Protonation of 18-crown-6 by dichloropicric acid in anhydrous and in water saturated 1,2-dichloroethane. Homoconjugation of dichloropicric acid

From conductometric and UV-VIS spectrophotometric studies of the reaction between 18-crown-6 (L) and dichloropicric acid (HA) in dry and water saturated 1,2-dichloroethane, it has been concluded that formation of a 1:1 homoconjugate HA ₂ ^– accompanies the simple protonation of L, viz, L+HALH⁺A^– and L+2HALH⁺HA ₂ ^– . The electrolytes LH⁺A^– and LH⁺HA ₂ ^– are extensively, or practically completely dissociated in both solvents under the experimental conditions. The specie LH⁺A^– appears to be a contact ion pair in DCE. The stability constant of HA ₂ ^– in the dry solvent, 5.7×10³ mol^–1-cm³, is some 10^2.4 times that in propylene carbonate reflecting the difference in H-bond accepting capacity of the two solvents. Hydration of HA, A^– and HA ₂ ^– in wet dichloroethane is negligible or slight. As expected, LH⁺ is rather strongly hydrated, the ratio of the hydration constants of LH⁺ and L being about 1×10¹.