Ion Pair pKs of Some Amines: Extension of the Computed Lithium pK Scale

The pK of p-(methylamino)biphenyl, 1, on our Li scale, pK(Li) = 22.09, compared to the cesium scale, pK(Cs) = 28.60. For hexamethyldisilazane, HMDS, pK(Li) = 23.05, pK(Cs) = 29.26. These results are those for the monomers in THF; corrections were made for dimers present in some cases. The pK(Li) of these two amines fit well the previously found correlation with Hartree-Fock calculations at 6-31+g(d) using RLi coordinated with three dirnethyl ethers as a computational model for RLi in THF. The results are also compared with earlier pK(Li)s reported from equilibria with lithium amides in which aggregation was not considered.