Thermodynamics of Ionic Association of Tetraphenylphosphonium, Tetraphenylarsonium, and Some Common Cations in 2-Methoxyethanol Using Conductometry and FT-Raman Spectroscopy

Precise measurements on electrical conductances and Fourier Transform (FT) Raman spectra of solutions of tetraphenylarsonium chloride (Ph 4 AsCl), tetraphenylphosphonium chloride (Ph 4 PCl), tetraphenylphosphonium bromide (Ph 4 PBr), lithium tetrafluoroborate (LiBF 4 ), and sodium tetrafluoroborate (NaBF 4 ) in 2-methoxyethanol (ME) at temperatures 288.15 ≤ T/ K ≤ 308.15 are reported. The conductance data were analyzed by the 1978 Fuoss conductance−concentration equation. Thermodynamics of the association processes were also studied, and the Coulombic forces are found to play a major role in the association processes. The Raman spectra suggest the presence of “spectroscopically free” Cl -, Br -, and BF 4 - ions in solution, thus substantiating the moderate ion-pair formation constants for these electrolytes obtained from conductometric measurements. The observed processes were interpreted by an Eigen multistep mechanism. Raman spectra also indicate that the cations get attached to the ME molecules through the ethereal oxygen atom rather than through the alcoholic oxygen of the solvent molecules.