Ion Pair Basicity of Some Amines in THF: Implications for Ion Pair Acidity Scales1

Amines form proton-transfer ion pairs of the type BH + In - with acidic indicator hydrocarbons InH in THF. Relative equilibrium constants measured for a number of amines in THF differ substantially from ionic p K a values for BH + in acetonitrile or DMSO. The results show that ion pair dissociation constants of the protonated amine ion pairs in THF vary by several orders of magnitude and point out that at the present time amines cannot be placed quantitatively on any of the ion pair acidity scales currently in use for neutral acids in THF.