Ionic equilibrium in mixtures of protophobic and protophilic polar non-hydrogen bond donor solvents: acids, salts, and indicators in acetone containing 5 mol% DMSO

摘要

Properties of a protophobic polar non-HBD solvent can be strongly modified by the introduction of a small amount of a protophilic polar non-HBD solvent. In this paper, acetone (AC) with 5 mol% additive of DMSO, a solvent with epsilon(25)(r) = 22, was considered as a media for acid-base reactions. Conductance was used for the determination of dissociation constants of a set of salts, hydrogen chloride, and picric acid. The last-named was also studied by UV-vis spectroscopy. The introduction of 5 mol% of DMSO results in suppressing, to some extent, the homoconjugation processes in AC media as well as of proton hydration by (possible) traces of water. The dissociation of salicylic acid and 2,4-dinitrophenol was examined utilizing quinhydrone electrodes in a cell with liquid junction. The pK(a) values of buffer acids and pa(H+)*, values of buffer solutions were calculated by taking into account the incomplete dissociation of salts. The response of the glass electrode appeared to be satisfactory, which allowed the estimation of the pK(a) value of benzoic acid. The apparent ionization constants of 22 acid-base indicators in buffer mixtures and perchloric acid solutions were determined in (AC + 5 mol% DMSO) using the spectrophotometric procedure. Copyright (C) 2009 John Wiley & Sons, Ltd.