Acid-base equilibria in nonpolar media.: 4.: Extension of the self-consistent basicity scale in THF medium.: Gas-phase basicities of phosphazenes

Eleven new phenyl-substituted phosphazenes (P-1-, P-3-, and P-4-bases) have been synthesized by the Staudinger or the Kirsanov reactions. The UV-vis spectrophotometric titration method was used to establish the relative basicity of them, and to extend the ion-pair basicity scale for THF medium. These measurements together with our previous work give a continuous basicity scale in THF ranging from 2.6 (2-MeO-pyridine) to 26.6 (2-Cl-C6H4P4(pyrr) phosphazene) in pK(alpha) units: that is for 24 orders of magnitude and containing 58 compounds (pyridines, anilines, amines, guanidines, amidines, phosphazenes). Ion-pair formation was taken into account by using the Fuoss equation. DeltapK(ip) values of some phosphazene indicators estimated earlier by the C-13 NMR method were revised. For some of the phosphazenes gas-phase basicities were measured.