Polarographic reduction of nickel in the presence of various alkyl substituted o-diaminobenzenes

The catalytic polarographic prewave for the reduction of Ni(H2O)62+ in the presence of a variety of alkyl substituted o-diaminobenzenes has been measured and compared to that observed with unsubstituted o-diaminobenzene. When the concentrations of the substituted diamines are low compared to [Ni2+] the prewaves are identical to those of the o-diaminobenzenes itself, indicating that the alkyl group has no effect on the formation of the activate intermediate. For comparable concentrations of the substituted diamines and [Ni2+], the prewave takes on an on–off step shape. Simple o-diaminobenzene does not show this behavior. Differential capacitance measurements and surface excess calculations show that no potential-dependent adsorption reorientation (two-dimensional phase change) occurs at these concentration–potential regions. Thus, some other phenomenon causes this on–off behavior.