Filatov D. The dissociation constants of electrolytes and acidity scale in acetone in the presence of dimethylsulfoxide

Object of study: acid-base equilibrium of organic acids and their salts in the solvent acetone-dimethyl sulfoxide (molar ratio 95: 5). Objective: to identify the influence of small additions of protophilic dipolar aprotic solvent on the acid-base equilibria in protophobic one, using the mixture of acetone with dimethyl sulfoxide as an example and quantitatively characterizing the most typical equilibria in this solvent. Methods and apparatus: to determine the characteristics of acid-base equilibria, spectrophotometry, potentiometry, and conductivity methods were used. Theoretical and practical results: the efficiency of the use of protophilic dipolar aprotic solvent additives to protophobic one is demonstrated for creating a new kind of media, where the lyonium ion is a proton, solvated by the protophilic solvent dimethyl sulfoxide. The majority of the pKa values of acids in pure acetone, currently existing in the literature, are shown to be unreliable. The differentiating effect of acetone, which contains five mole percent of dimethyl sulfoxide, upon the strength of acids and phenols is revealed. The possibility of utilization of the glass electrode in the solvent acetone-dimethyl sulfoxide (molar ratio 95: 5) is proved. Scientific novelty: the stoichiometry of proton solvation in the mixed solvent is stated, and the constant of proton exchange between the two solvents is estimated. It is demonstrated that the introduction of five molar percent of dimethyl sulfoxide results in a decrease in pKa value of picric acid by six units, essentially weakens the homoconjugation process of acids, and suppresses the influence of small water admixtures on acid-base equilibria in acetone. The values of dissociation constants of salts and acids, as well as the indicator constants in acetone-dimethyl sulfoxide solvent (molar ration 95 : 5) were determined, the role of homo- and heteroconjugation in the solvent studied was demonstrated. The degree of implementation and scope of usage: the results obtained in this work are used in the performance of budgetary research program of the Department of physical chemistry, in the lecture courses "Physical chemistry of nonaqueous solutions" (general course) and "Selected chapters of physical chemistry of solutions" (special course, specialization "Physical Chemistry") at the Chemistry Faculty of Kharkov V. N. Karazin National University.