Studies of the Interaction between the Hexyl Anion and Alkali Metal Ions

The Hexyl(2,4,6,2′,4′,6′-hexanitrodiphenylamine) anion forms ion-pairs with alkali metal cations to some extent in an aqueous solution. The association constants of these ion-pairs were determined both in nitrobenzene by conductivity measurements and in water by the solvent extraction method. The association constants in nitrobenzene (KoMR) decrease in the following order: Li>Na>K>Rb>Cs. The plot of log KoMR against the ionic potential of the alkali metal ions was found to be linear. In nitrobenzene saturated with water, however, the constants vary from 2 to 4. In water the asscoiation constants (KaMr) vary from about 10 to 400, and the value increases as follows: Li<Na<K<Rb (<Cs). A plot of log KaMR against the reciprocal of the effective diameter of the hydrated alkali metal ions was found to be linear.