Complexation of some univalent organic cations with benzo-18-crown-6 in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C⁺(aq) + 1·Na⁺(nb) ? 1·C⁺(nb) + Na⁺(aq) taking place in the two-phase water–nitrobenzene system (C⁺ = univalent organic cation, 1 = benzo-18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1·C⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated tyramine, protonated l-valine methyl ester < protonated dopamine < protonated serotonin < methylammonium < protonated hexamethylenetetramine < ethanolammonium < protonated dl-noradrenaline.