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 HA2- accompanies the simple protonation of L, viz, L + HA reversible LH+A- and L + 2HA reversible LH+HA2-. The electrolytes LH+A- and LH+HA2- 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 HA2- in the dry solvent, 5.7x10(3) 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 HA2- 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 1x10(1).