-diol (12.1 and 12.4), 2-methoxyethanol (15.2 and 14.8), 2-ethoxyethanol (15.0 and 14.5), and triethylene glycol (14.6 and 14.3). None of the 11 solvents shows appreciable basicity.