Effect of 14-s-14 dicationic surfactants on the solubility and acid–base properties of thymolphthalein in water

Abstract

The solubilization effect of 14-s-14 series dicationic surfactants is quantified via spectrophotometry using a thymolphthalein hydrophobic indicator. It is shown that the solubilization capacity of the studied micellar solutions with respect to the neutral form of thymolphthalein increases along with the length of the spacer moiety and grows by as much as five times upon transitioning from 14-2-14 to 14-6-14. It is concluded that the solubilization of thymolphthalein is accompanied by a shift in the acid-base equilibria in which this compound participates, as is reflected in the drop of its pK_a value and the shift of the region of color change.