Polarographic Behavior of Nickel(II) in Propionitrile and Benzonitrile in the Presence of Thiocyanate Ions

Abstract

Abstract The effect of the cation of the supporting electrolyte on the electrode reaction of nickel(II) in propionitrile and benzonitrile solutions containing thiocyanate ion was investigated by DC polarography and i-t curve analysis. In the absence of thiocyanate ion, a propionitrile solution of nickel(II) gives a single irreversible wave in LiClO4 and NaClO4 supporting electrolytes and a double wave in Et4NClO4 and n-Bu4NClO4, and a benzonitrile solution of nickel(II) gives a double wave in alkali metal and quaternary ammonium perchlorates. Nickel(II) in these nitrile solvents in the presence of thiocyanate ion exhibits a catalytic pre-wave in alkali metal perchlorates and a catalytic maximum wave in quaternary ammonium perchlorates. The double wave of nickel(II) in the absence of thiocyanate ion is due to the inhibition of the charge transfer process by the relatively weak adsorption of quaternary ammonium cations and not to the presence of two electroactive species. A mechanism which involves the cyclic regeneration of adsorbed thiocyanate ion for the catalytic pre-wave and the catalytic reduction of thiocyanate ion with the electroreduced metallic nickel for the maximum wave has been presented.