Analyses of the Acid Dissociation Constants of Multisubstituted Diarylamines Measured in Solvents and Micellar System

Abstract

Abstract The acid dissociation constants of a number of multisubstituted diarylamines measured in an α-dodecyl-ω-hydroxyocta(oxyethylene) micellar system (log ) were compared with those measured in 50% (v/v) EtOH–water mixture (log ). The electronic effects of substituents on log values were similar to, whereas the steric effect of substituents was larger than, those examined previously on the log values. The acid dissociation constant of each compound was generally larger in the less polar (ε: ca. 28) micellar system than that in 50% EtOH–water mixture (ε: ca. 52). To understand this phenomenon, solvent effects on the dissociation constant of compound 37 as a model were examined. We found that compound 37 forms a hydrogen-bonded or proton-transfer complex with DMSO in CHCl3. The anionic form of compound 37 was favored in partition at a higher DMSO content in a DMSO–water mixture compared to the neutral form. These results suggest that contributions of such as hydrogen bonding and dispersion force are of primary importance regarding the effect on the acid dissociation of the series of compounds in the micellar system.