POLAROGRAPHY OF INORGANIC COMPOUNDS IN ISOBUTYRONITRILE AS SOLVENT

Abstract

Metal ions generally are reduced at less negative potentials in isobutyronitrile than in acetonitrile, mainly because the dielectric constant of the former solvent is lower than that of the latter. However, half-wave potentials vary somewhat for different (non-complexing) supporting electrolytes. This variation is attributed to changes in the liquid junction potential and in the stability of the ion pairs formed by a given metal with different anions. The following half-wave potentials, vs. the aqueous saturated calomel electrode, were obtained at the dropping mercury electrode in 0.05 M tetraethylammonium perchlorate as supporting electrolyte (with an asterisk denoting a reversible or near-reversible electro-reaction): lithium, -1.90 v; sodium -1.77*; magnesium, - 1.68; cobalt(II), -0.60*; nickel(II), -0.33; copper(II) yields . copper(I), more positive than the anodic dissolution potential of mercury (+0.67); copper(I) yields copper amalgam, -0.25*; silver, +0.49*. In 0.05 M tetrabutylammontum iodide as supporting electrolyte, the following half-wave potentials were obtained: sodium, -1.70; potassium, -1.77*; rubidium, -1.79*; cesium, -1.80; in 0.05 M sodium perchlorate: thallium(I) (as the nitrate), -0.24*; and in 0.10 M sodium perchlorate: oxygen, -0.70 and -1.55 v. All metal ions studied, except copper(I) and silver, have lower solvation energies in isobutyronitrile than in water. Perchloric acid gives a well definedmore » but irreversible wave at a much less negative potential (E,/ =-0.62 v) than in water. The overpotential of hydrogen on mercury under polarographic conditions is approximately 0.8 v smaller in isobutyronitrile than in water, and virtually equal to the value in acetone. The effect of water on the perchloric acid and cobalt waves was determined. Halide ions, X-, give two anodic waves at the dropping mercury electrode, corresponding to successive formation of HgX3 and HgX2. Both iodide waves (in 0.05 M sodium perchlorate) are reversible, with halfwave potentials equal to -0.42 and +0.19 v, respectively. Methyl red suppressed the maxima produced by thallium(I) and silver.« less