Effect of protic solvents on the polarographic reduction of the alkali metal ions in hexamethylphosphoric triamide

Sodium and lithium ions are not reduced at the dropping mercury electrode in hexamethylphosphoric triamide containing 0.05 mol dm^?3 tetraethylammonium perchlorate while rubidium and caesium ions show diffusion controlled, l-electron reduction waves. The reduction of potassium ion is partially kinetic. When increasing amount of water is added to the solution, reduction waves of sodium and lithium begin to appear, and the kinetic contribution of potassium wave gradually disappears to give a diffusion controlled wave. The diffusion controlled waves of rubidium and caesium ions are essentially unaffected. The addition of methanol, ethanol, l-buthanol and dimethyl sulfoxide also has similar enhancing effects, which is attributed to the acceleration of the desolvation process by protons. These effects of protic solvent are apparently similar to that of the cation size of the supporting electrolytes, but of different origin, as indicated by the different behavior of the electrocapillary curves.