Para-Disubstituted Benzene Derivatives: Difference Between Chemical and Electrochemical Reactions

Terephthalaldehyde dioxime is reduced using DC polarography in diprotonated, monoprotonated, and unprotonated form. The diprotonated form is reduced in a single eight-electron step. In the monoprotonated form, the protonated oximino group is reduced by four electrons at more positive potentials than those of the four-electron reduction of unprotonated oximino group. There is a difference between the natures of the electrochemical and chemical reaction, involving the same molecule. Both protonated oximino groups in the diprotonated dioxime are reduced simultaneously, whereas protonation of the two groups occurs in a consecutive process. The difference is attributed to the difference between the homogeneous nature of the chemical and the heterogeneous one of the electrochemical process.