The Effect of the Counter Anion on the Complexation of Alkali Metal Salts to Polyethylene Glycol

The complexation of alkali metal salts by polyethylene glycol is strongly dependent on the counter anion of the salt. In general, potassium salts are more easily complexed. In fact, sodium salts at low free energy of formation are barely complexed at all. By conductometric and index of refraction measurements it was shown that anions capable of hydrogen bonding such as OH⁻, F⁻, HSO⁻₄ and HCO⁻₃ were ion paired to the complexed potassium cation and existed as relatively “naked” anions. Other anions such as Cl⁻, Br⁻, I⁻, SCN⁻, NO⁻₃, NO⁻₂ AND HF⁻₂ existed as disassociated anions with significant solvation shells. The use of polyethylene glycol as a phase transfer catalyst considering the results found is discussed.